Efflux pump inhibitor combined with ofloxacin decreases MRSA biofilm formation by regulating the gene expression of NorA and quorum sensing.

Carbonyl cyanide p -nitrophenylhydrazone (2e) displayed a lone or synergistic efficacy against MRSA ( RSC Adv. , 2020, 10, 17854). In this work, the synergistic mechanism of 2e with ofloxacin was studied. MRSA2858 had potential for biofilm formation, and the value of MBEC of 2e alone was 0.78-1.56 μM, while that of 2e + ofloxacin was 0.39-0.78 μM. 2e combined with ofloxacin showed a synergistic anti-biofilm effect against MRSA. Efflux pump inhibitor 2e can better bind to NorA protein. After MRSA2858 was treated with 2e of 1/2MIC (0.78 μM) and ofloxacin of 1/8MIC (0.097 μM), the transcript levels of efflux genes ( norA ) and quorum-sensing (QS) regulatory genes ( agrA , sarA , icaA , hla ) were substantially down-regulated, and alpha-hemolysin (Hla) was inhibited by 99.15%. 2e combined with ofloxacin was more effective than 2e alone in reducing bacterial load in vivo . All in all, efflux pump inhibitor 2e enhanced the bactericidal activities of antibiotics through regulating the gene expression of NorA and QS system.