Development of a 24 h screen to detect viable salmonellas in faeces |
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Authors: | Christina A Cherrington JHJ Huis in't Veld |
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Institution: | Department of the Science of Food of Animal Origin, Faculty of Veterinary Medicine, University of Utrecht, Utrecht, The Netherlands |
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Abstract: | A 24 h screen to detect viable salmonellas in faeces was developed by studying growth dynamics of salmonellas and competing flora in combinations of enrichment media and artificially-inoculated pig faeces. Muller-Kauffmann tetrathionate (MK) broth, incubated overnight at 42°C, maintained the lowest ratio of salmonella: competing flora and identified all inoculated samples. A 4 h postenrichment in M broth plus novobiocin reduced the number of false-positive results in subsequent ELISAs. Adjusting the negative cut-off values and incubation time of the chromogenic substrate from that recommended in the ELISA instructions reduced the rate of false-positive results further and allowed the detection of 103 salmonellas per ml in the presence of up to 107 ml?1 aerobic-competing cells. Suspension of faeces diluted 1 in 2 and 1 in 5, rather than 1 in 10 in MK broth did not necessitate further adjustments to the ELISA baseline values. The proposed screen protocol is an overnight incubation of faeces suspended 1 in 10 in MK broth, a 1 in 100 subculture into M broth plus 10 μg ml?1 novobiocin (MbN) for 4 h, steam inactivation of MbN cultures and testing by ELISA, and can detect three salmonella cells per g faeces. |
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