Sodium Dodecyl Sulfate-cured Nalidixic Acid Resistant 85-kb Plasmid Salmonella gallinarum Immunoglobulin G Response in Brown Layer Hens

Abstract

Aim: Fowl typhoid vaccination is a necessary complement to farm hygiene in reducing antimicrobial resistance caused by extensive prophylaxis of antibiotics in poultry. This study was undertaken to develop a vaccine candidate from a virulent strain by plasmid-curing. Place and Duration of Study: The research was carried out in the Department of Pharmaceutical Microbiology and Biotechnology, University of Nigeria Nsukka, for six months. Methodology: Thirty day-old pullets were divided into three groups of ten birds each. This comprised a negative control group (unvaccinated) (NEG), a live SG9R vaccine positive group (SG9R), and a nalidixic acid resistant plasmid-cured 85-kb plasmid Salmonella gallinarum (NAR). Plasmid curing of the virulent strain was done by incubating in sodium dodecyl sulfate (SDS) and loss of the 85-kb plasmid was identified and determined on agarose gel electrophoresis. Vaccination was done subcutaneously at 4 and 7 weeks of age, followed by challenge with the virulent S. gallinarum. IgG was measured using Enzyme-linked Immunosorbent Assay (ELISA). The scalability of the SDS-cured nalidixic acid resistant 85kb plasmid Salmonella gallinarum immunity was demonstrated by vaccinating layer birds and comparing the humoral immunity with that of a commercial fowl typhoid vaccine (SG9R). Results: There were higher IgG levels in the NAR group than the SG9R group. Protection was above 70 % in the vaccinated groups. Conclusion: The outcome of this present study shows that vaccination with viable cells of sodium dodecyl sulfate- cured nalidixic acid resistant 85-kb plasmid Salmonella gallinarum (NAR) provided layer birds with protective humoral immunity against subsequent challenge with the parent virulent strain containing the 85-kb plasmid.