The discovery of communication systems regulating bacterial virulence has afforded a novel opportunity to control infectious bacteria without interfering with growth. In this paper we describe the effect of subinhibitory concentrations of phenyllactic acid (PLA) on the pathogenicity of Pseudomonas aeruginosa in mice. The animals were inoculated by oral (p.o.), intranasal (i.n.), intravenous (i.v.) and intraperitoneal (i.p.) routes with P. aeruginoasa wild and PLA-treated cultures. The mice were followed up during 16 days after infection and the body weight, mortality and morbidity rate were measured every day. The microbial charge was studied by viable cell counts in lungs, spleen, intestinal mucosa and blood. The mice batches infected with wild P. aeruginosa bacterial cultures exhibited high mortality rates ( 100% after i.v. and i.p. route) and very high cell counts in blood, lungs, intestine and spleen. In contrast, the animal batches infected with PLA treated bacterial cultures exhibited good survival rates ( 0% mortality) and the viable cell counts in the internal organs revealed with one exception the complete abolition of the invasive capacity of the tested strains. In this study, using a mouse infection model we show that D-3-phenyllactic acid (PLA) can act as a potent antagonist of Pseudomonas ( P.) aeruginosa pathogenicity, without interfering with the bacterial growth, as demonstrated by the improvement of the survival rates as well as the clearance of bacterial strains from the body.