| Acinetobacter baumannii is one of the most important pathogens causing nosocomial infection in the world,which poses a great threat to human health because of its increasing drug resistance and pathogenicity.In recent years,related studies have shown that many kinds of antibiotics,including meropenem,are in the state of sub-inhibitory concentration(sub-MIC)in the treatment of A.baumannii infection.Sub-MIC antimicrobials not only affect the drug resistance,morphology and community structure of bacteria,but also significantly change the virulence of bacteria by affecting the production of bacterial toxins,exercise ability,adhesion and so on.Quorum sensing is a regulatory mechanism that widely exists in bacteria to coordinate their own group behavior,which is involved in the regulation of bacterial virulence,pathogenicity and other biological functions.However,there are few reports on the relationship between stress,bacterial virulence and quorum sensing system of sub-MIC antibiotics.Therefore,based on the clinical isolates of A.baumannii isolated from our province,and based on the detection of drug resistance,the effects of sub-MIC meropenem on the important virulence characteristics of A.baumannii such as biofilm formation,surface motility and pathogenicity in vivo and its correlation with quorum sensing signal molecules were discussed.So as to provide theoretical reference for rational use of antibiotics,effective control of A.baumannii infection and screening of new drug targets.Research methods and results:(1)Drug resistance characteristics of A.baumannii clinical isolates:in this study,60 clinical isolates of A.baumannii infected in Jilin Province were collected and identified.The sensitivity of A.baumannii to 18antibiotics was determined by Kmurb disk method,and the minimum inhibitory concentration((MIC),)of all isolates to meropenem was determined by microdilution method.The results showed that the resistance rate of 60 A.baumannii clinical isolates to?-lactam drugs was as high as 70%-83.33%,of which ampicillin was the highest;the resistance rates of carbapenem and imipenem were 60%and 71.67%respectively,and the resistance rates to aminoglycosides and quinolones were more than 50%.It is highly sensitive to minocycline and polymyxin B in tetracyclines.Of the 60 strains,48(80%)were identified as multi-drug resistant strains.35 strains(58.33%)were resistant to meropenem,the range of MIC was 8-64?g/ml;25(41.67%),and the range of MIC was 0.25-2?g/ml.(2)Effect of sub-MIC meropenem on biofilm formation ability of A.baumannii clinical isolates:1/2MIC and 1/4MIC meropenem were used to treat the above clinical A.baumannii strains,respectively,and crystal violet semi-quantitative method was used to detect the biofilm formation ability of A.baumannii clinical isolates.The results showed that compared with the control group,the biofilm formation ability of meropenem-resistant strains was significantly inhibited under the action of 1/2MIC meropenem,while there was no significant difference in biofilm formation ability of meropenem-sensitive strains under the action of sub-MIC meropenem.(3)Effect of sub-MIC meropenem on the surface motility of A.baumannii clinical isolates:the bacterial motility test medium was used to determine the surface motility of bacteria under the action of different sub-MIC meropenem.The results showed that in the absence of antibiotics,5 of the 60 isolates had significant surface-related motor ability.Under the action of 1/2MIC meropenem,the movement ability of the five strains decreased significantly compared with the control group.(4)Effect of sub-MIC meropenem on the pathogenicity of A.baumannii to Galleria mellonella:the clinical isolates of A.baumannii were treated with 1/2MIC and 1/4MIC meropenem respectively,and the pathogenicity of A.baumannii in vivo was observed by G.mellonella infection model.The results showed that the pathogenicity of meropenem sensitive strains to G.mellonella was significantly enhanced under the action of 1/2MIC and 1/4MIC meropenem,while the pathogenicity of meropenem resistant strains to G.mellonella had no significant change under the action of sub-MIC meropenem.(5)Correlation between the quorum sensing system of A.baumannii and the effect of sub-MIC meropenem:the production of AHLs of A.baumannii was detected by biosensor strains,and the correlation between AHLs production and sub-MIC meropenem action was analyzed.The results showed that 21 of 60 isolates produced AHLs.The production of AHLs changed under the action of sub-MIC meropenem,but the results were different.Further comparing the biofilm forming ability and the pathogenicity to G.mellonella of AHLs~+group and AHLs~-group under the action of different sub-MIC meropenem,it was found that the biofilm forming ability of AHLs~+group decreased significantly under the action of 1/2MIC meropenem,but there was no significant change in AHLs~-group.Under the action of 1/2MIC and 1/4MIC meropenem,the pathogenicity to G.mellonella increased more significantly in AHLs~-group.Conclusions:(1)sub-MIC meropenem could significantly reduce the biofilm forming ability of meropenem resistant A.baumannii,significantly inhibit the surface-related mobility of A.baumannii and significantly increase the pathogenicity of meropenem sensitive A.baumannii to G.mellonella.(2)The production of AHLs of A.baumannii could be changed by sub-MIC meropenem.The quorum sensing system may be involved in the regulation of sub-MIC meropenem on the biofilm formation and pathogenicity of A.baumannii. |
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