Decreased virulence of a strain of Pseudomonas aeruginosa O12 overexpressing a chromosomal type 1 beta-lactamase could be due to reduced expression of cell-to-cell signaling dependent virulence factors

Pseudomonas aeruginosa produces a large variety of virulence factors and is characterized by its capacity to rapidly develop resistance when exposed t o antibiotics. In order to evaluate a possible correlation between acquired resistance to antibiotics and virulence, we examined the virulence of four isogenic variants of P. aeruginosa O12 that differ in their resistance phe notypes to various beta-lactam antibiotics in a mouse model of acute pneumo nia. Strains overproducing a chromosomal type 1 beta-lactamase were less vi rulent in both immunocompetent and immunosuppressed animals. Whereas the pr oduction of the exopolysaccharide alginate was similar between the four str ains, extracellular virulence factors (elastase, rhamnolipid) that are cont rolled by the cell-to-cell signaling system circuit were detected in reduce d amounts in the supernatant of the two isolates overproducing type 1 beta- lactamase. These results suggest that strains overexpressing the chromosoma l type 1 beta-lactamase could be less virulent because of a reduction of ce ll-to-cell signaling dependent virulence factor production. (C) 2000 Federa tion of European Microbiological Societies. Published by Elsevier Science B .V. All rights reserved.