Antimicrobial susceptibility profile of molecular typed cystic fibrosis Stenotrophomonas maltophilia isolates and differences with noncystic fibrosis isolates

Multiresistance in Stenotrophomonas maltophilia limits the effectiveness of antimicrobial therapy for infections due to this organism. It can be of special concern in cystic fibrosis (CF) patients due to frequent antimicrobial administration. The in vitro activity of 41 antimicrobial agents against 76 epidemiologically defined CF S. maltophilia isolates by pulsed-field-gel electrophoresis (PFGE) technique under Xbal and Spel restriction was compared with that obtained with 51 non-CF strains recovered from respiratory sources. Minimal inhibitory concentrations (MICs) were determined with the standard National Committee for Clinical Laboratory Standards agar dilution technique, but with 24-hr incubation. Forty-seven different PFGE profiles were observed within 76 S. maltophilia CF isolates. Minocycline (resistance rate, 0%; MIC90, 1 mug/ml), doxycycline (6.4%; 8 mug/ml), trovafloxacin (4.2%; 2 mug/ml), moxifloxacin (6.3%; 2 mug/ml), clinafloxacin (6.3%; 2 g/ml), and moxalactam (17.0%; 64 g/ml) displayed low resistance rates. On the contrary, resistance rates were higher with ceftazidime (70.0%; 256 mug/ml), cefepime (83.0%; 128 mug/ml), piperacillin (87.2%; >1,024 mug/ml), ticarcillin (87.2%; >512 mug/ml), and aztreonam (95.7%; >1,024 mug/ml). Clavulanate reverted resistance to ticarcillin and aztreonam in 40.4% and 31.7% of strains, respectively. Aminoglycosides displayed reduced activities with susceptibility rates lower than 20% and MIC90 higher than 128 mug/ml. With the exception of trimethoprim-sulfamethoxazole (25.4 vs. 31.3%), CF isolates were more resistant than non-CF isolates. Remarkably, resistance was enhanced in S. maltophilia isolates persistently recovered in chronically colonized patients. Susceptibility analysis demonstrated higher resistance rates among CF S. maltophilia isolates when compared with respiratory isolates from non-CF patients. Moreover, persistently recovered CF S. maltophilia isolates were more resistant than sporadic non-CF isolates. (C) 2003 Wiley-Liss, Inc.