title: Control of Escherichia coli O157:H7 in contaminated alfalfa silage: Effects of silage additives.
abstract: This study was conducted to examine if adding microbial inoculants or propionic acid to alfalfa silages contaminated with Escherichia coli O157:H7 would inhibit the growth of the pathogen during or after ensiling. Alfalfa forage was harvested at the early bloom stage, wilted to a dry matter concentration of 54%, chopped to 19-mm lengths, and ensiled after treatment with one of the following: (1) distilled water (control); (2) 1×10(5) cfu/g of E. coli O157:H7 (EC); (3) EC and 1×10(6) cfu/g of Lactobacillus plantarum (EC+LP); (4) EC and 1×10(6) cfu/g of Lactobacillus buchneri (EC+LB); and (5) EC and 2.2g/kg of propionic acid (EC+PA). Each treatment was ensiled in quadruplicate in laboratory silos for 0, 3, 7, 16, and 100d and analyzed for EC counts, pH, and organic acids. In addition, samples from d 100 were analyzed for chemical composition, ammonia-N, counts of yeasts and molds, and aerobic stability. Escherichia coli O157:H7 was detected in all silages until d 7, but by d 16 it was not detected in those treated with EC+LB and EC+LP, though it was still detected in EC and EC+PA silages. However, by d 100, the pathogen was not detected in any silage. The rate of pH decrease to 5.0 was fastest for the EC+LP silage (7d), followed by the EC+LB silage (16d). Nevertheless, all silages had attained a pH of or less than 5.0 by d 100. The rapid decrease in pH in EC+LP and EC+LB silages was observed due to higher lactate and acetate concentrations, respectively, relative to the other silages during the early fermentation phase (d 3-16). Propionic acid was only detected in the EC+PA silage. Yeast counts were lowest in EC+LB and EC+PA silages. Subsamples of all d-100 silages were reinoculated with 1×10(5) cfu/g of EC immediately after silo opening. When the pathogen was subsequently enumerated after 168h of aerobic exposure, it was not detected in silages treated with EC+PA, EC+LB, or EC+LP, which all had pH values less than 5.0. Whereas the EC silage had a pH value of 5.4 and 2.3 log cfu/g of the pathogen. Certain bacterial inoculants can hasten the inhibition of E. coli O157:H7 during ensiling, such as propionic acid, and they can also prevent its growth on silage contaminated with the pathogen after ensiling.
authors.affiliation: Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32608.
authors.forename: I M
authors.initials: IM
authors.lastname: Ogunade
authors.affiliation: Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32608; Division of Applied Life Science (BK21Plus, Institute of Agriculture and Life Science), Gyeongsang National University, Jinju 660-701, South Korea.
authors.forename: D H
authors.initials: DH
authors.lastname: Kim
authors.affiliation: Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32608.
authors.forename: Y
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Department of Food Safety and Quality, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel 50250.
authors.forename: Z G
authors.initials: ZG
authors.lastname: Weinberg
authors.affiliation: Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32608.
authors.forename: K C
authors.initials: KC
authors.lastname: Jeong
authors.affiliation: Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32608. Electronic address: adesogan@ufl.edu.
authors.forename: A T
authors.initials: AT
authors.lastname: Adesogan
mesh_terms: D019453:Escherichia coli O157 / Q000502:physiology*; D005506:Food Contamination / Q000517:prevention & control*; D007778:Lactobacillus / Q000737:chemistry*; D048191:Lactiplantibacillus plantarum / Q000737:chemistry; D000455:Medicago sativa / Q000382:microbiology*; D011422:Propionates / Q000737:chemistry*; D012820:Silage / Q000382:microbiology*; D013997:Time Factors
chemical_list: D011422:Propionates; C029658:propionic acid
keywords: Escherichia coli O157:H7; alfalfa silage; microbial inoculants; propionic acid