Pseudomonas aeruginosa: susceptibility to antibiotics and distribution of beta-lactam resistance mechanisms. GERPB 1998.

In a prospective study carried out during a three-week period in October 19 98 in 13 teaching hospitals, 735 non-repetitive isolates of Pseudomonas aer uginosa were collected. In patients presenting cystic fibrosis (70 strains) , the main serotypes isolated were O:6 (14.3%) and O:1 (14.3%). Serotypes O :11 and O:12 were exceptional. In other patients (665 strains), the most fr equent serotypes were O:6 (15.9%), O:11 (15.6%), O:1 (10.7%) and O:12 (9.2% ). The antibiotic susceptibility rates were as follows (respectively, non-c ystic fibrosis and cystic fibrosis strains): ticarcillin, 55 and 59%, piper acillin, 71 and 67%, ceftazidime, 75 and 67%, cefepime, 56 and 43%, cefpiro me, 37 and 21%, aztreonam, 57 and 56%, imipenem, 83 and 70%, amikacin, 69 a nd 33%, ciprofloxacin, 56 and 61% and fosfomycin, 33 and 43%. Serotype O:12 was the least susceptible to antibiotics. Forty-five percent of the non-cy stic fibrosis strains presented intermediate susceptibility or resistance t o ticarcillin. The most frequent mechanisms of resistance were: non-enzymat ic resistance (14.3%), overproduction of the constitutive cephalosporinase (13.8%), production of transferable beta-lactamase (8.6%) and a combination of these mechanisms (4.2%). Among cystic fibrosis strains, resistance to b eta-lactam antibiotics was mainly due to overproduction of the constitutive cephalosporinase (18.6%), whereas production of a transferable beta-lactam ase was rare (1.4%). Susceptibility to aminoglycosides and fluoroquinolones was less frequent in isolates producing transferable beta-lactamases and/o r overproducing cephalosporinase. Decreased susceptibility to imipenem was more frequent in strains presenting a high level of cephalosporinase produc tion. Among the cephalosporins, cefepime was the least affected by the over production of constitutive cephalosporinase. Ceftazidime remained the most efficient antibiotic against both susceptible isolates and strains presenti ng a non-enzymatic or PSE-1 penicillinase-producing mechanism. (C) 2000 Edi tions scientifiques et medicales Elsevier SAS.