Microbes Slide 14

The Traditional View about human infections

microbes enter our bodies specifically evolved to attack human cells

The New Perspective about human infections

a majority of the microbes evolved to compete with each other for resources and human tissue is merely collateral damage

Examples of microbes evolved to directly attack host cells

tuberculosis and flesh-eating bacteria

direct infection

host-targeted virulent factors like toxins to infect human cells

direct infection example

E. coli forms colonies intracellularly, using cell resources until cell death when they leave the host cells

collateral damage

virulent factors to directly compete with other microbes for space, nutrients, or iron with host damage as an accidental byproduct

collateral damage example

E. coli and C. albicans fight each other for space in catheter-associated UTIs, releasing toxins that cause host inflammation

Microbial arsenal that cause collateral damage

chemical, mechanical, and nutritional warfare

Chemical warfare

micros secrete bacteriocins and broad-spectrum antibiotics to eliminate rival bacteria, but the microbial cell lysis debris induces mucosal barrier degradation which can lead to host tissue damage

Mechanical Warefare

microbe uses T6SS to directly inject target bacteria and kill them, the microbial cell lysis debris triggers inflammatory immune responses

Nutritional Warfare

microbes scavenge for iron and nutrients, but they end up depriving the epithelial cells of nutrients or iron, which disrupts host iron homeostasis and causes tissue damage due to intense metabolic stress

Clostridioides difficile collateral damage

1. after antibiotic treatment, C. diff proliferates

2. C. diff produces toxins to disrupt surrounding biofilms and deter competitors

3. C. diff produces siderophores to compete for iron

4. the toxins beak down the actin cytoskeleton of human intestinal epithelial cells, which leads to a leaky epithelium, mucosal ulceration, and diarrhea

Pseudomonas aeruginosa collateral damage in Cystic fibrosis patients

1. Cystic fibrosis patients have a lot of mucus, which has nutrients for Pseudomonas

2. P. aeruginosa builds thick biofilms and secrete pyocyanin to kill rival bacterial species

3. Pyocyanin generates reactive oxygen species (ROS) that destroy bacterial competitors, but inadvertently damage host lung epithelial tissue causing chronic inflammation and tissue loss