ELSEVIER: CHAPTER 1 MICROBIOLOGY (1-100) Questions and Answers

ELSEVIER: CHAPTER 1 MICROBIOLOGY (1-100) Questions and Answers 1. Spores are found in select groups of bacteria.Which of the following statements describes the major advantage to the bacteria that possess these structures? a. Spores are resistant to heat, cold, drying, most chemicals, and boiling b. Spores allow an organism to better control its local environment c. Spores allow bacteria to attach or adhere to host tissues d. Organisms with spores have a more efficient 1. a. Some bacteria form thick-walled structures termed spores. These structures are formed during a process that makes a copy of a chromosome and encloses it with a thick protein coat. This spore is resistant to heat, cold, drying, most chemicals, and boiling. Spores can remain viable for many years in soil or dust. 2. Choose the binomial name that is correctly written. a. Staphylococcus Aureus b. Staphylococcus species aureus c. Staphylococcus aureus d. Staphylococcus aureus 2. c. Genus and species are italicized or underlined. Genus is capitalized; species is lowercase. 3. Fermentation end-products are often used to aid in the identification of bacteria. Fermentation results in which of the following? a. Conversion of glucose to pyruvate b. Lactic acid, mixed acids, alcohols, CO2 production c. CO2 and water d. Specific teichoic acids 3. b. Bacterial cells generate stored energy in the form of ATP by one of two basic mechanisms: respiration or fermentation. Fermentation is metabolism in the absence of oxygen, an anaerobic process. In fermentation, glucose is converted into pyruvate by either the Embdem-Meyerhof pathway or glycolysis. Pyruvate can then enter several other cycles, and the end-products vary depending on cycle entered. In aerobic respiration, glucose usage under aerobic conditions and pyruvate enters the Kreb's cycle (TCA cycle). The end-products of respiration are carbon dioxide and water. The unique metabolic pathways and end-products produced by bacteria can be used to aid in the identification of particular genera or species 4. The exchange of cellular DNA between two living bacterial cells that involves an intercellular bridge is which of the following processes? a. Transformation b. Transduction c. Plasmidization d. Conjugation 4. d. Bacteria can acquire or exchange genetic material with other bacteria through several basic mechanisms: conjugation, transformation, or transduction. Conjugation involves cell-to-cell contact, a series of complex chemical signals between cells, and usually the formation of a bridge or sex pilus. Transformation is the uptake of free DNA by a recipient cell. Transduction is the acquisition of DNA through the action of a bacteria phage. 5. Transduction is defined as which of the following? a. The change of the bacterial genotypes through the exchange of DNA from one cell to another b. An internal change in the original nucleotide sequence of a gene or genes within an organism's genome c. The process by which genetic elements such as plasmids and transposons excise from one genomic location and insert into another d. A mechanism that is mediated by viruses, by which DNA from two bacteria may come together in one cell, thus allowing for recombination 5. d. Transduction refers to moving genetic information from one prokaryote to another via a bacteriophage or virus 6. A mordant that is applied after the primary stain to chemically bond the alkaline dye to the bacterial cell wall is which of the following? a. Safranin b. Crystal violet c. Gram's iodine d. Gram's decolorizer 6. c. The Gram stain procedure involves four steps: applying crystal violet—the initial purple dye that enters the cell; applying Gram's iodine—the mordent or chemical that binds to the crystal violet forming a complex; decolorizing—alcohol or acetone/alcohol is used to remove the crystal violet/ iodine complex from gram-negative cells; and safranin counter stain—the red dye is used as a second stain. Gram-positive bacteria retained the initial crystal violet, the red counter stain blends with the violet, and gram-negative bacteria are only stained with the safranin and appear red. 7. Which of the following bacteria should be considered important pathogens when reading gram-stained smears of soft tissue abscess? a. Streptococcus pneumoniae b. Neisseria gonorrhoeae c. Pseudomonas aeruginosa d. Staphylococcus aureus 7. d. Although many different bacteria can be isolated from skin and soft tissue infections, the two most common organisms are Staphylococcus aureus and Streptococcus pyogenes. We should be aware of these likely organisms as we read and report gram-stained smear results. S. pneumoniae and N. gonorrhoeae are important pathogens but rarely associated with skin infections. Although Pseudomonas can be associated with some unique infections of the skin, they are uncommon. 8. The most appropriate interpretation of a gramstained smear of a sputum specimen would be which of the following? (gram-stained smear, 400.) a. Few epithelial cells, many PMNs b. Inadequate specimen, do not culture for anaerobes c. Many cells, many gram-positive cocci in pairs and chains d. More than 25 epithelial cells, probable oral contamination, suggest recollect 8. d. The two major uses for gram-stained smears are to evaluate the quality of a specimen (inflammation versus normal flora contamination) and describe the types of bacteria—gram-positive versus gramnegative. For sputum specimens, expectorated lower respiratory tract specimens, the following criteria are often applied: (1) more than 25 epithelial cells/low-power field=saliva, significant number of normal flora bacteria. (2) Few epithelial cells, many white blood cells¼specimen more likely to yield a pathogen. In adult patients, specimens with significant numbers of epithelial cells often are not cultured and new samples are collected. 