UAMS Micro Lab Exam 1 Questions And 100% Verified Correct Answers Pass Guaranteed.

Why are agar plates incubated upside-down? - correct answers To keep condensation from forming on the lid and dripping onto the bacteria. Dripping liquid affects colony count and morphology. Why is the inoculating loop sterilized between streaking quadrants? - correct answers To facilitate isolation of microorganisms - form individual CFUs. Also provides accurate enumeration of bacteria. Why can a single colony on a plate be used to start a pure culture? - correct answers A single colony is started by a single bacterial cell. One bacterial cell can multiply to thousands/millions of bacterial cells given the right nutrients and incubation conditions. What is meant by "colonial morphology"? - correct answers The characteristics of a colony: size, shape, texture, hemolysis What are the signs of a growth in a liquid medium? - correct answers Cloudiness/turbidity in the sample Why is the bottom of an agar plate labeled and not the lid? - correct answers Because lids are not attached to the agar plate and can be dropped/fall off. If the lid falls off, the plate should be labeled with the patient information. Which media used in this exercise are selective for gram positive organisms? Gram negative organisms? - correct answers Gram positive media: CNA, PEA Gram negative media: EMB, MAC In a gram stained smear what color are the gram positive organisms? Gram negative organisms? - correct answers Gram positive MOs: purple Gram negative MOs: pink/red Why must young or actively growing cultures be used for the gram stain? - correct answers Older organisms may have atypical gram stains because they may not take up the stain very well. Gram positive MOs can appear gram negative after 24-48 hours. What is the color of an overdecolorized organism? An underdecolorized organism? - correct answersOverdecolorized MO: Pink/red (gram positives look gram negative) Underdecolorized MO: Purple (gram negatives look gram positive) What is the function of the iodine solution in the Gram stain? If it were omitted how would staining results be affected? - correct answersIodine functions as a mordant/fixative to keep the crystal violet inside the bacterial cell wall. It forms an crystal violet-iodine complex. If omitted, gram positive organisms appear gram negative. What is the purpose of the alcohol-acetone solution in the Gram stain? - correct answersThe decolorizer removes the crystal violet-iodine complex from gram negative organisms. What counterstain is used? Why is it necessary? Could colors other than red be used? - correct answersSafranin is the counterstain. It is necessary to stain the gram negative organisms pink/red. Other colors could be used but safranin is the typical counterstain. 5% sheep's blood agar - correct answersNon-selective media; good for culturing many species of GN and GP bacteria EMB - correct answersgram-negative bacilli MacConkey Agar - correct answersgram-negative bacilli CNA agar - correct answersgram-positive organisms PEA - correct answersgram-positive organisms what temperature should plates be incubated at? - correct answers35 degrees Celsius Levels of growth - correct answersNG: no growth 1+ = few = growth in first quadrant 2+ = moderate = growth in first and second quadrant 3+ = many = growth in all three quadrants E Coli grows on - correct answersBA, EMB, MAC S. aureus grows on - correct answersBA, CNA, PEA Gram stain procedure - correct answers1. Primary stain (Crystal violet- a basic stain) 2. Mordant (Gram's iodine- I2 + KI) (something that helps fix dye on or in a cell but does not itself contribute color) 3. decolorizing agent (Ethanol or acetone) 4. Counterstain (Safranin- a basic stain) E. Coli gram stain - correct answers S. aureus gram stain - correct answers Which medium should be used to accurately determine the type of hemolysis produced by an organism? - correct answers Blood agar Is hemolysis a reliable characteristic for differentiating staphylococci? Explain. - correct answers Not really- hemolysis is especially important for differentiating strep. Staph aureus can be beta or gamma hemolytic, but Coag Neg Staph can be beta or gamma as well. Which test(s) detects bound coagulase? Free coagulase? Protein A? - correct answers Bound Coagulase: Slide coagulase test Free Coagulase: Tube coagulase test Protein A: Staph Latex Agglutination test How is S. saprophyticus distinguished from S. epidermidis? - correct answers Novobiocin disk susceptibility test - S.saprophyticus is RESISTANT, while S. epidermidis is SUSCEPTIBLE. Catalase production - correct answers catalase breaks down H2O2 to water and oxygen = bubbles Slide coagulase - correct answers bound coagulase converts fibrinogen to fibrin = clot formation Tube coagulase - correct answers free coagulase converts fibrinogen to fibrin = clot formation Latex agglutination - correct answers Protein A on the bacterial cell wall agglutinates with the latex beads coated in Protein A antibodies Novobiocin susceptibility - correct answers disk placed on agar with organism - look for zone of inhibition around the novobiocin disk Alpha hemolysis - correct answers Greenish discoloration of the blood agar surrounding a bacterial colony; characteristic of Streptococcus pneumoniae Beta hemolysis - correct answers A zone of clearing in the blood agar surrounding a bacterial colony. It is a characteristic of Streptococcus pyogenes as well as some strains of Staphylococcus aureus. Gamma hemolysis - correct answers No hemolysis evident. It is frequently a characteristic of Enterococcus species. Staphylococci (aureus and epidermidis) and Micrococcus - correct answers catalase positive Streptococci - correct answers catalase negative Enterococci is a psuedocatalase because - correct answers It may give a false positive reaction. Compare the microscopic morphology of streptococci and staphylococci. - correct answers Streptococci: GPC in chains/pairs Staphylococci: GPC in clusters Which test distinguishes staphylococci from streptococci? - correct answers Catalase What type of hemolysis is produced by: - correct answers- GAS- beta - GBS- beta or gamma - Enterococci- alpha or gamma - Strep pneumo- alpha - Viridans strep- alpha or gamma Bacitracin Susceptibility - correct answers disk placed on agar with organism- look for zone of inhibition around the bacitracin disk CAMP Test - correct answers GBS produces CAMP factor + S.aureus produces beta-lysin = arrowhead hemolysis Optochin susceptibility - correct answers disk placed on agar with organism- look for zone of inhibition around the optochin disk Bile solubility - correct answers bile salts accelerate the autolytic properties of Strep pneumo Growth in 6.5% NaCl - correct answers determines ability of MO to grow in high salt concentrations PYR Hydrolysis - correct answers determines the presence of an enzyme to break down L-pyrrolidonal-b-naphthylamide