Portage Learning BIOD 171 Module 4

Portage Learning BIOD 171 Module 4 Exam Module 4 1. True or False: Growth media is best suited for distinguishing between two similar species of bacteria. False. Growth media is designed to simply support (and not restrict) microbial growth. 2. A researcher is asked to determine which of two vials contains E coli and which contains Salmonella. Knowing both are Gram-Negative while only one of them is capable of fermenting lactose, which type of media would be best suited: A. Growth media B. Differential media C. Selective media D. Selective and Differential media B. Differential media distinguishes between two, often related, microbes. 3. What are the requirements of a fastidious microbe? A 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. 4. True or False: LB agar is classified as a selective, non-differential media. False. LB agar is the most basic type of agar and like LB media supports the growth of virtually all microbes without restriction. 5. What is agar used for in microbiology? Agar is used to create a solid, smooth surface on which microbes can grow. 6. Match the following hemolytic class with its description of activity. 1. Alpha hemolysis B A. No hemolytic activity 2. Beta hemolysis C B. Incomplete hemolytic activity 3. Gamma hemolysis A C. Complete hemolytic activity 7. Columbia CNA agar is most closely related to which media: A. Trypticase Soy Agar B. MacConkey Agar C. Blood agar D. EMB agar C. CNA agar is similar to BAP as it is also enriched with blood and allows for differentiation based on hemolytic patterns. 8. True or False: Chocolate agar gets its brown color from cocoa to produce an enriched media. False. Chocolate (cocoa) is never added to the media. The name is derived simply based on the color that actually comes from the presence of ‘cooked’ (lysed) red blood cells in the media. 9. 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? No. 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. 10. In an attempt to detect the presence of the pathogenic strain of E. coli O157:H7, a researcher spread a culture onto a MacConkey agar with failed results. What type of agar should they (correctly) try next? Why? The 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; nonpathogenic) can be differentiated from non-fermenters (neutral to basic conditions; pathogenic). 11. What is the Gram status (Positive or Negative) of microbes growing on Eosin Methylene Blue (EMB) agar plates? Gram-Negative. EMB plates specifically restrict the growth of Gram-Positive bacteria. 12. Mannitol salt agar will turn what color in the presence of the pathogenic strain Staphylococcus aureus? Yellow. Pathogenic Staph aureus will turn the agar from red to yellow. 13. What is the process of spreading a bacterial culture onto a petri dish? Plating. 14. In order to visual individual colonies of bacteria would you culture your sample in a liquid media or on a solid (agar) media? Why? Solid (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. 15. True or False? The visualization of colonies on a petri dish represents bacterial cells that have often multiplied a million times over. True. To form a bacterial colony the initial cell must have multiplied many times over, often greater than a million, in order for the naked eye to resolve it. 16. True or False. The purpose of a quadrant streak is to expand a bacterial population. False. The purpose of the quadrant streak is to generate individual colonies such that a single (pure) bacterial sample can be isolated. 17. To be considered a ‘pure’ culture, the sample (1) can be traced back to a single cell and (2) ? The culture must also be free from external contaminants. Simply put, a pure sample would never contain multiple bacterial species (ie) Strep and Staph. 18. When performing a quadrant streak, the sample is spread across the plate in such as way as to form what? A dilution gradient is formed. The resulting gradient should always contain within it the growth of individual colonies. 19. In what phase of a dilution streak would you expect to find the lowest concentration of bacteria, P2 or P4? P4 (Phase 4) would contain the lowest concentration of bacteria. The phases rank (from highest to lowest), P1 > P2 > P3 > P4. 20. True or False. When performing a dilution streak a new (or sterilized) loop must be used for each phase. True. Failure to do so would prevent the establishment of a dilution gradient, as the same bacterial concentration would be spread across both phase regions. 21. In order to encourage growth of a slow growing microbe what might a researcher do during a phase dilution streak? A 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). 22. True or False. To restrict the growth of a pathogenic microbe a researcher might decrease an incubator from 37°C to 25°C. True. Pathogenic strains of bacteria tend to grow faster than non-pathogenic strains at 37°C, so researchers may set incubators at 25°C to restrict its growth. 23. 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? A. MSA agar B. LB media C. MacConkey agar D. Columbia CNA agar B. LB media. All other options (A, C and D) are all forms of selective media, meaning they may potentially inhibit the growth of the unknown sample. The culture should be first expanded and then place onto selective/differential agar plates.