Potential of cell-free supernatants from cultures of selected lactic acid bacteria and yeast obtained from local fermented foods as inhibitors of Listeria monocytogenes, Salmonella spp. and Staphylococcus aureus

Abstract

BackgroundFood-borne infections cause huge economic and human life losses worldwide. The most common contaminants of foods include Listeria monocytogenes Salmonellae and Staphylococcus aureus. L. monocytogenes is most notorious due to its tolerance to common food preservation methods and the risks it poses, including higher fatality rates. Safer, more efficacious control methods are thus needed. Along with food-borne pathogens, lactic acid bacteria (LAB) can also be found in foods. Some LAB isolates inhibit pathogenic bacteria by various mechanisms, including by production of antimicrobial metabolites.MethodsThe potential of cell-free culture supernatants (CFS) derived from broth cultures of selected local LAB and yeast isolates, some of which were subjected to various treatments, were tested for inhibition of L. monocytogenes, Salmonella spp. and S. aureus in in vitro culture by incorporating various proportions of the CFSs into the growth medium concurrently with inoculation (co-cultures) or following limited proliferation after inoculation of the pathogens (delayed cultures). The effects of the CFSs on various growth parameters were assessed.ResultsCFS from the LAB isolates were strongly inhibitory when co-cultured. The inhibitory activities were stable following heat or protease treatment of the CFSs. Inhibitory activity was dependent primarily on active substance(s) secreted into the supernatant. In all co-cultures, CFS proportion-dependent progressive decrease in the number of colonies was observed and both growth rates and number of generations were reduced with significantly fewer numbers of colony forming units, whereas generation times were significantly increased compared to those of controls. Transfer from co-cultures to fresh broth showed inhibited cultures contained bacteria that can re-grow, indicating the presence of viable bacteria that are undetectable by culture. Growth rates in CFS-treated delayed cultures were also reduced to varying degrees with the number of colonies in some cultures being significantly less than the corresponding control values. CFSs were active against both Gram-positive and –negative bacteria.ConclusionsActive metabolites produced and secreted by LAB into the growth medium were effective in inhibiting the tested pathogens. Early addition of the CFSs was necessary for significant inhibition to occur. Further studies will help make these findings applicable to food safety.

Organic whey as a source of Lactobacillus strains with selected technological and antimicrobial properties

“…Other researchers have also demonstrated that LAB strains are strongly active against indicator species (Fraga Cotelo et al ., ; Mariam et al ., ; Patel & Parikh, ). However, most researches (Sip et al ., ; Choesri et al ., ; Cizeikiene et al ., ; Wang et al ., ) demonstrated strong antilisterial activity of LAB isolates from foods, which was not observed in our study.…”

Membrane disruption and DNA binding of Staphylococcus aureus cell induced by a novel antimicrobial peptide produced by Lactobacillus paracasei subsp. tolerans FX-6

“…Additionally, there are approximately 1.6 million cases of foodborne illnesses occurring related to 30 specified pathogens each year in Canada (Thomas, et al, 2013). Among the most widespread foodborne pathogenic organisms, Staphylococcus aureus is an important foodborne pathogen causing foodborne illnesses (Mariam et al, 2014;Wang, et al, 2013;Wang, et al, 2014).…”

Lactic acid bacteria from traditionally processed corn beer and palm wine against selected food-borne pathogens isolated in south west region of Cameroon

“…The exploitation of the inhibitory activity of the lactic bacteria appeared in recent years as an alternative treatment and even prevention of some foodborne toxiinfection (Mezaini et al, 2009;Obi et al, 2015;Khalid, 2011). Indeed the lactic acid bacteria are known to be non-pathogenic and Generally Regarded as Safe, and are increasingly used because of their probiotic properties (Zacharof and Lovitt, 2012;Mariam et al, 2014).…”