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 × 10 cfu/g of EC (ECCH); (3) EC and 1 × 10 cfu/g of Lactobacillus plantarum (ECLP); (4) EC and 1 × 10 cfu/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 × 10 cfu/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.

The Bacterial Community Associated with the Amarillo Zamorano Maize (Zea mays) Landrace Silage Process

“…The high bacterial composition and diversity of AZS and AS during the entire fermentation process ( Table 3 ) contrasts with the previously reported lower values for maize and other crops silages, as the result of a low pH and 80–95% of relative abundance of the Lactobacillus genus [ 23 , 27 , 28 , 29 , 30 , 33 ], but similar to the high values of diversity obtained from the silages of alfalfa, maize from Iran [ 26 , 33 ], and other fermentative processes. Although the AS and AZS had a low pH in all evaluations, the lower relative abundance of Lactobacillus in AS and AZS (0.3–44.5%) reflects that other members of the microbial community were involved in this process, likely as a result of the type of maize, stage of maturity at harvest, local conditions during crop growth or climate [ 52 ].…”

“…Data from NGS studies on different crop silages have shown a wide view of the silage microbial composition and dynamics [ 26 , 29 , 30 ]. Thus, in the present study, the bacterial community associated with the maize silage process of a forage Mexican landrace and a commercial hybrid, both commonly used in the Los Altos region, Jalisco, were surveyed by a massive high-throughput sequencing approach.…”

“…Several bacterial species in the different silage phases have been described through studies with culture and DNA-based profiling techniques, i.e., facultative aerobic microorganisms, such as Erwinia herbicola and Rahnella aquitilis in the aerobic phase; lactic acid bacteria of Enterococcus , Lactococcus , Lactobacillus , Leuconostoc , Paralactobacillus , Pediococcus , Streptococcus, and Weissella genera, as well as different enterobacteria and clostridia in the fermentation and stabilization phases; and acetic acid and aerobic bacteria in the feeding out phase, depending on the quality of the silage [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Although several bacterial species have been isolated and characterized by the following method: 16S ribosomal RNA (16S rRNA) gene, massive next-generation sequencing (NGS) studies on the silages of alfalfa, grasses, small grains, maize, maize-sorghum, and soybean have provided a larger view on silage microbial community and dynamics [ 21 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. Specifically, in maize silages, NGS studies have also shown the effects of additives or silage size on the bacterial community and silage quality of maize hybrids or corn stover [ 33 , 34 , 35 , 36 , 37 , 38 , 39 ].…”

Effects of inoculants Lactobacillus brevis and Lactobacillus parafarraginis on the fermentation characteristics and microbial communities of corn stover silage

“…Nowadays, the high-throughput sequencing method has opened a new way to explore complex microbial ecosystems, and this technique has been widely applied across a range of systems. As reported with this technique to investigate the bacterial diversity of the day 120 corn silage samples 25 . Sufficient data are not yet available on the bacterial community dynamics involved in corn stover ensiling.…”

Innovative approaches for the analysis and decontamination of mycotoxins from feed and milk – Review

“…Mycotoxins are found in a variety of animal feeds including concentrates, green forests, hay and silages (OGUNADE et al, 2017). Naturally, there are more than 400 mycotoxins, but only a few have been widely studied (NJUMBE et al, 2015).…”