EVOLUTION OF SUSCEPTIBILITY TO CEFTAZIDIM E AND 3 OTHER BETA-LACTAM AGENTS AGAINST GRAM-NEGATIVE BACILLI IN-HOSPITAL BETWEEN 1989 AND 1993

The aim of this study was to determine changes in susceptibility to ce ftazidime, cefotaxime, imipenem and ticarcillin among the following ba cterial species possessing acquired mechanisms of resistance to these agents: Klebsiella, Enterobacter, Serratia, Pseudomonas aeruginosa, Bu rkholderia (Pseudomonas) cepacia, Stenotrophomonas (Xanthomonas) malto philia and Acinetobacter baumannii. From 1989 to 1993 (1994 in the cas e of P. aeruginosa), all non repetitive strains belonging to these spe cies were collected, during the first month of each 3-month period, fr om the bacteriology laboratories of 12 French university hospitals. An timicrobial susceptibility was determined by the standard agar diffusi on method and interpreted according to the cutoff values of the Comite de l'Antibiogramme de la Societe 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 ceftazidim e and cefotaxime, after peaking at 24% in 1991, fell to 18% in 1993. T he frequency of ticarcillin-resistant strains among Enterobacter cloac ae and Serratia marcescens also fell during the study period. The freq uency of P. aeruginosa strains resistant to ceftazidime remained fairl y stable (7% in 1989, 8% in 1994). The same was true for ticarcillin r esistance (30-40% of strains), while the proportion of strains resista nt to imipenem increased from 12% in 1989 to 18% in 1994. Regarding re sistance 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 199 2 to 8.1% in 1994, and a fall in isolated resistance to ticarcillin (1 6.3% in 1994). Resistance to ceftazidime and cefotaxime increased amon g A. baumannii isolates, contrasting with a fall in resistance to tica rcillin and little change in resistance to imipenem (< 1%). Ceftazidim e 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 m onitoring of antibiotic resistance among the principal bacterial patho gens forms the basis for rational and economic use of probabilistic ch emotherapy Studies of the resistance mechanisms involved would also be of value.