Bordin, Angela Ilha (2014-05). Immunogenicity and Effects on Fecal Microbiome of an Electron-Beam Inactivated Rhodococcus equi Vaccine in Neonatal Foals. Doctoral Dissertation. | Thesis individual record

Rhodococcus equi is a bacterium commonly isolated from soil that primarily
causes pneumonia in foals and immunocompromised adult horses. Many vaccines were
designed and tested to protect foals from developing pneumonia; however, to date, there
is no vaccine that will protect foals from intrabronchial challenge with R. equi, except
live, virulent R. equi. To evaluate electron-beam (e-beam) irradiation as a method of
inactivation of R. equi, 2 concentrations (Concentration 1, 1 x 10^(8) colony-forming
units/ml [CFU/ml] or Concentration 2, 1 x 10^(9) CFU/ml) of R. equi were submitted to a
range of e-beam radiation doses, ranging from 0 to 7 kGy. All microorganisms of
Concentrations 1 and 2 were adequately inactivated by 4 and 5 kGy, respectively, and
the bacterial cell wall remained intact, whereas heat-inactivated samples indicated a
compromised cell wall. Both concentrations were tested for immunogenicity and effects
on fecal microbiome in neonatal foals. Mucosal and serum antibody responses were
studied, as well as cell-mediated immune responses. Enteral administration of e-beam
inactivated R. equi increased IFN-? production and generated naso-pharyngeal
R. equi-specific IgA in newborn foals. The inactivated vaccine appeared safe and
immunogenic in neonatal foals in the presence of maternal antibody. No impact of
treatment on fecal microbiome composition or diversity was observed among vaccinated
foals; however, marked and significant differences in microbial communities and
diversity were observed between foals at 32 days of age relative to 2 days of age
regardless of treatment.

In conclusion, electron-beam irradiation is an appropriate method for inactivation
of R. equi, and e-beam irradiated R. equi vaccine is immunogenic in neonatal foals. Also,
age-related changes in immune responses and the fecal microbial population occurred in
healthy foals vaccinated enterally with e-beam inactivated R. equi. Mucosal vaccination
does not result in major changes of the fecal microbiome in foals.

etd chair
publication date