Saturday, May 9, 2015

Microbial ecology: Keeping one step ahead of the bad bugs

File:Clostridium difficile 01.pngTwo papers were published recently that apply notions of bacterial interference and competition rather elegantly. The first was a study by Dale Gerding et al on administering nontoxigenic Clostridium difficile spores to prevent recurrent C. diff infection. The study aimed to determine the safety, fecal colonization, recurrence rate, and optimal dosing schedule of nontoxigenic C. difficile, and the authors found that
Among patients with CDI who clinically recovered following treatment with metronidazole or vancomycin, oral administration of spores of NTCD-M3 was well tolerated and appeared to be safe. Nontoxigenic C. difficile strain M3 colonized the gastrointestinal tract and significantly reduced CDI recurrence. 
It's a fascinating study and I recommend reading it. In addition to contemplating this as a potential future treatment for recurrent CDI, it's intriguing to wonder if patients could have their GI tracts colonized by nontoxigenic C. diff prophylactically before receiving antibiotics associated with CDI.

The other study, by Alice Deasy et al, demonstrates how nasal inoculation with the commensal Neisseria lactamica inhibits carriage of N. meningitidis in young adults. N. lactamica is a commensal occupying the same ecological niche (the nasopharynx) as the pathogenic organism N. meningitidis, which is associated with epidemic meningitis. They observed a significant inhibition of meningococcal carriage in carriers of N. lactamica, which was attributed to displacement of existing meningococci and to inhibition of new acquisition. Their findings suggest N. lactamica as a potential "novel bacterial medicine to suppress meningococcal outbreaks". Again, I recommend reading the complete study.

The notion of exploiting microbial ecology is appealing for many reasons, including that it doesn't require developing intrinsically new pharmacologic compounds and that it may have no significant side effects. At the same time, its important to remember previous trials employing bacterial interference, such as the deliberate colonization of newborn children with "low virulence" Staph. aureus, so that old missteps aren't repeated.

(image source: Wikipedia)

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