Microbiology: organism interactions

Define virulence.

The ability of a microorganism to cause disease

Define infective dose.

The quantitation of virulence; how much of a microorganism’s presence is needed to cause infection

Are virulence and infective dose directly or inversely related?

Inverse; low infective dose = more virulent, high infective dose = less virulent

Define virulence factors.

factors that allow the pathogen to escape host defenses

What are examples of virulence factors?

Resisting phagocytosis, biofilm formation, bacterial structures

What bacterial structures are virulence factors?

Adherence: adhesins and receptors help adhere pathogens to the host

Polysaccharide capsule: protects pathogens from being engulfed

Protein A: interferes with host’s activation of antibodies, protecting pathogens from phagocytosis

Lipid A: found in the cell wall of GNB, functions as an endotoxin

What are some mechanisms that help pathogens survive intracellularly?

proliferation, invasion, dissemination, biofilm formation

Define exotoxin.

proteins inside living bacteria that are released when excreted or if the cell is lysed

(think exo=excreted)

Define endotoxin.

lipid parts of the lipopolysaccharide outer membrane of the cell wall in GNB; only effective after cell is lysed or cell death

(think endo=in the cell wall)

What are the effects of exotoxins?

They have specific targets, kill the host cell, aid in spreading, destroy/interfere with intracellular activity

What are the effects of endotoxins?

Disrupts clotting, causes fever, activates complement/immune system, causes circulatory changes, causes septic shock

Define enterotoxin.

Exotoxin that specifically affects intestinal mucosa

Define neurotoxin.

Exotoxin that destroys nerve tissue

Define cytotoxin.

Exotoxin that destroys cells

What is a protease and how can it be harmful?

Enzyme for breaking down protein; it can act as an exotoxin to destroy extracellular structures

What is a hyaluronidase and how can it be harmful?

Enzyme for breaking down hyaluronic acid in the host’s extracellular matrix; it increases tissue permeability of pathogens which helps them evade immune detection and spread faster

What are some examples of human host defenses?

Physical barriers, natural cleaning mechanisms, antimicrobial substances, normal flora, phagocytosis, inflammation

Phagocytes and inflammation are part of what type of immunity?

Natural/Innate immunity

Humoral and cell-mediated immunity are part of what type of immunity?

Adaptive/Acquired immunity

I got salmonella from eating undercooked chicken. What kind of transmission is this?

Ingestion (eating, smoking, mouth pipetting)

I got Hepatitis B from stepping on a used syringe. What kind of transmission is this?

Percutaneous (needle sticks, sharps)

I did not wear a mask or facial protection when seeing a patient that potentially had tuberculosis. Later, I got tuberculosis. What kind of transmission is this?

Airborne/Inhalation

I was plating throat swabs, and itched my eye without taking off my gloves. Later on, I got strep throat. What kind of transmission is this?

Permucosal (specimen splash or entry into mouth, nose, eyes, or mouth pipetting)

I wasn’t wearing gloves when examining plates for possible MRSA. While writing down notes, I got a papercut, but it wasn’t bleeding so I didn’t get a bandaid. I started showing symptoms of MRSA on my hands later on. What kind of transmission is this?

Non-intact skin

Define local infection.

An organism enters the body and remains confined to a specific tissue.

Define systemic infection.

An infection that spreads to several sites and tissue fluids.

Define acute infection.

An infection that appears rapidly with severe symptoms, but rapidly vanishes

Define chronic infection.

An infection that usually has less severe symptoms, but persists for long periods of time

What is the distribution of epidemiology?

The who, when, where

What are the determinants of epidemiology?

The causes, risk factors, and mechanisms

What are the patterns of epidemiology?

Patterns of disease evaluated across defined populations