PURPOSE: Most of the patient affected of CF are chronically colonized by P. aeruginosa (PA), B. cepacia (BC), S. maltophilia (SM) and A. xilosoxydans, all of them multidrug-resistant (MDR) to individual antibiotic treatments. Since antimicrobial therapy in front of these microorganisms is limited, the purpose of this study was to evaluate the activity of antibiotic combinations against these MDR isolates.
METHODS: We studied 65 strains of PA, 15 of BC and 15 of SM isolated from patients affected of CF. The following antibiotics were evaluated singly and in combination using the checkerboard method: imipenem (IMI), meropenem (MER), piperacillin-tazobactam (PT), cefepime (CEP), colistin (COL), aztreonam (AZT), ceftazidime (CAZ), ciprofloxacin (CIP), levofloxacin (LEV), chloramphenicol (CLOR), cotrimoxazole (SXT), minocycline (MIN), doxicycline (DOX), gentamicin (GEN), amikacin (AK) and tobramycin (TOB).
RESULTS: IMP-TOB, IMP-CIP, IMP-LEV, MER-TOB, MER-GEN, MER-CIP, MER-LEV, AZT-LEV, PT-TOB, PT-COL, PT-CIP, PT-LEV, CAZ-TOB, CAZ-AK, CAZ-LEV, CEP-TOB, CEF-GEN, CEF-CIP and CEP-LEV were synergistic against PA. MER-TOB, MER-LEV, MER-SXT, PT-AK, CEP-TOB, CEF-GEN, CEF-AK, CEP-CIP and CEP-LEV were synergistic against BC. CIP-DOX and MIN-CIP showed synergy against SM. COL alone was susceptible in 100% of PA, MIN and DOX in 100% of SM and CLOR in 100% of BC.
CONCLUSION: Combination of betalactams with LEV had the most consistently synergistic effect against PA, but antibiotic combinations that contained TOB were the most effective against BC. MIN alone was susceptible in 100% of SM but also combinations of CIP-DOX are effectives.
CLINICAL IMPLICATIONS: Since antimicrobial therapy in front of these MDR microorganisms is limited, the development of preventive strategies and therapeutical treatments based on synergistic combinations would be of great help.
DISCLOSURE: Dolors Mariscal, None.