Are Microbial Swords Really Plowshares?

Science's STKE  02 Jan 2007:
Vol. 2007, Issue 367, pp. tw1
DOI: 10.1126/stke.3672007tw1

The production of antibiotics by microorganisms has generally been interpreted as a microbial mechanism for killing off competitors. If this were the case, even suboptimal concentrations of antibiotics that were inadequate to inhibit growth might be expected to reduce the fitness and virulence of bacterial pathogens. Linares et al. investigated this hypothesis by exposing Pseudomonas aeruginosa, a major opportunistic bacterial pathogen, to concentrations of three antibiotics (tobramycin, tetracycline, and ciprofloxacin) just below those required to visibly decrease bacterial growth and found that subinhibitory concentrations of these antibiotics actually enhanced various adaptive traits. All three antibiotics stimulated biofilm formation. Tobramycin also stimulated swimming and swarming, whereas tetracycline increased the expression of genes associated with type III secretion and enhanced P. aeruginosa cytotoxicity toward a macrophage cell line. The authors argue that, aside from the clinical implications, their work suggests that—rather than being used as weapons—antibiotics may be used as intermicrobial signaling molecules involved in regulating the homeostasis of microbial communities.

J. F. Linares, I. Gustafsson, F. Baquero, J. L. Martinez, Antibiotics as intermicrobial signaling agents instead of weapons. Proc. Natl. Acad. Sci. U.S.A. 103, 19484-19489 (2006). [Abstract] [Full Text]