In vitro activity of amdinocillin in combination with other beta-lactam antibiotics against aminoglycoside-susceptible and resistant gram-negative bacteria

Amdinocillin alone and in combination with other beta-lactam antibiotics was tested for in vitro activity against aminoglycoside-susceptible and resistant gram-negative bacteria. Amdinocillin alone or in combination with ampicillin, ticarcillin, piperacillin, cefazolin, cefoxitin, and cefamandole had little to no activity against aminoglycoside-resistant E. coli, E. cloacae, K. pneumoniae, and S. marcescens. There was better activity with aminoglycoside-susceptible organisms, however, Overall, there was significantly more antagonism of amdinocillin combinations when tested with aminoglycoside-resistant organisms than with aminoglycoside-susceptible strains.