Mechanism on antibacterial effect in vitro and biofilm eradication effect of Xiaochaihu Decoction and imipenem-cilastatin for carbapenem-resistant Acinetobacter baumannii

Objective To analyze the mechanism on antibacterial effect in vitro and biofilm eradication effect of Xiaochaihu Decoction and imipenem-cilastatin for carbapenem-resistant Acinetobacter baumannii (CRAB).

Methods A total of 60 strains of CRAB isolated from different samples were randomly collected. The minimal inhibitory concentrations (MIC) of Xiaochaihu Decoction combined with imipenem-cilastatin in different concentration combinations for 60 CRAB strains were detected by micro-checkerboard dilution method, and fractional inhibitory concentration (FIC) was calculated. The inhibition effect of antimicrobial agents for biofilm was detected by microplate reader; real-time fluorescent quantitative polymerase chain reaction (RT-PCR) was used to detect the transcription level of drug-resistant genes.

Results MIC values of Xiaochaihu Decoction and imipenem-cilastatin for CRAB were 32 and 16 μg/mL, respectively. The combination of Xiaochaihu Decoction and imipenem-cilastatin was able to synergistically inhibit the growth of CRAB. Compared with 1/16 of MIC imipenem-cilastatin alone, the A₅₇₀ value decreased after adding 1/16 MIC, 1/4 MIC or 1 of MIC of Xiaochaihu Decoction combined with 1/16 of MIC of imipenem-cilastatin, the difference was statistical significant (t=4.513, 10.515, 19.802, P < 0.05); compared with 1/16 of MIC of Xiaochaihu Decoction alone, the A₅₇₀ value decreased after adding 1/16 of MIC, 1/4 of MIC or 1 of MIC of imipenem-cilastatin combined with 1/16 of MIC of Xiaochaihu Decoction, and the difference was statistically significant (t=3.109, 5.657, 15.461, P < 0.05). Compared with growth control group, expression levels of adeJ and CarO were significantly lower in the imipenem-cilastatin group, while their expression levels were significantly higher in the combination group(P < 0.05).

Conclusion Xiaochaihu Decoction combined with imipenem-cilastatin can synergistically inhibit the growth of CRAB and reduce the adhesion of biofilm, and the mechanism may be achieved by activating the expression of adeJ and CarO genes.