Cambios en aislamientos de Listeria innocua conservados en un medio bifásico durante ocho meses

Listeriainnocua is a bacterium phylogenetically related to Listeriamonocytogenes, the causative agent of foodborne listeriosis.Published studies regarding the long-term survival of L.innocua have been performed on short periods and single cell observationfrom liquid media, but studies in biphasic media with an emphasis on colonies have not been published. The objective of this workwas to describe the survival, during 8 months, of 30 Listeriainnocua isolates in a biphasic médium composed in its liquid part byBrain Heart Infusion Broth added with 0.6 % Yeast Extract and in its solid part by Tripticasein Soy Agar added with 0.6 % YeastExtract. Observations with the naked eye and photographic record were made monthly, focusing the observations on the presenceof colonies in the slant front side área. Through descriptive statistics, the changes in the frequency and type of colonies, as well asin the generation time were identified.All the isolates showed at least one type of change, consisting of the emergence, increase, decrease and disappearance of colonieswith different morphologies, ora n increase in the biomass density of some colonies. Chages can be attributed to factors such as pH,temperatura, nutrient limitation, quorum sensing and genetics. The procedures and results described in this work can serve as aneducational model for showing bacterial long term persistence, research on genetic diversity, survival in starvation and persistencestudies of strains related to resistance to antimicrobials or disinfectants