9. 85% N2, 10% H2, 5% CO2 is the environmental condition that best suits which type of organism? a. Aerobes b. Anaerobes c. Capnophiles d. Microaerophiles 9. b. The atmosphere in which specimens are incubated can have a significant effect on the growth of potential pathogens. Many bacteria isolates will grow easily in routine air or with a slight increase in carbon dioxide, 3% to 5% CO2 (aerobes). Other pathogens require special atmospheres for optimal growth, including increased CO2, nitrogen, or decreased or complete absence of oxygen: Microaerophilic: 5% O2, 10% CO2, 85% N Anaerobic: 85% N2, 10% H2, 5% CO2 10. Whichmedium can be described ascontaining bile salts and dyes (bromothymol blue and acid fuchsin) to selectively slow the growth of most nonpathogenic gramnegative bacilli found in the gastrointestinal tract and allow Salmonella spp. and Shigella spp. to grow? a. Thayer-Martin b. MacConkey c. PEA (phenylethyl alcohol) d. Hektoen 10. d. Hektoen enteric (HE) contains meat peptones and yeast extract, bile salts (inhibit gram-positive organisms), lactose, sucrose, salacin (carbohydrate sources), pH indicators (bromophenol blue and acid fuchsin), and ferric ammonium citrate for the detection of H2S production. This medium is very selective for enteric pathogens and is differential for Salmonella and Shigella. Yellow-orange colonies¼lactose fermenter (E. coli), colorless/ green colonies with unchanged medium¼non- lactose fermenter (Shigella, Providencia), and black colonies¼H2S production (Salmonella). 11. Choose the group of bacteria that is described as catalase-positive, gram-positive cocci that grow facultatively anaerobic and that form grapelike clusters. a. Neisseria spp. b. Rothia (Stomatococcus) spp. c. Staphylococcus spp. d. Micrococcus spp. 11. c. The genus Staphylococcus represents one of the most important groups of potentially pathogenic bacteria and most common normal flora organisms. This genus has the general characteristics of gram-positive cocci in clusters and is catalasepositive, facultative anaerobic, ferments glucose, and nonmotile. 12. The slide coagulase test is a rapid screening test for the production of which of the following? a. Clumping factor b. Free coagulase c. Extracellular coagulase d. Catalase 12. a. A unique pathogenic factor of Staphylococcus aureus is the production of coagulase. This protein is responsible for the formation of fibrin clots in the host. Coagulase is found in two basic forms: bound to the surface of the cell, also known as clumping factor, and free in the medium. The bound form can be detected with several tests that demonstrate clumping of the bacterial cell or sensitized red blood cells, and the free form is most often detected by clot formation with rabbit plasma 13. The first identification test performed on a clinical isolate of gram-positive, catalase-positive cocci should be which of the following? a. Penicillin test b. Gram stain c. Oxidase test d. Coagulase test 13. d. The initial testing of an isolate of a gram-positive cocci is catalase to differentiate the staphylococci (catalase-positive) from enterococci and streptococci (catalase-negative). If an isolate is catalase-positive and fits the general characteristics of a Staphylococcus spp., the coagulase test is used to differentiate S. aureus from the other species of the genus. 14. The Staphylococcus sp. that is more likely to cause uncomplicated urinary tract infections in nonhospitalized hosts, especially sexually active young women, is which of the following? a. Staphylococcus saprophyticus b. Staphylococcus aureus c. Staphylococcus epidermidis d. Staphylococcus intermedius 14. a. Staphylococcus saprophyticus is normal flora of the mucous membranes of the urogenital tract. It causes urinary tract infection in some populations, especially young, sexually active women. In this population, it is considered significant in urine cultures even if it is found in small numbers. 15. The toxic shock syndrome toxin-1 is an important virulence factor in staphylococcal disease. This toxin is classified into which of the following groups of toxins? a. Cytolytic toxin b. Leukocidin c. Phospholipase d. Enterotoxin 15. d. Staphylococcus aureus is capable of producing a large number of molecules, which may contribute to its ability to cause disease. Toxic shock syndrome is a disease associated with the production of a specific toxin, toxic shock syndrome toxin-1 (TSST-1), which belongs to the group of toxins known as enterotoxins. 16. Mannitol salt agar is selective and differential for which group of organisms? a. Staphylococcus spp. b. Enterococcus spp. c. Gram-positive cocci d. Streptococcus spp. 16. a. Several media can be used for selection of Staphylococcus aureus from mixed cultures. PEA or CNA would select for gram-positive organisms but are not specific for S. aureus. Mannitol salt agar was developed specifically to select for Staphylococcus spp. and to differentiate between S. aureus and other Staphylococcus spp., because S. aureus ferments mannitol and other species generally do not. More recently, chromogenic agars have been developed that are more specific for S. aureus and some have been designed to specifically detect methicillin-resistant S. aureus 17. Within 5 hours of returning home from lunch at your most favorite fast food restaurant you feel very sick and are vomiting. Which of the following is the most likely causative organism? a. Staphylococcus aureus b. Vibrio parahaemolyticus c. Shigella sonnei d. Escherichia coli 17. a. Although some bacterial pathogens can cause vomiting and diarrhea, the hallmark of the staphylococcal enterotoxins is that because the toxins are preformed in the contaminated food, the organism does not need to grow in the host and therefore the action is very rapid. Most other enteric pathogens need to proliferate before the host experiences disease. 