Bacterial Community Profiling of Milk Samples as a Means to Understand Culture-Negative Bovine Clinical Mastitis

Inflammation and infection of bovine mammary glands, commonly known as mastitis, imposes significant losses each year in the dairy industry worldwide. While several different bacterial species have been identified as causative agents of mastitis, many clinical mastitis cases remain culture negative, even after enrichment for bacterial growth. To understand the basis for this increasingly common phenomenon, the composition of bacterial communities from milk samples was analyzed using culture independent pyrosequencing of amplicons of 16S ribosomal RNA genes (16S rDNA). Comparisons were made of the microbial community composition of culture negative milk samples from mastitic quarters with that of non-mastitic quarters from the same animals. Genomic DNA from culture-negative clinical and healthy quarter sample pairs was isolated, and amplicon libraries were prepared using indexed primers specific to the V1–V2 region of bacterial 16S rRNA genes and sequenced using the Roche 454 GS FLX with titanium chemistry. Evaluation of the taxonomic composition of these samples revealed significant differences in the microbiota in milk from mastitic and healthy quarters. Statistical analysis identified seven bacterial genera that may be mainly responsible for the observed microbial community differences between mastitic and healthy quarters. Collectively, these results provide evidence that cases of culture negative mastitis can be associated with bacterial species that may be present below culture detection thresholds used here. The application of culture-independent bacterial community profiling represents a powerful approach to understand long-standing questions in animal health and disease

Changes in bacterial populations in refrigerated raw milk collected from a semi-arid area of Algeria

Most of the studies on milk microbiota have been performed on cows’ milk from animals reared in temperate and humid areas. In this work, changes in the bacterial consortium of refrigerated raw milk collected from cows grazed in a semi-arid area of Algeria were studied during 21 days of refrigerated storage. Twenty bacterial morpho-physiotypes were selected among 150 isolates from milk at different times over storage and identified by partial 16S rRNA gene sequencing. The dominant bacterial populations were characterized by a few species. Stenotrophomonas rhizophila, S. maltophilia and Chryseobacterium indologenes were predominant during the first 7 days, Lactobacillus pentosus and L. plantarum were isolated only after the 10th day, while Acinetobacter spp. was isolated at the end of storage. Compared to the current literature on milk from temperate zones, sluggish and incomplete microbial growth was observed with a long incubation phase ranging from 6.7 to 10.5 days and a maximum growth not exceeding 5.3 log colony-forming units (CFU) · mL−1. The composition of milk microbiota and its evolution over refrigeration suggest a bio-geographical characterization due to environmental factors. In particular, the possible presence of antimicrobial molecules coming from plants grazed in the semi-arid zone around the farm may account for the presence of selected microbial species and the extended milk shelf-life. Despite this being a preliminary work, these results encourage the use of arid herbs in animal feed and motivate scientists to focus their efforts on the study of biochemical composition of plants from arid areas and their antimicrobial activity