Comparative in-vitro activity of quinolone carboxylic acids against Proteeae.

The in-vitro susceptibilities of 198 isolates of precisely identified Proteeae species to six quinolone antimicrobials were determined. Significant differences in susceptibility patterns among various Proteeae to the quinolones examined were demonstrated. Although Providencia stuartii was found to be the most resistant to quinolones including the very active agent ciprofloxacin, fully speciated Prov. rettgeri were also markedly resistant as well. in contrast Prov. alcalifaciens was extremely sensitive to these agents. Some strains of Proteus penneri were more resistant to the three newer compounds (ciprofloxacin, enoxacin and norfloxacin) than strains of Pr. vulgaris suggesting that recognition of this species may be important in surveys of the in-vitro activity of antibiotics. Pr. mirabilis and Morganella morganii were very sensitive to the newer agents. The patterns of resistance seen in the three newer agents were reflected in the older agents acrosoxacin and cinoxacin. Accurate speciation of Proteeae in surveys of susceptibilities to antimicrobial agents is important if misleading results are not to be reported.