Subtypes of Type I-E CRISPR-Cas Systems Distribution in Human Escherichia coli Isolates from China

The correlation between CRISPR-Cas systems and plasmid-mediated bacterial antibiotic resistance is increasingly growing attention. However, currently no reports exist on the relationship between the CRISPR-Cas systems and the carriage of blaNDM or plasmids in E.coli. Here, molecular characterization and phylogenetic analysis of 639 E.coli isolated from humans in China were carried out. Depending on similarity in sequence, the type I-E CRISPR-Cas systems in E.coli can be grouped into two distinct clades, which we refer to for descriptive purposes within this study as the type I-E-S1 and I-E-S2, whereas the type I-E-S2 CRISPR-Cas system is further divided into I-E-S2a and I-E-S2b systems based on the presence of cas8e and cas11. ST167 (phylogroup A) and ST410 (phylogroup C) E. coli were observed bearing the type I-E-S1 and I-E-S2b systems, respectively. Compared with strains carrying the I-E-S1 type CRISPR-Cas system, the blaNDM carrying rate, the positive rate of IncX3 plasmid, and the positive rate of IncF plasmid of strains with the I-E-S2a type CRISPR-Cas system were evidently lower (p < 0.05); the blaNDM carrying rate and the positive rate of IncF plasmid of strains with the I-E-S2b type CRISPR-Cas system were evidently higher (p < 0.05). The blaNDM positive rate and IncF plasmid positive rate of strains carrying the I-E-S2a type CRISPR-Cas system were significantly lower than those of strains carrying the I-E-S2b type CRISPR-Cas system (p < 0.001). It proves that the I-E-S1, I-E-S2a, and I-E-S2b type CRISPR-Cas systems are beneficial for spreading blaNDM and IncX3 plasmids. We found significant differences in the cas gene sequences of the I-E-S1 and I-E-S2 type CRISPR loci. The type I-E CRISPR-Cas systems in E. coli isolated from Chinese sources are classified further for the first time, revealing their high correlation with blaNDM, phylogenetic groups, and multilocus sequence typing. This work paves the way for a deeper understanding of the role that CRISPR-Cas systems play in the rise of resistant E.coli ST167 and ST410.