Pseudomonas aeruginosa virulence factors: modifications by sub-inhibitory concentrations of carbenicillin or gentamicin.

A virulent strain of Pseudomonas aeruginosa was assayed for adhesion to HEp-2 cells, production of toxin A, and production of elastase, in the presence of sub-inhibitory concentrations of carbenicillin and gentamicin. Both antibiotics, assayed in a concentration of 1:12 of their minimum bactericidal concentration (MBC), inhibited the production of toxin A. Gentamicin at this concentration totally abolished the production of elastase, whereas carbenicillin had little or no effect on this factor. Both antibiotics inhibited the bacterial adhesion, but in different ways. While gentamicin had a strong activity of slow onset, carbenicillin had a transitory activity of rapid onset, with return towards normal values after 90 min incubation.