The Elements of Evolution (42-8) Pathogens


The pathogenesis of infection is a continuously evolving battle between the host and the infecting microbe. ~ American physician Marcia Goldberg et al

Pathogens present a constant adaptive pressure (as well as facing it themselves). Germs have been a primary driver of human evolution, more so than diet or climate conditions, precisely because survival is instantly at stake; and the tools are found within, as pathogens leave genetic material that provides an investigative basis for intelligent adaptation.

Adaptation includes going about business at different paces. This involves distinct subpopulations of invading cells employing their own alleles to set their rate of development. How this is accomplished is not known, but pathogenic bacteria employ this approach to evade host defense systems.

Plants and animals have self-produced antibiotics and immune systems to fight off pathogens. Invading bacteria evolved a 2-pronged strategy to deal with these destructive powers. 1st, multiply fast. One bacterium can become millions within hours. Overwhelming numbers may prevail. The 2nd stratagem is a fail-safe: lay low.

Antibiotics kill rapidly populating bacteria. Immune system macrophages gobble up marauders and apply microbiocidal remedy.

For pathogens to survive, the solution is to slow down. This confers antibiotic resistance simply by not taking the bait. If digested by a macrophage, a sluggish bacterium simply has to wait out its imprisonment before being pronounced dead and disgorged. Free at last, the little germ can go about its business of mayhem.

Salmonella take this 2-track approach to cause gastric distress and other ailments in vertebrates. While the majority go gangbusters, a few leisurely reproduce and bide their time.