Evaluation of Streptococcus uberis surface proteins as vaccine antigens to control S. uberis mastitis in dairy cows

Authors: KERRO DEGO, OUDESSA - University Of Tennessee; ALMEIDA, RAUL - University Of Tennessee; IVEY, SUSAN - University Of Tennessee; Agga, Getahun

Submitted to: Vaccines
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2021
Publication Date: 8/5/2021
Citation: Kerro Dego, O., Almeida, R.A., Ivey, S., Agga, G.E. 2021. Evaluation of Streptococcus uberis surface proteins as vaccine antigens to control S. uberis mastitis in dairy cows. Vaccines. 9(8). Article 868. https://doi.org/10.3390/vaccines9080868.
DOI: https://doi.org/10.3390/vaccines9080868

Interpretive Summary: Streptococcus uberis is a gram-positive environmental bacterium. It is a frequent cause of mammary infections that leads to a disease called mastitis in dairy cows. Mastitis caused by Streptococcus uberis can be manifested clinically with obvious swelling of the udder. However, it also causes not easy to identify infections called subclinical infections. Cows with clinical infections can be treated with antibiotics and get cured. The subclinical infections are difficult to identify and affect milk production and quality. The quality of bulk tank milk produced by a dairy farm is tested by counting the number of indicator cells for infections of the udder. Bulk tank milk is discarded if it fails the test, resulting in milk loss and economic loss to the producers. Control measures are required to overcome the impact of antibiotic resistance, to control subclinical infections, to improve animal welfare, to increase milk production and quality, as well as for sustainable and profitable dairy cattle production. Vaccination is one of the most important interventions. However, developing a safe and effective vaccine for the control and prevention of mastitis in dairy cattle has been a challenge. In this study, we developed a method of developing Streptococcus uberis. We then inoculated groups of cows with varying doses of the vaccine, in addition to a control group receiving no vaccine, to optimize the dose and examine the immune response. Finally, we experimentally challenged the cows with the vaccine strain of the bacteria to examine its effectiveness in preventing infection. We found that the Streptococcus uberis vaccine contains multiple proteins. Cows vaccinated with medium and high dose of the vaccine produced higher immune responses to the vaccine compared to the low dose vaccine and the unvaccinated control. After experimental infection, indicator cells for mammary infection increased in the first 48 hours in all groups, thereafter, declining in the vaccinated cows. The bacterial number in the milk of vaccinated cows was lower than the control group. Taken together, this study succeeded in developing Streptococcus uberis vaccine, and that at least 1 mg of the vaccine is required for effectiveness. Field study is required to further ascertain the effectiveness of the optimized vaccine in preventing mastitis caused by Streptococcus uberis in dairy cows.

Technical Abstract: There is no effective vaccine against Streptococcus uberis mastitis in dairy cows. Objectives of this study were (1) to extract S. uberis surface proteins (SUSP) and determine immunoreactivity in vitro and (2) immunogenicity and efficacy in vivo. SUSP was extracted from S. uberis, and their immunoreactivity was tested by western blot. In total, 26 Jersey dairy cows were randomly divided into four groups. Groups 1, 2, and 3 were vaccinated subcutaneously with 4 mg, 1 mg, and 100 µg of SUSP, respectively, with Freund’s incomplete adjuvant. Group 4 (control) was injected with placebo. S. uberis UT888 was infused into two contralateral quarters of each cow during early lactation. Somatic cell count (SCC), bacteria count in milk, and mastitis were monitored. Our results show that SUSP contains multiple protein bands, that ranged from 10 to 100 kDa. All vaccinates showed an increased anti-SUSP IgG antibody. The SCC of all experimentally infected quarters increased after challenge but slightly decreased after day 3 with no significant difference among groups. Milk bacterial count was significantly (p < 0.05) reduced in high and medium doses vaccinated groups than low and control groups. In conclusion, SUSP vaccine is immunogenic and showed a promising efficacy to control bovine S. uberis mastitis.