Microbiology Lab Review Exercise Points

Comprehensive practice flashcards covering microbiology lab safety, microscopy, staining techniques, media types, biochemical tests, and specific lab exercises like HIV ELISA and API 20, derived from Dr. Bauer's lab review transcript.

What are the primary pieces of Personal Protective Equipment (PPE) used in the lab this semester?

The main PPE used were lab coats, goggles, and gloves, in addition to tying hair back.

Which Biosafety Levels (BSL) were used during the lab this semester?

Only BSL 1 and BSL 2 were used.

What is an example of a BSL level 3 organism discussed by Dr. Bauer?

Mycobacterium tuberculosis.

Where should heat-fixed slides be disposed of?

They should be placed in the gray tin containers (glass waste) at the front or back of the room.

Where should slides with live bacteria be placed if they have not been heat-fixed?

They must be placed in the Clorox beaker to kill the bacteria.

How is total magnification calculated for the compound light microscopes used in lab?

By multiplying the ocular magnification ($10 \times$) by the objective lens magnification (ranging from $4 \times$ to $100 \times$).

What is the resolving power of a compound light microscope?

The resolving power is $0.2 \text{ micrometers}$, which is the closest two objects can be and still be seen as distinct.

What does the term 'parfocal' mean in microscopy?

It means that once the specimen is focused under the initial objective ($4 \times$), it will remain nearly in focus when moving to higher powers, requiring only the fine adjustment.

How many seconds should you wait for a loop to cool after sterilization before touching live bacteria?

You should wait approximately $20$ to $30 \text{ seconds}$.

Why do bacterial cells typically take up simple stains like safranin or methylene blue?

Bacterial cell membranes have an overall negative charge, so they attract cationic stains, which are positively charged.

What are two examples of negative stains?

Negrosin and India ink.

Why is negative staining preferred over simple staining for determining true morphology?

Negative staining does not require heat fixation, which avoids the distortion of proteins and cell structure caused by heat.

What is the primary structural difference between Gram-positive and Gram-negative cell walls?

Gram-positives have a thick layer of peptidoglycan, while Gram-negatives have a thin layer of peptidoglycan and an additional outer membrane composed of lipopolysaccharide.

What happens if the counterstain (safranin) is omitted during a Gram stain of Gram-negative cells?

The Gram-negative cells would appear clear instead of red.

What is the purpose of a streak plate?

To isolate different types of bacteria from a mixed culture sample by diluting them over quadrants to form individual colonies.

What are the three types of hemolysis observed on Blood Agar?

Beta (complete hemolysis, yellowish/clear hue), Alpha (partial hemolysis, green hue), and Gamma (no hemolysis).

How does Phenylethyl Alcohol Agar (PEA) select for Gram-positive organisms?

The phenylethyl alcohol disrupts the outer membrane of Gram-negative bacteria, preventing their growth.

What does a bright pink color on MacConkey (MAC) agar indicate?

It indicates that the Gram-negative bacteria can ferment lactose.

How do you determine the Zone of Inhibition (ZOI) if the antibiotic disc is placed near the edge of the plate?

Measure the radius and multiply it by $2$ to calculate the diameter in millimeters.

Which biochemical test distinguishes staphylococci from streptococci?

The catalase test; staphylococci are catalase positive (produce bubbles), while streptococci are catalase negative.

What specific protein on the surface of Staphylococcus aureus allows it to test positive in a coagulase test?

Protein A.

What color change occurs on Mannitol Salt Agar (MSA) when bacteria ferment mannitol?

The media color changes from red/pink to yellow.

What is the first step of an indirect HIV ELISA?

Coating the plate with HIV proteins (antigen).

What enzyme was attached to the secondary antibody in the HIV ELISA lab to produce a color change?

Horseradish peroxidase.

What is the secondary, more accurate test used to confirm a positive HIV ELISA result?

The western blot.

Which antibiotic is used to identify Streptococcus pyogenes (Group A Strep)?

Bacitracin; S. pyogenes is the only streptococcus susceptible to it.

What positive result is seen in a bile esculin test for Enterococcus faecalis?

A black growth on the slant agar.

What is the purpose of the API 20 strip?

It allows for the performance of $20$ different biochemical tests simultaneously to identify Gram-negative rods (Enterobacteriaceae).

Why is mineral oil added to some cupules in the API 20 strip?

To create an anaerobic environment by blocking out oxygen.

In a Snyder test, what color indicates susceptibility to tooth decay?

A change from greenish-blue media to yellow indicates high susceptibility due to sucrose fermentation.