ICMSF methods studies. IX. The influence of selective enrichment broths, differential planting media, and incubation temperatues on the detection of Salmonella in dried foods and feed ingredients.

Ninety-eight dried foods and feed ingredients were analyzed for Salmonella using tetrathionate brilliant green (T) and selenite cystine (S) broths incubated at 35 and 43 degrees C. The four enrichment cultures for each sample were subcultured in duplicate onto brilliant green (BG) , Salmonella--Shigella (SS), and bismuth sulfite (BS) agars, one plate of each being incubated at 35 degrees C, the other at 43 degrees C. Salmonellae were isolated from 44 of the 98 samples. Differences in the Salmonella recovery rates from the four selective enrichment conditions were not significant. However, there was a trend toward a higher proportion of Salmonella colonies on the selective media when the enrichment broths were incubated at 43 degrees C, although the differences were significantly only with BG and SS subcultured from T. While the four enrichment systems were not significantly different, the trend toward a higher proportion of Salmonella colonies on the differential media subcultured from 43 degrees C enrichment broths indicates an advantage to incubation at the elevated temperature. Incubation of selective agars at 35 degrees C was best because at 43 degrees C Salmonella recovery was significantly reduced. Detection of salmonellae on BS was significantly better than on BG or SS.