Super Fantastically Mediocre Evolution Blog : Game of Evolution

Hopefully Not Like Game of Thrones

For the game presented to us for module two, I wanted to look at examples of microevolution, as it's one of my favorites (thanks, microbiology). There are various strains of bacteria that are resistant to a lot of treatments today. One particular type that I want to talk about it Pseudomonas aeruginosa. Anyone who has taken microbiology or dealt with bacteria is probably familiar with this species, since it's super common.

P. aeruginosa is known as an opportunistic pathogen that can target humans and plants. That means it goes for the people or plants who already have something wrong with them, something that broke down their defenses enough for them to break through and spread. Typically, you can find it in soil, vegetation, and in water. In more rare cases, you can find it in a human's throat, or in human fecal matter. It's predominantly found in hospitals and spreads through human contact, surfaces, being carried over by patients from other hospitals, and on produce. It has the biggest effect on people with preexisting conditions and has a 50% mortality rate on those who are already sick (if they have cancer, severe burns, or cystic fibrosis (CF), to name a few -- the more immunocompromised the patient is, the higher the risk).

What makes P. aeruginosa a great example of microevolution that we can witness is its resistance to antibiotics. In Microbiology, we ran an antibiotic resistance test called the Kirby-Bauer Method that tests for resistances and zones of inhibition for bacteria (tests to see how effective an antibiotic is on a bacteria type). This was done on P. aeruginosa, Staphylococcus aureus and Enterococcus faecalis. S. aureus and E. faecalis were shown to be susceptible to antibiotics - namely Vancomycin, Penicillin, Erythromycin, and Tetracycline. However, when looking at P. aeruginosa, we saw that only Tetracycline was effective against it, and it was able to resist all of the others. What's more, P. aeruginosa can develop resistances through chromosomal mutations and acquire antibiotic resistant genes. It's both an amazing, ever-evolving bacteria, and also terrifying because it's the cause of severe infections and death in hospitalized people.

Another example for it is from the article titled, "Pseudomonas aeruginosa Evolutionary Adaptation and Diversification in Cystic Fibrosis Chronic Lung Infections," written by Craig Winstanley, Siobhan O’Brien, and Michael Brockhurst for Science Direct in 2016: "Populations of P. aeruginosa in chronic CF lung infections typically exhibit high phenotypic diversity, including for clinically important traits such as antibiotic resistance and toxin production, and this diversity is dynamic over time, making accurate diagnosis and treatment challenging."