How predictable is development of resistance after ß-lactam therapy in Enterobacter cloacae infection?
Certain non-fastidious Gram-negative bacilli, notably Enterobacter cloacae, although classified as susceptible by usual in-vitro susceptibility testing, often become resistant in patients treated with newer ß-lactam antibiotics. Here various in-vitro tests were carried out together with an animal model allowing the quantification of resistance that emerges after short term therapy. Mice were challenged (102 cfu plus talcum) intraperitoneally with one each of four strains of Ent. cloacae. Two hours later, a single ß-lactam dose was administered subcutaneously. The following day, the peritoneal bacterial population was analysed by using antibiotic-containing gradient plates. Development of resistance after therapy varied according to the compound considered. Imipenem (50 mg/kg) produced no resistance, and piperacillin (200 mg/kg) only a few, while resistance occurred frequently after therapy with aztreonam (50 mg/kg), ceftazidime (50 mg/kg), cefotaxime (50 mg/kg) and cefpirome (50 mg/kg)
