TETRATHIONATE AND SELENITE ENRICHMENT BROTHS FOR THE ISOLATION

SUMMARY An artificial test system was used to determine the capability of several enrichment media for isolation of arizonae that are present in small numbers (2-15/ml) with substantial numbers of competitors. Ten isolates each of serotypes 7:1,7,8 and 7:1,2,6 as well as single isolates of ten other serotypes were tested in media incubated at both 37 and 43 C and subcultured after 24 and 48 hr. The enrichment broths tested were tetrathionate, tetrathionate brilliant-green, selenite brilliant-green sulfapyridine, selenite cystine, selenite F, and selenite F with 1% sodium selenite. Under the conditions of the test system the tetrathionates performed well at both incubation periods and temperatures. The selenites were variable in effectiveness, and results were sometimes markedly influenced by time and temperature of incubation; several isolates grew very poorly or not at all in some of the selenite broths. Also determined were pure-culture growth curves of a representative isolate of Arizona 7:1,7,8 in the several enrichments.