STREPTOCOCCUS-PYOGENES INFECTION IN MICE

We inoculated 5 to 7-week-old female C3HeB/FeJ mice with Streptococcus pyogenes strain B514-Sm (type M50) by both an intranasal and intratra cheal route and characterized the resulting illness. Following intrana sal inoculation, the animals developed signs of illness within 1 to 8 days post-inoculation which correlated with acute, suppurative, bronch opneumonia during histopathologic analysis; however, the relationship of response to dose was non-linear, as seen previously in a small grou p of mice.(1) Intratracheal inoculations were then performed to increa se the quantitative reliability of the model. Following intratracheal inoculation, the animals succumbed to an illness that was indistinguis hable from that seen after intranasal inoculation, and the incidence o f pneumonia followed a steep dose response curve. The dose at which 50 % of the animals exhibited signs of respiratory illness within 72 h wa s 1.0 x 10(7) colony forming units. All of the animals that appeared i ll had lung lesions as determined by gross and histopathologic examina tion. Bacteraemia followed pneumonia in two-thirds of the intratrachea lly inoculated animals, indicating that the S. pyogenes had crossed ti ssue barriers. We hope that this model will be useful in future studie s concerning the role of suspected streptococcal virulence factors in the later stages of pathogenesis of invasive S. pyogenes infection. (C ) 1996 Academic Press Limited