Evolution de la sensibilité des bacilles à Gram négatif à la ceftazidime et à trois autres bêta-lactamines en milieu hospitalier de 1989 à 1993

The aim of this study was to determine changes in susceptibility to ceftazidime, cefotaxime, imipenem and ticarcillin among the following bacterial species possessing acquired mechanisms of resistance to these agents: Klebsiella, Enterobacter, Serratia, Pseudomonas aeruginosa, Burkholderia (Pseudomonas) cepacia, Stenotrophomonas (Xanthomonas) maltophilia and Acinetobacter baumannii. From 1989 to 1993 (1994 in the case of P. aeruginosa), all non repetitive strains belonging to these species were collected, during the first month of each 3-month period, from the bacteriology laboratories of 12 French university hospitals. Antimicrobial susceptibility was determined by the standard agar diffusion method and interpreted according to the cutoff values of the Comité de l'Antibiogramme de la Société Francaise de Microbiologie. A yearly average of 7000 strains were studied. They were isolated from various body sites, especially urine and the respiratory tract. The in vitro activity of ceftazidime and cefotaxime, expressed as the percentage of resistant strains, remained relatively stable. It is noteworthy that the frequency of Klebsiella pneumoniae strains resistant to ceftazidime and cefotaxime, after peaking at 24 % in 1991, fell to 18 % in 1993. The frequency of ticarcillin-resistant strains among Enterobacter cloacae and Serratia marcescens also fell during the study period. The frequency of P. aeruginosa strains resistant to ceftazidime remained fairly stable (7 % in 1989, 8 % in 1994). The same was true for ticarcillin resistance (30-40 % of strains), while the proportion of strains resistant to imipenem increased from 12 % in 1989 to 18 % in 1994. Regarding resistance phenotypes, while the proportion of strains sensitive to the three antibiotics remained stable (approx. 60 %), there was an increase in the frequency of isolated resistance to imipenem, from 4.6 % in 1992 to 8.1 % in 1994, and a fall in isolated resistance to ticarcillin (16.3 % in 1994). Resistance to ceftazidime and cefotaxime increased among A. baumannii isolates, contrasting with a fall in resistance to ticarcillin and little change in resistance to imipenem (<1 %). Ceftazidime activity on B. cepacia remained stable (2-10 % of resistant strains), as did that on K. oxytoca (1-3 %) and S. maltophilia (70-80 %). Close monitoring of antibiotic resistance among the principal bacterial pathogens forms the basis for rational and economic use of probabilistic chemotherapy. Studies of the resistance mechanisms involved would also be of value.