Effect of hyperbaric oxygen and penicillin in a murine model of streptococcal myositis

We investigated the effect of hyperbaric oxygen (HBO2) and penicillin therapy in a murine model of group A streptococcal myositis. The thighs of mice were inoculated with Streptococcus pyogenes. Four groups were evaluated: 1) control (n = 13), 2) HBO2 treatment (n = 15), 3) penicillin treatment (n = 12), and 4) penicillin and HBO2 treatment (n = 13). Histologic methods were utilized to prove the existence of myositis and histologic changes in tissues following experimental intramuscular inoculation of mice with Streptococcus pyogenes. Mortality (day of death) and the number of colony forming units (cfu) were measured. Microscopic sections of the left thighs revealed extensive necrosis of muscle with acute inflammatory infiltrate in all groups. Penicillin significantly lowered cfu count in comparison to the control (P < 0.01). Cfu's in group 4 were significantly lower than in group 3 (P < 0.01). Survival was significantly longer in the penicillin group compared to the control (P < 0.01). Survival in the combined treatment group was significantly longer than penicillin alone (P < 0.01). These results suggest that 1) HBO2 treatment alone does not decrease mortality significantly in vivo, 2) penicillin therapy alone improves outcome significantly, and 3) the combined treatment of penicillin and HBO2 exerts synergistic effects in both decreasing bacterial counts in vivo and increasing survival in this model.