Temporal Comparison of Virulence-Associated Characteristics and Metabolic Activity in Fluoroquinolone-Resistant Escherichia coli O25 ST131 Urinary Isolates from Croatia

The aim of this study was to compare the virulence-associated characteristics and metabolic activity of fluoroquinolone-resistant (FR) Escherichia coli O25 ST131 isolates recovered from urine samples of outpatients in Zagreb, Croatia, during two study periods, 2011/2012 and 2017/2018. The O25 ST131 clonal lineage was identified by rapid multiplex PCR targeting the O25pabB and trpA genes. PCR was used to detect blaCTX-M, blaCTX-M-15, blaTEM, and blaSHV β-lactamase genes, as well as the virulence-associated genes fimH, papC, hlyA, cnf1, and traT. Metabolic activity was evaluated using the VITEK 2 GN card, and serum resistance was assessed using a serum susceptibility assay. Differences between study periods were analyzed using linear regression and the chi-square test. A total of 4354 and 7717 E. coli isolates were recovered during the first and second study periods, respectively, and 170 FR E. coli O25 isolates were collected. Among the O25 ST131 isolates, 30/45 (66.7%) from the first study period and 75/114 (65.8%) from the second study period were ESBL-positive, with CTX-M-15 predominating. The fimH gene was detected in all 159 O25 ST131 isolates (100%), whereas hlyA, papC, cnf1, and traT were detected in 35 (22%), 43 (27%), 35 (22%), and 123 (77%) isolates, respectively. Compared with the first study period, isolates from the second period showed significantly higher frequency of papC, hlyA, and cnf1, as well as higher serum resistance and metabolic potential (p < 0.01). These findings demonstrate temporal differences in selected virulence-associated characteristics, serum resistance, and metabolic activity among FR E. coli O25 ST131 isolates and support the need for continued surveillance of this clinically important clonal lineage in the community.