High occurrence of shiga-like toxin-producing strains among diarrheagenic Escherichia coli isolated from raw beef products in Rio de Janeiro City, Brazil

Raw beef samples (n=105) were examined for diarrheagenic Escherichia coli (DEC) using standard methods. The isolates obtained (n=1,066) were screened for Shiga-like toxins (SLT-I and SLT-II), cytolethal distending toxin (CLDT), enterotoxins (LT-I and STa), and classical enteropathogenic (EPEC) and enteroinvasive (EIEC) serogroups. Seventy-three (6.8%) DEC isolates representing 42 strains isolated from 34 (32.4%) beef samples were detected. SLT-producing E. coli (SLTEC) was the most frequent DEC category found and corresponded to 21 (50%) of the 42 DEC strains. Several serotypes were detected among the SLTEC and some of them have been found previously in animal and human isolates, but E. coli O157:H7 was not isolated. Other virulence markers found in DEC strains included enterotoxin production (38.1%), CLDT (7.1%), and EPEC serogroups (4.3%). This is the first report of CLDT-producing E. coli (CLDTEC) isolated from food samples in Brazil. Production of both SLT-I and LT-I was found in one E. coli isolate, and 3 beef samples harbored both SLTEC and ETEC strains. Although a high frequency of DEC groups was found in commercial beef samples in Rio de Janeiro City, Brazil, the significance of these strains as agents of human diarrhea remains to be established.