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Abstract
A total of 450 different colonies, isolated from 25 samples of dromedary milk collected from Laâyoune region of Morocco, were tested for antimicrobial compounds production. Out of these, 30 were determined to be lactic acid bacteria (LAB) and able to inhibit the growth of the indicator strain Listeria innocua CECT 4030. Seven isolates were selected by the large and clear zones of inhibition when tested by the agar well diffusion assay. They were classified by phenotypic and biochemical analysis as two Enterococcus durans (E204 and E214), two Lactococcus lactis (R75 and R76), one Enterococcus faecium R111, one Lactococcus cremoris R112 and one Enterococcus avium R122. Their antimicrobial compounds were detected in cell-free culture supernatant fluids under conditions that eliminate acid and hydrogen peroxide inhibition. The antimicrobial activity was altered after treatment with trypsin, -chymotrypsin, pepsin or papain which confirms the proteinaceous nature of the inhibition. It was heat stable even at autoclaving temperature (121°C for 15 min) and also active over a wide pH range (2 to 10). This fact suggests that bacteriocin-like produced by the seven LAB strains may find application as biopreservatives in food products. Key words: Dromedary milk, lactic acid bacteria, bacteriocin-like substances, antimicrobial activity.
Highlights
Lactic acid bacteria (LAB) can produce antimicrobial substances with capacity to inhibit the growth of pathogenic and spoilage microorganisms in foods
lactic acid bacteria (LAB) produce various antimicrobial compounds, which can be classified as low-molecularmass compounds such as hydrogen peroxide (H2O2), carbon dioxide (CO2), diacetyl (2,3-butanedione), uncharacterized compounds and high-molecular-mass compounds like bacteriocins (Jay, 1982; Klaenhammer, 1988; Piard and Desmazeaud, 1991, 1992)
We reported on the study of antibacterial activities and the characterization of antibacterial compounds of seven strains isolated from Moroccan dromedary milk against L. innocua CECT 4030
Summary
Lactic acid bacteria (LAB) can produce antimicrobial substances with capacity to inhibit the growth of pathogenic and spoilage microorganisms in foods. The primary antimicrobial effect exerted by LAB is the production of lactic acid and reduction of pH (Daeschel, 1989). Bacteriocins have attracted a great interest in food industry due to their application potentiality in food preservation. They are antimicrobial proteinaceous substances secreted by some bacteria against microorganisms that are usually closely related to the producer organism (klaenhammer, 1988). LABbacteriocins comprise a heterogeneous group of physicochemically diverse ribosomally-synthesized peptides or proteins showing a narrow or broad antimicrobial activity spectrum against Gram-positive bacteria. Bacteriocins are classified into separate groups such as the lantibiotics (class I); the small (30 kDa) heat-labile non-lantibiotics (class III) and complex bacteriocins containing chemical moieties such as lipid and carbohydrate (class IV) (Klaenhammer, 1993)
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