The effects of some antibiotic and antibiofilm peptide combinations on Staphylococcus aureus biofilm structure

Due to the rapid spread of antibiotic resistance and the difficulty of discovering new antimicrobials, the reuse and combinational strategies of previously discovered antibiotics have come to the fore. In this study, the combinational efficacy of chloramphenicol and ciprofloxacin with nisin against the ATCC 6538 strain of Staphlococcus aureus were investigated. The MIC values of ciprofloxacin, nisin and chloramphenicol were 0,25, >64 and 32 μg/mL, respectively. The checkerboard assay was carried out for the inspection of synergism between nisin with ciprofloxacin 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. 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. However, no efficacy was determined between nisin and ciprofloxacin.