Abstract
The objective of this study was to use pyrosequencing of the 16S rRNA genes to describe the microbial diversity of bovine milk samples derived from clinically unaffected quarters across a range of somatic cell counts (SCC) values or from clinical mastitis, culture negative quarters. The obtained microbiota profiles were used to distinguish healthy, subclinically and clinically affected quarters. Two dairy farms were used for the collection of milk samples. A total of 177 samples were used. Fifty samples derived from healthy, culture negative quarters with a SCC of less than 20,000 cells/ml (group 1); 34 samples derived from healthy, culture negative quarters, with a SCC ranging from 21,000 to 50,000 cells/ml (group 2); 26 samples derived from healthy, culture negative quarters with a SCC greater than 50,000 cells/ml (group 3); 34 samples derived from healthy, culture positive quarters, with a SCC greater than 400,000 (group 4, subclinical); and 33 samples derived from clinical mastitis, culture negative quarters (group 5, clinical). Bacterial DNA was isolated from these samples and the 16S rRNA genes were individually amplified and pyrosequenced. All samples analyzed revealed great microbial diversity. Four bacterial genera were present in every sample obtained from healthy quarters (Faecalibacterium spp., unclassified Lachnospiraceae, Propionibacterium spp. and Aeribacillus spp.). Discriminant analysis models showed that samples derived from healthy quarters were easily discriminated based on their microbiota profiles from samples derived from clinical mastitis, culture negative quarters; that was also the case for samples obtained from different farms. Staphylococcus spp. and Streptococcus spp. were among the most prevalent genera in all groups while a general multivariable linear model revealed that Sphingobacterium and Streptococcus prevalences were associated with increased 10 log SCC. Conversely, Nocardiodes and Paenibacillus were negatively correlated, and a higher percentage of the genera was associated with a lower 10 log SCC.
Highlights
Mastitis is a disease in dairy cows with a high incidence and prevalence and arguably one of the most important for the dairy industry worldwide
We present the average prevalence of the twenty most prevalent bacterial genera for each of the five groups of samples. Four of these bacterial genera (Faecalibacterium, unclassified Lachnospiraceae, Propionibacterium and Aeribacillus) were found to be present in all the studied samples derived from healthy quarters, regardless of their Somatic cell counts (SCC) or culture status
Four bacterial genera were present in every sample obtained from healthy quarters (Faecalibacterium, unclassified Lachnospiraceae, Propionibacterium and Aeribacillus)
Summary
Mastitis is a disease in dairy cows with a high incidence and prevalence and arguably one of the most important for the dairy industry worldwide. Somatic cell counts (SCC) have been extensively used to distinguish healthy quarters from quarters with an inflammatory response most likely due to an intramammary infection [4,5]. 30% of samples from cows or quarters with high SCC (subclinically affected quarters) were reported to be culture negative [9]. Most quarters with a low SCC, usually defined as values below 200,000 cells/ml, are culture negative in aerobic and modified anaerobic culture. Empirical evidence for the importance of native bacterial populations within the mammary gland, comes from the reports of clinical Escherichia coli mastitis outbreak following ‘‘blitz’’ therapy (simultaneous antibacterial treatment of all infected mammary glands within a herd to eliminate Streptococcus agalactiae infection from a herd) [12]. More detailed evidence of a native bacterial population in healthy quarters was previously reported by our research team [10]
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