18. The bacterial species that can be described as susceptible to bile and optochin, a-hemolytic, a major cause of bacterial meningitis, and often carrying an antiphagocytic capsule is which of the following? a. Enterococcus faecalis b. Streptococcus pneumoniae c. Streptococcus pyogenes d. Streptococcus agalactiae 18. b. Of the organisms listed, only Streptococcus pneumoniae exhibits these characteristics. The two laboratory tests are bile solubility, which is the characteristic of S. pneumoniae isolates lysing when a solution of bile is dropped on the colony, and resistance to optochin. The optochin test is performed by streaking a lawn of organism onto a blood agar plate and then placing a standardized disk containing the chemical optochin onto the plate. After incubation, S. pneumoniae will not grow up to the disk—that is, growth is inhibited, demonstrating that the organism is susceptible to the chemical agent. Viridans group streptococci, S. pyogenes, and enterococci, do not autolyze in the presence of bile and are resistant to optochin. 19. The bacterial species that can be described as susceptible to penicillin and bacitracin, b-hemolytic, a major cause of bacterial pharyngitis, and often carrying an antiphagocytic M protein is which of the following? a. Enterococcus faecalis b. Streptococcus pyogenes c. Streptococcus agalactiae d. Viridans streptococci 19. b. Of the organisms listed, only Streptococcus pyogenes exhibits these characteristics. Clinically, S. pyogenes is the most important bacterial cause of pharyngitis. All isolates are susceptible to penicillin at this time. In the laboratory, b-hemolytic streptococci that are susceptible to bacitracin, also known as the A disk, are presumptively identified as S. pyogenes, or group A b-hemolytic Streptococcus. The PYR test also can be used, because this pathogen is PYR-positive. 20. The bacterial species that can be described as able to hydrolyze hippurate, b-hemolytic, a major cause of neonatal meningitis and sepsis, and producer of the CAMP factor is which of the following? a. Streptococcus pneumoniae b. Streptococcus pyogenes c. Streptococcus agalactiae d. Viridans streptococci 20. c. Of the organisms listed, only Streptococcus agalactiae exhibits these characteristics. Clinically, this organism, also known as group B Streptococcus, is an important cause of neonatal meningitis and sepsis. Of the b-hemolytic streptococci, it is unique in being hippurate hydrolysis-positive and CAMP test-positive. Latex or other grouping tests are usually used in clinical laboratories rather than hippurate or CAMP testing 21. The rapid antigen detection methods for throat swabs used for screening patients for streptococcal pharyngitis can be best described by which of the following statements? a. They can be useful in quickly identifying most cases of streptococcal pharyngitis b. They are a quick way to rule out streptococcal pharyngitis and avoid giving antibiotics when not needed c. They are always very sensitive and specific for streptococcal pharyngitis d. They are a quick and accurate way to diagnose bacterial and viral pharyngitis 21. a. Rapid antigen detection tests are often used to aid in the diagnosis of group A pharyngitis. The present generation of tests are rapid, approximately 15 minutes, and reasonably sensitive—65% to 85% in general. Therefore (1) they can be useful in quickly identifying most cases of streptococcal pharyngitis. (2) Because of limits to the sensitivity, a negative test does not mean that the patient does not have the bacteria present and additional testing is often needed, so this statement is not true. (3) As stated, the major limitation in this test method is the limits to detecting small numbers of organisms—sensitivity. (4) The rapid antigen tests for group A streptococci is only for those bacteria and is not useful for the detection of viruses. Rapid antigens for viruses may detect some, but not all, causes of pharyngitis and are in general designed for bronchitis, bronchiolitis, and pneumonia. 22. The hemolysis of this Streptococcus spp. would best be described as which of the following? a. b-Hemolysis b. g-Hemolysis c. a-Hemolysis d. k-Hemolysis 22. c. The ability of streptococcal species to produce compounds that can alter the appearance or integrity of the red blood cells in 5% sheep blood agar can be used to help presumptively identify potential pathogens. a-Hemolysis is the appearance of a "green" band of red blood cells around a colony. This greening is due to the conversion of hemoglobin to methemoglobin. b-Hemolysis is the actual lysis of the red blood cells resulting in a clear area around the colony, g-hemolysis is a term that historically was applied to colonies that did not alter the red blood cells, hence no zone around the colony. k-Hemolysis is a nonsensical term. This image shows greening and thus a-hemolysis. 23. Enterococcus spp. can be differentiated from most Streptococcus spp. by which of the following tests? a. Growth in presence of 6.5% salt b. Production of catalase c. Production of coagulase d. Growth on PEA medium 23. a. Two easily performed laboratory tests allow the differentiation of clinically important isolates of the genera Enterococcus from Streptococcus: growth in presence of 6.5% salt and growth on bile/esculin medium. Streptococci and enterococci are catalase-negative, do not produce coagulate, and will grow on PEA medium. 