How Bacteria Cause Disease: Six Pathogenic Mechanisms

Bacteria induce disease through diverse mechanisms:

1. Direct tissue invasion & damage: Streptococcus pyogenes (pharyngitis), S. aureus (abscesses).
2. Toxin production: Exotoxins (e.g., C. difficile toxins A/B, E. coli Shiga toxin, C. botulinum neurotoxin); Endotoxins (LPS → septic shock).
3. Immune-mediated pathology: M. tuberculosis granulomas; rheumatic fever (molecular mimicry post-GAS).
4. Sepsis/septic shock: Bacteremia → systemic cytokine storm → multi-organ failure.
5. Immune evasion: Capsules (anti-phagocytic), IgA proteases, antigenic variation (N. gonorrhoeae), intracellular survival (Listeria, Salmonella).
6. Biofilm formation: P. aeruginosa on catheters, S. epidermidis on implants; resist antibiotics/phagocytes.

Therapeutic Implications

• Antibiotics target specific processes (cell wall, protein synthesis, DNA replication).
• Antitoxins (diphtheria, botulism).
• Vaccines induce protective antibodies (pneumococcal, meningococcal, Hib).
• Biofilm disruption: mechanical removal, combination antibiotics, novel agents.