Mesophilic Lactic Acid Bacteria Diversity Encountered in Brazilian Farms Producing Milk with Particular Interest in Lactococcus lactis Strains.

The milk produced in regions with different traditions in Brazil is used for artisanal product production, which is characterized by different sensorial characteristics. This study aimed to identify the bacterial ecosystem of farms located in a traditional dairy region in the state of Minas Gerais and to characterize Lactococcus lactis strains, the species of interest in this study, using a multilocus sequence typing (MLST) protocol and pulsed-field gel electrophoresis (PFGE) technique. Samples were collected from raw milk and dairy environment from six farms. A total of 50 isolates were analyzed using 16S rRNA sequencing and species-specific PCR. Five genera were identified: Lactobacillus, Leuconostoc, Lactococcus, Enterococcus, and Staphylococcus, from ten different species. MLST (with six housekeeping genes) and PFGE (with SmaI endonuclease) were used for the characterization of 20 isolates of Lactococcus lactis from a dairy collection in this study. Both methods revealed a high clonal diversity of strains with a higher discriminatory level for PFGE (15 pulsotypes), compared to MLST (12 ST). This study contributes to the preservation of the Brazilian dairy heritage and provides insights into a part of the LAB population found in raw milk and dairy environment.

The long-term survival of Propionibacterium freudenreichii in a context of nutrient shortage.

AIMS: Propionibacterium freudenreichii is an actinobacterium widely used in dairy industry during the ripening process of Swiss-type cheeses and which presents probiotic properties. P. freudenreichii is reportedly a hardy bacterium, able to survive during the cheese-making process and when subjected to digestive stresses. During this study the long-term survival (LTS) of P. freudenreichii was investigated for 11 days by means of phenotypic characterization in a culture medium without the addition of any nutrients. METHODS AND RESULTS: For 11 days, in a non-nutrient supplemented culture medium, eight strains were monitored by measuring their optical density, counting colony-forming units (CFU) and using LIVE/DEAD staining and microscopy observation. Under these conditions, all strains displayed high survival rates in the culture medium, their culturability reaching more than 9 log10 CFU ml(-1) after 2 days. After 11 days, this value ranged from 7·8 to 8·2 log10 CFU ml(-1) depending on the strain, and at least 50% of the P. freudenreichii population displayed an intact envelope. As lysis of part of a bacterial population may be a microbial strategy to recover nutrients, in CIRM-BIA 138 (the strain with the highest population at day 11), cell lysis was assessed by quantifying intact bacterial cells using qPCR targeting the housekeeping gene tuf. No lysis was observed. CONCLUSION: Taken together, our results suggest that P. freudenreichii strains use a viable but nonculturable state to adapt to the LTS phase. SIGNIFICANCE AND IMPACT OF THE STUDY: Assessing the viability of P. freudenreichii and understanding their mechanisms for survival should be of great interest regarding their potential probiotic applications.