Piperacillin: evaluation against inpatient and gentamicin-resistant bacteria

When species-matched collections, each consisting of 128 bacterial strains, were compared, inpatient organisms were found to be significantly more resistant to piperacillin than outpatient organisms. A collection of 143 gentamicin-resistant gram-negative bacilli was significantly more resistant to piperacillin than a species-matched collection of gentamicin-sensitive organisms. Piperacillin resistance was transferred by conjugation from isolates of 8 different Enterobacteriaceae species to a recipient Escherichia coli strain. In each of 67 mating experiments in which transfer of carbenicillin resistance by conjugation occurred, resistance to ticarcillin, azlocillin and piperacillin was also transferred. As in previous studies, piperacillin was found to be markedly more active against non-fastidious gram-negative bacilli than carbenicillin, ticarcillin or azlocillin. Nevertheless, piperacillin resistance, apparently plasmid mediated, was detected in multiple species.