more on the pau d’arco question

The question in question was about the proposed use of the herb pau d’arco as a prophylactic against MRSA: Evaluate the claims of the therapist, then use your biological knowledge to discuss the advice given. What are the possible evolutionary & ecological outcomes of the proposed treatment?

Well, the plant extract was tested for its antibacterial activity. Was the method used a valid method for looking at the effectiveness of a drug proposed as a treatment for MRSA? I’d have to say no, not really. This supposed new antibiotic was trialled against lab-synthesised derivatives of the same chemical. A more reliable test would be to compare this possible anti-MRSA drug with one or more proven anti-MRSA antibiotics.

What’s more, the CAM practitioner suggested given a potentially valuable (albeit unproven) new anti-microbial to someone possibly exposed to wild strains of MRSA. This chemical was available by mail-order and the dosage wasn’t regulated – in other words, the dose in each pill could well be at a subtherapeutic level. (I vaguely remember that Consumer magazine did something on this, looking at a range of alternative health products & what you were actually getting in them in terms of the active ingredients.)

So, what are the possible ecological & evolutionary outcomes of such a treatment? Bacteria develop resistance to antibiotics through exposure: those bacteria with mutations giving resistance survive and reproduce (natural selection in action), & so resistance spreads through the bacterial population. This particular patient would be taking the therapy prior to surgery, when he had not yet been placed in an environment with a high risk of exposure to MRSA. However, all the other bacteria in his body (trillions of them) would be exposed to this new selection pressure and might develop resistance to this particular bactericide. (There could also be mass die-offs of non-resistant microbes, which would throroughly upset his gut ecology.) Then, when he did go into hospital, these resistant bugs might then share their resistance with MRSA bacteria, through horizontal gene transfer.

In other words, this was not good advice, & could potentially have had very wide-ranging consequences.

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