Permeability and penicillin-binding protein alterations in Salmonella muenchen: stepwise resistance acquired during beta-lactam therapy

Abstract

A patient with Salmonella muenchen sepsis was unsuccessfully treated with ampicillin. During therapy, four strains that showed stepwise ampicillin resistance and affected other beta-lactams and unrelated antibiotics were isolated sequentially. Resistance was caused by decreased outer membrane permeability associated with diminished expression of porin OmpF. Furthermore, the most resistant isolate overproduced the PBP 3 target molecule.