24. A pure culture of a b-hemolytic Streptococcus sp. recovered from a leg ulcer gave the following reactions: CAMP test = Negative Bile esculin slant=No growth Optochin=Resistant Hippurate hydrolysis¼Negative 6.5% Salt=No growth Bacitracin=Resistant SXT=Sensitive Which of the following is the most likely identification of this organism? a. Streptococcus pyogenes b. Streptococcus agalactiae c. Enterococcus faecalis d. Streptococcus sp., not groups A, B, or D 24. d. Of the organisms listed, only Streptococcus sp., not groups A, B or D meets these criteria. Streptococcus pyogenes is PYR positive and bacitracin susceptible. S. agalactiae is CAMP and hippurate positive. Enterococcus faecalis is bile esculin and salt positive. 25. The ability to grow well at refrigerator temperatures is a characteristic of which of the following organisms? a. Mycobacterium gordonae b. Listeria monocytogenes c. Erysipelothrix d. Bacillus cereus 25. b. Some bacteria that are environmental have a broad range of permissive growth temperatures. Among potentially pathogenic, gram-positive bacilli, the ability of Listeria monocytogenes to grow well at refrigerator temperatures can be used to select for this organism. 26. A catalase-positive, gram-positive bacillus that is not acid-fast, does not branch, and does not form spores could possibly belong to which group of bacteria? a. Corynebacterium b. Bacillus c. Nocardia d. Mycobacterium 26. a. Among the gram-positive bacilli, several basic characteristics can be used to help differentiate the groups, including catalase, acid-fast, and modified acid-fast stains; bacterial cells that branch; and spore formation. Of the organisms listed, only Corynebacterium is a catalasepositive, gram-positive bacillus that is not acidfast, does not branch, and does not form spores; the genus Bacillus forms spores, Mycobacterium is acid-fast, and Nocardia cells branch. 27. A throat culture was taken from a 6-year-old boy with a gray pseudomembrane covering his oropharynx. A catalase-positive organism was isolated on cysteine-tellurite medium and subcultured to Tinsdale medium, where it grew as black colonies with brown halos. A Gram stain was performed on these colonies. Which of the following cellular morphologies was most likely seen? a. Gram-positive branching bacilli b. Gram-positive cocci in short chains c. Gram-positive bacilli in irregular clublike shape d. Gram-positive cocci in grapelike clusters 27. c. This clinical description is of diphtheria. Corynebacterium diphtheriae grows on tellurite medium, grows as black colonies with brown halos in Tinsdale medium, and shows gram-positive bacilli in irregular clublike shapes on gram-stained smears. 28. A blood culture is positive for gram-positive bacilli that gave the following growth characteristics and biochemical reactions: MacConkey agar: No growth Catalase: Positive H2S on TSI: negative Growth of blood agar, nonhemolytic Nonmotile No spores These reactions are consistent with which of the following organisms? a. Listeria spp. b. Group B b Streptococcus c. Erysipelothrix spp. d. Corynebacterium spp. 28. d. The genus Corynebacterium is a catalase-positive, gram-positive bacillus that is not acid-fast, does not branch, and does not form spores. It shows gram-positive bacilli in irregular clublike shapes on gram-stained smears. Group B Streptococcus would be seen as cocci in chains on gram-stained smear and would be catalase-negative, Erysipelothrix is H2S-positive, and Listeria is motile 29. A skin lesion was opened and drained in surgery. The culture was positive for a gram-positive bacillus, which gave the following growth characteristics and biochemical reactions: MacConkey agar: No growth Catalase: Negative H2S on TSI: Positive Growth of blood agar, nonhemolytic Nonmotile No spores These reactions are consistent with which of the following organisms? a. Listeria spp. b. Group B b Streptococcus c. Erysipelothrix spp. d. Corynebacterium spp. 29. c. The clinical description is classic for Erysipelothrix infection. This organism is positive for the production of H2S on triple sugar iron (TSI) slants. The genus Corynebacterium is catalase-positive, gram-positive bacillus. Group B Streptococcus would be seen as cocci in chains on gram-stained smear and would be catalase-negative and bhemolytic. Listeria would be motile and show hemolysis on blood agar. 30. Which of the following sets of tests provide the best differentiation of Erysipelothrix from Listeria monocytogenes? a. Gram-stained smear, oxidase, and optochin b. Gram-stained smear, catalase, and motility c. CAMP test, hydrogen sulfide production, esculin hydrolysis d. Reverse CAMP, gram-stained smear, b-hemolysis 30. c. Although the clinical disease has little overlap, in the laboratoryErysipelothrix and Listeria monocytogenes can appear similar. The most common tests for differentiating these organisms include: CAMP test (Listeria, positive; Erysipelothrix, negative), hydrogen sulfide production (Listeria, negative; Erysipelothrix, positive), and esculin hydrolysis (Listeria, negative; Erysipelothrix, positive). 31. Neonatal meningitis is an uncommon but significant disease. Two important causes of this disease may be somewhat difficult to differentiate on preliminary observation. Which of the following sets of tests provide the best differentiation of Streptococcus agalactiae from Listeria monocytogenes? a. Gram-stained smear, oxidase, and optochin b. Gram-stained smear, catalase, and motility c. CAMP test, hydrogen sulfide production, b-hemolysis d. Reverse CAMP, gram-stained smear, b-hemolysis 31. b. Although Streptococcus agalactiae and Listeria monocytogenes may cause somewhat similar diseases and appear similar on 5% sheep blood agar, they can be differentiated with gramstained smear (S. agalactiae, gram-positive cocci in chains from L. monocytogenes, gram-positive bacilli), catalase (S. agalactiae, negative from L. monocytogenes, positive), and motility (S. agalactiae, negative from L. monocytogenes, positive). 