Enterotoxigenic Escherichia coli (ETEC) is a pathogenic type of commensal E. coli that produces watery diarrhea and affects children and travelers in developing countries. ETEC cause disease by the combination of colonization factors that bind to intestinal epithelial cells and the secretion of two toxins: heat-labile toxin and heat-stable toxin. There are many types of colonization factors that combine with one or both toxins. One of those colonization factors is called CS23, a chaperone/usher class fimbriae, which is related to the F4 colonization factor present in ETEC strains causing disease in pigs. This colonization factor is encoded by an operon called aal comprised by nine genes. CS23 has been thought to be a less prevalent colonization factor so far.
The aim of this study was to characterize ETEC genomes harboring CS23 to better understand the virulence genes and antibiotic resistance genes present in these strains. To achieve that, long read assemblies of twelve ETEC genomes spread in different strains were analyzed, of which only six passed quality control. These six genomes could be divided into two groups based on plasmid synteny. The first group harbored a single plasmid with CS23 and both toxins, belonging to IncFIA/IncFII or IncFIA incompatibility groups. The second group had CS23 in IncFIA/IncI-gamma/K1 plasmids and the toxin genes in IncFII plasmids. In addition, all genomes were resistant to beta-lactam, with one of them presenting multidrug resistance. Most of the antibiotic resistance genes were in chromosomes, except for two genomes that had them in plasmids.
In conclusion, a better knowledge of ETEC strains harboring CS23 has been achieved, with a more detailed description of virulence genes, antibiotic resistance genes and plasmids.