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).