This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pneumococci, Subject name: Microbiology
In vitro test for virulence of pneumococcus: 
Select and explain. 
A. Intra peritoneal inoculation in mice, B. Rat tail inoculation, C. Mouse foot pad inoculation, D. Armadillo inoculation
A: Intra peritoneal inoculation in mice
Answer: A: Intra peritoneal inoculation in mice 
Explanation: Ans: a (Intra peritoneal inoculation in mice) RefAnanthanarayan, ed, p. 220When pneumococci are scanty with negative cultures, isolation can be done by intra peritoneal inoculation in mice for virulent strains. Inoculated mice will die within 1 -3 days and pneumococci may be isolated from peritoneal fluid or heart blood. This will be negative with avirulent strains e.g., type 14.Other tests employed are:1) Gram stain - gram positive, lanceolate diplococcic2) Sputum culture in blood agar3) Blood culture - isolation from blood indicates bad prognosis4) CSF - Gram staining and cultureDemonstration of SSS by precipitation5) Capsular polysaccharide - Quellung reaction, counter immune electrophoresis