Epidemiology of CTX-M Extended-Spectrum β-Lactamases in Escherichia coli Clinical Isolates in Mexico: A Systematic Review

Introduction
The global spread of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli, particularly those harboring CTX-M enzymes, represents a major public health concern due to their association with multidrug resistance and limited therapeutic options. In Mexico, increasing reports of CTX-M–producing E. coli have been documented in both hospital and community settings. However, the epidemiological and molecular characteristics of these isolates remain fragmented across individual studies. This study aimed to review the available evidence on the prevalence and molecular features of CTX-M–producing E. coli in clinical isolates from Mexico.

Methods
A systematic review was conducted in PubMed and Scopus to identify studies reporting ESBL or CTX-M–producing E. coli in Mexico. Eligible studies included original research articles describing clinical human isolates. Studies focusing exclusively on animals, food, environmental sources, or non-E. coli organisms were excluded. Data extracted included study location, infection type, number of isolates, prevalence of CTX-M genes, and molecular characteristics such as sequence types or plasmid profiles.

Results
Nine studies met the inclusion criteria, encompassing clinical isolates obtained from hospitals and outpatient settings across several regions of Mexico. The majority of studies reported CTX-M enzymes as the predominant ESBL type among E. coli isolates. CTX-M-15, CTX-M-14, and CTX-M-27 were the most frequently identified variants. Several studies also reported the presence of high-risk clones such as sequence type ST131 and plasmids belonging to the IncF family, highlighting the role of mobile genetic elements in the dissemination of resistance. Uropathogenic E. coli was commonly associated with multidrug resistance phenotypes and multiple virulence determinants.

Conclusions
CTX-M–producing Escherichia coli are widely distributed among clinical isolates in Mexico and represent a significant contributor to antimicrobial resistance in both hospital and community infections. The predominance of CTX-M variants and the circulation of high-risk clones underscore the importance of molecular surveillance and antimicrobial stewardship programs to limit the spread of resistant strains.