Studies on Strangles. I — Research on naturally antibitiotic-resistant

Abstract

The Author investigated the occurrence of naturally antibiotic- resistant strains of Streptococcus equi. A lot of 31 strains was isolated from nostrils or suppured lymph glands of race horses, along a survey of strangles in Jockey Club Paulistano — São Paulo — Brasil. Between them, there were 31 animals with active strangles, 93 clinically healed and 101 healthy adult horses. All strains identified as Streptococcus equi were tested by the disc-plate method against penicillin, streptomycin, aureomycin, terramycin and chloromycetin in variable concentrations of the antibiotics. Seven out of all showed resistance against 0,5 unit of penicillin and two others against 1 meg of streptomycin. Repeating the test, now by the dilution test tube method, the same strains did not confirm those fastness properties. The results suggest two possibilities:
a) the disc-plate method was not so accured as the dilution test tube method;
b) the strains were really resistant when recently isolated but along subcultures they have lost their drug-fastness. As a matter of fact, this condition was confirmed in another investigation, when resistant strains were obtained by successive transfers in broth with penicillin.
The actual data suggest that naturally antibiotic-resistant strains of Streptococcus equi do not occur, exception not so clear being made for some strains in relation to penicillin.