Objective: We aimed to establish a tool for rapid identification of KL49 Acinetobacter baumannii .
Methods: Based on the capsular polysaccharide (CPS) synthesis genes database, we investigated the distribution of K locus type 49 (KL49) genes in other KL types and established a rapid identification method for KL49. We collected 61 clinical carbapenem-resistant A. baumannii  (CRAB) strains, identified KL49 by gtr100  detection, and used whole genome sequencing (WGS) for verification. A mouse pneumonia model was used to confirm the hypervirulence phenotype. We tested the presence of gtr100  gene in 165 CRAB strains from three provinces in China and evaluated the correlation of gtr100  carrying CRAB infection with mortality.
Results: The gtr100  gene is the CPS synthesis gene found only in KL49. We screened out nine WGS-validated KL49 strains from 61 CRAB clinical strains using polymerase chain reaction (PCR) to detect the gtr100  gene. The survival rates of KL49 strains were significantly lower than nonKL49 strains in a mouse pneumonia model. The survival rates of LAC-4 gtr100  knockout strain decreased significantly. Analysis of phylogenetics showed the worldwide spread of KL49 A. baumannii . Infection of gtr100  carrying CRAB is an independent risk for mortality (OR, 10.76; 95%CI: 3.08– 37.55; p < 0.001).
Conclusion: The hypervirulence phenotype of KL49 CRAB and the association with mortality highlight the urgent need for implementing control measures. The rapid identification assay has the potential to facilitate early medical intervention and worldwide surveillance.
Keywords: Acinetobacter baumannii , hypervirulent, K locus, Kaptive, mortality