Two simple techniques were developed to demonstrate bactericidal activity of bacteriocins. Both were based on allowing a lawn of indicator strain to grow first, then exposing the lawn to bacteriocin-containing cell-free supernatants in a well cut in the seeded agar lawn or by inoculating the bacteriocin-producing strain onto the indicator lawn. Lysis of cells of the indicator strain resulted in a clear zone. These techniques may be adapted to test antimicrobial substances other than bacteriocins and to help to determine their modes of action.

Bacteriocin‐producing (Bac+) Lactococcus lactis ssp. lactis CCMM/IAV/BK1 isolated from traditional lben was used in the preparation of lben from pasteurized milk to assess its potential inhibitory activity against Listeria monocytogenes ATCC 7644. Production of bacteriocin (arbitrary units, AU) in MRS broth fortified with yeast extract (MRSY) in a fermentor under controlled and uncontrolled pH conditions was also investigated. This Bac+ strain yielded about 35 times more bacteriocin when the pH was maintained constant at 6.5 than under varying pH conditions. To test the effect of in situ bacteriocin production against L. monocytogenes, lben was made from cow's milk artificially contaminated with approximately 107 cfu/mL and fermented with a mixed mesophilic starter culture consisting of the lactococcal Bac+ organism and Lc. lactis ssp. lactis biovar diacetylactis 66, a diacetyl‐producing strain, in a ratio of 1 : 1. Numbers of L. monocytogenes were monitored during fermentation and storage of lben at refrigeration temperature (c. 7°C) for up to 6 days. Performances of the Bac+ starter were compared to those of an isogenic Bac− derivative strain obtained from the Bac+ starter by curing with ethidium bromide. The results showed that the amount of L. monocytogenes decreased to below the detectable level in a 1‐mL sample within 24 h of storage at 7°C in lben fermented with the Bac+ starter culture. On the contrary, L. monocytogenes survived for 6 days of storage at 7°C in lben made with the Bac− starter. The Bac+ wild strain of the starter studied could be adequately used to produce lben or similar indigenous fermented milks of improved hygienic quality on an industrial scale. Alternatively, it could be used as an adjunct in minimally processed products or in products obtained from raw milk to add a safety factor.

The aim of this work is to determine the chemical composition of the essential oil of Origanum compactum, from the region of Meknes (Morocco), and their antimicrobial effect, and on the other hand, to carry out a comparison between the chemical composition of this essential oil with the six regions of Morocco: Larache, Chefchaouen, Al Hoceïma, Tetouan, Taounate and Rabat. The essential oils of Origanum compactum thus obtained were analyzed and identified by gas chromatography coupled with mass spectrometry (GC/MS). To determine the similarities and dissimilarities between the chemical compositions of the essential oil of Origanum compactum from the Meknes region with the other six regions of Morocco, we performed the principal component analysis (ACP). Regarding antimicrobial activity, the essential oils of Origanum compactum have shown significant inhibitory activity against the bacteria and molds studied.

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