Antimicrobial effects of a bioactive glycolipid on spore-forming spoilage bacteria in milk

Abstract

The growth of psychrotolerant aerobic spore-forming bacteria during refrigerated storage often results in the spoilage of fluid milk, leading to off-flavors and curdling. Because of their low toxicity, biodegradability, selectivity, and antimicrobial activity over a range of conditions, glycolipids are a novel and promising intervention to control undesirable microbes. The objective of this study was to determine the efficacy of a commercial glycolipid product to inhibit spore germination, spore outgrowth, and the growth of vegetative cells of Paenibacillus odorifer, Bacillus weihenstephanensis, and Viridibacillus arenosi, which are the predominant spore-forming spoilage bacteria in milk. For spore germination and outgrowth assays, varying concentrations (25-400 mg/L) of the glycolipid product were added to commercial UHT whole and skim milk inoculated with ~4 log 10 spores/mL of each bacteria and incubated at 30°C for 5 d. Inhibition of spore germination in inoculated UHT whole milk was only observed for V. arenosi, and only when glycolipid was added at 400 mg/L. However, concentrations of 400 and 200 mg/L markedly inhibited the outgrowth of vegetative cells from spores of P. odorifer and B. weihenstephanensis, respectively. No inhibition of spore germination or outgrowth was observed in inoculated UHT skim milk for any strain at the concentrations tested (25 and 50 mg/L). The effect of glycolipid addition on vegetative cell growth in UHT whole and skim milk when inoculated with ~4 log 10 cfu/ mL of each bacteria was also determined over 21 d of storage at 7°C. Glycolipid addition at 50 mg/L was bactericidal against P. odorifer and B. weihenstephanensis in inoculated UHT skim milk through 21 d of storage, whereas 100 mg/L was needed for similar control of V. arenosi. Concentrations of 100 and 200 mg/L inhibited the growth of vegetative cells of B. weihenstephanensis and P. odorifer, respectively, in inoculated UHT whole milk, whereas 200 mg/L was also bactericidal to B. weihenstephanensis. Additional studies are necessary to identify effective concentrations for the inhibition of Viridibacillus spp. growth in whole milk beyond 7 d. Findings from this study demonstrate that natural glycolipids have the potential to inhibit the growth of dairy-spoilage bacteria and extend the shelf life of milk.

Evaluating Paenibacillus odorifer for its potential to reduce shelf life in reworked high-temperature, short-time fluid milk products

“…Maximum growth rates over the first 7 to 10 d were similar between unflavored and flavored milk products for all strains at both temperatures (4°C = 0.39-0.53 log cfu/mL per day; 7°C = 0.83-0.98 log cfu/mL per day). Similar growth rates for P. odorifer in whole milk (7°C = 1.01 cfu/mL per day) and SMB (6°C = 0.6 cfu/mL per day) have been reported (Buehler et al, 2018;Sun et al, 2021); however, this is the first report of P. odorifer growing at temperatures below 5°C (Berge et al, 2002;Priest, 2015), as predicted by Buehler et al (2018).…”

“…No psychrotrophic sporeformers were included in that study, and the authors report a correlation of maximum growth temperature and spore death temperature, suggesting that psychrotrophic sporeformers may be underestimated by this method. Sun et al (2021) also considered this methodological concern and opted to enumerate P. odorifer spores following a thermal treatment of 63°C for 30 min. Additional research on thermal treatments for quantification of psychrotrophic spores or other heat-resistant bacterial subpopulations would facilitate improved understanding of the source and behavior of Paenibacillus on farm and during raw milk handling.…”

Keeping up with the Bacillus cereus group: taxonomy through the genomics era and beyond

“…that belong to panC Group III have been referred to as (i) "emetic B. cereus," (ii) "cereulide-producing B. cereus," (iii) "B. cereus" (Agata et al 1994;Apetroaie et al 2005;Dierick et al 2005;Ehling-Schulz, Frenzel, and Gohar 2015;Ehling-Schulz et al 2006;Ehling-Schulz et al 2005;Fiedoruk et al 2016;Granum and Lund 2006;Mahler et al 1997;Rouzeau-Szynalski et al 2020;Schoeni and Wong 2005;Shiota et al 2010;Vassileva et al 2007), and (iv) "B. paranthracis" (Carroll et al 2019). In addition, panC group III isolates that are incapable of producing cereulide but may still produce diarrheal toxins have been referenced as (i) "emetic- Guerin et al 2019;Kim et al 2021;Miller et al 2018;Modugno et al 2019;Nakano 2020;Sun et al 2021;Trunet et al 2020), despite the fact that Liu, Lai, and Shao (2018) published a proposal to merge the species into B. mycoides in 2018. Additionally, the species name "B. thuringiensis" has been simultaneously used to refer to (i) any B. cereus s.l.…”

Teicoplanin Suppresses Vegetative Clostridioides difficile and Spore Outgrowth

“…There are reports showing that some antibiotics can inhibit vegetative cells but not outgrowth [ 34 ]. Certain antibiotics inhibit both spore outgrowth and vegetative cells but at different concentrations, implying that there are underlying differences between these stages [ 35 ].…”