[Molecular epidemiological study of diarrheagenic Escherichia coli among diarrhea patients in Guangdong Province, 2023-2025].

Objective

To understand the infection types, antimicrobial resistance, and molecular epidemiological characteristics of diarrheagenic Escherichia(E.) coli (DEC) among diarrhea patients in Guangdong Province.

Methods

A total of 128 DEC strains collected from the Guangdong Provincial Pathogen Identification Network between 2023 and 2025 were included, and species identification was performed using mass spectrometry. Five DEC pathotypes were determined by fluorescent PCR targeting virulence genes. Antibiotic susceptibility testing was conducted using the broth microdilution method. Whole-genome sequencing (WGS) was employed to analyze multilocus sequence typing (MLST), serotype prediction, resistance and virulence genes, and phylogenetic tree construction based on core single-nucleotide polymorphisms (core-SNPs).

Results

Among the 128 DEC strains, enteroaggregative E. coli (EAEC) accounted for the higher proportion at 71.87% (92/128), followed by enteropathogenic E. coli (EPEC) at 16.41% (21/128), enterotoxigenic E. coli (ETEC) at 10.94% (14/128), and enterohemorrhagic E. coli (EHEC) at 0.78% (1/128). Infections predominantly occurred in children aged 0-6 years, accounting for 39.84% (51/128) of DEC Strains. Zhanjiang, Qingyuan, and Dongguan exhibited higher DEC infection rates at 25.78% (33/128), 21.88% (28/128), and 15.63% (20/128), respectively. High susceptibility rates were observed for amikacin (97.66%, 125/128), meropenem (95.31%, 122/128), ceftazidime/avibactam (95.31%, 122/128), and tigecycline (95.31%, 122/128). High resistance rates were observed for ampicillin (73.44%, 94/128), tetracycline (65.62%, 84/128), streptomycin (57.81%, 74/128), and trimethoprim/sulfamethoxazole (56.25%, 72/128). The multidrug resistance rate of DEC was 64.84% (83/128), and the MDR rate for EAEC was 70.65% (65/92). WGS analysis showed that the predominant sequence types (ST) were ST117 (8.59%, 11/128), ST31 (6.25%, 8/128), and ST38 (5.47%, 7/128). Serotype prediction by WGS showed an O-antigen typing rate of 72.66% (93/128) and an H-antigen typing rate of 100.00% (128/128). The most common serotype was O130:H27 (4.69%, 6/128). The non-typable rate for O-antigen was 27.34% (35/128), among which O17:H18, O44:H18, or O77:H18 accounted for the higher proportion (4.69%, 6/128). The overall concordance rate between predicted resistance genes and phenotypic resistance was 91.52%, with 100.00% concordance for colistin, ertapenem and meropenem. A total of 213 virulence genes were predicted. A statistically significant difference in the number of virulence genes among EAEC, EPEC and ETEC was not observed (Kruskal-Wallis test, H=1.018, P=0.601). However, ten characteristic virulence genes exhibited a highly type-specific distribution.

Conclusions

EAEC was the predominant DEC pathotype circulating in Guangdong Province from 2023 to 2025. The main prevalent ST were ST117, ST31, and ST38. WGS showed a relatively high serotype prediction rate. There was a high concordance between predicted resistance genes and phenotypic resistance. While no statistically significant difference in the number of virulence genes was observed among the major pathotypes of diarrheagenic E. coli, 10 characteristic genes exhibited marked pathotype specificity. Multidrug resistance among DEC is relatively severe, highlighting the need for enhanced monitoring of DEC antimicrobial resistance.