IN-VITRO BACTERICIDAL EFFECT OF A BETA-LACTAM PLUS AMINOGLYCOSIDE COMBINATION AGAINST MULTIRESISTANT PSEUDOMONAS-AERUGINOSA AND ACINETOBACTER-BAUMANNII

Pseudomonas aeruginosa and Acinetobacter baumannii are frequently isol ated in hospital outbreaks of nosocomial infections. In our hospital, among 1018 strains isolated one year in an intensive care unit, 84 str ains (8.3%) of P. aeruginosa and 155 strains (15.2%) of A. baumannii w ere considered responsible for infections. The major problem related t o these bacteria is their multiresistant characteristic which confers great difficulty in treating infections. We carried out a 24 h time-ki ll study to assess the bactericidal effect of three beta-lactams [imip enem (IPM), ticarcillin + clavulanic acid (TCC), piperacillin + tazoba ctam (PTB)] in combination with each other and with sulbactam (SUL) an d amikacin (AKN) against 8 P. aeruginosa strains and 8 A. baumannii st rains. The initial inoculum was 10(6) cfu/ml. Antibiotics were tested at clinically achievable concentrations: TCC (112 mg/l), PTB (100 mg/l ), IPM (25 mg/l) and AKN (15 mg/l). The results showed: IMP+TCC+AKN = PTB+SUL+AKN = PTB+TCC+AKN much greater than IMP+SUL+AKN against P. aer uginosa; and PTB+SUL+AKN = PTB+TCC+AKN > IMP+SUL+AKN or IMP+TCC+AKN ag ainst A. baumannii. When infection due to these multiresistant strains was suspected, PTB+AKN combined with either TCC or SUL was bactericid al against both strains. These combinations appeared to be an alternat ive therapy in the treatment of undocumented nosocomial infections in intensive care units. These in vitro results are being evaluated in pa tients and seem to give good results for the moment.