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Microbiome and Infectious Disease

Pathogens, the human microbiome, and host-pathogen interactions

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gut_flora_gf 23 terms Jan 7, 2026
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Terms 23

1
Microbiome
Community of microorganisms living in or on a host; 10¹³–10¹⁴ microbes in/on human body
2
Dysbiosis
Imbalance in microbiome composition associated with disease (IBD, obesity, depression)
3
Horizontal Gene Transfer (HGT)
Transfer of genes between organisms without reproduction; transformation, transduction, conjugation
4
Conjugation
Direct DNA transfer between bacteria via pilus; spreads antibiotic resistance genes on plasmids
5
Transduction
Bacteriophage carries bacterial DNA from one cell to another
6
Transformation
Bacteria uptake free DNA from environment; basis of genetic engineering
7
Virulence Factor
Molecule enabling pathogen to colonize, evade immunity, or damage host; toxins, adhesins, capsules
8
Endotoxin (LPS)
Lipopolysaccharide in gram-negative outer membrane; triggers inflammatory response; septic shock
9
Exotoxin
Secreted bacterial protein causing specific disease effects; cholera toxin, botulinum toxin
10
Antibiotic Resistance Mechanisms
Efflux pumps, enzyme inactivation (β-lactamase), target modification, reduced permeability
11
Biofilm
Microbial community embedded in self-produced matrix; highly antibiotic resistant; e.g. dental plaque
12
Quorum Sensing
Bacteria coordinate behavior via chemical signals at threshold density; controls biofilm, virulence
13
Viral Life Cycle (lytic)
Attachment → injection → replication → assembly → lysis and release of new virions
14
Viral Life Cycle (lysogenic)
Phage integrates into host genome as prophage; replicates with host; can enter lytic cycle
15
Viral Tropism
Specificity of virus for particular host cells; determined by receptor-ligand interaction
16
Innate vs Adaptive Response to Infection
Innate (immediate, nonspecific) → adaptive (days, specific, memory); complement, interferon, T/B cells
17
Immune Evasion Strategies
Pathogens hide in cells, alter surface antigens, inhibit complement, suppress cytokines
18
Antigenic Variation
Pathogen changes surface antigens to escape immune recognition; influenza, HIV, trypanosomes
19
Koch's Postulates
Framework proving causation of infectious disease; organism found in sick, isolated, causes disease, re-isolated
20
Basic Reproduction Number (R₀)
Average new cases from one case in susceptible population; R₀>1 epidemic spreads
21
Herd Immunity
Enough population immune to block pathogen spread; threshold = 1 − 1/R₀
22
Zoonosis
Disease transmitted from animals to humans; HIV (primates), influenza (birds/pigs), COVID-19 (bats)
23
Prion
Misfolded protein causing aggregation cascade; no nucleic acid; TSEs (mad cow, CJD)