Bovine mastitis is a polymicrobial disease requiring a polydiagnostic approach

Bovine mastitis, an inflammation of the udder, is associated with increases in milk somatic cell count usually resulting from bacterial infection. We analysed 50 mastitic milk samples via cultivation, 16S rRNA sequencing and a combination of the two (culturomics) to define the complete microbial content of the milk. Most samples contained over 10,000 cfu mL⁻¹ total bacterial counts including isolates that were haemolysin positive (n = 36). Among colonies isolated from blood agar plates, Streptococcus uberis was dominant (11/50) followed by Streptococcus dysgalactiae (6/50), Pseudomonas (6/50), Enterococcus faecalis (6/50), Escherichia coli (6/50), Staphylococcus argenteus (4/50), Bacillus (4/50) and Staphylococcus aureus (2/50). 16S rRNA profiling revealed that amplicons were dominated by Rhodococcus, Staphylococcus, Streptococcus and Pseudomonas. A higher inter-sample diversity was noted in the 16S rRNA readouts, which was not always reflected in the plating results. The combination of the two methods highlights the polymicrobial complexity of bovine mastitis.