Staphylococcus epidermidis |
You may not have heard of Staphylococcus epidermidis but you have almost certainly heard of its close cousin, S. aureus, that in its antibiotic resistant form (MRSA) has become such a problem in hospitals, causing life-threatening infections in wound sites. Now, scientists have warned that S. epidermidis, an abundant, commensal bacterium on human skin, has the potential to become a serious health risk.
If you subscribe to the intelligent design notion, the only possible interpretation of this news is that a designer with malevolent intent has prepared for the eventuality of human medical science overcoming its current favourite harmful pathogens, like MRSA and Escherichia coli.
S. epidermidis is a close relative of S. aureus, the antibiotic-resistant form of which (MRSA) is a major health risk, especially in hospitals, following surgery. S. epidermidis is a normal, commensal bacterial species found on the skin of every human being. Normally, it is harmless but, in the right circumstances, it is also a serious health risk following surgery when it infects operation sites.
The researchers from the Milner Centre for Evolution, University of Bath, UK, have identified a set of 61 genes that allow it to become pathological in wound sites.
By comparing the genome of S. epidermidis recovered from infected wounds with the genome of those recovered by skin swabs of healthy individuals, they found that the pathological form had these 61 genes not shared with the non-pathological form. However, they found that some healthy individuals are carriers of the potentially deadly form.
These genes enable S. epidermidis to:
- Live in the bloodstream of their host.
- Avoid the host's immune system.
- Make the bacterial cell wall sticky, so it can make biofilm and increase antibiotic resistance.
Abstract
Some of the most common infectious diseases are caused by bacteria that naturally colonise humans asymptomatically. Combating these opportunistic pathogens requires an understanding of the traits that differentiate infecting strains from harmless relatives. Staphylococcus epidermidis is carried asymptomatically on the skin and mucous membranes of virtually all humans but is a major cause of nosocomial infection associated with invasive procedures. Here we address the underlying evolutionary mechanisms of opportunistic pathogenicity by combining pangenome-wide association studies and laboratory microbiology to compare S. epidermidis from bloodstream and wound infections and asymptomatic carriage. We identify 61 genes containing infection-associated genetic elements (k-mers) that correlate with in vitro variation in known pathogenicity traits (biofilm formation, cell toxicity, interleukin-8 production, methicillin resistance). Horizontal gene transfer spreads these elements, allowing divergent clones to cause infection. Finally, Random Forest model prediction of disease status (carriage vs. infection) identifies pathogenicity elements in 415 S. epidermidis isolates with 80% accuracy, demonstrating the potential for identifying risk genotypes pre-operatively.
Guillaume Méric, Leonardos Mageiros, Johan Pensar, Maisem Laabei, Koji Yahara, Ben Pascoe, Nattinee Kittiwan, Phacharaporn Tadee, Virginia Post, Sarah Lamble, Rory Bowden, James E. Bray, Mario Morgenstern, Keith A. Jolley, Martin C. J. Maiden, Edward J. Feil, Xavier Didelot, Maria Miragaia, Herminia de Lencastre, T. Fintan Moriarty, Holger Rohde, Ruth Massey, Dietrich Mack, Jukka Corander & Samuel K. Sheppard
Disease-associated genotypes of the commensal skin bacterium Staphylococcus epidermidis
Nature Communications volume 9, Article number: 5034 (2018). DOI: 10.1038/s41467-018-07368-7
Copyright: © 2018 The Authors
Open Access
Reprinted under a Creative Commons Attribution 4.0 International License (CC-BY 4.0)
For any evolutionary biologist this is no surprise, of course. We know how bacteria can exchange genetic information and how due to intense selection pressure, the danger of using antibiotics is that resistent forms are almost guaranteed to evolve. The causes are well understood and the consequences are entirely predictable and can even be reproduced in a laboratory.
But, for the ID movement, since intent and purpose are integral to the notion of design, any explanation of what is going on here must include an explanation of purpose. Given that any intelligent designer, and especially an omniscient designer, would be well aware of the result of its design; indeed would have intended it, the conclusion must be that a putative designer has this organism in reserve with all the potential to become harmful, just waiting for humans to have beaten it's current favourite harmful pathogens.
In other words, from evidence such as this, the ID movement needs to explain what appears to be the malevolent intent of their hypothecated designer in terms which are not simply an abandonment of the myth that ID is not a religious movement by a scientific alternative, and the invocation of Christian religious dogma of the Fall.
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