1 Bacteria (Host Pathogen Interactions)

Question 1

What organisms make up the normal flora (microbiome) of the human body?

Answer 1

Fungi, Viruses, Bacteria, Helminths/Protozoans

prevent pathogen infections, stimulate immune system, provide nutrients

Question 2

Bacteria classification

Answer 2

• Shape: Coccus (round), bacillus (rod), coccobacillus (oval), fusiform bacillus (stretched oval), vibrio (boomerang), spirrillum, spirochete
• Gram staining: Gram positive, Gram negative
• Metabolic requirements: Aerobic vs anaerobic, fermenters vs non-fermenters

Question 3

Gram Stain

Answer 3

Differentiating step is ACETONE/ALCOHOL

Question 4

Metabolic Pathways

Answer 4

• Aerobic respiration: oxygen is final electron acceptor
• Anaerobic respiration: inorganic compounds are electron acceptor
• Facultative anaerobe: respire aerobically until oxygen depleted, then ferment

Question 5

Metabolic products and enzymes

Answer 5

-Coagulase (staphylococcus), Catalase (staph vs strep), Oxidase (cytochrome c oxidase), Hemolysis (alpha, beta, gamma)

Question 6

Bacterial Cell Wall Structure/Components

Answer 6

• Gram (+) cell wall: teichoic/teichuronic acids –> Major surface antigen, influences virulence, helps in attachment
• Gram (-) cell wall: lipopolysaccharide (endotoxin) –> shock due to LPS and Lipid A cause systemic effects
• Flagella, Fimbriae (Pili), Cell membrane

Question 7

Bacterial Cell Wall

Answer 7

• Alt molecules of NAG and NAM joined by Beta 1-4 link
• NAM PEPs are crosslinked: DAP at 3rd/D-Ala at 4th spot
• Beta lactam antibiotics prevent crosslinking

Question 8

Gram positive bacteria use a _____ bridge to crosslink N-acetylmuramic acid units

Answer 8

PENTAGLYCINE

Question 9

Glycocalyx

Answer 9

• Made of polysaccarides
• Mediates adherence
• Protects from phagocytosis and antibodies

Question 10

Appendages

Answer 10

• Pili (Fimbriae): mediate attachment

- Flagella: mediated motility/highly antigenic

Question 11

Ribosomes

Answer 11

Prokaryotic ribosomal differences allow for antibiotic targeting

Question 12

Bacterial Pathogenesis

Answer 12

1. Entry (air, food, water, damage to skin)
2. Adhesion (fimbriae, pili, glycocalyx, biofilm)
3. Invasion (degradative enzymes, inflammation, tissue cell penetration, intracellular growth)
4. Propagation (bacterial replication)
5. Damage to host (toxin/immune-mediated)
6. Progression, resolution or chronic

Question 13

Toxins

Answer 13

• Endotoxin: LPS triggers potent inflammatory response
• AB toxins: toxin binds (B) to membrane –> The A subunit “actively” cleaves/modifies target (ie diptheria, cholera)
• Superantigens: induce inflammation by binding MHC molecules and T-cell receptors (TCR)

Question 14

Bacterial Host Evasion Mechanisms

Answer 14

Phagosome evasion; Antigenic mimicry; Intracellular growth; Inactivation of complement or antibody; Destruction of phagocytes; Resisitance to lysozyme enzymes; Antigenic switching

Question 15

Antibiotic Resistance

Answer 15

Enzymes destroy antibiotics; Change in permeability to antibiotic; Altered metabolic pathway; Altered enzymes; Efflux pumps