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The objectives of this study were (1) to estimate the prevalence and concentration of the seven major Shiga toxin-producing Escherichia coli (STEC) serogroups (O26, O45, O103, O111, O121, O145, and O157), collectively called STEC-7, on cattle hides collected in different seasons and beef processing plants; and (2) to determine associations of season, plant, and hide cleanliness scores with the prevalence and concentration of STEC-7. A total of 720 hide surface samples (240/season) were collected over three seasons (summer and fall 2015 and spring 2016) from beef cattle carcasses in four commercial processing plants in the United States. Samples were subjected to selective culture and spiral plating methods. Overall model-adjusted mean prevalence (95% confidence interval) was 0.3% (0.03-2.3%) for STEC O26; 0.05% (<0.01-8.5%) for STEC O45; 0.2% (0.02-1.9%) for STEC O103; 0.05% (<0.01-8.5%) for STEC O145; and 3.1% (0.6-15.2%) for STEC O157. Four percent of hide samples were enumerable for STEC O157; mean concentration (standard deviation) = 2.1 (0.7) log 10 colony-forming units (CFUs)/100 cm 2. No samples were enumerable for non-O157 STEC. Hide-on prevalence of STEC O157 and STEC non-O157 (specifically of STEC O103) was higher in summer and spring, respectively. Across seasons and plants, the most common STEC non-O157 serogroups in this study (O26 and O103) were associated with a higher prevalence of STEC O157. Season and plant played a role in prevalence and concentration of STEC in beef cattle hides, varying by serogroup. Tailoring mitigation strategies at the plant can be challenging and processors would benefit from supplementary preharvest interventions to reduce overall contamination pressure at the plant, especially in fall and spring months when hide-on prevalence of STEC non-O157 is higher.

Condensed tannins (CT), prior dietary CT exposure, animal species, and antimicrobial inclusion effects on 48 h extent of in vitro fermentation were measured in an experiment with a 3 × 2 × 2 × 3 factorial arrangement of treatments. Treatments included species of inoculum donor (Bos taurus, Ovis aries, or Capra hircus; n = 3/species), prior adaptation to dietary CT (not adapted or adapted), culture substrate (low-CT or high-CT), and antimicrobial additive (none, bacterial suppression with penicillin + streptomycin, or fungal suppression with cycloheximide). Low-CT or high-CT substrates were incubated in vitro using inoculum from animals either not exposed (period 1) or previously exposed to dietary CT (period 2). The extent of IVDMD after 48 h of incubation was greater (P < 0.001) for cultures with low-CT substrate (21.5%) than for cultures with high-CT substrate (16.5%). Cultures with high-CT substrate or with suppressed bacterial activity had less (P < 0.001) gas pressure than cultures with low-CT substrate or cultures with suppressed fungal activity. Total VFA concentrations were greater (P < 0.001) in low-CT cultures when inoculum donors were without prior CT exposure (83.7 mM) than when inoculum was from CT-exposed animals (79.6 mM). Conversely, total VFA concentrations were greater (P < 0.001) in high-CT cultures with tannin-exposed inoculum (59.4 mM) than with nonexposed inoculum (52.6 mM). As expected, CT and suppression of bacterial fermentative activities had strong negative effects on fermentation; however, prior exposure to dietary CT attenuated some negative effects of dietary CT on fermentation. In our experiment, the magnitude of inoculum-donor species effects on fermentation was minor.

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