Stx genotypes and antimicrobial resistance profiles of Shiga toxin-producing Escherichia coli strains isolated from human infections, cattle and foods in Brazil

A total of 107 Shiga toxin-producing Escherichia coli strains (STEC) isolated from different origins in Sao Paulo, Brazil, and belonging to different serotypes were characterized regarding stx subtypes and susceptibility to antimicrobial agents. Most of the human STEC strains harbored stx(1) (85.7%), while stx(2), associated or not to stx(1), was identified preferentially in the animal and food strains. None of the STEC strains carried stx(1c). Some genotypes occurred exclusively among strains of bovine origin as stx(2c), stx(1+2+2c) (16.5% each), and stx(2d) (0.9%), whereas stx(2+2c(2vha)) was only identified among the O157:H7 human strains. Moreover, the stx(2c(2vhb)) subtype was found more frequently among bovine than human strains (39% vs. 4.8%). The highest frequencies of susceptibility to antimicrobial agents were observed among bovine (87%) and food (100%) STEC strains, while 47.6% of the human isolates were resistant to at least one drug. Multiresistance occurred among O111 STEC strains from human and bovine origin. The antimicrobials to which resistance was most frequently observed were tetracycline (90%) and streptomycin (75%) among human strains, and also sulphazotrin (88%) in animal strains. A few serotypes were commonly identified among STEC strains isolated from diverse sources in Brazil, but in general the strains presented distinct stx subtypes and/or antimicrobial resistance profiles.