Determination of In Vitro Synergy of Ampicilin and Chloramphenicol against Multidrug Resistant Bacillus cereus Species

Abstract

Nowadays, combination therapy has become one of the most effective clinical practices in treating infections due to the emergence of multi-resistant microorganisms. In this study, minimum inhibitory concentrations (MICs) of six selected antibiotics; ampicillin, gentamicin, tetracycline, rifampicin, chloramphenicol, and ciprofloxacin were screened towards five Bacillus cereus isolates; KS2, E2, F2, F6, and K2W2 isolated from aquaculture sources and river in Kukup, Johor, Malaysia. Determination of MICs on tested antibiotics showed that all B. cereus isolates were resistant towards ampicillin and rifampicin but most sensitive to chloramphenicol, ciprofloxacin, and gentamicin. Apart from that, this investigation also provides the synergistic effect of ampicillin and chloramphenicol against the B. cereus isolates. On contrary, K2W2 resulted as an antagonism while F6 resulted as indifference. In particular, synergy or double therapy of antibiotics may be required to treat multiresistant organisms. Furthermore, the observed synergy between ampicillin and chloramphenicol opens a new window of using bacteriocins and antibiotics in combination therapy of infections.