Immunological responses and evaluation of the protection in dairy cows vaccinated with staphylococcal surface proteins.

Bovine mastitis is a significant cause of economic losses in the dairy industry. Staphylococcus aureus is one of the most common contagious mastitis pathogens, whereas Staphylococcus chromogenes increasingly became a significant cause of subclinical mastitis in dairy cows. Current mastitis control measures are not effective on all mastitis pathogens. There is no effective vaccine to control Staphylococcal mastitis in dairy cows. The objective of this study was to evaluate the immune responses and protection in dairy cows vaccinated with S. aureus surface proteins (SASP) or S. chromogenes surface proteins (SCSP). We divided eighteen Holstein dairy cows randomly into three groups of 6 animals each. We vaccinated group 1 and 2 animals with SASP and SCSP with Emulsigen-D adjuvant, respectively. We injected control (group 3) animals with PBS (pH 7.2) in Emulsigen®-D. We vaccinated animals three times at 28 and 14 days before drying off, and at dry off. Two weeks after the third vaccination, we challenged each animal by dipping all teats in S. aureus culture suspension once daily for 14 consecutive days. We evaluated milk or mammary secretion and serum antibody titers during vaccination and challenge periods. We evaluated milk samples for the number of bacteria shedding and somatic cell counts (SCC). Out of six cows vaccinated with SASP, one cow was removed from the study due to injury, two were infected clinically, another two were infected subclinically, and the remaining cow was not infected. No SCSP vaccinated cows developed clinical or subclinical mastitis. Out of six control cows, two developed clinical mastitis whereas four were infected subclinically. The SCSP vaccine cross-protected against S. aureus mastitis and reduced number of S. aureus shedding in milk. We concluded that the SCSP is a promising vaccine to control Staphylococcal mastitis in dairy cows.

Bovine intramammary infection associated immunogenic surface proteins of Streptococcus uberis.

In spite of the increasing prevalence of Streptococcus uberis mastitis, its pathogenesis and associated virulence factors are not clearly defined. The aim of this study was to identify virulence associated genes and their products that can be used to develop effective vaccine to control bovine S. uberis mastitis. S. uberis was co-cultured with primary bovine mammary epithelial cells (PBMEC) or infused into mammary gland of dairy cows. The messenger RNA (mRNA) from S. uberis associated with PBMEC after 2 h or 4 h of co-culture was purified and sequenced. Results showed that virulence-associated genes such as surface lipoprotein (slp), infection induced histidine kinase (iihK), infection induced response regulator (iirR) and extracellular sugar binding protein 1 and 2 (exsbP1 and exsbP2) were among the top-up-regulated genes. To verify this observation in vivo, quantitative real time PCR (qRT - PCR) was conducted on mRNA of S. uberis recovered from milk of infected mammary glands 24 h post infection. Results revealed that in vitro up-regulated virulence-associated genes were also significantly up regulated under in vivo conditions. The iihK and iirR are flanked by exsbP1 and exsbP2 genes and this entire operon seems to be involved in adaptation to glands micro-environment, survival and colonization of the bovine mammary glands. Based on immunogenic epitope prediction of proteins encoded by these up-regulated genes during early stages of host-bacterial interactions slp, exsbP1 and exsbP2 genes were selected, cloned and expressed in E. coli. The purified recombinant proteins (rSlP, rExsbP1 & rExsbP2) reacted strongly with convalescent serum from cows experimentally infected with S. uberis confirming that they are immunogenic. These proteins may serve as potential targets to develop an effective vaccine against S. uberis mastitis.