Effect of type of enrichment and duration of incubation on salmonella recovery from meat-and-bone meal

Abstract

Twenty-five meat-and-bone meal samples were enriched with either selenite-cystine or tetrathionate and incubated for 1 and 2 days. Seven were previously found to be positive; of the other 18, 16 were positive for salmonella. The number of somatic serogroups per sample ranged from 1 to 11 with a mean of 3.8. Significantly more (P < 0.01) group C(1) salmonellae were isolated using tetrathionate than selenite, whereas significantly more of groups G, 35, and Difco poly-valent D were isolated from selenite than tetrathionate. Seventy-six percent of the presumptive colonies from Brilliant Green agar showed a positive lysine decarboxylase reaction, and there were no differences between media or times of incubation. Ninety-four per cent of the lysine decarboxylase-positive cultures showed a positive somatic antiserum response; again there were no differences between times or enrichments although there were significantly more total positive serogroups at 2 days than at 1 day from tetrathionate but not from selenite. There were indications that certain serogroups preferred either one or the other enrichment. There were no differences in total positive samples with the two enrichments although neither alone was sufficient to identify all positives. Several lactose-positive salmonellae were recovered.