Salicylate decreases production of AmpC type β-lactamases and increases susceptibility to β-lactams in a Morganella morganii clinical isolate

The effect of salicylate, a marRAB inducer, on the resistance to β-lactams was characterized in an AmpC β-lactamase hyperproducer Morganella morganii clinical isolate (the M1 strain). Results were compared with those of the effect of salicylate in a wild-type M. morganii strain. Salicylate induced a decreased susceptibility to nalidixic acid, norfloxacin and tetracycline and simultaneously increased the susceptibility to β-lactams apparently due to the repression of AmpC β-lactamase synthesis in the M1 strain. Likewise, salicylate only repressed 46 kDa outer membrane protein expression in the wild-type strain, since the clinical isolate M1 did not express it.