32. Which of the following tests is important as a part of the genus identification or as part of a preliminary identification but is not used as a confirmatory identification of Bacillus anthracis? a. Demonstration of a capsule b. Demonstration of spore formation c. Positive PCR test d. Lysis of the strain by specific bacteriophages 32. b. Endospores are unique to Bacillus sp. among aerobic gram-positive bacilli. All Bacillus spp. are catalase-positive. Once the genus is established, confirmation of B. anthracis requires additional testing such as demonstration of a capsule and lysis of the strain by specific bacteriophage 33. Bacillus anthracis and Bacillus cereus can be differentiated in the laboratory by a variety of different test results. Which of the following sets of tests best differentiate these two species? a. Catalase and glucose fermentation b. Motility and lecithinase production c. Oxidase and b-hemolysis on 5% sheep blood agar d. Motility and b-hemolysis on 5% sheep blood agar 33. d. Bacillus anthracis and Bacillus cereus can be differentiated in the laboratory by a variety of different test results. Of the combinations listed, motility (B. anthracis nonmotile and B. cereus motile) and b-hemolysis on 5% sheep blood agar (B. anthracis nonhemolytic and B. cereus hemolytic) best differentiate these two potential pathogens. 34. Which of the following specimens would be best for identifying Bacillus cereus as the cause of an outbreak of food poisoning? a. Blood b. Rectal swabs c. Stool samples d. Food 34. d. In a food-borne outbreak, Bacillus cereus can be found in the food. It does not cause a systemic infection but rather a toxin-mediated disease. 35. A first morning sputum sample is received for acidfast culture. The specimen is centrifuged, and the sediment is inoculated on two Lowenstein-Jensen slants that are incubated at 35 C with 5% to 10% CO2. After 1 week, the slants show abundant growth over the entire surface. Stains reveal gram-negative bacilli. Which of the following should be done to avoid this problem? a. Use a medium specifically designed for the growth of AFB b. Dilute out the sediment before inoculation with saline c. Decontaminate the specimen with NALC- sodium hydroxide mixture d. Incubate the tubes at room temperature to retard bacterial growth 35. c. The single biggest challenge for the laboratory isolation of Mycobacterium tuberculosis from respiratory samples is the presence of normal organisms that grow more rapidly. Therefore the decontamination of these sputum samples with processes such as decontaminating the specimen with N-acetyl-L-cysteine (NALC)-sodium hydroxide mixture is critical for the successful isolation of M. tuberculosis. 36. A patient recently arrived in the United States from Africa presents with a long-standing cutaneous lesion, which is cultured for bacteria, fungi, and AFB. An AFB smear is made and is reported as positive for AFB. After 8 weeks of culture on both nonselective and selective AFB media, no colonies appear. Which of the following organisms should be suspected? a. M. kansasii b. M. tuberculosis c. M. leprae d. M. avium-intracellulare complex 36. c. The clinical description, the presence of acid-fast bacilli (AFB) in the sample, and the lack of growth in the laboratory, would raise suspicion that this sample contained an unusual and potentially noncultivatable AFB, such as Mycoplasma leprae. The other organisms listed should grow within 8 weeks on standard medium. 37. The mycobacterial species that occur in humans and belong to the M. tuberculosis complex include which of the following? a. M. tuberculosis, nontuberculous Mycobacteria, M. bovis, and M. africanum b. M. tuberculosis, M. gordonae, M. bovis BCG, and M. africanum c. M. tuberculosis, M. bovis, M. avium, and M. intracellulare d. M. tuberculosis, M. bovis, M. bovis BCG, and M. africanum 37. d. The Mycoplasma tuberculosis complex is made up of several closely related organisms that primarily cause disease in humans. This group includes: M. tuberculosis, M. bovis (historically found in cattle), M. bovis BCG (vaccine strain for the BCG vaccine), and M. africanum (found in Western Africa and clinically similar to M. tuberculosis). 38. The Runyon system of classification is based on which of the following? a. Colony and microscopic morphology b. Biochemical characteristics c. Growth rate and colonial pigmentation d. All of the above are correct 38. c. Nontuberculous mycobacteria (atypicals, mycobacteria other than tuberculosis [MOTT]), can be classified by a system first described by Ernest Runyon in 1959. This system classified organisms into four Runyon groups, based on: Presence or absence of pigmentation? Pigment production light dependent or not? Growth rate slow or fast? Runyon I: Photochromogens—slow growing, and produce a yellow-orange pigment when exposed to light. Runyon II: Scotochromogens—slow growing, and produce a yellow-orange pigment in light or in the dark. Runyon III: Nonchromogenic—slow growing, and do not produce pigment. Note that some may produce very pale yellow, buff, or tan pigment but do not intensify upon light exposure Runyon IV: Rapid growers. 