Inhibitory potential against Listeria spp and Staphylococcus aureus of the strain of Brevibacterium linens producing linenscin OC2

Twenty-four strains of the genus listeria (14 of L monooytogenes and 10 of L innocua) along with 24 strains of Staphylococcus aureus were tested for their sensitivity to the culture filtrate of Brevibacterium linens OC2, an orange cheese coryneform bacterium producing linenscin OC2, an inhibitory peptidic compound. All strains were inhibited, staphylococci being slightly more sensitive than listeria. The inhibitory potential of the filtrate towards L monooytogenes and L innocua (one strain of each), and two strains of S aureus was investigated using three concentrations of the filtrate (0.1, 1 and 10%). A viability loss ora bacteristatic effect was observed, depending on the strain and the amount of filtrate in the culture medium. The length of the phase of inhibition was correlated with filtrate concentration, after which all strains resumed growth at a rate decreasing as the percentage of filtrate increased. Regrowth of the survivors was also observed in mixed cultures of B linens OC2 (10(7) cfu/mL in the inoculum) and a cocktail of four L monocytogenes strains (10(4) cfu/mL of each in the inoculum). As it has been shown that the inhibitory activity of the filtrate was stable over time, the presence of very low proportions of resistant cells in the sensitive population was investigated. Their level was predicted from the analysis of regrowth curves and confirmed using the Most Probable Numbers (MPN) technique of bacterial enumeration in liquid medium containing the filtrate in which five tubes were inoculated from each of three successive ten-fold dilutions. The proportion of listeria resistant to 10% of filtrate in the medium was in the range of 10(-4) of the total population. Therefore, it can be predicted that if the contamination level of listeria is above 10(4) listeria on the surface of a piece of smear cheese at the time B linens reaches a sufficient level to produce enough inhibitory substance, then linenscin-resistant survivors might survive and proliferate. Washing and brushing the surface of this kind of cheese during curing would contribute to the contamination of other cheeses and subsequently the entire factory environment by linenscin-resistant listeria. This would eventually abolish the possibility of controlling listeria and other undesirable bacteria on the surface of this kind of cheese by use of the strain of B linens producing linenscin OC2. It is concluded that this strain must be used with care and only after full assessment of ifs efficacy on cheese surfaces in experiments carried out under strict containment conditions.