Portage Microbiology Exam #4

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

A researcher is asked to determine which of two vials contains e coli and which contains salmonella. Knowing both gram-negative while only one of them is capable of fermenting lactose, which type of media would be best suited (multiple choice)

Differential media distinguishes between two, often related, microbes

What are the requirements of a fastidious microbe? (short answer)

A fastidious microbe is an organism with complex growth requirements such that is 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 selective, non-differential media

False

What is agar used for in microbiology? (short answer)

Agar is used to create a solid, smooth surface on which microbes can grow

Alpha hemolysis (matching)

Incomplete hemolytic activity

Beta hemolysis (matching)

Complete hemolytic activity

Gamma hemolysis (matching)

No hemolytic activity

Colombia CNA agar is most closely related to which media (multiple choice)

CNA agar is similar to VAP as it is also enriched with blood and allows for differentiation based on hemolytic patterns

True or False: Chocolate agar gets its brown color from cocoa to produce an enriched media

False

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? (short answer)

No. A gram stain would not be necessary, as only gram negative microbes will grown on MacConkey agar. Thus, e coli is a gram negative microbe

In an attempt to detect the presence of the pathogenic strain of e coli O157:H7, a researcher spread culture onto a MacConkey agar with failed results. What type of agar should they (correctly) try next? Why? (short answer)

The microbe should be plated on SMAC as it is specifically formulated to detect O157:H7. Pathogenic e coli cannot ferment sorbitol while non-pathogenic e coli can ferment both sorbitol and lactose. Therefore, colonies that ferment can be differentiated from non-fermenters.

What is the gram status of microbes growing on eosin methylene blue agar plates? (short answer)

Gram-negative

What is the process of spreading a bacterial culture onto a petri dish? (short answer)

Plating

Mannitol salt agar will turn what color in the presence of the pathogenic strain staphylococcus aureus? (short answer)

Yellow

In order to visual individual colonies of bacteria, would you culture your sample in a liquid media or on a solid (agar) media? Why? (short answer)

Solid 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 a way as to form colonies

True or False: the visualization of colonies on a petri dish represents bacterial cells that have often multiplied a million times over

True

True or False: the purpose of a quadrant streak expand a bacterial population

False

To be considered a pure culture, the sample can be traced back to a single cell and _________

The culture must also be free from external contaminants. Would not contain multiple bacterial species

When performing a quadrants streak, the sample is spread across the plate in such as way as to form what? (short answer)

A 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? (short answer)

P4, phases rank from highest to lowest

True or False: when performing a dilution streak a new loop must be used for each phase

True

In order to encourage growth of a slow growing microbe what might a researcher do during a phase dilution streak? (short answer)

A researcher may either opt to perform only a 3-phase dilution streak or pass the loop through the previous phase multiple times

True or False: to restrict the growth of a pathogenic researcher might decrease an incubator from 37C to 25C

True

When given an unknown bacterial sample the first step is to expand the current bacterial population. Which form of media best suits this need? Why?

LB media. All the other options 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 placed onto selective/differential plates

True or False: Differential media is best suited for distinguishing between two similar species of bacteria

True