Study On Drug Resistance And Virulence Characteristics Of Acinetobacter Baumannii Clinical Strains And Its Correlation With Abal/AbaR Quorum Sensing System

Acinetobacter baumannii is currently the most important clinical opportunistic pathogen in the world and plays an important role in nosocomial infections.The failure of clinical anti-infective treatment and the outbreak of nosocomial infection caused by the resistance of A.baumannii pose a great threat to human health.Quorum sensing（QS）is the mechanism by which bacteria can coordinate their group behavior by sensing population density.It is widely found in bacteria and participates in the regulation of various biological functions including bacterial virulence and pathogenic processes.The A.baumannii QS system has recently been discovered,consisting of the AbaI/AbaR two-component system.Currently,the regulatory role and mechanism of A.baumannii quorum sensing system on bacterial virulence and drug resistance remain unclear.This study investigated the drug resistance and virulence characteristics of A.baumannii clinical isolates from Jilin Province,identified the presence of AbaI/AbaR quorum sensing system and explored their relationship with bacterial virulence and drug resistance.The clarification of the above problems is of great significance for us to regulate the virulence of A.baumannii by using QS system and effectively control A.baumannii infection.Methods and results:（1）Drug resistance characteristics of A.baumannii clinical isolates:A total of 80 clinical isolates of A.baumannii from Jilin Province were collected and identified in this study.The antimicrobial resistance characteristics of these clinical strains were identified by antibiotic sensitivity test,resistance gene screening and international clonal typing.At present,the resistance of A.baumannii causing noscomial infection in Jilin Province was serious.The detection rate of multi-drug resistant A.baumannii was as high as 75%.The resistance rate of A.baumannii isolates to 17 antibiotics commonly used in clinic was more than 50%.Minocycline and polymyxin still maintain a high sensitivity rate.These strains carried a variety ofβ-lactamase resistance genes,including bla_TEM（40/80,50%）,bla _IMP1（61/80,76.25%）,bla _AmpC（33/80,41.25%）,bla_OXA-23-like（42/80,52.5%）and bla_OXA-51-like（80/80,100%）.The cloning typing results showed that international clone II（IC-II）was the most prevalent clone type.（2）Virulence characteristics of A.baumannii clinical isolates:We evaluated the ability of biofilm formation,surface motility,the ability of adherence and invasion to human alveolar epithelial cells A549,and the virulence of A.baumannii to the Galleria mellonella in all 80 clinical isolates.The results showed that the virulence characteristics of different clinical strains were significantly different.95%（76/80）of A.baumannii isolates had the ability of biofilm formation,of which38 showed strong biofilm formation ability（+++）,and 4 strains showed no obvious biofilm formation（-）.The surface-related motility was generally weak,and only 5（5/80,6.25%）strains showed strong surface-related exercise capacity.The 80 clinical isolates exhibited apparently different abilities of adherence and invasion to A549 cells,among which 35isolates（35/80,43.75%）showed relatively strong adherence ability,and 56 isolates（56/80,70%）showed slightly stronger invasive ability.The Galleria mellonella infection experiments found that 16 isolates（16/80,20%）showed strong virulence（survival rate was less than 50%after infection for 1 day,and survival rate was 0 after 6 days of infection）.（3）Study on the presence of quorum sensing system and its correlation with bacterial virulence and drug resistance:The carrying status of the abaI and abaR genes of quorum sensing system was detected by PCR method.Biosensing bacteria were used to detect the production of acyl homoserine lactone（AHLs）signaling molecules.Results showed that 62 strains（62/80,77.5%）of A.baumannii carried abaI and abaR genes,of which 24（24/80,30%）produced AHLs signaling molecules detected by biosensors.Correlation analysis revealed that the carrying of abaI and abaR genes was positively correlated with the bacterial resistance rate.All strains showing surface-related motility carried abaI and abaR genes and produced AHLs signaling molecules.The isolates carrying the abaI gene and the abaR gene and producing AHLs showed stronger invasive abilities to A549 cells.The A.baumannii isolates producing AHLs showed significantly stronger pathogenicity to Galleria mellonella than the isolates that do not produce AHLs signaling molecules.Conclusion:（1）Currently,the A.baumannii causing noscomial infection in Jilin Province were highly resistant toβ-lactams,aminoglycosides,quinolone and sulfonamides antimicrobial agents and carried a variety ofβ-lactamase resistance genes.International clone II（IC-II）was the most popular clone type.（2）The virulence characteristics of A.baumannii clinical isolates were apparently different.Most of isolates showed the biofilm formation ability,some strains showed obvious surface-related motility,relatively strong ability of adhesion and invasion to A549 cells,and strong virulence to Galleria mellonella.（3）These clinical strains widely carried the AbaI/AbaR quorum sensing system,and this system was significantly correlated with bacterial resistance,invasive ability to A549 cells,and virulence to the Galleria mellonella.