CTX-M-Producing Escherichia coli: History, Molecular Epidemiology and Laboratory Detection

From being a curiosity in the 1990s, CTX-M-producing Escherichia coli invaded most parts of the globe during the 2000s and 2010s, with multidrug-resistant (MDR) clone ST131 and CTX-M-15 leading the charge. The most widely distributed CTX-M types, with the highest global frequencies (up to 70% in certain lower- and middle-income countries), are CTX-M-15, CTX-M-14 and CTX-M-27. E. coli isolates with bla _CTX-M-27 are currently emerging globally. The worldwide ascendancy of E. coli with bla _CTX-M genes occurred via the spread of IncF plasmids between isolates and the existence of certain successful clones (eg, ST131) that acted as repositories for these genes. This is an impressive "gene survival strategy" that aided with the endurance of bla _CTX-M in different environments, including the community and hospitals. The detection of extended-spectrum β-lactamase (ESBL)-producing E. coli (including CTX-M isolates) in clinical laboratories is reasonably straightforward. However, different methodologies (eg, immunogenic and genomic) have recently become available to specifically identify CTX-Ms in bacterial isolates as well as human specimens. The role of such tests is currently unclear. E. coli with CTX-M β-lactamases have indirectly been driving the carbapenemase pandemic and are forces to be reckoned with.