Microbiology Laboratory Techniques Review

These flashcards cover essential vocabulary and concepts related to microbiology laboratory techniques, with a focus on bacterial identification methods and their implications.

What are two purposes for using MSA in an unknown lab?

To isolate Staphylococcus species and to differentiate S. aureus (mannitol fermenter) from other staphylococci.

Give the Genus and species names of two bacteria likely isolated using MSA.

Staphylococcus aureus and Staphylococcus epidermidis.

What is the selective agent in MSA?

High salt concentration (NaCl).

What is the differential agent in MSA?

Mannitol.

What is the pH indicator in MSA?

Phenol Red.

Which of these plates is positive for fermentation of the differential agent in MSA?

Yellow colonies/agar (due to acid production).

What category of medium is BA (Blood Agar)?

Differential.

Which plate shows beta hemolysis?

Plate B (complete lysis of red blood cells).

Which plate shows gamma hemolysis?

Plate A (no hemolysis).

What toxic substance does catalase break down?

Hydrogen peroxide (H2O2).

What are the two end products of this enzymatic reaction?

Water (H2O) and oxygen (O2).

What bacterium is detected by the coagulase test?

Staphylococcus aureus.

How does coagulase increase virulence?

It clots blood plasma, helping the bacteria evade phagocytosis.

How do organisms use coagulase as a virulence factor?

Coagulase helps bacteria form fibrin clots that protect them from the immune system.

What is the Gram reaction of organisms on MacConkey or EMB plates?

Typically Gram-negative.

Which plate demonstrates lactose fermentation on MacConkey or EMB?

The plate showing pink/red colonies (acid production).

What is the selective agent on MacConkey or EMB?

Bile salts and crystal violet (inhibit Gram-positive bacteria).

What is the differential agent on MacConkey or EMB?

Lactose.

What is the pH indicator on MacConkey?

Neutral red.

On a MacConkey plate, which plate is positive for fermentation of the differential agent?

The plate with pink/red colonies (or pink agar) indicates lactose fermentation.

Describe three steps for obtaining a clean catch urine sample.

Wash hands, clean genital area, collect midstream urine.

What is a clean catch? When is it important to obtain a clean catch? When is it not important?

A urine sample collected to avoid contamination, important when diagnosing a UTI. It's not important when sterility isn't required, like a pregnancy test or urinalysis.

Most common genus and species that cause a UTI.

Escherichia coli (E. Coli).

What role does urease play in a UTI?

It breaks down urea into ammonia, raising pH and promoting stone formation.

Give one alkaliphilic bacterium associated with UTIs.

Proteus mirabilis.

What is the clinical significance of finding high glucose levels in the urine?

It indicates possible diabetes.

What is detected in urine if a female is pregnant?

Pregnancy tests detect human chorionic gonadotropin (hCG) in the urine.

What are the three SIM readings for test tube A?

Sulfide (+/–), Indole (+/–), Motility (+/–). (The specific result depends on the sample.)

What are the three SIM readings for test tube B?

Sulfide (+/–), Indole (+/–), Motility (+/–). (The specific result depends on the sample.)

What are the common pathogens (genus and species) associated with beta-hemolytic bacteria in the throat?

Streptococcus pyogenes.

What are the common pathogens (genus and species) associated with alpha-hemolytic bacteria in the throat?

Streptococcus pneumoniae.

List two characteristics of the family Enterobacteriaceae.

Gram-negative rods; ferment glucose; oxidase-negative.

Give two members of the Enterobacteriaceae family.

Escherichia coli, Klebsiella pneumoniae.

What enzyme is detected in a positive test result for indole production? Interpret the results for this SIM test tube.

Enzyme = Tryptophanase. Result: Red layer = positive for indole; Yellow = negative for indole.

Name the reagent used to test for tryptophanase in SIM.

Kovac’s reagent.

Which of the three SIM tests is used in IMViC?

Indole test.

Describe the family Enterobacteriaceae and give the Genus of two microbes that are part of this family.