39. In identification of mycobacterial isolates, the Tween 80 test involves which of the following? a. An enzyme that is able to produce Tween 80 from certain ingredients found in the medium b. Lipase that is able to hydrolyze polyoxyethylene sorbitan monooleate into oleic acid and polyoxyethylated sorbitol c. The metabolism of niacin to nicotinic acid by enzymatic action d. Testing the isolate for susceptibility to Tween 80 39. b. In identification of mycobacterial isolates, the Tween 80 test involves testing for lipase using polysorbate 80 (Tween 80). Certain mycobacterial species possess a lipase that splits polysorbate 80 into oleic acid and polyoxyethylated sorbitol. The test contains phenol red, which is stabilized, when the polysorbate 80 is hydrolyzed, the pH shifts and the phenol red indicator changes from yellow to pink. 40. The gram-negative bacillus that can be described as oxidase-negative, nitrate-positive, indole-negative, citrate-positive, methyl red-positive, ureasenegative, and H2S-positive is most likely which of the following? a. Klebsiella pneumoniae b. Salmonella enteritidis c. Escherichia coli d. Shigella sonnei 40. b. For the organisms listed, the Enterobacteriaceae are, in general, oxidase-negative (this entire listed group). Traditionally, various biochemical characteristics are used to differentiate members of the large group of organisms. Salmonella enteritidis is oxidase-negative, nitrate-positive, indolenegative, citrate-positive, methyl red-positive, urease-negative, H2S-positive; Klebsiella pneumoniae is indole-negative, citrate-positive, usually methyl red-negative (variable), urease-positive, H2S-negative; Escherichia coli is indole-positive, citrate-negative, methyl red-positive, ureasenegative, H2S-negative; Shigella sonnei is indolenegative, citrate-negative, methyl red-positive, urease-negative, H2S-negative. 41. The swarming gram-negative bacillus that can be described as oxidase-negative, nitrate-positive, indole-negative, and H2S-positive is mostly likely which of the following? a. Proteus aerogenes b. Proteus vulgaris c. Proteus mirabilis d. Escherichia coli 41. c. For the organisms listed, the Enterobacteriaceae are, in general, oxidase negative (this entire listed group). Traditionally, various biochemical characteristics are used to differentiate members of the large group of organisms. Proteus aerogenes is not a valid name. Escherichia coli is indolepositive, H2S-negative, and, although usually motile, not described as swarming. Proteus mirabilis and Proteus vulgaris can be differentiated using indole; P. mirabilis is negative and P. vulgaris is positive. 42. Profuse watery diarrhea ("rice water stools"), leading to dramatic fluid loss, severe dehydration, and hypotension that frequently leads to death, is the hallmark of which toxin activity? a. Cholera toxin b. Enteric endotoxin c. Shiga toxin d. Toxin A 42. a. A significant cause of worldwide clinical disease is diarrhea. Cholera is an important cause of diarrhea and results in massive fluid loss, "rice water stools" (white blood cells and blood absent), and often death within 24 hours. Shiga toxin is a cytotoxin that causes inflammation and ulcerative lesions, destroys epithelial cells, and results in bloody, mucous-laden stools. 43. The selective medium thiosulfate citrate bile salts sucrose (TCBS) agar is especially formulated for isolating which pathogen from stool cultures? a. Vibrio spp. b. Salmonella spp. c. Shigella spp. d. Plesiomonas spp. 43. a. Thiosulfate-citrate-bile salts-sucrose agar (TCBS agar) is selective medium designed to aid in the isolation of Vibrio spp. TCBS agar contains sodium thiosulfate and sodium citrate to inhibit members of the Enterobacteriaceae. Grampositive bacteria are inhibited by bile salts. Ferric citrate is used to detect hydrogen sulfide production. Sucrose is included as a fermentable carbohydrate to help differentiate V. cholera from other species. Bromothymol blue is included as an indicator of pH changes. 44. The majority of human infections with Campylobacter spp. are caused by which of the following? a. Direct contact with carriers of the bacterium b. Contamination of food, milk, or water with animal feces c. Multiplication of the organism in food products d. Direct contact with persons infected with the bacterium 44. b. C. jejuni is the most common human pathogen of this genus. It is associated with food-borne gastroenteritis because of its presence in poultry, raw milk, and water. It is one of the most common causes of human bacterial gastroenteritis in numerous parts of the United States. 45. In the test for urease production, the presence of the enzyme hydrolyzes urea to which of the following? a. Ammonia and CO2 b. Putrescine c. Amines and CO2 d. Amines and water 45. a. The urea slant can be used to aid in identification of enteric gram-negative bacilli. The test detects the ability of bacteria to hydrolyze urea to ammonia and CO2; ammonia release causes pH change. A positive test yields a bright pink slant. 46. The bacterial isolate on XLD agar shown in the image was isolated from a routine stool culture. Which of the following genera and species is the most likely identification for this organism? a. Klebsiella pneumoniae b. Salmonella enteritidis c. Shigella sonnei d. Serratia marcescens 46. b. Salmonella enteritidis grows well on XLD agar and is a nonfermenting organism that produces H2S, resulting in the black pigment. Shigella sonnei would appear as clear colonies, Serratia and Klebsiella are both lactose fermenting and would appear as yellow colonies. 47. The bacterial isolate shown below on CIN agar was isolated from a routine stool culture. Which of the following genera and species is the most likely identification for this organism? a. Shigella flexneri b. Salmonella enteritidis c. Yersinia enterocolitica d. Escherichia coli 47. c. Growth on CIN agar with this characteristic colonial morphology is indicative of Yersinia enterocolitica. 