In 2012, chocolate bars from Belgium were rejected for import into the US after a Belgium laboratory reported the product as Salmonella positive. The product was destroyed. After an investigation, the Salmonella strain identified was the same strain found by the laboratory in fish meal. Cross contamination in the laboratory? That is what is believed. Unfortunately, a few years back, there were not the whole genomic sequencing tools readily available as we do today.
This puts a light on laboratories and the impact of poor practices can have on a company's product. Tight controls need to be in place to prevent cross contamination. Companies need to question results that seem unlikely. Today, further investigation can be completed using whole genome sequencing to rule out laboratory error, including excluding the laboratory's positive control sample.
Case report of Salmonella cross-contamination in a food laboratory
Geertrui Rasschaert1Email author, K. De Reu1, M. Heyndrickx1, 2 and L. Herman1
BMC Research Notes20169:156
© Rasschaert et al. 2016
Received: 10 September 2015
Accepted: 29 February 2016
Published: 10 March 2016
This paper describes a case of Salmonella cross-contamination in a food laboratory. In 2012, chocolate bars shipped from Belgium to the USA were prevented from entering the USA because a Salmonella Rissen strain had been isolated from one of the chocolate bars in a Belgian food laboratory. However, a retrospective study of the Salmonella isolates sent from the laboratory to the Belgian National Reference Laboratory for Salmonella revealed that 7 weeks prior, a Salmonella Rissen strain has been isolated from fish meal in the same food laboratory. The chocolate bars were not expected to be contaminated with Salmonella because the ingredients all tested negative during the production process. Furthermore, because Salmonella Rissen is only rarely isolated from food, it was hypothesized that the two Salmonella Rissen isolates belonged to the same strain and that the second isolation event in this laboratory was caused by cross-contamination. To confirm this hypothesis, both Salmonella Rissen isolates were fingerprinted using different molecular techniques. To evaluate the discriminatory power of the techniques used, 11 other Salmonella Rissen isolates from different origins were included in the comparison. Pulsed-field gel electrophoresis, repetitive element palindromic PCR and three random amplified polymorphic DNA PCR assays were used.
Repetitive element palindromic PCR and random amplified polymorphic DNA PCR assays were insufficiently discriminatory, whereas pulsed-field gel electrophoresis using the combination of two restriction enzymes showed sufficient discrimination to confirm the hypothesis.
Although cross-contamination in food laboratories are rarely reported, cross-contamination can always occur. Laboratories should therefore always be aware of the possibility of cross-contamination, especially when enrichment is used in the microbiological analysis. Furthermore, it is advised that results showing isolates of the same serotype isolated in a short time frame from unrelated food products should be interpreted carefully and should be confirmed with additional strain typing.
KeywordsSalmonella Cross-contamination Food laboratory