[Failure of new beta-lactam antibiotics in the treatment of severe Enterobacter cloacae infections].

In 12 patients infected with an Enterobacter cloacae (E. cl.) initially susceptible to the 3rd generation cephalosporins, we observed the emergence in vivo of variants resistant to most of the new beta-lactam antibiotics (carboxy-penicillins, ureido-penicillins, 3rd generation cephalosporins and aztreonam). These variants remained susceptible to mecillinam and imipenem. The variant emerged under treatment with cefotaxime in 3 cases, with moxalactam in 3 cases, with aztreonam, carbenicillin, and ticarcillin in 1 case each and without treatment in 1 case. An aminoglycoside was combined with the beta-lactam antibiotic in 6 cases. Therapeutic failure was attributed to emergence of the resistant variant in 6 out of 12 cases (with an aminoglycoside in 3 cases, with the beta-lactam antibiotic alone in 3 cases). These case reports underline the importance of bacteriological monitoring of patients infected with E. cl. treated with a beta-lactam antibiotic. The susceptibility to beta-lactam antibiotics of the E. cl. strains isolated during treatment should be systematically retested.