title: Virulence of Streptococcus pneumoniae in mice: a standardized method for preparation and frozen storage of the experimental bacterial inoculum.
abstract: Animal models of pneumococcal infection are important to evaluate the protective capacity of new vaccine candidates. We have established a method to prepare and store the experimental inoculum without loss of virulence or number of bacteria. This allows a standardized inoculum from the same culture batch to be used in several experiments. Pneumococci were cultured to mid-logarithmic growth phase in Todd-Hewitt broth with 17% fetal calf serum. The bacterial broth was distributed into smaller volumes and immediately frozen on liquid nitrogen and stored at -70 degrees C. We have tested the virulence of five different pneumococcal serotypes in BALB/c, C57BL/6, and NIHS mice using inocula prepared by this method and stored without loss of virulence for up to 4 years. Serotypes 1, 4, 5 and 8 were highly virulent for the strains of mice tested whereas type 6B showed lower virulence and a peculiar, protracted course of infection. There were no clear differences in virulence between the different strains of mice with the exception of serotype 6B, which showed higher virulence in BALB/c and NIHS mice than in C57BL/6 mice.
authors.affiliation: Department of Vaccine, National Institute of Public Health, Oslo, Norway.
authors.forename: I S
authors.initials: IS
authors.lastname: Aaberge
authors.forename: J
authors.initials: J
authors.lastname: Eng
authors.forename: G
authors.initials: G
authors.lastname: Lermark
authors.forename: M
authors.initials: M
authors.lastname: Løvik
mesh_terms: D000818:Animals; D001431:Bacteriological Techniques; D015169:Colony Count, Microbial; D015925:Cryopreservation / Q000592:standards*; D003470:Culture Media; D006801:Humans; D007116:Immunization, Passive; D007928:Lethal Dose 50; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D011008:Pneumococcal Infections / Q000235:genetics* / Q000276:immunology / Q000382:microbiology; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D013997:Time Factors; D014611:Vaccination; D014774:Virulence
chemical_list: D003470:Culture Media