Elevated temperature technique for the isolation of salmonellas from sewage and human faeces

Summary

Modified Moore's swabs, placed in sewers for 5 days, were used to concentrate salmonellas from sewage. Duplicate cultures of swab strips in selenite broth were incubated at 41 and 37°C. respectively. Salmonella organisms were recovered consistently from the swabs when the enrichment broths were incubated at 41°C., However, when equal portions of the same swabs were incubated at 37°C., only 22% of them yielded Salmonella organisms. These results indicate an advantage in incubating the selenite broths at 41°C. rather than 37°C. in attempting to isolate salmonellas from sewage.

One hundred and fifty faecal samples were examined for salmonellas by culture in selenite broths incubated at 41 and 37°C. Twelve (8%) samples were positive at 41°C. compared to only 10 (6·7%) positive samples at 37°C. This difference is not statistically significant to indicate an advantage of the elevated-temperature of incubation over the conventional temperature in attempting to isolate salmonellas from human faeces. Moreover, results of the recovery rates of S. paratyphi B, S. typhi, and S. typhimurium indicate that an incubation temperature of 37°C. is more appropriate for recovering salmonellas from artificially infected faecal samples than an incubation temperature of 41°C. This stresses the inability of laboratory studies to mimic conditions in nature.