INTEGRATED PHENOTYPIC AND MOLECULAR CHARACTERIZATION OF ESBL-PRODUCING ESCHERICHIA COLI: A COMBINED SURVEILLANCE STUDY FROM SOUTH INDIA
DOI:
https://doi.org/10.22159/ajpcr.2026v19i6.59432Keywords:
Antimicrobial resistance, Bloodstream infection,, CTX-M,, Escherichia coli, Extended-spectrum beta-lactamase, Multiplex polymerase chain reaction,, TEMAbstract
Objectives: The objective of the study is to integrate phenotypic antimicrobial susceptibility data with molecular detection of extended-spectrum β-lactamases (ESBL), OXA carbapenemase, and selected virulence genes among clinical Escherichia coli isolates from South India.
Methods: This combined retrospective and laboratory-based observational study included 385 non-duplicate clinical E. coli isolates for phenotypic antimicrobial susceptibility analysis. Susceptibility testing was performed using the Kirby–Bauer disk diffusion method according to Clinical and Laboratory Standards Institute M100 (2024) guidelines. ESBL prevalence in the phenotypic arm was estimated using a surveillance proxy based on ceftazidime resistance (CAZ-R) with amoxicillin-clavulanate susceptibility, as confirmatory clavulanate synergy testing was not performed. A subset of 72 viable isolates underwent multiplex polymerase chain reaction (PCR) for the detection of ESBL genes (TEM, CTX-M, SHV), OXA carbapenemase genes, and virulence markers (stx1, stx2, eae).
Results: CAZ-R was observed in 231/385 isolates (60.0%), while the proxy-based ESBL estimate was 46/385 (11.8%). Carbapenems retained high activity, with >90% susceptibility. Among the 72 molecularly tested isolates, ESBL-associated genes were detected in 56 isolates (77.8%). TEM was the predominant gene (54/72, 75.0%), followed by CTX-M (26/72, 36.1%), while SHV was not detected. Co-carriage of TEM and CTX-M was observed in 24 isolates (33.3%). OXA genes were detected in 41/72 isolates (56.9%). Virulence markers were also identified, including eae (15.2%), stx1 (9.7%), and stx2 (2.7%).
Conclusion: The study demonstrates a major discrepancy between proxy-based phenotypic ESBL estimation and molecular ESBL gene detection. Since confirmatory clavulanate synergy testing was not performed, the 11.8% estimate should not be interpreted as true ESBL prevalence. The high burden of ESBL and OXA genes indicates the need for molecular surveillance, antimicrobial stewardship, and careful interpretation of virulence gene detection in bloodstream E. coli isolates.
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