Question 1

Which of the following best explains why penicillin is effective against many Gram-positive bacteria but not against Mycoplasma species?

Accepted Answer

Mycoplasma species lack a peptidoglycan cell wall, which is the target of penicillin.

Question 2

A patient develops a severe infection after a urinary catheter is placed. The causative organism is found to form a biofilm and has a capsule. Which of the following best describes why this infection is difficult to treat?

Accepted Answer

Biofilms and capsules protect bacteria from both antibiotics and immune responses, making eradication challenging.

Question 3

Which of the following statements about Koch's postulates is correct?

Accepted Answer

They cannot be fully applied to viruses like HIV because some pathogens cannot be cultured in artificial media.

Question 4

Which of the following best describes the difference between active and passive immunity?

Accepted Answer

Active immunity involves the host's own immune response to an antigen, while passive immunity involves receiving pre-formed antibodies.

Question 5

A patient with Clostridioides difficile infection is treated with alcohol-based hand sanitizer. The infection persists. Which property of C. difficile explains this outcome?

Accepted Answer

C. difficile forms endospores that are resistant to alcohol-based sanitizers.

Question 6

Which of the following best explains why 70% isopropyl alcohol is more effective as a disinfectant than 100% alcohol?

Accepted Answer

Water in 70% alcohol facilitates protein denaturation and better penetration into cells.

Question 7

During aerobic respiration in bacteria, which of the following is the final electron acceptor in the electron transport chain?

Accepted Answer

Oxygen ($$\mathrm{O}_2)$$

Question 8

A patient is diagnosed with tuberculosis. The acid-fast stain is positive. What component of the bacterial cell wall is responsible for this staining property?

Accepted Answer

Mycolic acid

Question 9

Which of the following best describes the mechanism of action of sulfonamide antibiotics?

Accepted Answer

They competitively inhibit bacterial folic acid synthesis enzymes.

Question 10

A hospital outbreak of MRSA is traced to the transfer of resistance genes between bacteria. Which mechanism of horizontal gene transfer most likely explains this event?

Accepted Answer

Conjugation, which requires direct cell-to-cell contact and a pilus.

Question 11

Which of the following best explains why endospores are killed by autoclaving but not by boiling or alcohol?

Accepted Answer

Autoclaving uses high pressure and temperature ($$121\ ^\circ\mathrm{C}$$, 15 psi) to denature proteins and destroy endospore structures.

Question 12

A patient receives antibodies through breast milk. Which type of immunity is this?

Accepted Answer

Natural passive immunity

Question 13

Which of the following best distinguishes Gram-negative from Gram-positive bacteria?

Accepted Answer

Gram-negative bacteria have an outer membrane containing lipopolysaccharide (LPS), while Gram-positive bacteria do not.

Question 14

A patient with a deep puncture wound develops tetanus. Which property of Clostridium tetani explains its ability to cause disease in this environment?

Accepted Answer

It is an obligate anaerobe that thrives in oxygen-poor, deep tissue environments.

Question 15

Which of the following best describes the function of an enzyme in a metabolic pathway?

Accepted Answer

It lowers the activation energy ($$E_a) $$required for a chemical reaction to proceed.

Question 16

A laboratory technician is using MacConkey agar to culture bacteria from a urine sample. Which of the following best describes this medium?

Accepted Answer

It is both selective (for Gram-negative bacteria) and differential (for lactose fermentation).

Question 17

Which of the following best explains why a fever can be dangerous if prolonged?

Accepted Answer

Prolonged high temperatures can denature host proteins, including enzymes, disrupting cellular function.

Question 18

A patient is exposed to botulinum toxin and endotoxin (lipid A) from Gram-negative bacteria. Which statement is correct regarding their relative toxicity?

Accepted Answer

Botulinum toxin is far more potent than endotoxin; even small amounts can be lethal.

Question 19

Which of the following best describes the difference between sensitivity and specificity in diagnostic testing?

Accepted Answer

Sensitivity is the ability of a test to correctly identify true positives, while specificity is the ability to correctly identify true negatives.

Question 20

A patient is given a live attenuated vaccine. Which of the following is a major contraindication for this type of vaccine?

Accepted Answer

Severe immunocompromise or pregnancy

BIO 175 Microbiology Midterm Study Guide: Chapters 1, 2, 3, 5, 7, 8, 9, 10, 14

Study Guide - Practice Questions

Study Guide - Flashcards