In vitro antibiotic susceptibility of pseudomonads other than Pseudomonas aeruginosa recovered from cancer patients.

The increase in occurrence of infections due to opportunistic gram-negative bacilli in patients with impaired host defenses emphasizes the need for information on the antibiotic susceptibility of the organisms that colonize such patients. During a 20-month period, more than 100 pseudomonads which were not Pseudomonas aeruginosa were recovered from cancer patients at the Baltimore Cancer Research Center. These included P. fluorescens, P. putida, P. multivorans (cepacia), P. maltophilia, P. stutzeri, P. alcaligenes, and P. pseudoalcaligenes. Susceptibility tests with 12 antibiotics indicated that the intraspecies antibiograms for many of these species were more uniform than those of P. aeruginosa. The stability of susceptibility patterns allowed the antibiograms to be used as aids in the preliminary differentiation of these organisms. Variable antibiogram patterns were noted among certain species, i.e., P. fluorescens, P. stutzeri, and P. multivorans, whereas each of the other species had essentially one pattern. These in vitro studies showed that some of the Pseudomonas species other than P. aeruginosa were resistant to a number of antibiotics. Among these were antibiotics that are in general use for P. aeruginosa infections. Such differences in antibiotic susceptibilities emphasize the necessity for careful speciation of this group of microorganisms to assure proper epidemiological documentation of colonization and infection, as well as to ensure therapy with an antimicrobial agent to which the organism is susceptible in vitro.