Evaluation and cluster analysis of inflammatory reactions of dairy cattle mastitis pathogens in milk samples submitted for microbiological examination

Abstract

Aim of study: We have classified into homogenous groups a wide spectrum of mammary pathogens according to their frequency of isolation in clinical mastitis and their somatic cell counts in non-clinical mastitis.Area of study: The study was conducted in Galicia (NW Spain)Material and methods: 163,741 dairy cattle quarter milk samples were analyzed. We identified mastitis pathogens to the species level and performed a cluster analysis to classify these microorganisms by their median of Linear Score (mLS), percentage of isolation in clinical mastitis samples (%ICS) and percentage of isolation in samples with somatic cell counts under 100,000 cells/mL (%ISU100).Main results: Forty-three different species were isolated. Cluster analysis identified 4 groups of pathogens; mLS and %ICS progressively increased from Group I to Group IV and %ISU100 decreased. However, several pathogens included in groups II and III showed %ISU100 values higher than 2% and 3%. Minor pathogens were mainly clustered in Group I (e.g., Corynebacterium spp. and most of Staphylococcus spp.), while known major pathogens were included in Groups II, III y IV. Species of the same family, genus or microbiological group like Enterobacteriaceae or Enterococcus spp. were frequently separated into different groups, thus showing heterogeneity among the members of these groups.Research highlights: Results obtained here may aid in assessing the pathogenicity of sporadic pathogens in relation to more well-known pathogens and suggest that the traditional classification between minor and major pathogens is an oversimplification of the reality, especially for the latter category.