Action of ethylenediaminetetra-acetic acid (EDTA) on carbenicillin-resistant strains of Pseudomonas aeruginosa.

Abstract

Summary Sub-inhibitory concentrations of EDTA reduce the resistance of strains of Pseudomonas aeruginosa to carbenicillin in vitro. With strains made resistant by habituation, the extent of the reduction of carbenicillin resistance produced by a fixed subinhibitory dose of EDTA (200 μg per ml) did not vary with the degree of resistance even though the development of this habituated resistance was associated with a loss of sensitivity of the bacterial cells to EDTA. This suggests (1) that the reduction of habituated carbenicillin resistance by EDTA is due to a synergistic effect of the EDTA-carbenicillin combination, and (2) that the development of habituated carbenicillin resistance in Ps. aeruginosa is due to a change in type or amount, or in both, of cell-wall lipopolysaccharide. In carbenicillinase-producing resistant strains of Ps. aeruginosa, the amount of reduction of carbenicillin resistance by EDTA is variable and appears to be inversely related to the quantity of carbenicillinase produced by the bacterial strain.