Antibiotic combination effect on the clinical isolates of Aeromonas hydrophila

The effect of antibiotic combinations on 191 clinical strains of Aeromonas hydrophila was analysed by checkerboard microdilution methods. The combinations of antibiotics were as follows: amikacin (AN) + carbenicillin (CB), AN + cephalexin (CLX), AN + piperacillin (PIP), AN + cefoperazone (CFP), AN + ceftriaxone (ROC), gentamicin (GM) + CB, GM + CLX, GM + PIP, GM + CFP, GM + ROC, GM + tetracycline (TC). The results of this study indicated that (i) the effect of AN + CB and AN + PIP was considered synergistic (their fractional inhibitory concentration (FIC) index of less than or equal to 0.5 was equal to 85.9% and 83.2%); (ii) the combination of GM + PIP, GM + CB, AN + CLX and GM + CLX was considered additive (their FIC index of = 1 were 79.0%, 82.7%, 76.4% and 93.2%, respectively); and (iii) the combination of GM + TC, GM + CFP, AN + ROC, AN + CFP and GM + ROC was considered antagonistic (their FIC index of = 2 was 55.0%, 67.6% 61.3% 68.6% and 71.2%, respectively). AN + CB, and AN + PIP combinations revealed the highest bactericidal activity, based on conclusions drawn from the bacterial killing curve study. Therefore, it is suggested that when clinicians attempt to use a drug combination to treat infection caused by A. hydrophila, they should consider the possible outcome of antibiotic combinations and choose the appropriate therapy.