Emerging virulent clones of community-onset Acinetobacter baumannii in Taiwan

Acinetobacter baumannii has emerged as a significant global pathogen, and community-acquired infections are concerning due to their severe clinical outcomes and high mortality. Despite this, the molecular epidemiology and phenotypic characteristics of community-acquired/community-onset A. baumannii (CAAB/COAB) strains remain poorly understood. This study analyzed the genotypes, virulence traits, and clinical manifestations of 32 COAB isolates collected in Taiwan between 2015 and 2017.

Capsular types (KLs), sequence types (STs) from the Oxford and Pasteur schemes, and international clones (ICs) were identified among the 32 COAB isolates. In vitro virulence was assessed by evaluating biofilm formation, motility, resistance to desiccation and serum, and in vivo virulence was confirmed in a Galleria mellonella larvae model. Associations between KL/ST types and virulence phenotypes, as well as between KL/ST types and the clinical manifestations of patients, were also analyzed.

The results showed that among the tested COAB isolates, KL49 was the predominant capsular type, representing 18.8% (n = 6) of samples, and ST10^Pas/IC8 (ST10^Pas: ST10 under the Pasteur scheme, IC8: international clone 8) was the major clone (15.6%, n = 5). Interestingly, we found that KL49/ST10^Pas, which is predominant in America and Australia but has never been reported for CAAB/COAB in Taiwan, had a hypervirulent phenotype with high serum resistance and high mortality in the G. mellonella larvae model. Furthermore, clinical records showed higher incidences of chronic obstructive pulmonary disease, pneumonia, elevated Pitt bacteremia scores, and 30-day mortality for patients with KL49/ST10^Pas infections than for patients with non-KL49/ST10^Pas infections.

This is the first report identifying KL49/ST10^Pas as a major clone of COAB in Taiwan. Its high virulence was demonstrated, highlighting a potential public health threat. This study lays a foundation for understanding the molecular epidemiology of COAB in Taiwan and supports future research on virulence and disease control strategies.