The Effect of Nisin and Chloramphenicol Combinationon Staphylococcus aureus ATCC 6538 Biofilm Structure

Nowadays, due to the rapid spread of antibiotic resistance and the difficulty of discovering new antimicrobial agents, the reuse and combinational strategies of old antibiotics have come to the fore. In this study, we investigated the combinational efficacy of nisin and chloramphenicol against the ATCC 6538 strain of Staphylococcus aureus. The MIC values of nisin and chloramphenicol were >64 and 32 µg/mL, respectively. The checkerboard assay was carried out for the inspection of synergism between nisin and chloramphenicol. Furthermore, the crystal violet assay was employed to assess antibiofilm effects. Additionally, the expressions of various virulence genes (agrA, spa, icaA and saeR) were investigated using the colony biofilm assay and qRT-PCR methods. In combination application, MIC values of nisin and chloramphenicol was decreased. In addition, biofilm formation was decreased.It was shown that the expression level of the agrA gene decreased compared to the control in the nisin, chloramphenicol and combinational applications. The expression levels of other genes were increased compared to the control. The results showed that the activities of nisin and chloramphenicol combinations had synergistic and antibiofilm activity. This study sheds light on the combinatorial use of older antibiotics.