Jan-Ingmar Flock Project


Development and assessment of a vaccine against Streptococcus equi

Our research has for several years been to analyse surface structures on Gram positive bacteria and their potential use as vaccine candidates. In collaboration with a team in Uppsala, we have analysed a number of surface antigens from Streptococus equi and focussed on some antigens, which have potential roles in pathogenicity of S. equi. Several proteins from S. equi are involved in neutralization of the function of protective IgG. We have e.g. shown that EndoSe can hydrolyse glycosyl groups on IgG and thereby severely block the opsonic function of IgG directed against S. equi. We have also shown that antibodies against EndoSe can effectively neutralize this function.

Streptococcus equi gives rise to a severe infection in horses, called strangles (Sw. “kvarka”) affecting upper respiratory airways and the lymphatic system. It is one of the most feared and highly contagious infections in the horse due to the severe consequences of an outbreak; racing events are inhibited and riding schools, breeding units and trading of horses have to close. There is presently no safe and efficacious vaccine available against strangles. S. equi resembles Streptococcus pyogenes, which can cause tonsillitis, scarlet fever and necrotising fasciitis in humans, both by sequence similarity and mode of infection. Development of a vaccine against S. equi will give valuable experience also for a vaccine against S. pyogenes

Fig. 1. Temperature curves (A) and post mortem (PM) scoring (B) of horses subjected to experimental infection with S. equi. Horses (n=16) (squares) were vaccinated via intranasal and subcutaneous routes with Strangvac. Control horses (n=16) (circles) were given placebo, containing adjuvant only. Normal rectal temperature of a horse is 38-38.3°C (p<10-5 (t-test) on day 10). PM scoring is based on observations such as abscessation of submandibular lymph nodes (p<10-5 (Mann Whitney)). Only one of sixteen vaccinated horses became pyrexic, (the one with the highest PM score) whereas all in the placebo group became pyrexic.

Based on the research till today, a vaccine against strangles in the horse has now been developed. The vaccine (Strangvac) is based on eight recombinant proteins, fused into three proteins to bring down production costs. The proteins were chosen largely based on efficacy studies in a mouse model of strangles. The three fusion proteins have been produced in large scale to demonstrate scalability and feasibility of using recombinant proteins as vaccine components, as opposed to conventional strategy with killed or attenuated live strains. The process is now being transferred to GMP (Good Manufacturing Practice) facilities, required for commercialisation. The vaccine has been used in clinical tests for efficacy in horses challenged with experimental infection. We have so far seen that immunizations via combined intra nasal and subcutaneous routes give an excellent level of protection with an onset of immunity of only two weeks, based on clinical observations and post mortem analysis (Fig. 1) in the target animal (Fig. 2).

However, traditionally, most equine vaccines are given intramuscularly (i.m.) since it is simpler and more user friendly than other routes in the horse. Current research therefore addresses the mucosal immune response obtained after i.m. immunization. Recent results indicate that protective mucosal antibodies protecting against infection can indeed be obtained also after i.m. vaccination. Our studies will lead to a better understanding of the nature of protecting antibodies after Strangvac vaccination. We are e.g. studying duration of protective antibodies, the effect of repetitive immunizations over long term, correlation between protection and antibody levels in mucosa and sera. The investigations will generate data required for central registration of Strangvac at European Medicinal Agency, EMA.

We have also developed a novel murine model of Staphylococcus aureus wound infection. Necrotization of muscle tissue with snake venom (Bothrops asper) simplifies infection with S. aureus; less than 50 CFU gives rise to infection compared with 107 CFU without necrotization. The model mimics an infection in traumatized or burn-damaged tissue. Three proteins in combination from S. aureus were used for vaccination. This led to significant protection against wound infection with S. aureus.


Strangvac: A recombinant fusion protein vaccine that protects against strangles, caused by Streptococcus equi.
Robinson C, Frykberg L, Flock M, Guss B, Waller A, Flock J
Vaccine 2018 03;36(11):1484-1490

Protective immunization against Staphylococcus aureus infection in a novel experimental wound model in mice.
Schennings T, Farnebo F, Szekely L, Flock J
APMIS 2012 Oct;120(10):786-93

Antiphagocytic function of an IgG glycosyl hydrolase from Streptococcus equi subsp. equi and its use as a vaccine component.
Flock M, Frykberg L, Sköld M, Guss B, Flock J
Infect. Immun. 2012 Aug;80(8):2914-9

Extracellular adherence protein (Eap) from Staphylococcus aureus does not function as a superantigen.
Haggar A, Flock J, Norrby-Teglund A
Clin. Microbiol. Infect. 2010 Aug;16(8):1155-8

Levels of antibody against 11 Staphylococcus aureus antigens in a healthy population.
Colque-Navarro P, Jacobsson G, Andersson R, Flock J, Möllby R
Clin. Vaccine Immunol. 2010 Jul;17(7):1117-23

Ovine clone ST1464: a predominant genotype of Staphylococcus aureus subsp. anaerobius isolated from sheep in Sudan.
Elbir H, Feil E, Drancourt M, Roux V, El Sanousi S, Eshag M, et al
J Infect Dev Ctries 2010 May;4(4):235-8

Extracellular adherence protein (Eap) from Staphylococcus aureus does not function as a superantigen.
Haggar A, Flock J, Norrby-Teglund A
Clin. Microbiol. Infect. 2010 Aug;16(8):1155-8

Getting to grips with strangles: an effective multi-component recombinant vaccine for the protection of horses from Streptococcus equi infection.
Guss B, Flock M, Frykberg L, Waller A, Robinson C, Smith K, et al
PLoS Pathog. 2009 Sep;5(9):e1000584

Two novel IgG endopeptidases of Streptococcus equi.
Hulting G, Flock M, Frykberg L, Lannergård J, Flock J, Guss B
FEMS Microbiol. Lett. 2009 Sep;298(1):44-50

Staphylococcus epidermidis isolated from newborn infants express pilus-like structures and are inhibited by the cathelicidin-derived antimicrobial peptide LL37.
Nelson A, Hultenby K, Hell E, Riedel H, Brismar H, Flock J, et al
Pediatr. Res. 2009 Aug;66(2):174-8

Further publications

publications 1998-2008 (pdf)



Professor, senior

Jan-Ingmar Flock

Organizational unit: Birgitta Henriques Normark group
E-mail: Jan-Ingmar.Flock@ki.se