Purpose: To assess role of bloodline, maturity, and physical proximity of cattle in presence and distribution of STEC.
Methods: Angus cows (n = 90) and their calves (n = 90) were maintained in paddocks in groups of 7 or 8 pairs. Fecal samples were collected per rectum at 3 time points in July, August, and September, and enriched for STEC. Screening for virulence genes stx1, stx2, eaeA, and hlyA was done using multiplex polymerase chain reaction (mPCR). Stx+ fecal samples were cultured on MacConkey Agar, and a maximum of 6 colonies from each sample were randomly picked. Determination of serogroups O26, O45, O91, O103, O111, O113, O121, O145, and O157 was performed for each stx+ colony using mPCR. Fingerprinting of stx+ colonies was done through repetitive sequence-based PCR. Comparison of STEC distribution across time points, maturity and paddocks was done using Pearson Chi-Square or Fisher’s exact tests with Monte Carlo simulations.
Results: STEC prevalence was 93.3% (84/90) in adults, and 95.6% (86/90) in calves. Preliminary results show that calves were less likely to be stx+ in August (P < 0.001). Differences were present between paddocks for stx1 in July (P = 0.027) and September (P = 0.011), and eaeA in August (P = 0.026). Stx+ E. coli colonies were obtained for 49.4% (68/170) of animals with stx+ fecal samples. Of 744 E. coli colonies, 335 were positive for at least one virulence gene, with 28 being positive for two virulence genes, 21 for three, and 1 for all four. Fingerprinting of stx+ colonies identified limited clustering of isolates by paddocks, but not by bloodlines.
Significance: Results show high prevalence of stx-positive animals in the herd. The role of current physical proximity (paddock) seems to be more important than bloodline in the establishment of dominant STEC populations. Animals within bloodline do not share STEC populations.
Disclaimer: Virginia Tech Institutional Animal Care and Use Committee has reviewed and granted approval to this project #09-147-FST.