Decreased production of AmpC-type beta-lactamases associated with the development of resistance to quinolones in Citrobacter freundii strains

The effect of fluoroquinolones in Citrobacter freundii strains that results in a decreased expression of cephalosporin-hydrolysing beta-lactamases was studied. Resistance to broad-spectrum cephalosporins and penicillins in tw o C, freundii clinical isolates was associated with moderate production of chromosomal AmpC-type-beta-lactamase in addition to changes in the outer me mbrane proteins profile with respect to wild-type C. freundii strains. Ten quinolone-resistant mutants were derived from the two clinical isolates usi ng increasing fluoroquinolone concentrations. The level of susceptibility t o cephalosporins and meropenem of these 10 mutants was increased and was as sociated with a 3.6-32% diminution in the hydrolyzing activity of their per iplasmic extracts containing beta-lactamases on cephaloridine as compared w ith those from their parent strains, Susceptibility to cephalosporins and m eropenem, as well as the expression of chromosomal AmpC-type-beta-lactamase in C, freundii strains, was influenced by the exposure to quinolones.