Bacterial isolation of milk samples submitted from clinical mastitis buffaloes during 2007 to 2016

The present study determined trends in the isolation of bacterial pathogens in milk samples submitted from clinical mastitis buffaloes at the University mastitis laboratory during 2007 to 2016. Culture results (n = 3945) were classified into six categories (Staphylococcus spp., 28.7%; Streptococcus spp., 1%; Corynebacterium spp., 1.1%; gram-negative organisms, 3.2%; others including mixed growths, 3.3%; and no growth, 62.7%). Overall, culture results were significantly associated with year (χ² = 112.28; df = 10; P < 0.001) and season (χ² = 136.03; df = 20; P < 0.001). From 2007-2009 to 2013-2016, the isolation of Staphylococcus spp. increased from 28.2 to 48.4%, while isolation of Streptococcus spp. (50 to 20%) and Corynebacterium spp. (65.1 to 16.3%) decreased. The proportion of samples characterized as no growth increased from 26.4% (2007-2009) to 46.3% (2013-2016). Further, the proportion of clinical mastitis cases increased over the study years (goodness-of-fit χ² = 59; df = 2; P < 0.001). With respect to season, the proportion of Staphylococcus spp. (30.6%; 346/1132), Corynebacterium spp. (48.8%; 21/43), and gram-negative bacteria (55.9%; 71/127) were more associated with the monsoon, and that of Streptococcus spp. (47.5%; 19/40) with the winter. Seasonal effects were also observed on the occurrence of clinical mastitis cases; comparatively, more clinical mastitis cases (35.6%; 523/1473) were observed during the monsoon season (goodness-of-fit χ² = 276.7; df = 4; P < 0.001) as compared with other seasons. The present study concludes that Staphylococcus spp. are the major cause of intramammary infections in buffaloes with clinical mastitis, demanding more studies regarding its epidemiology and pathogenicity. Also, more efforts are needed in the prevention and control of clinical mastitis in buffaloes, especially, during the monsoon season.