title: Fate of Escherichia coli O157:H7 and bacterial diversity in corn silage contaminated with the pathogen and treated with chemical or microbial additives.
abstract: Inhibiting the growth of Escherichia coli O157:H7 (EC) in feeds may prevent the transmission or cycling of the pathogen on farms. The first objective of this study was to examine if addition of propionic acid or microbial inoculants would inhibit the growth of EC during ensiling, at silo opening, or after aerobic exposure. The second objective was to examine how additives affected the bacterial community composition in corn silage. Corn forage was harvested at approximately 35% dry matter, chopped to a theoretical length of cut of 10 mm, and ensiled after treatment with one of the following: (1) distilled water (control); (2) 1 × 105cfu/g of EC (ECCH); (3) EC and 1 × 106cfu/g of Lactobacillus plantarum (ECLP); (4) EC and 1 × 106cfu/g of Lactobacillus buchneri (ECLB); and (5) EC and 2.2 g/kg (fresh weight basis) of propionic acid, containing 99.5% of the acid (ECA). Each treatment was ensiled in quadruplicate in laboratory silos for 0, 3, 7, and 120 d and analyzed for EC, pH, and organic acids. Samples from d 0 and 120 were also analyzed for chemical composition. Furthermore, samples from d 120 were analyzed for ammonia N, yeasts and molds, lactic acid bacteria, bacterial community composition, and aerobic stability. The pH of silages from all treatments decreased below 4 within 3 d of ensiling. Escherichia coli O157:H7 counts were below the detection limit in all silages after 7 d of ensiling. Treatment with L. buchneri and propionic acid resulted in fewer yeasts and greater aerobic stability compared with control, ECCH, and ECLP silages. Compared with the control, the diversity analysis revealed a less diverse bacterial community in the ECLP silage and greater abundance of Lactobacillus in the ECLP and ECA silages. The ECLB silage also contained greater abundance of Acinetobacter and Weissella than other silages. Subsamples of silages were reinoculated with 5 × 105cfu/g of EC either immediately after silo opening or after 168 h of aerobic exposure, and EC were enumerated after 6 or 24 h, respectively. All silages reinoculated with EC immediately after silo opening (120 h) had similar low pH values (<4.0) and EC counts were below the detection limit. The ECCH and ECLP silages reinoculated with EC after 168 h of aerobic exposure had relatively high pH values (>5.0) and EC counts (5.39 and 5.30 log cfu/g, respectively) 24 h later. However, those treated with L. buchneri or propionic acid had lower pH values (4.24 or 3.96, respectively) and lower EC counts (1.32 log cfu/g or none, respectively). During ensiling, EC was eliminated from all silages at pH below 4.0. During aerobic exposure, the growth of EC was reduced or prevented in silages that had been treated with L. buchneri or propionic acid at ensiling, respectively.
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.
authors.forename: Y
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: 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: A A Pech
authors.initials: AAP
authors.lastname: Cervantes
authors.affiliation: Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32608.
authors.forename: K G
authors.initials: KG
authors.lastname: Arriola
authors.affiliation: Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32608.
authors.forename: D
authors.initials: D
authors.lastname: Vyas
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: D000332:Aerobiosis; D000818:Animals; D019453:Escherichia coli O157; D005285:Fermentation; D007778:Lactobacillus; D012820:Silage; D003313:Zea mays / Q000737:chemistry / Q000382:microbiology*
keywords: Escherichia coli; bacterial community; corn silage