Synergistic effects of RNAⅢ inhibitory peptide (RIP) and antibiotics on Staphylococcus aureus infections

XING Qingchang; HU Wenhui; HAO Libo; WANG Jifang

Abstract：Objective To investigate the efficacy of RNAⅢ inhibitory peptide (RIP) combined with antibiotics in the control of staphylococcal infections.Methods Five types of clinically commonly-used antibiotics, including penicillin, cefazolin, levofloxacin, vancomycin and teicoplanin,and RIP were respectively used against Staphylococcus aureus ATCC29213, ATCC25923 and Staphylococcus epidermidis ATCC35984. The MIC values of different inhibitors against three strains of Staphylococcus aureus were compared. The synergistic inhibition of Staphylococcus epidermidis ATCC35984 by RIP and levofloxacin was further analyzed.Results The MIC value of RIP against the three strains of Staphylococcus aureus exceeded 128μg/ml. The MIC values of levofloxacin, ampicillin, cefazolin and vancomycin and teicoplanin against Staphylococcus aureus ATCC29213 and ATCC25923 were within the sensitive range, while that of penicillin and cefazolin against Staphylococcus epidermidis ATCC35984 MIC exceeded the normal range. The combination with RIP could effectively improve the bactericidal effect of levofloxacin. RIP at the concentrations of 5, 10μg/ml , when used in combination with levofloxacin at twice the MIC, could completely remove the biofilm bacteria of ATCC35984.Conclusion RIP has no direct effect on Staphylococcus aureus or Staphylococcus epidermidis, so it cannot take the place of antibiotics, but the combined use of RIP can effectively improve the effect of levofloxacin on Staphylococcus aureus.