48. Decarboxylation of the amino acids lysine, ornithine, and arginine results in the formation of which of the following products? a. Ammonia b. Urea c. CO2 d. Amines 48. d. Decarboxylation of the amino acids lysine, ornithine, and arginine results in the formation of the following amine end-products: Ornithine decarboxylase (ODC), ornithine ! putrescine; lysine decarboxylase (LDC), lysine ! cadaverine; arginine dihydrolase (ADH), arginine ! citrulline. 49. An organism was inoculated into a TSI tube and gave the following reactions: Alkaline slant Acid butt H2S: Not produced Gas: Not produced The organism is most likely which of the following? a. Klebsiella sp. b. Shigella sp. c. Salmonella sp. d. Escherichia coli 49. b. Triple sugar iron (TSI) slants have traditionally been used to help identify and differentiate stool pathogens. These reactions are characteristic of Shigella spp. 50. The best specimen for the isolation of Bordetella pertussis is which of the following? a. Throat swabs b. Sputum c. Nasopharyngeal aspirates d. Anterior nose swab 50. c. Bordetella pertussis infects the upper airway. The best specimen for identification of this pathogen has been shown to be collected from the nasopharynx. 51. Organisms belonging to the genus Brucella are best described by which of the following statements? a. Gram-positive diplococci b. Gram-positive diphtheroid bacilli c. Gram-negative coccobacilli d. Gram-negative bacilli 51. c. When stained using the Gram stain, members of the genus Brucella usually appear as gramnegative coccobacilli. 52. Serum samples collected on a patient with pneumonia demonstrate a rising antibody titer to Legionella. A bronchoalveolar lavage sample was collected and revealed a positive DFA test for Legionella, but no organisms were recovered from this specimen when it was cultured on the appropriate medium and incubated for 2 days at 35 C in CO2. Which of the following is the best explanation? a. Culture was not incubated long enough b. Antibody titer c. Specimen was incubated at the wrong temperature d. Positive DFA test result is a false positive 52. a. Legionella pneumophila requires specialized medium, 35 C, carbon dioxide, and extended incubation; hold for 2 weeks. 53. Of the following media, which provides the NAD necessary for the growth of Haemophilus spp.? a. 5% sheep blood agar b. Brain heart infusion agar c. Chocolate agar d. Nutrient agar 53. c. Of the media listed, only chocolate agar provides the X and V factors required for the growth of Haemophilus spp. 54. Performing the factor requirement test for Haemophilus involves which of the following processes? a. Inoculation of unsupplemented media with a light suspension of the organism and placement of factors X and V disks on the agar surface b. Inoculation of liquid media, unsupplemented and supplemented with factors X and V c. Detecting the presence of enzymes that convert aaminolevulinic acid (ALA) into porphyrins d. Growth of the organism in the presence of bacterial species that produce X and V factors as metabolic by-products 54. a. Most members of the genus Haemophilus require X and V factors, and these factors are a key characteristic in the identification of this genus. The factor requirement test involves inoculation of unsupplemented media with a light suspension of the organism and placement of X and V factor disks on the agar surface. Growth around only the X/V combination supports the identification of Haemophilus spp. 55. Of the asaccharolytic, oxidase-positive bacilli that do not grow on MacConkey agar, which one is among the HACEK group of bacteria known to cause subacute bacterial endocarditis? a. Eikenella corrodens b. Weeksella virosa c. Pseudomonas maltophilia d. Sphingomonas paucimobilis 55. a. Eikenella corrodens is an asaccharolytic, oxidase-positive bacillus that does not grow on MacConkey agar and that produces a bleachlike odor. Eikenella has been referred to as part of the HACEK group of organisms along with Hemophilus, Actinobacillus, Cardiobacterium, and Kingella. It is most often associated with wounds of the mouth or teeth or other wounds originating with contact with the mouth or teeth, but has been known to cause subacute bacterial endocarditis. 56. Which of the following statements best completes the following thought: Presumptive identification of an oxidase-positive, gram-negative diplococcus on Thayer-Martin medium from genital sites of a 6- year-old female as Neisseria gonorrhoeae? a. Provides the physician with quick and reliable results at minimal cost b. May sometimes be incorrect, and a repeat culture should be collected c. May sometimes be incorrect and should not be reported until confirmed d. Should be done only when venereal disease is suspected 56. c. Reporting of a sexually transmitted infection (STI) from a child younger than 12 years of age usually has significant social and legal ramifications. Because other Neisseria spp. can be incorrectly identified as Neisseria gonorrhoeae, particular care and additional confirmatory testing are often the most appropriate course of action. 57. The bacterial species that can be described as oxidasepositive, glucose-positive, maltose-positive, sucrosenegative, lactose-negative, and a major cause of bacterial meningitis is most likely which of the following? a. Neisseria meningitidis b. Neisseria gonorrhoeae c. Streptococcus pneumoniae d. Viridans group Streptococcus 57. a. Of the species of Neisseria found in humans, N. meningitidis is a glucose-positive, maltosepositive, sucrose-negative, lactose-negative major cause of bacterial meningitis. 