The use of thermophilic lactic starters in the dairy industry is discussed. The functions of the thermophilic lactic starters in cooked cheese production and its ripening, the bacteria of the starter cultures and various types of starters are described.

Etude des interactions entre diverses bactéries lactiques thermophiles et mésophiles, en relation avec la fabrication des fromages

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SummaryMilk from eigh heifers experimentally inoculated with a virulent strain of Brucella abortus, and excreting large numbers ofthese bacteria at calving, was used to make three successive batches of a soft, camembert-type, cheese. Lactic fermentation was induced by a Streptococcus lactis and S. cremoris starter that caused the pH to fall to 4.5-4.6 after 20 hours. Surface inoculation of the curd with Penicillium caseicolum was performed before ripening at 12 oc. Brucella were enumerated by plating milk or liquid suspensions of chee se on a selective medium. Initially, Brucellae in the milk became concentrated in the curd and counts remained high up to 20 hours, subsequently declining regularly. No Brucella were found after eighteen days. Two groups of 20 mice were each fed 600-670 g of 22-25-day-old cheeses. No Brucella were isolated from these mice autopsied 15 days later. The scientific literature reports long survival times for Brucellae in cheeses of different types prepared from milk to which laboratory-grown cells had been added. It appears that Brucella cells which have multiplied in vivo and been excreted in the milk along with antibodies and inflammatory cells, may be more susceptible to inactivation during the cheesemaking process than laboratory-grown Brucella cells.Key words: Soft cheese -Brucella -Survival. Résumé Survie de Brucella abortus dans un fromage à pâte molle fabriqué avec du lait de vaches infectéesLe lait de huit vaches infectées expérimentalement par une souche virulente de Brucella abortus, et excrétant massivement cette bactérie au vêlage a servi à la fabrication de trois lots successifs d'un fromage à pâte molle de type camembert. Après emprésurage et acidification par un levain de Streptococcus lactis et S. cremoris donnant après 20 heures un pH de 4,5-4,6 dans la pâte, le caillé démoulé puis ensemencé par Penicillium caseicolum a été mis à maturer à 12 "C en ambiance humide. Les Brucella ont été dénombrées dans le lait et dans le fromage par ensemencement sur milieu sélectif. Après une augmentation initiale des Brucella dans le caillé jusqu'à la 20 c heure, leur nombre a ensuite décru régulièrement jusqu'à disparition après le ISe jour. Mots clés: Fromage à pâte molle -Brucella -Survie.

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