Abstract
Enterococci (118) from Italian sausages were tested for the production of antimicrobial substances. Of these, 7.6% showed antibacterial activity against one or several closely related microorganisms used as indicators. Enterococcus casseliflavus IM 416K1 in particular produced a bacteriocin (Enterocin 416K1) with strong anti-listerial antagonistic activity. The bacteriocin withstood heating at 90 °C for 120 min and storage at 4 °C for 6 months. The mode of action was identified as bactericidal. The crude activity of Enterocin 416K1 was linked to a molecule with an apparent molecular weight smaller than 5 kDa. Plasmid analysis of E. casseliflavus IM 416K1 revealed the presence of four plasmids with different molecular weights (34, 11, 7 and 3.3 MDa). All the Bac− variants produced by curing experiments showed loss of the single plasmid of 34 MDa. Bacteriocin activity and immunity production may be linked to genes located on that same plasmid.
Highlights
The discovery of inhibitory substances active against pathogens have become of great interest in the past few years, in relation to the increase of food-borne illness caused by microbial contamination (Gravani, 1987; Klaenhammer, 1993; Jack et al, 1995)
These antibacterial substances are called enterocins. They generally belong to class II bacteriocins and have the potential to inhibit the growth of a narrow range of strains closely related to the producer microorganism (Tagg et al, 1976; Klaenhammer, 1993); some are active against Grampositive food-borne pathogens and spoilage bacteria
Crude filtrate supernatant fluid (CFSF) of the best producer, Enterococcus casseliflavus IM 416K1, was tested by agar well diffusion assay (Rogers and Montville, 1991) against : (i) enterococci found to be sensitive in the initial screening, (ii) Gram-positive and Gram-negative indicator bacteria belonging to different genera (Table 1)
Summary
The discovery of inhibitory substances active against pathogens have become of great interest in the past few years, in relation to the increase of food-borne illness caused by microbial contamination (Gravani, 1987; Klaenhammer, 1993; Jack et al, 1995). Bacteriocin production seems to be a common trait among strains associated with food They generally belong to class II bacteriocins and have the potential to inhibit the growth of a narrow range of strains closely related to the producer microorganism (Tagg et al, 1976; Klaenhammer, 1993); some are active against Grampositive food-borne pathogens and spoilage bacteria Among the bacteriocin-like substances observed, Enterocin 416K1 was studied and partially characterized with the aim of assessing its use as ‘‘natural preservative’’ for application in food production
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