Development of a 24 h screen to detect viable salmonellas in faeces.
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.
Cherrington
C A
CA
Department of the Science of Food of Animal Origin, Faculty of Veterinary Medicine, University of Utrecht, The Netherlands.
Huis in't Veld
J H
JH
D000818:Animals; D003470:Culture Media; D004797:Enzyme-Linked Immunosorbent Assay; D005189:False Positive Reactions; D005243:Feces / Q000382:microbiology*; D012475:Salmonella / Q000254:growth & development / Q000302:isolation & purification*; D012680:Sensitivity and Specificity; D013552:Swine / Q000382:microbiology*
D003470:Culture Media