Genome Sequence of Lactococcus lactis subsp. cremoris Mast36, a Strain Isolated from Bovine Mastitis

From Genome to Phenotype: An Integrative Approach to Evaluate the Biodiversity of Lactococcus lactis

Lactococcus lactis is one of the most extensively used lactic acid bacteria for the manufacture of dairy products. Exploring the biodiversity of L. lactis is extremely promising both to acquire new knowledge and for food and health-driven applications. L. lactis is divided into four subspecies: lactis, cremoris, hordniae and tructae, but only subsp. lactis and subsp. cremoris are of industrial interest. Due to its various biotopes, Lactococcus subsp. lactis is considered the most diverse. The diversity of L. lactis subsp. lactis has been assessed at genetic, genomic and phenotypic levels. Multi-Locus Sequence Type (MLST) analysis of strains from different origins revealed that the subsp. lactis can be classified in two groups: “domesticated” strains with low genetic diversity, and “environmental” strains that are the main contributors of the genetic diversity of the subsp. lactis. As expected, the phenotype investigation of L. lactis strains reported here revealed highly diverse carbohydrate metabolism, especially in plant- and gut-derived carbohydrates, diacetyl production and stress survival. The integration of genotypic and phenotypic studies could improve the relevance of screening culture collections for the selection of strains dedicated to specific functions and applications.

The Lactococcus genus as a potential emerging mastitis pathogen group: A report on an outbreak investigation

The bacterium Lactococcus lactis is widely used in food production and in medical applications, and is considered safe for human and animal use. However, studies have also linked Lactococcus bacteria to infection. For example, certain variants of Lactococcus species have been associated with bovine mastitis (e.g., Lactococcus lactis and Lactococcus garvieae). In this study, we investigated an outbreak of bovine mastitis thought to be associated with Lactococcus bacteria by using microbiological and molecular techniques. We used bacterial isolation, next-generation sequencing, DNA fingerprinting, and other methods to test our hypothesis that Lactococcus microbes were the primary pathogen causing the mastitis outbreak. Twenty-eight Lactococcus isolates were obtained from mastitic milk of 28 dairy cows. The isolates were identified as L. lactis (27 isolates) and L. garvieae (1 isolate). Phylogenetic analysis based on 16S rDNA gene sequence comparison indicated similarity among the L. lactis isolates as well as between the isolates and reference sequences. The DNA fingerprinting analysis based on random amplified polymorphic DNA results of the 27 L. lactis isolates identified different random amplified polymorphic DNA profiles, which suggests they originated from multiple sources. Microbiome analysis determined Lactococcus to be the dominant genus in the majority of the mastitic milk samples, whereas it was found in low relative abundance in healthy milk samples. The Lactococcus genus was detected in all environmental samples tested, and sampling of bulk tank milk corroborated that Lactococcus was not abundant in healthy milk from the same dairy herd. In summary, our findings suggest that Lactococcus bacteria are a potential etiological agent in the mastitis outbreak studied. Further studies should be conducted to understand the importance of Lactococcus, especially L. lactis, as pathogenic microbes in veterinary medicine and food safety.