Antimicrobial resistance profiles and molecular characterization of Escherichia coli strains isolated from healthy adults in Ho Chi Minh City, Vietnam

In this study, we attempted to isolate Escherichia coli from healthy adults in Ho Chi Minh City, Vietnam, and characterized its antimicrobial resistance profile, extended-spectrum β-lactamase (ESBL) genotype, phylogenetic grouping and virulence gene profile. A total of 103 E. coli isolates were obtained, and most of them were antimicrobial resistant such to streptomycin (80.6%), tetracycline (67.0%), ampicillin (65.0%), sulfamethoxsazole/trimethoprim (48.5%), nalidixic acid (43.7%), chloramphenicol (34.0%), cefotaxime (15.5%), ciprofloxacin (15.5%), kanamycin (12.6%), ceftazidime (10.7%), fosfomycin (4.9%) and gentamicin (2.9%). However, all these E. coli strains were susceptible to imipenem. Surprisingly, of 103 strains, 74 (71.8%) and 43 (41.7%) strains showed resistance to more than 3 and 5 classes of antimicrobials, respectively. Furthermore, 10 E. coli strains were ESBL-producers and positive for blaCTX-M genes (7 for blaCTX-M-9 and 3 for blaCTX-M-1), while five were additionally positive for blaTEM genes. S1-nuclease pulsed-field gel electrophoresis analysis revealed that 7 and 3 strains of E. coli carry blaCTX-M genes on their large plasmid and chromosome, respectively. Phylogenetic analysis exhibited that majority of the E. coli strains was grouped into A (44.7%), followed by B1 (23.3%), B2 (18.4%) and D (13.6%). Virulence genes associated with diarrheagenic E. coli, such as astA, EAF, eaeA, elt and eagg were also detected in ESBL-producing E. coli as well as antimicrobial resistant strains. These data suggest that commensal E. coli of healthy human could be a reservoir for antimicrobial resistance determinants and some of them might be harmful to human.