MYCOPLASMA BOVIS MASTITIS: PREVALENCE, IDENTIFICATION OF VIRULENCE FACTORS AND HOST IMMUNE RESPONSE GENES

Mycoplasma bovis is the most prevalent Mycoplasma species that causes mastitis in the United States (U.S.). M. bovis mastitis (MBM) is highly contagious and characterized by resistance to antimicrobial treatments. Reduction in milk yield and culling of infected cows are the major contributors to the substantial economic losses. Reports on MBM prevalence in Tennessee dairy farms are limited. To date, there is no effective commercial vaccine mainly due to lack of understanding about MBM pathogenesis and M. bovis virulence factors. The major objectives of this dissertation were to determine the prevalence of M. bovis in bulk tank milk in Tennessee dairy farms and identify M. bovis virulence factors and host immune response genes. Culture and PCR were used to determine the prevalence of M. bovis in bulk tank milk. Whole transcriptome analysis was performed following co-infection of M. bovis with bovine mammary epithelial cells and intramammary challenge of dairy cows by M. bovis. To investigate the virulence role of surface lipoproteins mnuA and 5’-nucleotidase, M. bovis mutants were developed and in vivo intramammary cow and murine challenges were conducted. Prevalence of M. bovis in bulk tank milk in Tennessee dairy farms was found to be 5.3% and 76.7% using culture and PCR, respectively. Following co-infection with mammary epithelial cells, transposase activity was significantly upregulated in M. bovis whereas genes involved in protein translation were significantly downregulated. Genes associated with apoptosis pathways and pro-inflammatory cytokines were significantly upregulated in M. bovis infected bovine mammary epithelial cells whereas genes involved in cell cycle, ribosome biogenesis, and steroid biosynthesis were significantly down-regulated. Genes encoding pro-inflammatory pathways and formation of neutrophil extracellular traps were significantly upregulated in mammary glands of M. bovis challenged cows whereas steroid biosynthesis and metabolism was significantly down-regulated. The 5’-nucleotidase gene was found to be a virulence factor of M. bovis which determines its fitness and survival. In conclusion, the high prevalence reported here is concerning and further studies involving repeated sampling from individual cows using combination of tests is highly recommended. The identified virulence factors can be used as an important intervention targets.