Virulence determinants in multidrug-resistant Acinetobacter baumannii: comparative phenotypic and genomic analysis of clinical and patient-environmental isolates

Abstract

Acinetobacter baumannii is a major cause of healthcare-associated infections owing to its ability to acquire multidrug resistance and express multiple virulence determinants that facilitate persistence in both clinical and hospital environments. However, comparative studies evaluating the phenotypic expression of virulence factors alongside their genomic determinants in paired clinical and patient-environmental isolates remain limited. This study investigated the phenotypic virulence characteristics and corresponding genomic distribution of virulence-associated genes among multidrug-resistant (MDR) A. baumannii isolated from clinical specimens and patient environmental surroundings. A total of 110 non-duplicate MDR A. baumannii isolates, comprising 55 clinical and 55 corresponding patient-environmental isolates, were included. Biofilm formation, haemolytic activity, proteolytic activity, and siderophore production were evaluated using standard phenotypic assays. Whole-genome sequencing was performed on all isolates using the Illumina MiSeq platform, followed by genome assembly, annotation, and identification of virulence-associated genes using the Virulence Factor Database (VFDB). Comparative analyses were performed between clinical and environmental isolates. Clinical isolates demonstrated significantly higher frequencies of strong biofilm formation (34/55, 61.8% vs. 6/55, 10.9%), haemolytic activity (29/55, 52.7% vs. 13/55, 23.6%), and siderophore production (31/55, 56.4% vs. 17/55, 30.9%) than environmental isolates (P < 0.05), whereas proteolytic activity was comparable between the two groups (36/55, 65.5% vs. 33/55, 60.0%). Whole-genome sequencing revealed a high prevalence of virulence-associated genes involved in biofilm formation, haemolysis, proteolysis, and iron acquisition among phenotypically positive isolates. Several virulence-associated genes were also detected in a subset of phenotypically negative isolates, indicating a phenotype–genotype discordance and suggesting that gene carriage alone does not necessarily predict phenotypic expression. Clinical MDR A. baumannii isolates exhibited greater virulence than corresponding patient-environmental isolates; however, environmental isolates retained multiple virulence-associated genes, highlighting their potential role as reservoirs for persistence and transmission within healthcare settings. Integrating phenotypic virulence assays with whole-genome sequencing provides a comprehensive understanding of the virulence potential of MDR A. baumannii and underscores the importance of continuous environmental surveillance and infection prevention strategies to limit the dissemination of highly virulent strains.