Epidemiological And Genomic Characterization Of Acinetobacter Baumannii In Bloodstream Infections

Objectives:To analyze the genomic characteristics of Acinetobacter baumannii isolated from clinical bloodstream infections and to explore the correlation between genomic characteristics and clinical phenotypes.Methods:Clinical data of patients with A.baumannii bloodstream infections were collected for analysis of infection risk factors.Acinetobacter baumannii isolated from bloodstream infections were subjected to drug sensitivity assays and analyzed for drug resistance characteristics.The strains were also subjected to whole genome sequencing to derive homologous relationships,drug resistance genes and virulence genes.And the corresponding strains were selected according to the homology relationship for virulence assays,including biofilm assay,serum resistance assay and greater wax borer infection assay.The virulence characteristics of Acinetobacter baumannii were analyzed.Results:After collecting the clinical data of 152 cases of Acinetobacter baumannii bloodstream infection,the risk factors were analyzed.Indwelling central venous catheter and mechanical ventilation were the independent influencing factors.After uploading the genome sequence to the relevant website,multi-locus sequence results were obtained.Using the Oxford typing results,a total of 148 strains were identified with 18 ST types,namely ST195,ST208,ST540,ST368,ST1779,ST938,ST369,ST373,ST191,ST229,ST2371,ST1684,ST381,ST2339,ST1598,ST1482,ST1377,ST1110.The newly assigned ones are ST2457,ST2458,ST2459,ST2460.The obtained ST types were clonotyped and could be divided into CC92 groups including ST369,ST540,ST1684,ST1779,ST191,ST195,ST208,ST368,ST381 and ST938,and the remaining ST types were non-CC92 clonotypes.According to the results of COG annotation,most of the gene functions are in"translation,ribose structure and biogenesis","translation and transcription","amino acid transport and metabolism","energy production and conversion" and "cell membrane and cell wall formation".Virulence and drug resistance analysis of genomic sequences showed that the CC92 grouping virulence genes were almost identical,except for ST1779 and ST369,which carried the hemE gene.There were also pilE genes carried in some of the STs.The drug resistance genes in CC92 were more numerous than those in non-CC92,and basically covered the common clinical drugs.All strains in the CC92 grouping carried the blaOXA-23 gene.In the biofilm assay,the positive rate of biofilm forming ability in the CC92 group was 48.39%.In the non-CC92 group the positive rate of biofilm forming ability was 66.67%.The difference in biofilm forming ability between the two groups was not statistically significant(P=0.1379).In the serum resistance assay,23 strains had high resistance to human serum,and their survival in human serum ranged from approximately 53.55%to 140.23%.In the greater wax borer experiment,there was a correlation between the ST type of A.baumannii and its mortality after infection with greater wax borer(P<0.05).There were 22 strains with higher mortality rates than the AB5075 strain after infection,including ST1684,ST369,ST368,ST195,ST191,ST2371,ST2339,ST2459,ST1779,ST1598,ST540,ST373,and ST208.Conclusions:The high rate of drug resistance in A.baumannii in bloodstream infections can be attributed to the blaOXA-23 gene.CC92 is the major clone among A.baumannii carrying this gene and should be monitored.We need to focus on virulence factors involved in bacterial motility and polysaccharide biosynthesis that are widespread in clinical Acinetobacter baumannii.Drug resistance and virulence should be monitored in our hospital in a timely manner to reduce the spread of resistance and mortality that may be caused by highly virulent Acinetobacter baumannii.