The search for a bacteriological infection sometimes seems to be looking for a needle in the haystack. Fortunately, techniques have now been developed to make it easier for you to find this pin. One of these techniques is 'DNA profiling', which is increasingly being used in microbiology. What this is and how you can use it is explained below.
Cause analysis
If the standard is exceeded, the quality system requires a cause analysis and, of course, you want to know for yourself how contamination can be prevented in the future. But where do you start searching and when do you know for sure that you have the right source? And how can you prevent the entire haystack from having to fumigate? Starting at the right point will save you a lot of time (and money).
DNA profile
Take Listeria monocytogenes. Not every Listeria monocytogenes strain is the same (compare it to people, they differ from each other). These differences are recorded in the DNA sequence of each strain. By comparing the DNA sequences of two strains, it can be deduced how closely related they are to each other. If it concerns offspring of, for example, a bacterium that has managed to settle in a production area, one can find out in this way whether new isolates originate from this bacterium. In this way, it can also be determined, for example, whether a Listeriathat has been isolated from a patient with Listeriosis originates from the same source as another Listeria isolate, which has been isolated from contaminated food, for example. The opposite is of course also possible; you can also exclude that a pathogen is the same as an isolate found on a product.
It may be interesting for producers to find out whether bacteriën found in the plant have always come from the same source or whether they have ended up in the plant in different ways. It also makes it possible to establish a link between the source of contamination, such as a raw material, and the bacterium found in an end product.
On this basis, more targeted measures can be taken.
Techniques
A relatively inexpensive way to compare isolates is the MLVA/MLST technique, in which, after multiplication by PCR, the DNA is strictly analyzed and compared with reference DNA from a public database. This results in a percentage similarity. In order to be able to use this technique, the type of bacterium/strain must be known before this DNA analysis can be carried out.
Nowadays, however, it is increasingly decided to determine the sequence of the entire genome of a bacterium; "Whole Genome Sequence (WGS)". This can then be compared with the genome sequence of other strains for which it has been determined so that, for example, in a crisis situation it becomes clear whether there is a connection or not.
Storage of isolates
Usually laboratories keep the stems of positive samples, but of course it is good to ask your lab what service they offer for this. If you would like to know more about DNA techniques, comparing strains or troubleshooting in case of calamities, you can also contact the experts of Eurofins Food Safety Solutions.
Call us on +31 (0)88 8310330 or send us an e-mail, foodsafetysolutions@ftbnl.eurofins.com