2.1 - Pathogenesis of Bacterial Infection and Normal Human Microbiota

1.) The organism must always be found in humans with the disease but not found in healthy ones
2.) The organism must be isolated from human with the disease and grown in pure culture
3.) The organism isolated in pure culture must initiate disease when reinoculated into susceptible animals
4.) The organism must be isolated from the experimentally infected animals

Identify the 4 criteria of Koch’s Postulate

ITAPAT

• Invasion of Host cells and tissues

• Transmissibility

• Adherence to host cells

• Persistence

• Ability to evade

• Toxigenicity

Give the 6 characteristics of pathogenic bacteria

Pathogenicity

This is the ability of an infectious agent to cause disease

Virulence

This is the quantitative ability of an agent to cause disease

Microbiota

These are microbial flora harbored by normal, healthy individuals

Pathogen

This is a microorganism capable of causing disease

Opportunistic Pathogen

This is a microorganism capable of causing disease only when the host’s resistance is compromised

Respiratory, GI, Genitourinary tracts, and abnormal areas of skin (Cuts)

Identify the most common portals of entry of pathogenic bacteria

Animals

Pathogens such as Salmonella, Campylobacter, Y. pestis. B. anthracis, and Clostridium usually cause disease in humans via which source of infection?

Colonization

This is the establishment of a stable population of bacteria on a host’s skin or mucous membranes

ATE AIRA

• Adherence Factors

• Toxins

• Enzymes

• Antiphagocytic Factors

• Intracellular Pathogenicity

• Requirement for Iron

• Antigenic Homogeneity

Identify the 7 virulence factors of bacteria

F; Increased hydrophobicity = Better Adherence

T/F: Increasing hydrophobicity of bacterial cell surface leads to worse adherence

Pili

These are long and thick rod-like appendages that help with adherence

Fimbriae

These are short and thin hair-like appendages that help with adherence

T

T/F: Pili can only be seen in Gram (-) organisms while Fimbriae is found in both Gram (+) and (-) Organisms

Invasion

This is the penetration of bacteria into the host cells and tissues

T
F; Both Gram (+) and (-)
T
T
F; Can be converted to toxoid
T
F; usually do not produce fever
F; Found in cells

MTF: Characteristics of Exotoxins

1.) Excreted by a living cell
2.) Produced only by Gram (-) bacteria
3.) Heat Labile
4.) Highly Antigenic
5.) Cannot be converted to toxoid and cannot be used to immunize
6.) Highly Toxic
7.) Usually produce fever in host
8.) Bind to specific receptors not found in cells

F; Excreted on bacterial death
T
F; Heat Stable
F; Weakly Immunogenic
T
F; Moderately Toxic
T
T

MTF: Characteristics of Endotoxins

1.) Excreted by a living cell
2.) Produced only by Gram (-) bacteria
3.) Heat Labile
4.) Highly Antigenic
5.) Cannot be converted to toxoid and cannot be used to immunize
6.) Highly Toxic
7.) Usually produce fever in host
8.) Bind to specific receptors not found in cells

Necrotizing and Hemolytic Toxins

Which toxins of C. perfringens contribute to tissue necrosis and hemolysis, and together with gas production and impaired blood supply, produce gas gangrene?

Alpha Toxin

Which toxin of C. perfringes damages cell membranes by splitting lecithin to phosphorylcholine and Diglyceride?

Collagenases and DNAses

This C. perfringes toxin can help the organism to spread by damaging the connective tissue matrix which can loosen up the tissue fibers

B subunit

In A-B type toxins, which subunit mediates the adherence of the toxin complex to a host cell?

A Subunit

In A-B type toxins, which subunit primarily provides the toxic activity

Membrane-Damaging Proteins

These types of toxins enzymatically digest the phospholipid components of membranes or behave as detergents

Enterotoxins

These are a type of exotoxins associated with diarrheal diseases and food poisoning

Lipopolysaccharide (LPS)

This is considered the most potent endotoxin

F; Gram (-) Bacteria

T/F: LPS is only found in Gram (+) bacteria

Peptidoglycan

Instead of LPS, what endotoxin is found in the thick cell wall of Gram (+) bacteria?

A

QC: Potency of (1) LPS (2) Peptidoglycan

IgA1 Proteases

This enzyme allows the pathogen to inactivate the primary antibody found on the mucosal surfaces

Resident Microbiota

This group of microbiota consists of relatively fixed type of microorganisms that reestablishes itself when left undisturbed

Transient Microbiota

This group of microbiota consists nonpathogenic or potentially pathogenic microorganisms that only inhabit the skin or mucous membranes for hours to weeks

Commensals

What term refers to microorganisms that normally live in or on the human body without causing disease and may contribute to maintaining normal bodily functions?

F; May cause disease when moved to an entirely new environment

T/F: Members of normal microbiota are incapable of causing disease under any circumstance

1.) Nonhemolytic Aerobic and Anaerobic Staphylococci
2.) Alpha-hemolytic Streptococci
3.) Gram Positive, Aerobic, Spore-forming Bacili
4.) Aerobic and Anaerobic Diphtheroid Bacili
5.) Gram negative coliform bacili and Acinetobacter

Give the 5 types of normal microbiota found in the skin

T/F: Most microorganisms in the skin are

F; Gram (-) and Anaerobic

T/F: Most microorganisms in the GI are Gram (+) and Aerobic

Blood, Brain and its surrounding meninges, Respiratory Tract, and CSF

Give the parts of the body that are normally sterile