Insights from 30 years of Salmonella proficiency testing
Case study: investigation of unsatisfactory performance
PT schemes occasionally include low-CFU samples and atypical strains, to challenge detection workflows under realistic conditions, as required by ISO 17043. These challenges can reveal weaknesses that may not be apparent in routine testing, and performance occasionally falls below expected levels. In the oatmeal matrix round MC 267 (July 2018), for example, only 86% of participants reported the correct result.
Round MC 267 – Food Microbiology QMS scheme: sample 06F report, analyte Salmonella species
Comments
Lab ID Method
Results
MC6838 Other
Not Detected
The sample contained Salmonella Bredeney at an approximate inoculum level of 10 CFU/g. The assigned value is therefore Salmonella species ‘detected’. This strain of Salmonella Bredeney is atypical of the genus on selective media and in confirmatory tests. It is H 2 S variable, lactose positive and shows poor growth in Simmons' citrate agar. The organism is typically motile and urease negative. It is a group B Salmonella according to the Kauffmann-White Scheme, with a full serological profile of ‘O’ antigen: 1, 4, 12, 27; ‘H’ phase 1 antigen: l, v and ‘H’ phase 2 antigen: 1, 7. Primary sources of Salmonellae are the gastrointestinal tract of animals; the organism can be transmitted via faeces into soil, water, feeds, foods and other animals, including humans.
MC6838 Broth 37/agar 37 (Various)
Not Detected
MC6954 Other
Detected
MC7139 PCR
Detected
MC7173 VIDAS
Detected
MC7213 Other
Detected
MC7233 PCR Detected MC7251 MKTT/RV + XLD + BGA 37 Detected MC7281 MKTT/RV + XLD + BGA 37 Detected MC7321 VIDAS Detected MC7415 MKTT/RV + XLD + BGA 37 Not Detected MC7458 Broth 37/agar 37 (Various) Detected MC7679 MKTT/RV + XLD + BGA 37 Detected MC7727 MKTT/RV + XLD + BGA 37 Detected MC7799 Other Detected MC7800 Other Detected MC7801 Other Detected MC7853 PCR Detected MC7926 Other Detected MC8152 MKTT/RV + XLD + BGA 37 Not Detected MC8174 VIDAS Detected MC8231 Other Detected MC9081 PCR Detected MC9208 PCR Detected MC9282 Chromogenic agar Not Detected MC9419 MKTT/RV + XLD + BGA 37 Detected MC9427 PCR Detected MC9474 Other Detected MC9502 PCR Detected MC9528 MKTT/RV + XLD + BGA 37 Not Detected
Methodology Summary
Method
% Satisfactory
77%
MKTT/RV + XLD + BGA 37
Broth 37/agar 37 (Various)
86%
VIDAS
94%
Rapid test (Various)
100%
Chromogenic agar
88%
PCR
100%
ELISA
100%
Other
90%
Data Statistics
Round
Detected
Assigned Value
Number of Results
154
Satisfactory
86%
8
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