Bio 171 module 4 review Exam Questionsb And Answers Verified Solution

What is another name for a liquid growth media, and what are the basic components? - ANSWERSGrowth media in a liquid form is often referred to as nutrient broth. As the name implies its composition consists primarily of essential 'ingredients' such as a rich source of sugars, amino acids and vitamins. Together, a nutrient broth provides the microbe with a source of carbon/energy, which, in turn, encourages its expansion. What is selective media? - ANSWERSSelective media allows for only the growth of certain microbes while restricting the growth of all others What is differential media - ANSWERSDifferential media is used to distinguish between two (or more) related microbes. Is media distinguish two often related microbes. Ex: E. Coli and salmonella. They can grow up in a differential media but only E. Coli would react to lactose and become red colored while salmonella will stay white/tan in color. What are the requirements of a fastidious microbe? - ANSWERSfastidious microbe is an organism with complex growth requirements such that if absent it will not grow. Enriched medias thus contain these specific and essential nutrients required for the growth of a particular subset of microorganisms. What is agar? - ANSWERSIn its simplest form agar is liquid growth media that has had a hardening agent added to it. Agar is created when a polysaccharide derived from seaweed (algae) extract is added to growth media. Agar is used to create a solid, smooth surface on which microbes can grow. True or False: LB agar is classified as a non-selective, differential media - ANSWERSLB agar is both a non-selective and non-differential media. LB agar is often used to expand unknown microbial population because it encourages microbial growth due to the presence of universal nutrients (non-differential) and absence of restrictive factors (non-selective). What are the three forms of hemolysis found on blood agar plates? - ANSWERSAlpha (green), Beta (clear zones) and Gamma (white/tan). Microbes capable of alpha hemolysis present with greenish-brown color colonies due to the incomplete (partial) lysis of red blood cells. Beta hemolysis is classified as the capacity of a microbe to completely lyse red blood cells. The resulting lysis presents as a distinct zone of clearing around the growing colony. Gamma hemolysis designates the absence or lack of hemolytic activity and the resulting colonies are often white/tan in color growing on the red background color of the unaffected blood agar plate. What is the primary purpose of Columbia CNA agar? - ANSWERSAs it suppresses the growth of Gram-negative bacteria CNA agar is, therefore, used for isolation of Gram-positive microbes. Name the type of plate derived from BAP that contains lysed red blood cells. - ANSWERSLysed red blood cells (RBCs) are a primary component in the formulation of Chocolate agar. Define the selective and differential abilities of a MacConkey agar plate. - ANSWERSMacConkey agar is selective in that only Gram-negative microbes will grow on the agar—Gram-positive microbes simply do not grow. MacConkey agar is also considered a differential media as it distinguishes between microbes capable of fermenting lactose (red colonies) and those that are non-fermenters (white/tan colonies). What colors would you expect to see on an EMB plate containing E. coli? - ANSWERSThe EMB plate itself is red in color while in the presence of E coli, the growing colonies will take on a distinctive metallic green sheen. Note: You are responsible for knowing the color and general properties (selective vs differential) of all of the agar plates described within this module, with a special emphasis on how a particular agar plate aids in identifying select microbes. What is the name of the process of spreading a bacterial culture onto a petri dish? - ANSWERSPlating. Plating microbes can be done using a sterile loop, a sterile swab, or a sterilized wire loop. Each device is simply a means of spreading the bacteria, most commonly in a simple back-and-forth motion, across the plate. What is the primary advantage of plating a bacterial culture as opposed to having it grow in solution? - ANSWERSThe primary advantage of plating a bacterial sample onto agar is that cells are held in place. Unlike in a nutrient broth where bacterial cells can multiply but are free to move around in solution, bacteria plated onto agar are fixed in such a way as to support the formation and visualization of colonies. What is the purpose of the quadrant streak approach? - ANSWERSThe purpose of this method is to generate an individual colony so that a single (pure) bacterial sample can be picked from the plate. In a three-phase dilution gradient, which phase most likely contains individual colonies: phase 1 (P1) or phase 3 (P3)? - ANSWERSIndividual colonies are most likely going to appear within the phase 3 streaks. You begin with P1 (highest concentration), dilute during P2 and then further dilute the sample in P3. However, it is possible to see individual colonies in P2 if only a small portion of P1 was carried over into P2. True or False: Differential media is best suited for distinguishing between two similar species of bacteria. - ANSWERSTrueRUE (Growth media does not contain restrictive factors, while selective media is best used to encourage the growth of one microbe while simultaneously discouraging the growth of the other. Since two similar species of microbes are being studied they must be differentiated under similar but just slightly different conditions (differential media). A researcher is asked to determine if a sample contains Neisseria meningitides. Knowing Neisseria meningitides is slow growing and other foreign microbes may also be present in the culture, which type of media would be best suited? - ANSWERSSelective media What are the requirements of a fastidious microbe? - ANSWERSA fastidious microbe is an organism with complex