Swarming modulatory effects of some amino acids on Proteus strains from Lagos, Nigeria

Swarming motility, a multicellular behaviour characterized by periodic concentric growth on solid media has severally been reported as a constraint in the clinical investigation of mixed- culture infections involving Proteus and as a requirement for virulence. While media are being formulated to restrain swarming in this organism, the roles played by amino acids in the biogenesis of swarming have not been fully clarified. The effects of 20 amino acids on swarming, extracellular protease activity, cellular RNA level and total protein concentration in 20 clinical Proteus strains from Lagos, Nigeria were investigated. At 0.5mM concentration, glutamine, serine, and methionine were the only amino acids found to enhance swarming motility on M9 minimal medium (7.1-11.3 mm), cause significant increases in protease activity (33.7-48.3 units/ml), total protein concentration (22.5-28.6 mg/ml) and cellular RNA concentration (192.8-264.7 g/ml) when compared to values obtained for other 17 amino acids (P < 0.05). Furthermore, the amino acid induced swarming in these strains was found to vary directly and significantly (P < 0.05) with protease activity and cellular RNA concentration. The exclusion of methionine, serine and glutamine when supplementing antiswarming media for clinical investigation of Proteus - associated polymicrobial infections in Nigeria is suggested.