Prevalence and Characterization of Shiga toxin-producing Escherichia coli O157:H7/NM in commercial beef cattle in processing plants of Argentina.

MASANA M., ; LEOTTA G.A., ; DEL CASTILLO L.L., ; DASTEK B.A., ; PALLADINO P.M., ; VILACOBA E., ; GALLI L., ; CARBONARI C.C., ; TEITELBAUM D., ; RIVAS M.

Campinas, Brasil

Simposio; Latin American Food Safety Symposium; 2008

The International Association for Food Protection

Introduction Shiga toxin-producing Escherichia coli O157:H7/NM (STEC O157) can cause severe diseases, and occasional deaths in humans. Cattle have been established as the primary reservoir of the microorganism, through which it can reach the food supply (2). Though, Argentina is one of the largest beef producing countries, and has one of the highest rates of Hemolytic-Uremic Syndrome (HUS) worldwide (5), the prevalence of STEC O157 in beef cattle feces and carcasses within Argentine abattoirs, have not been assessed. Objective The aim of this study was to survey the presence of STEC O157 within the first steps of the beef industrialization chain, during one year, in Argentina. The goal comprises to establish the prevalence of STEC O157 in the bovine fecal content at the arrival to the abattoir, and in the carcasses produced. Materials and Methods Six animals from a lot of 30-60 bovines, with identified origin, were sampled in each visit to a slaughter-house. Sampling was conducted to obtain fecal and carcass samples from the same animal. Fecal sample (FS) was collected from the descendent colon near to the rectum. Carcasses samples were obtained by swabbing the carcass surface (CS) with a humidified sponge according to USDA (7). At the laboratory, samples were primarily enriched as follows: 10 g of fecal samples in 90 ml of GN Hajna (Difco, USA) at 37ºC for 5 h; carcass sponges in 90 ml of mEC for 2 h at 37ºC. After the primary enrichment, noboviocin was added up to 20µg/ml and the enrichment broths were further incubated for 18 h at 37ºC. Enriched samples (1 ml) were processed by inmunomagnetic separation (IMS) according to a modification of the USDA/FSIS procedure for STEC O157:H7/NM isolation from foods (6). Confluent growth zone and colony pools were screened for stx1, stx2 and rfbO157 genes by a multiplex polymerase chain reaction (4). Multiplex PCR of at least 20 colonies per PCR-positive sample were performed for confirmation. Isolates were characterized by biochemical tests, and the genetic profile of STEC O157 for virulence markers (stx1, stx2, ehxA, eae, rfbO157) putative adhesion gene (saa), and H7 flagellar antigen (fliCH7) was established. Results and Discussion Between November 15, 2006 and November 14, 2007, a total of 1131 samples (567 CS, 564 FS) were collected in nine abattoirs. These abattoirs, most of them working under HACCP, contribute with approximately the 20% of the animals slaughtered per year in Argentina. The cattle were from 8 provinces, being Buenos Aires the biggest supplier (41%). The animals were classified as steers (50%), young steers (15%), cows (22%), calves (7%), and heifers (6%). STEC O157 was isolated from 40 samples (3.5%), 16 of CS (2.8 %) and 24 of FS (4.3 %). The carriage of STEC O157 in FS varied in the different types of cattle: steers (3.5%), young steers (5.9%), cows (2.5%), calves (2.9%), and heifers (12.5%). The contamination of carcass together feces also varied between abattoirs from 1.7% to 7.6%. The total number STEC O157 isolates recovered was 41, 16 from CS and 25 from FS. The genotype prevalent was stx2/eae/ehxA/fliCH7 (27/41, 66%), and the prevalent stx variant was stx2/stx2c (vh-a) (11/41, 27%). These data are significant because in HUS cases the genotype stx2/stx2c (vh-a) is prevalent in O157-HUS cases (>90%). The epidemiological link between isolates from human and animal origin will be established after the PFGE analysis. It is worth noting that the cattle tested in this work is mostly representative of the common grass feeding production systems of the country, and that the degree of carriage of STEC O157 in cattle, at the entrance of the abattoirs, is comparable, or lower, to other international reports (1,3). Conclusions To our knowledge, this work is the first attempt made in Argentina to establish in a large scale, the prevalence of STEC O157 under the current commercial operation of national abattoirs. The information gathered in this study will aid to the development of sound risk assessment for STEC O157, and help to improve the sanitary condition of the beef supply.