Prevalence and Diversity of Leuconostoc spp. in Raw Milk
Research Poster Health & Life Sciences 2025 Graduate ExhibitionPresentation by Songyi Yoo
Exhibition Number 186
Abstract
This study investigated the prevalence and diversity of Leuconostoc spp. in raw milk silo samples from a Mid-Atlantic dairy processor over six months (April–October 2024). Weekly samples were analyzed for milk composition and microbial quality. Leuconostoc spp. were isolated using selective plating with vancomycin, verified by PCR and 16S rRNA sequencing, and classified into species and genotypes. Representative isolates were further characterized for carbohydrate utilization, exopolysaccharide (EPS) production on sucrose agar, growth at different temperatures, and survival after laboratory pasteurization. A total of 569 Leuconostoc isolates were identified, including six Leuconostoc species: L. lactis, L. mesenteroides, L. citreum, L. falkenbergense, L. pseudomesenteroides, and L. holzapfelii, further classified into ten different genotypes. Representative isolates from each genotype were further characterized. All selected isolates (n=29) fermented galactose, glucose, fructose, N-acetylglucosamine, lactose, and sucrose. EPS production was observed in all representative L. citreum isolates, as well as in three representative L. mesenteroides and L. falkenbergense isolates. L. lactis and L. mesenteroides grew well in unflavored milk at 4°C after 15 days, while all representative isolates grew at 10°C and 20°C. Only one representative L. lactis isolate survived after laboratory pasteurization. Leuconostoc spp. were consistently present in raw milk (~10–100 CFU/ml). The identification of six species and ten genotypes highlights their diversity. EPS production and cold-temperature growth may contribute to defects in chilled products, while survival after low-temperature long-time (LTLT) pasteurization could lead to spoilage in pasteurized milk.
Importance
This study provides essential baseline information on the prevalence and diversity of Leuconostoc in raw milk. The identification of six species and ten genotypes highlights the significant diversity of this genus in raw milk. The ability of certain isolates to grow at refrigeration temperatures and survive post lab pasteurization raises concerns about their persistence during processing and storage, which may contribute to quality defects in dairy products. These findings are important for improving dairy safety and quality control strategies.