growth requirements such that if absent it will not grow. Enriched medias thus contain these specific and essential nutrients required for the growth of a particular subset of microorganisms. True or False: LB agar is classified as a non-selective, non-differential media. - ANSWERSTRUE LB agar is the most basic type of agar and like LB media supports the growth of virtually all microbes without restriction. What is agar used for in microbiology? - ANSWERSAgar is used to create a solid, smooth surface on which microbes can grow. Blood agar is which type of medium? Select all that apply - ANSWERSBlood agar can be used to differential between species based on its hemolytic activity. ENRICHED DIFFERENTIAL Match the following hemolytic class with its description of activity. - ANSWERS1Alpha hemolysis—INCOMPLETE HEMOLYTIC ABILITY Beta 2hemolysis---COMPLETE HEMOLYTICABILITY 3Gamma hemolysis---NO HEMOLYTIC ABILITY Columbia CNA agar is most closely related to which media: - ANSWERSBLOOD AGAR (CNA agar is similar to BAP as it is also enriched with blood and allows for differentiation based on hemolytic patterns True or False: Chocolate (cocoa) is not a component of Chocolate agar plates. - ANSWERSTRUE The name is derived simply based on the color that actually comes from the presence of 'cooked' (lysed) red blood cells in the media. A researcher is studying a strain of E. coli currently growing on a MacConkey plate. However, the researcher can't remember if E. coli is Gram-positive or Gram-negative. Would a Gram stain be necessary to confirm? Why or why not? - ANSWERSNo. A Gram stain would not be necessary, as only Gram-Negative microbes will grow on MacConkey agar. Thus, E. coli is a Gram-Negative microbe. In an attempt to detect the presence of the pathogenic strain of E. coliO157:H7, a researcher spread a culture onto a MacConkey agar with failed results. What type of agar should they (correctly) try next? Why? - ANSWERSThe microbe should be plated on SMAC (Sorbitol-MacConkey agar) as it is specifically formulated to detect O157:H7. Pathogenic E. coli (O157:H7) cannot ferment sorbitol while non-pathogenic E. coli can ferment both soribitol and lactose. Therefore, colonies that ferment (acidic conditions; non-pathogenic) can be differentiated from non-fermenters (neutral to basic conditions; pathogenic). What is the Gram status (positive or negative) of microbes growing on Eosin Methylene Blue (EMB) agar plates? - ANSWERSGram-Negative. EMB plates specifically restrict the growth of Gram-Positive bacteria. QUESTION 13 Mannitol salt agar will turn what color in the presence of the pathogenic strain Staphylococcus aureus? - ANSWERSYELLOW; Pathogenic Staph aureus will turn the agar from red to yellow. What is the process of spreading a bacterial culture onto a petri dish called - ANSWERSplating n order to visual individual colonies of bacteria would you culture your sample in a liquid media or on a solid (agar) media? Why? - ANSWERSSolid (agar) media. The primary advantage is that cells are held into place. When grown in a nutrient broth, bacterial cells can multiply but are free to move around in solution. When grown on agar within a petri dish the fixed in such as way as to form colonies. True or False: The visualization of colonies on a petri dish represents bacterial cells that have multiplied ~2- 3 times. - ANSWERSFALSE; When an individual colony is visible on agar the bacterial cell has multiplied often a million times over. True or False. The purpose of a quadrant streak is to expand a bacterial population. - ANSWERSFalse. The purpose of the quadrant streak is to generate individual colonies such that a single (pure) bacterial sample can be isolated. To be considered a pure culture, the sample (1) can be traced back to a single cell and (2) ...... - ANSWERSThe culture must also be free from external contaminants. Simply put, a pure sample would never contain multiple bacterial species (ie) Strep and Staph. When performing a quadrant streak, the sample is spread across the plate in such as way as to form what? - ANSWERSA dilution gradient is formed. The resulting gradient should always contain within it the growth of individual colonies. In what phase of a dilution streak would you expect to find the lowest concentration of bacteria, P2 or P4? - ANSWERSP4 (Phase 4) would contain the lowest concentration of bacteria. The phases rank (from highest to lowest), P1 > P2 > P3 > P4. True or False. When performing a dilution streak a new (or sterilized) loop is not required for each phase as long as the bacterial culture is pure. - ANSWERSFalse. A new or sterilized loop is absolutely required for each phase. Failure to do so would prevent the establishment of a dilution gradient, as the same bacterial concentration would be spread across both phase regions, regardless of whether or not the culture is pure. In order to encourage growth of a slow growing microbe what might a researcher do during a phase dilution streak - ANSWERSA researcher may either (1) opt to perform only a 3-phase dilution streak or (2) pass the loop through the previous phase multiple times (as opposed to only once). True or False. Pathogenic strains of bacteria tend to grow slower than normal non-pathogenic bacterial strains. - ANSWERSFalse. Pathogenic strains of bacteria tend to grow faster than non-pathogenic strains at 37°C, which is why researchers may set incubators at 25°C to restrict its growth. When given an unknown bacterial sample the first step is to expand the current bacterial population. Which form of media best suites this need? Why? MSA Agar, LB media containing ampicillin and neomycin, MacConkey agar, Blood agar - ANSWERSBlood agar. All other options (A, B and C) are all forms of selective media, meaning they may potentially inhibit the growth of the unknown sample. Although blood agar is considered a differential media, it is, most importantly, a non-selective media. Given the alternatives, this is the best option.