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

Abstract

Raw beef samples (n = 105) were examined for diarrheagenic Escherichia coli (DEC) using standard methods. The isolates obtained (n = 1,006) were screened for Shiga-like toxin (SLT-1 and SLT-II), cytoletha distending toxin (CLDT), enterotoxins (LT-1 and STa), and classical enteropathogenic (EPEC) and entero-invasive (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-1 and LT-1 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 significant of these strains as agents of human diarrhea to be established.