58. The bacterial species that can be described as oxidasepositive, glucose-positive, maltose-negative, sucrosenegative, lactose-negative, and a major cause of venereal disease is most likely which of the following? a. Neisseria meningitidis b. Neisseria gonorrhoeae c. Streptococcus pyogenes d. Viridans group Streptococcus 58. b. Of the species of Neisseria found in humans, N. gonorrhoeae is an oxidase-positive, glucosepositive, maltose-negative, sucrose-negative, lactose-negative major cause of venereal disease. 59. Organisms belonging to the genus Neisseria are described as which of the following? a. Gram-positive diplococci b. Gram-negative diplococci c. Gram-negative coccobacilli d. Gram-negative bacilli 59. b. When seen in a gram-stained smear, Nesseria spp. are gram negative diplococci. 60. The following were observed when the Hugh-Leifson oxidative-fermentative test was performed on a bacterial isolate. Which of the options below best describes the organism's reaction? a. Oxidizer b. Nonoxidizer c. Fermenter d. Nonviable 60. a. The Hugh-Leifson oxidative-fermentative (OF) test shows a pH shift in the open glucose tube and no pH in the closed tube. This indicates that this organism is an oxidizer. 61. The oxidase test is a critical test when attempting to identify nonfermenting gram-negative bacilli. This test is designed to determine the presence of which of the following? a. b-Galactosidase b. Cytochrome oxidase c. Glucose oxidizing enzymes d. Oxygen 61. b. The oxidase test detects the presence of cytochrome oxidase. This enzyme is part of the energy transfer cascade of intermediate metabolism. 62. The blood culture of a patient with a central venous catheter yielded a gram-negative bacillus growing on MacConkey agar with the following reactions: Oxidase=Negative Motility=Positive Glucose oxidative=fermentative open=Positive (weak) Maltose oxidative=fermentative open=Positive (strong) Catalase= Positive Esculin hydrolysis=Positive Which of the following is the most likely identification of this organism? a. Burkholderia cepacia b. Pseudomonas aeruginosa c. Acinetobacter baumannii d. Stenotrophomonas maltophilia 62. d. In the laboratory, Stenotrophomonas maltophilia has unique characteristics, including growth on blood agar and chocolate agar with a greenlavender or yellow pigment. Colonies are non- lactose fermenting on MacConkey agar, oxidase-negative, catalase-positive, and esculinpositive. This gram-negative bacillus strongly oxidizes maltose but only weakly oxidizes glucose. 63. Which organism is associated with the disease Melioidosis? a. Burkholderia ralstonia b. Burkholderia pseudomallei c. Burkholderia mallei d. Burkholderia cepacia 63. b. Melioidosis is caused by Burkholderia pseudomallei. 64. Differentiation of Stenotrophomonas maltophilia and Burkholderia cepacia is best accomplished by which of the following tests? a. Oxidase test b. Maltose and glucose medium c. Tyrosine-enriched heart infusion agar d. Growth at 42 C 64. a. Stenotrophomonasmaltophilia is oxidase-negative, and Burkholderia cepacia is oxidase-positive. 65. The respiratory culture of a patient with cystic fibrosis yielded a gram-negative bacillus with the following reactions: Oxidase¼Positive Motility¼Positive Glucose oxidative-fermentative open¼Positive Gelatin hydrolysis¼Positive Soluble green pigment on TSA slant Arginine dihydrolase¼Positive Growth at 42 C¼positive Which of the following is the most likely identification of this organism? a. Burkholderia cepacia b. Pseudomonas aeruginosa c. Acinetobacter baumannii d. Stenotrophomonas xylosoxidans 65. b. Acinetobacter and Stenotrophomonas are oxidasenegative. The soluble green pigment differentiates Pseudomonas aeruginosa from Burkholderia. 66. Which test group best differentiates Acinetobacter baumannii from Pseudomonas aeruginosa? a. Oxidase, motility, nitrate reduction b. Growth on MacConkey agar, catalase, nitrate reduction c. Growth on blood agar, oxidase, catalase d. TSI, urea, motility 66. a. Key tests can be used to differentiate Acinetobacter from Pseudomonas. Two easy tests are oxidase (Pseudomonas is positive and Acinetobacter is negative) and motility (Pseudomonas is positive and Acinetobacter is negative). 67. Which of the following sets of results represent the most common reactions for Moraxella catarrhalis when tested in CTA sugar tubes? a. Glucose: Negative; Maltose: Negative; Lactose: Negative; Sucrose: Negative b. Glucose: Positive; Maltose: Negative; Lactose: Negative; Sucrose: Negative c. Glucose: Positive; Maltose: Positive; Lactose: Negative; Sucrose: Negative d. Glucose: Positive; Maltose: Negative; Lactose: Positive; Sucrose: Negative 67. a. Cystic tryptic agar (CTA) sugar reactions are used to differentiate Neisseria species. If Moraxella catarrhalis is tested in this system, the isolate will be glucose-negative, maltose-negative, lactosenegative, and sucrose-negative. 68. A soluble, bright green pigment can be produced by Pseudomonas aeruginosa. This pigment is known as which of the following? a. Pyoverdin b. Pyocyanin c. Pyorubin d. Pyophena 68. b. Of the organisms listed, only Pseudomonas aeruginosa produces the pigment pyocyanin. 69. A small portion of a colony of a gram-negative bacilli was smeared onto a filter paper test system. One percent tetramethyl-p-phenylenediamine dihydrochloride was added. At 10 seconds, a dark purple color developed where the colony was added to the paper. Which of the following statements best describes the test results? a. Positive indole test b. Positive oxidase test c. Positive urea test d. Positive esculin test 69. b. Of the tests listed, the oxidase test is the only test that exhibits a dark purple color.