The effect of penicillin on bacterial interference in vivo.

The study was designed to analyse the effect of penicillin on interference between alfa-streptococci and group A streptococci in vivo. Tissue cages were implanted subcutaneously in 9 rabbits and inoculated with 10(5) cfu of alfa- and beta-streptococci together as well as separately. Both streptococci were recovered 96 h after the inoculation in the untreated rabbits. Alfa-streptococci inhibiting the growth of beta-streptococci in vitro retained this capacity under the experimental in vivo conditions. Higher penicillin concentration did not increase the killing rate of beta-streptococci grown separately while a faster killing was observed with low penicillin levels in the presence of inhibiting alfa-streptococci, indicating synergistic effect.