Studies on Strangles. II — The “ in vitro” behaviour of induced penicillin-resistant strains of STREPTOCOCCUS EQUI

Abstract

In this additional paper, the Author has obtained induced resistant strains of Streptococcus equi through serial transfers in penicillin-added broth. These resistant strains exhibited morphological and cultural alterations, having lost their hemolytic power and virulence for mice. After 55 transfers, the degree of resistance attained a minimum of 9.2 times and a maximum of 100.0 times, comparatively with the sensible parents. The resistant strains were then sub-cultivated in penicillin free broth and all of them have re-acquired their original properties, including the virulence for mice and the sensitivity to penicillin. Considering the hypothesis that these phenomena could be established “ in vivo” , during a survey of strangles, it is suggested that the occurrence of penicillin-resistant variants of St. equi would not have any epidemiological significance because they would not be able to produce the disease. Even considering that these strains could be disseminated by contagium they would not represent any problem because the resistant phase is transitory and reversible.