ID: Pathogenicity and Host Response

Question 1

What is colonization?

Answer 1

Microorganism occupies an ecological niche in a host, grows, but does not overcome host resistance or cause invasive disease.

Question 2

Virulence, commonly recognized as the measure of a microbe’s ability to invade and create disease in a host, is determined by….

Answer 2

1. characteristics that relate to the favored site of invasion.
2. Disease induction
3. Avoidance of host defense mechanisms of resistance.

Question 3

What are the two elements of virulence?

Answer 3

1. Ability of the organism to survive in the external environment during transit between hosts
2. A mechanism for transmission to a new host.

Question 4

When a microorganism reaches a favourable site for inducing disease, it must adhere to the structure that it will infect.

Answer 4

Once a pathogen adheres, it must have a mechanism for proliferation. Electrostatic negative charges on most bacteria favor adherence to human cells, and specific adhesions on bacterial surfaces favor attachment to sites of infection.

Following local proliferation by a pathogen, elements of virulence favor invasion and dissemination.

Question 5

Virulence is the measure of a microbe’s ability to invade and create disease in a host and is determined by characteristics that relate to the favored site of invasion, disease induction, and avoidance of host resistance.

Answer 5

1. Initial Element: ability to survive in the external environment during transit between hosts.
2. Mechanism for transmission to a new host.

Question 6

Binding to foreign bodies, such as IV or indwelling catheters by bacteria, often involves a bacteria-secreted glycocalyx (slimy covering excreted by bacteria).

Answer 6

Bacteria may also form biofilms: self-produced, polymeric conglomerations of extracellular DNA, proteins, and polysaccharides that confer resistance against different environmental stresses, including immune responses and antimicrobial agents.

This encapsulation of bacteria gives an enhanced ability for surface attachment, cell-to-cell communication and genetic exchange. Resistance to antibiotics in biofilms can increase from 10-1000 fold more compared to planktonic bacteria.

Question 7

Bacteria often secrete enzymes that enhance spread through tissues.
Streptococcus pyogenes

Answer 7

Most immediate postoperative SSI, beginning <24 hours are from S pyogenes.

Recent radical change in enzyme production of MRSA- elaborating the Panton-Valentine leukocidin. This allows Staph to spread rapidly like strep, creating an entirely new clinical syndrome for staph infections.