In a prospective study carried out during a three-week period in October 1998 in 13 teaching hospitals, 735 non-repetitive isolates of Pseudomonas aeruginosa 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 frequent 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-
cystic fibrosis and
cystic fibrosis strains):
ticarcillin, 55 and 59%,
piperacillin, 71 and 67%,
ceftazidime, 75 and 67%,
cefepime, 56 and 43%,
cefpirome, 37 and 21%,
aztreonam, 57 and 56%,
imipenem, 83 and 70%,
amikacin, 69 and 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-
cystic fibrosis strains presented intermediate susceptibility or resistance to
ticarcillin. The most frequent mechanisms of resistance were: non-enzymatic 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
beta-lactam antibiotics was mainly due to overproduction of the constitutive
cephalosporinase (18.6%), whereas production of a transferable
beta-lactamase was rare (1.4%). Susceptibility to
aminoglycosides and
fluoroquinolones was less frequent in isolates producing transferable
beta-lactamases and/or overproducing
cephalosporinase. Decreased susceptibility to
imipenem was more frequent in strains presenting a high level of
cephalosporinase production. Among the
cephalosporins,
cefepime was the least affected by the overproduction of constitutive
cephalosporinase.
Ceftazidime remained the most efficient
antibiotic against both susceptible isolates and strains presenting a non-enzymatic or PSE-1
penicillinase-producing mechanism.