From Phenotype to Genotype: A Clonal Perspective on Virulence and Biofilm Formation in Bloodstream-Derived Escherichia coli.

BACKGROUND

Bloodstream infections, BSIs caused by Escherichia coli are a major healthcare concern due to the increasing emergence of multidrug-resistant and virulent strains. This study aimed to investigate the phenotypic and genotypic characteristics of bloodstream-derived E. coli isolates, with a focus on antimicrobial resistance, biofilm formation, virulence-associated genes, phylogenetic distribution, and clonal diversity.

METHODS

A total of 150 blood culture samples were collected from patients with suspected BSIs, of which 60 (40%) E. coli isolates were recovered and confirmed using conventional microbiological methods. Antimicrobial susceptibility testing was performed according to the CLSI2026 guidelines, whereas biofilm formation was assessed using a microtiter plate assay. Virulence genes, phylogenetic groups, and clonal relationships were evaluated using polymerase chain reaction-based, PCR methods.

RESULTS

High susceptibility rates were observed for colistin (96.7%) and meropenem (93.3%), whereas the highest rates of resistance were detected against ciprofloxacin (93.3%) and co-trimoxazole (61.7%). Multidrug resistance, MDR was detected in 41.7% of the isolates, while 31.7% were phenotypically characterized as Extended-Spectrum Beta-Lactamase, ESBL producers. Biofilm analysis revealed that 75% of the isolates were capable of biofilm formation. Among the investigated virulence genes, fimH (88.3%), ompT (73.3%), and irp2 (58.3%) were most prevalent. Phylogenetic analysis revealed a predominance of groups B2 (26.7%), B1 (23.3%), and D (23.3%). The ERIC-PCR analysis classified the isolates into 26 distinct ERIC types, indicating substantial genetic diversity.

CONCLUSION

The coexistence of virulence-associated genes, biofilm-forming ability, antimicrobial resistance, and genetic diversity among bloodstream-derived E. coli isolates highlights the circulation of potentially high-risk lineages in healthcare environments. These observations underscore the necessity for ongoing molecular epidemiological monitoring and the implementation of effective infection control strategies.