Effect of beta-lactam antibiotics on the in vitro development of resistance in Pseudomonas aeruginosa.

Objective: To investigate whether stepwise selection of resistance mutations maz mirror the continued bacterial exposure to antibiotics that occurs in the clinical setting.

Methods: We examined the in vitro development of resistance to a number of commonly used antibiotics (cefepime, cefpirome, ceftazidime, cefataxime, piperacillin and imipenem) in Pseudomonas aeruginosa, a significant nosocomial pathogen. Stepwise resistance was assessed by serial passage of colonies located nearest to the inhibition zone on antibiotic-containing gradient plates.

Effect of beta-lactam antibiotics on the in vitro development of resistance in Pseudomonas aeruginosa.

Objective: To investigate whether stepwise selection of resistance mutations may mirror the continued bacterial exposure to antibiotics that occurs in the clinical setting.

Methods: We examined the in vitro development of resistance to a number of commonly used antibiotics (cefepime, cefpirome, ceftazidime, cefotaxime, piperacillin and imipenem) in Pseudomonas aeruginosa, a significant nosocomial pathogen. Stepwise resistance was assessed by serial passage of colonies located nearest to the inhibition zone on antibiotic-containing gradient plates.

In vivo emergence of multidrug-resistant mutants of Pseudomonas aeruginosa overexpressing the active efflux system MexA-MexB-OprM.

During a 6-month period, 21 pairs of Pseudomonas aeruginosa isolates susceptible (pretherapy) and resistant (posttherapy) to antipseudomonal beta-lactam antibiotics were isolated from hospitalized patients. In vivo emergence of beta-lactam resistance was associated with the overexpression of AmpC beta-lactamase in 10 patients. In the other 11 patients, the posttherapy isolates produced only low, basal levels of beta-lactamase and had increased levels of resistance to a variety of non-beta-lactam antibiotics (e.