$$\text{Infection (infectious disease)} = \frac{\text{No. of organisms} \times \text{Virulence}}{\text{Host resistance}}$$

Question 1

Which equation best describes the relationship between infection, number of organisms, virulence, and host resistance?

Accepted Answer

$$	ext{Infection (infectious disease)} = \frac{	ext{No. of organisms} 	imes 	ext{Virulence}}{	ext{Host resistance}}$$

Question 2

Based on the LD$$_{50}$$ graph, which agent is more virulent?

Accepted Answer

Agent 1, because it has a lower LD$$_{50}$$ value ($$LD_{50} = 400)$$

Question 3

Which of the following is NOT considered a virulence factor?

Accepted Answer

Siderophore

Question 4

A patient receives antibiotics and develops a Clostridioides difficile infection. What is the most likely explanation?

Accepted Answer

Antibiotics reduce gut microbial diversity, allowing C. difficile to overgrow

Question 5

Which bacterial group is predominant in the urogenital tract of healthy females?

Accepted Answer

Lactobacillus

Question 6

What is the primary function of hyaluronidase as a virulence factor?

Accepted Answer

It breaks down hyaluronic acid in the extracellular matrix, allowing bacteria to invade deeper tissues

Question 7

Which of the following best describes the role of IgA1 protease in bacterial infection?

Accepted Answer

It breaks down IgA1 antibodies, helping bacteria evade immune detection

Question 8

Which portal of entry is most commonly associated with vertical transmission of infectious agents?

Accepted Answer

Placenta (mother to fetus)

Question 9

What is the effect of endotoxin (LPS) on the host during systemic infection?

Accepted Answer

It causes vasodilation and can lead to hypotension, organ failure, and septic shock

Question 10

Which bacterial species is most associated with dental caries due to lactic acid production?

Accepted Answer

Streptococcus

Question 11

In the context of the gut microbiome, which enterotype is associated with a diet high in fat and protein?

Accepted Answer

Enterotype 1 (Bacteroides)

Question 12

What is the significance of LD$$_{50} in $$measuring bacterial virulence?

Accepted Answer

It is the dose required to kill 50% of a population, with lower LD$$_{50}$$ indicating higher virulence

Question 13

Which step in the infectious process is NOT required for all bacteria to cause disease?

Accepted Answer

Invasion into host cells

Question 14

What is the primary mechanism by which Salmonella typhi invades host cells?

Accepted Answer

It releases proteins that disrupt actin filaments, causing membrane ruffles that engulf the bacteria

Question 15

Which of the following is a real-world application of fecal microbiota transplantation (FMT)?

Accepted Answer

Treating patients with recurrent Clostridioides difficile infections by restoring microbial diversity

Question 16

Which of the following best describes the hygiene hypothesis?

Accepted Answer

Reduced microbial exposure in early life increases risk of allergies and asthma

Question 17

What is the function of siderophores in bacterial pathogenesis?

Accepted Answer

They bind iron from host proteins and deliver it to bacteria for growth

Question 18

Which bacterial group is predominant in the skin microbiota?

Accepted Answer

Actinobacteria

Question 19

Why does saliva contain relatively few microbes compared to other body sites?

Accepted Answer

The concentration of antimicrobial enzymes limits their growth

Question 20

Which of the following is a consequence of dysbiosis in the human microbiome?

Accepted Answer

Imbalance in microbial communities can lead to disease or inflammation

Microbial Pathogenesis, Human Microbiome, and Virulence Factors

Study Guide - Practice Questions