Enterobacteriaceae is Gram-negative, facultative anaerobic rods that ferment glucose and are oxidase-negative. Examples: Escherichia and Salmonella.

What fermentation products are determined by the MR test? Which tube is positive?

Mixed acids (lactic, acetic). Red color = positive.

What does the VP test detect? Which tube is positive for this result?

Acetoin (neutral end product of glucose fermentation). Red color = positive.

What is added to show the fermentation products for the MR test?

Methyl red indicator.

What fermentation products are determined by the VP test? Which tube is positive?

Acetoin (2,3-butanediol pathway). Red color = positive.

What is added to show these products for the VP test?

Barritt’s reagents A (\alpha-naphthol) and B (KOH).

What is the purpose of the CIT test in IMViC?

Tests if bacteria can use citrate as a carbon source.

Which tube is positive for the CIT test?

Blue color = positive.

What is indicated by growth and a gas bubble in the LSB tube from meat?

Coliform bacteria; lactose fermentation and gas production.

Where did contamination in the LSB tube from meat come from?

Fecal contamination.

What is indicated by growth on an MSA plate from meat?

Staphylococcus species present.

Where did contamination on the MSA plate from meat come from?

Human handling (skin, nasal passages).

What category of medium is PA (Pseudomonas Agar)?

Selective and differential.

What Genus is isolated on PA medium?

Pseudomonas.

What were the two genes on the plasmid and what were their gene products?

amp^R gene \rightarrow \beta-lactamase (provides ampicillin resistance), GFP gene \rightarrow Green Fluorescent Protein (glows under UV).

Explain the purpose of the (-) plasmid on TSA only plate in this experiment.

Shows normal bacterial growth (negative control).

Explain the purpose of the (-) plasmid on TSA + ampicillin plate in this experiment.

Shows that bacteria without plasmid cannot grow on ampicillin.

Explain the purpose of the (+) plasmid on TSA only plate in this experiment.

Shows that bacteria with plasmid are healthy and viable.

Explain the purpose of the (+) plasmid on TSA and ampicillin plate in this experiment.

Shows growth only if plasmid was taken up (amp-resistance expressed). Also shows GFP expression if an inducer (arabinose) is present.

Food infection: Cause, Primary symptom, Duration.

Cause: Ingestion of live microbes. Primary symptom: Diarrhea. Duration: Longer (1–3 days).

Food intoxication: Cause, Primary symptom, Duration.

Cause: Ingestion of preformed toxin. Primary symptom: Vomiting. Duration: Short (hours).

How to determine susceptibility to Gentamicin?

Based on inhibition zone size (use NCCLS chart).

If two antibiotics show “S” (susceptible), how do you choose one?

Consider allergies, pregnancy, drug interactions, and cost.

What type of DNA damage does UV light cause?

Thymine dimers.

Why did Bacillus megaterium survive longer under UV exposure?

It forms endospores that resist UV damage.

Name the two genes on the plasmid used in transformation.

amp^R (ampicillin resistance) and GFP (green fluorescent protein).

What causes the halo effect around glowing colonies?

Diffusion of ampicillin degradation products.

Purpose of (–) plasmid TSA + ampicillin plate?

Negative control; shows no growth without plasmid.

Purpose of (+) plasmid TSA + ampicillin plate?

Shows successful transformation (growth & fluorescence).

What blood type is the universal donor?

O–.

If a person has Type A+ blood, what are possible genotypes?

AA or AO with Rh+.

If a person has Type O+ blood, what antibodies are present?

Anti-A and Anti-B.

Blood clumps only with anti-B \rightarrow blood type?

Type B+.

What does an indirect ELISA detect?

Antibodies in patient serum.

Why is it important to detect antibodies in someone not sick (via indirect ELISA)?

Indicates early or past infection (carrier or early-stage detection).

Which blood type match could cause hemolytic disease of the newborn?

(b) Mother A–, Father B+.

Why does Mother A–, Father B+ blood type match cause hemolytic disease of the newborn?

Rh– mother can form antibodies against Rh+ fetal blood in later pregnancies.