Characterization and typing of Escherichia coli O157:H7/NM strains recovered from feces and carcasses in commercial beef cattle processing plants in Argentina.

DEL CASTILLO L., LEOTTA G.A., MASANA M., CARBONARI C., D’ASTEK B., PALLADINO M., MILIWEBSKY E., VILACOBA E., GALLI L., TEITELBAUM D., RIVAS M.

Buenos Aires

Simposio; 7th International Symposium on Shiga Toxin (Verocytotoxin) - Producing Escherichia coli infections.; 2009

The purpose of this study was to characterize E. coli O157:H7/NM (STEC O157) strains recovered, from feces and carcasses, during a prevalence study conducted in nine abattoirs from Argentina, by typing methods and to establish their clonal relationship. One hundred and two strains, comprising toxigenic and non-toxigenic isolates, from 811 fecal samples (n=71) and 811 carcasses (n=31), were analyzed. The clonal relatedness of these strains was established by phage typing and pulsed-field gel electrophoresis (PFGE) of genomic DNA after digestion with XbaI as first enzyme and BlnI as a second enzyme. E. coli O157 strains were previously characterized by biochemical test and molecular methods. This analysis revealed that 54 E. coli O157 strains were toxigenic and 48 non-toxigenic. Stx2 was identified in all STEC and Stx1 in only 16.7%. The most frequent stx genotype was stx2/stx2c (vh-a) (53.7%). All STEC strains harbored the eae and ehxA genes. Only one non-toxigenic strain was eae-positive and enterohemolysin-positive. As a result of this work, the 54 STEC isolates were categorized into 11 different phage types (PTs). The frequency of PTs was: 25.9% PT2, 16.7% PT39, 11.1% PT4 and PT49, 7.4% PT21, 5.6 PT26, 2.7% PT8, PT33, and PT43, 1.9% PT10, PT31, and PT51, and 3 strains were untypified (UT). Twenty-nine different patterns were obtained by XbaI-PFGE with at least 75% similarity, 36 strains were grouped in 11 clusters and 18 strains showed unique patterns. The clusters were: #1 (3 strains, PT49, AREXHX01.0267); #2 (2 strains, PT2, AREXHX01.0545); #3 (2 strains, PT4 and UT, AREXHX01.0011); #4 (3 strains, PT4, AREXHX01.0458); #5 (4 strains, PT4, AREXHX01.0543); #6 (3 strains, PT2, AREXHX01.0460); #7 (6 strains, PT39, AREXHX01.0507); #8 (2 strains, PT43, AREXHX01.0514); #9 (3 strains, PT33 and UT, AREXHX01.0517); #10 (4 strains, PT2, AREXHX01.0076); and #11 (4 strains, PT21, AREXHX01.0544). They were indistinguishable by BlnI-PFGE, phages typing and stx-genotyping, except the 3 strains grouping in cluster #4 which were split by stx genotyping and BlnI patterns. By PFGE, the 48 non-toxigenic E. coli generated 34 different patterns whit 7 indistinguishable clusters. In general, the isolates grouping in clusters were recovered from samples taken in the same plant, and in most cases belonged to the same lot. In some cases, strains included in the same cluster were isolated from feces and carcass of the same animal. In two cases, the isolates included in the same cluster were recovered in the same abattoir in different dates, lots, animal types and origin. In conclusion, direct contamination and cross-contamination between animals within a same lot were recognized by phage typing and PFGE. The data showed a strong relationship between pre-harvest and post-harvest prevalence within a lot and provided evidence that feces were the source de STEC O157 on the carcasses. On the other hand, in some cases, the patterns suggested that the isolates were endemic in the plants, given that they were recovered in different sampling dates.