CTX-M-Producing Escherichia coli in Lithuania: Associations Between Sites of Infection, Coresistance, and Phylogenetic Groups

Increasing resistance of Escherichia coli (E. coli) to antibiotics, especially to the third-generation cephalosporins, has prompted studies on widespread resistance genes such as bla_CTX-M and differentiation of E. coli to phylogenetic groups. The aim of this study was to determine the associations between the CTX-M type and the phylogenetic group, the site of infection, and coresistance in Lithuanian E. coli isolates producing β-lactamases.
Material and Methods. A total of 90 E. coli ESBL strains were recovered from the lower respiratory tract, the urinary tract, sterile body sites, wounds, and other body sites between 2008 and 2012. The E. coli isolates resistant to at least 2 antibiotics with different modes of action along with resistance to cefotaxime were considered as multiresistant. The bla_CTX-M, bla_TEM, bla_OXA-1, and blaSHV genes, the phylogenetic groups, and the resistance profiles were analyzed.
Results. Of the 90 isolates, 84 (93.3%) were classified as multiresistant and 6 (6.6%) as resistant. The bla_CTX-M-15 gene was the most prevalent gene followed by the bla_CTX-M-14 and bla_CTX-M-92 genes. The logistic regression analysis revealed the associations between CTX-M-15 and resistance to ceftriaxone, between CTX-M-14 and resistance to cefoxitin, aztreonam, ampicillin/sulbactam, ticarcillin/clavulanic acid, and tobramycin, and between CTX-M-92 and resistance to cefepime, piperacillin/tazobactam, gentamicin, and tobramycin.
Conclusions. The results of this study showed a significant association between CTX-M-15, CTX-M-14, and CTX-M-92 β-lactamases and resistance to some antibiotics as well as CTX‑M-14 β-lactamase and phylogenetic group A in the Lithuanian population. The associations between the CTX-M type and the site of infection were not determined.