Development of a 24 h screen to detect viable salmonellas in faeces

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 degrees 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 10(3) salmonellas per ml in the presence of up to 10(7) 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 micrograms 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.

Alternative antigens reduce cross‐reactions in an ELISA for the detection of Salmonella enteritidis in poultry

“…The classical salmonella monitoring system, i.e. bacteriological sampling of the faeces, is known to be fallible as none of the methods of enrichment and selection can detect all salmonellas of public health significance (Tate et al 1990;Cherrington and Huis in 't Veld 1993). Furthermore, excretion of the organism in the faeces is intermittent (Williams 1972).…”