RESUMEN
In vitro susceptibility of several strains of six different species of clinical facultative pathogens involved in nosocomial infections in our hospital was investigated by a series of disc diffusion, broth dilution and Chequerboard titration testing. With disc diffusion method all the test strains, except Streptococcus pyogenes, were resistant to penicillin. 46% of the Klebsiella aerogenes and 73% of the Pseudomonas strains were generally resistant to cefotaxime. The minimum inhibitory concentration (MIC) of the antibiotics correlated well with the results of the disc diffusion tests. Synergistic effects were demonstrated by various combinations of gentamicin, ampicillin, clindamycin, colistin, cefoxitin, and ceftriazone against resistant strains of S. aureus, Pseudomonas aeruginosa, Escherichia coli and Klebsiella aerogenes. Against S. aureus the effect of gentamicin/clindamycin demonstrated indifference. The need for stringent caution is strongly advocated in the selection of combination therapy for serious infections caused by some hospital bacterial strains particularly in acute care units. The clinical microbiologist should be consulted at all times during the process of selection of an appropriate combined therapy for expert guidance.