title: Comparative effect of direct-fed microbials on fecal shedding of Escherichia coli O157:H7 and Salmonella in naturally infected feedlot cattle.
abstract: The effect of direct-fed microbials (DFM) on fecal shedding of Escherichia coli O157:H7 and Salmonella in naturally infected feedlot cattle was evaluated in a clinical trial involving 138 feedlot steers. Following standard laboratory methods, fecal samples collected from steers were evaluated for change in the detectable levels of E. coli O157:H7 and Salmonella shed in feces after DFM treatment. Sampling of steers was carried out every 3 weeks for 84 days. A significant reduction (32%) in fecal shedding of E. coli O157:H7 (P < 0.001), but not Salmonella (P = 0.24), was observed among the treatment steers compared with the control group during finishing. The probability of recovery of E. coli O157:H7 from the feces of treated and control steers was 34.0 and 66.0%, respectively. Steers placed on DFM supplement were almost three times less likely to shed E. coli O157:H7 (odds ratio, 0.36; 95% confidence interval, 0.25 to 0.53; P < 0.001) in their feces as opposed to their control counterparts. The probability of recovery of Salmonella from the feces of the control (14.0%) and the treated (11.3%) steers was similar. However, the DFM significantly reduced probability of new infections with Salmonella among DFM-treated cattle compared with controls (nontreated ones). It appears that DFM as applied in our study are capable of significantly reducing fecal shedding of E. coli O157:H7 in naturally infected cattle but not Salmonella. The factors responsible for the observed difference in the effects of DFM on E. coli O157:H7 and Salmonella warrants further investigation.
authors.affiliation: The Great Plains Institute of Food Safety, North Dakota State University, Fargo, North Dakota 58105-5727, USA.
authors.forename: Ebot S
authors.initials: ES
authors.lastname: Tabe
authors.forename: James
authors.initials: J
authors.lastname: Oloya
authors.forename: Dawn K
authors.initials: DK
authors.lastname: Doetkott
authors.forename: Marc L
authors.initials: ML
authors.lastname: Bauer
authors.forename: Penelope S
authors.initials: PS
authors.lastname: Gibbs
authors.forename: Margaret L
authors.initials: ML
authors.lastname: Khaitsa
mesh_terms: D000284:Administration, Oral; D000821:Animal Feed; D000818:Animals; D000898:Antibiosis; D002417:Cattle; D015169:Colony Count, Microbial; D016001:Confidence Intervals; D019453:Escherichia coli O157 / Q000254:growth & development* / Q000302:isolation & purification; D005243:Feces / Q000382:microbiology*; D005506:Food Contamination / Q000517:prevention & control*; D005516:Food Microbiology; D007779:Lactobacillus acidophilus / Q000502:physiology*; D008297:Male; D016017:Odds Ratio; D019936:Probiotics; D011424:Propionibacterium / Q000502:physiology*; D011897:Random Allocation; D012475:Salmonella / Q000254:growth & development* / Q000302:isolation & purification