Monitoring antibiotic sensibility of bacterial isolates from nosocomial infections in intensive care units of French military hospitals

OBJECTIVE: The aim of this study, conducted in the French Military hospital s, was to monitor the course of the antimicrobial sensibility of bacteria i solated from nosocomial infection in intensive care units. PATIENTS AND METHODS: A prospective study has been conducted from January t o December 1998 in all the intensive care units of the French Army. All the non-repetitive strains isolated from nosocomial infection were collected a nd senile a reference centre. Antimicrobial susceptibility was determined b y the agar dilution method. Beta-lactamase were identified by iso-electro-f ocalisation. Antibiotics choice and interpretative criteria were those of t he "Comite Francais de l'Antibiogramme de la societe Francaise de Microbiol ogie. RESULTS: A total of 849 strains are included in this study. Pseudomonas aer uginosa was the most frequently isolated bacterium (20%) followed by Escher ichia coli (19%) Staphylococcus aureus (15%), coagulase-negative Staphyloco cci (CoNS) (11%) and Enterococci (7%). Imipenem was the most effective antibiotic against enterobacteriaceae (336 isolates; 100% susceptibility). Gentamicin (92%), amikacin (92%) third gene ration cephalosporins (83%), aztreonam (83%) and ciprofloxacin (78%) were a lso very effective. Resistance to III generation cephalosporins was correlated with an extended spectrum beta-lactamase (BLSE) in 36% of cases. This ELSE could be associa ted with an over production of the constitutive cephalosporinase. The most frequent species producing ELSE were Enterobacter aerogenes (75% of ELSE) a nd Klebsiella pneumoniae (17%). Among the 172 P. aeruginosa isolated, antimicrobial susceptibility were res pectively: 71% for imipenem, 62%: tobramycin, 60%: amikacin 59%: ciprofloxa cin 59% piperacillin + tazobactam, 55% piperacillin, 53%: ceftazidime and 4 4% for ticarcillin. Seventy per cent of the 96 CoNS and 50.2% of the 126 S, aureus isolated wer e resistant to methicillin. A strain of S. aureus and 2 CoNS strains had in termediate resistance to teicoplanin. Twenty per cent of the 59 Enterococci strains isolated were resistant to am inopenicillins (10/11 strains of E, faecium), and 9% presented a high level of resistance to gentamicine. One strain of E. faecium was resistant to va ncomycin. CONCLUSION: The evolution of the susceptibility to antibiotics in intensive care units reflects the antibiotic pressure and level of cross-transmissio n. High rates of meticillin-resistance among staphylococci, of resistance t o beta-lactams antibiotics among P. aeruginosa and of ciprofloxacin among E nterobacteriaceae are shown in this study. The implementation of appropriat e strategies for surveillance and prevention is necessary.