低氧环境下鲍曼不动杆菌外膜囊泡分泌特征及其对碳青霉烯类抗生素耐药性的影响OA

Objective:The resistance rate of Acinetobacter baumannii to carbapenem antibiotics continues to increase.This study aims to investigate the secretion characteristics of bacterial outer membrane vesicles(OMVs)of Acinetobacter baumannii under hypoxic conditions and their effects on carbapenem antibiotic resistance. Methods:The standard susceptible strain Acinetobacter baumannii ATCC 19606 was divided into a normoxia group(20%oxygen concentration)and a hypoxia group(3%oxygen concentration)according to different culture conditions.The effects of different oxygen environments on the growth characteristics and biofilm formation of Acinetobacter baumannii were compared using spectrophotometry and crystal violet staining.The minimum inhibitory concentration(MIC)of imipenem against the 2 groups was determined using the agar plate twofold dilution method.OMVs secreted by the 2 groups were extracted by differential centrifugation.Transmission electron microscopy and nanoparticle tracking analysis(NTA)were used to compare the characteristics of OMVs under different oxygen conditions.Real-time quantitative polymerase chain reaction(RT-qPCR)was used to detect the expression levels of periplasmic quality control factors(SurA,Skp,DegP)in the two groups.OMVs secreted by the normoxia and hypoxia groups were co-incubated with the standard strain Acinetobacter baumannii ATCC 17978,and a blank incubation group without OMVs was set as a control.The MIC of imipenem for the recipient strain after co-incubation was determined using the agar dilution method. Results:The growth rate of Acinetobacter baumannii in the hypoxia group was significantly lower than that in the normoxia group(P<0.05),while its biofilm formation ability was significantly higher(P<0.05).The MIC value in the hypoxia group was significantly higher than that in the normoxia group(P<0.05).The yield and diameter of OMVs in the hypoxia group were both higher than those in the normoxia group(both P<0.05).Compared with the normoxia group,the expression levels of SurA and Skp in the hypoxia group were significantly upregulated(P<0.05),while the expression level of DegP was significantly downregulated(P<0.05).The MIC of the recipient strain co-incubated with OMVs from the hypoxia group was significantly increased compared with that of the blank incubation group(P<0.05),whereas no significant difference was observed between the recipient strain co-incubated with OMVs from the normoxia group and the blank incubation group(P>0.05). Conclusion:Hypoxic conditions can promote the secretion of OMVs by Acinetobacter baumannii,thereby mediating carbapenem antibiotic resistance.This mechanism is associated with the expression of quality control factors DegP,SurA,and Skp.