High-Yield Study Guide for MCB2004L Quiz 5: Microorganisms, Antibiotics, Water Testing, and Food Microbiology

How do lactic acid bacteria contribute to tooth decay?

They produce acid that demineralizes enamel, leading to cavities.

What is the role of Streptococcus mutans in tooth decay?

It produces glucans that contribute to sticky plaque formation and ferments sugars to produce lactic acid.

What is the function of Lactobacillus acidophilus in dental caries?

It produces large amounts of acid, lowering pH and causing enamel breakdown.

At what pH does enamel begin to dissolve?

Enamel dissolves when pH is less than 5.

What does the Snyder Test measure?

It measures acid production, with a positive result indicated by a yellow color change.

What is the importance of standardization in the Kirby-Bauer procedure?

Standardization ensures that results are comparable and reliable.

What media is used in the Kirby-Bauer procedure?

Mueller-Hinton agar.

What is the bacterial concentration standard for the Kirby-Bauer test?

0.5 McFarland standard.

How long and at what temperature should the Kirby-Bauer test be incubated?

Incubate for approximately 24 hours at a specific temperature.

How do you read the results of an antibiotic susceptibility plate?

Measure the zone of inhibition and compare it to a breakpoint chart.

What do the SIR designations stand for in antibiotic susceptibility testing?

S = susceptible, I = intermediate, R = resistant.

What are the characteristics of antibiotics?

Antibiotics are produced by microbes, work in small doses, and can kill or inhibit bacteria.

Why are antibiotics ineffective against viruses?

Antibiotics target bacterial functions, not viral ones.

What are two strategies to prevent antibiotic resistance?

Combination therapy (multiple targets) and drug rotation/scheduling (prevents adaptation).

What is the difference between antiseptics and disinfectants?

Antiseptics are used on living tissue (e.g., alcohol), while disinfectants are used on nonliving surfaces (e.g., bleach).

What is tested for in fecal coliform testing?

Indicator organisms like E. coli, not pathogens directly.

What are the characteristics of coliforms?

Coliforms are Gram-negative rods that ferment lactose to produce acid and gas.

What are the three steps in the fecal coliform testing process?

1. Presumptive test (Lauryl-tryptose broth), 2. Confirmed test (BGLB broth), 3. Completed test (EMB plate).

What indicates a positive result in the presumptive test for fecal coliforms?

Gas production in Lauryl-tryptose broth.

What does a metallic green sheen on an EMB plate indicate?

It indicates the presence of E. coli.

What is the difference between food infection and food intoxication?

Food infection involves microbes growing inside the host, while food intoxication involves toxins already present in food.

How does microbial quality relate to microbial load?

Higher microbial load indicates lower microbial quality.

What are the selective and enriching factors in sauerkraut production?

Salt kills Gram-negative spoilage bacteria, brine inhibits fungi, and sugars feed lactic acid bacteria.

What is microbial succession in the context of sauerkraut?

Different microbes dominate over time, eventually leading to acid-producing bacteria taking over.