Molecular Epidemiology Of Acinetobacter Baumannii In The Burn ICU

Acinetobacter baumannii is a common opportunistic pathogen in hospital,which is closely associated with severe infections in patients and often leads to ventilator-associated pneumonia,urinary tract infections,septicemia,wound infections,central nervous system infections,and so on.The simplicity of the nutritional requirements of A.baumannii enables this pathogen to survive and spread easily in the hospital environment,leading to frequent hospital outbreaks of A.baumannii infection.The latest Pubmed data showed that clonal complex 92(CC92)of A.baumannii is distributed all over Asia,Europe,America,Australia,and most parts of China,and it now becomes the most popular clonal complex worldwide.In addition,the drug resistance of A.baumannii cannot be neglected either,mainly due to the abuse of antibiotics and high transmission rate of antibiotic resistance genes among different A.baumannii isolates.In severe burn patients,a number of risk factors including the loss of skin barrier,interventional operations,overuse of broad-spectrum antibiotics,and low immunity,all provide a good chance for A.baumannii invasion.During the period between 2011 and 2012,we investigated the prevalence and resistance characteristics of A.baumannii isolated from severe burn patients hospitalized in the burn ICU of the Southwest Hospital in Chongqing,China.The experimental results showed that the detection rate of A.baumannii from severe burn patients is as high as 34.4%,and the resistant rate to Carbapenems is up to 89.5%.We further identified A.baumannii from the burn intensive care unit(ICU)environments,such as the patient’s bedside,the electrocardiogram(ECG)monitor button,infusion pump button,and the hands of medical personnel.What is the relationship between A.baumannii isolates from patients in the burn ICU and the ward environment? Why are the drug resistance rates so high? The answers to these questions remain elusive.This work is designed to address these issues.In this study,pulsed-field gel electrophoresis(PFGE)and multi-locus sequence typing(MLST)methods were used to evaluate the genomic features of A.baumannii isolates from the ward environment and patients in the burn ICU.Our genotyping results showed that these A.baumannii strains could be clustered into 4 major PFGE types and 4 main sequence types(ST368,ST369,ST195,and ST191).Isolates from both the patients and ward environment can be detected in the dominant type of the two genotyping methods.Furthermore,we also examined the mechanisms of resistance to β-lactam antibiotics in the isolates from two different sources,including the most common β-lactamase resistance genes and the most complicated efflux pump mechanisms.The detection results revealed that A.baumannii isolates from both the ward environment and patients were frequently found to possess β-lactamase genes,including the class A blaPER gene,the class B blaVIM gene,the class C blaAmp C gene,and the class D blaOXA-23 and blaOXA-51 genes.More strikingly,the blaOXA-51 gene was detected in all A.baumannii strains.Among the efflux pumps of A.baumannii,antibiotics extruded by the AdeABC efflux pump are widely employed in clinical therapy.In addition,the ade ABC operon is tightly regulated by the upstream Ade R/Ade S two-component system.Sequencing of A.baumannii isolates showed that mutations accumulated within the two-component system encoding genes,which resulted in amino acid substitutions.As a result,these mutations lead to a significant upregulation of the ade B efflux pump gene,which accounts,at least in part,for the high resistance rates of A.baumannii isolates in this study.