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.

Effects of calcium propionate on the fermentation quality and aerobic stability of alfalfa silage

“…The AA concentration in control was 30.2 g/kg, which is higher than that in other studies [ 17 ]. The high numbers of enterobacteria observed in the fresh alfalfa prior to ensiling caused the AA production, since enterobacteria is facultatively anaerobic and ferments sugars to acetic acid and other products before the silo becomes anaerobic [ 1 ].…”

Influence of lactic acid bacteria, cellulase, cellulase-producing Bacillus pumilus and their combinations on alfalfa silage quality

“…The possible explanation for the high efficiency of the LAB a214, that was originally isolated from alfalfa silage, is because of its strong ability to adapt to the specific environment (low epiphytic LAB, WSC concentrations and high buffering capacity) of alfalfa silage. This adaptability results in its rapid multiplication, enabling it to overwhelm the growth of undesirable microorganisms to eventually dominate the silage fermentation process and effectively preserve silage nutrients (Ogunade et al 2016;Silva et al 2016).…”

Effects of sodium diacetate on the fermentation profile, chemical composition and aerobic stability of alfalfa silage

“…Although legume silages have been reported to be aerobically relatively stable [26], environmental conditions encountered in the tropics can enhance growth of spoilage microorganisms and accelerate the aerobic spoilage during the feed-out. The proliferations of yeasts, aerobic bacteria and molds cause the increase in temperature and pH, result in the nutrients loss and increase the risk of proliferation of potential pathogenic or undesirable microorganisms, thus affecting the performance of animals fed the silage [27].…”