Application of median lethal concentration (LC50) of pathogenic microorganisms and their antigens in vaccine development

Abstract Objective Lack of ideal mathematical models to qualify and quantify both pathogenicity, and virulence is a dreadful setback in development of new antimicrobials and vaccines against resistance pathogenic microorganisms. Hence, the modified arithmetical formula of Reed and Muench has been integrated with other formulas and used to determine bacterial colony forming unit/viral concentration, virulence and immunogenicity. Results Microorganisms’ antigens tested are Staphylococcus aureus, Streptococcus pneumoniae , Pseudomonas aeruginosa in mice and rat, Edwardsiella ictaluri , Aeromonas hydrophila , Aeromonas veronii in fish, New Castle Disease virus in chicken, Sheep Pox virus, Foot-and-Mouth Disease virus and Hepatitis A virus in vitro, respectively. The LC 50 s for the pathogens using different routes of administrations are 1.93 × 10 3 (sheep poxvirus) and 1.75 × 10 10 for Staphylococcus aureus (ATCC29213) in rat, respectively. Titer index (TI) equals N log 10 LC 50 and provides protection against lethal dose in graded fashion which translates to protection index. N is the number of vaccine dose that could neutralize the LC 50 . Hence, parasite inoculum of 10 3 to 10 11 may be used as basis for determination of LC 50 and median bacterial concentrations (BC 50 ).Pathogenic dose for immune stimulation should be sought at concentration about LC 10 .