Beyond species analysis detection testing.

Beyond species analysis

When carrying out food micro testing there are a whole host of testing options. Broadly speaking, these can be classified into two different types - enumeration testing and detection testing. Here, ALS outline the latter.

DETECTION

Where the presence or absence of a specific organism is needed, detection testing is used as it has the lowest limit of detection (LOD), often providing a LOD of 1cfu/25g.

Detection testing is used to show absence of notorious pathogens such as E.coli O157 or Listeria species. The vast majority of these tests thankfully return “not detected” results, demonstrating absence of the target pathogen in the product tested and giving both the producer and the consumer reassurance in a product’s safety. Occasionally however, positive results are obtained and sometimes these pathogen detections occur in groups.

The ability to make or rule out a link between these detections is key in discerning the root cause of an issue and therefore, addressing the problem. When such an event transpires, it is typically required that as part of the investigative process further analysis of several isolates be carried out. In the case of ALS, this analysis was previously subcontracted to a laboratory capable of carrying out advanced testing such as, Multilocus Sequence Typing (MLST), Ribotyping or even Whole Genome Sequencing (WGS

FOOD SAFETY CONSIDERATIONS

There are several times in the not too distant past where beyond species analysis has had a huge impact on food safety, such as in the outbreak of Listeria monocytogenes infections associated with hospital-provided pre-prepared sandwiches in 2019. In this outbreak the Listeria monocytogenes isolates from each case of Listeriosis were linked together using WGS and the outbreak strain was subsequently linked back to a chicken sandwich product. This enabled an effective root cause analysis of the outbreak to be carried out and ultimately, to put corrective actions into place to reduce the likelihood of such an event occurring in the future.

Whilst the techniques used in the above incident were well established and recognised methods, they also incur significant costs and have lengthy turnaround times. The high cost of this analysis in some cases is prohibitive to actually carrying the analysis out and the long turnaround times often means that the important information obtained from this type of analysis loses its meaning and value as more time elapses. As such, faster alternatives to these techniques have been sought after to provide good results in a meaningful timeframe. This can in turn assist with investigative procedures and ultimately, contribute to improving food safety standards.

MALDI-TOF MS

MALDI-TOF MS is a type of mass spectrometry typically used in food microbiology to confirm the identity of presumptive pathogens. In this analysis samples are analysed individually and a spectrum is produced for each sample, like the one pictured to the right. Just like a fingerprint, each spectrum produced is unique to a bacterial species and so the spectrum produced can be compared to those in a database and an identification can then be made. Below is an example of a MALDI-TOF MS spectrum.

MALDI-TOF MS can however, also be used to get some resolution beyond species. This is achieved by carrying out a full biochemical extraction on a bacterial sample, producing a series of high-quality

BACKGROUND

ALS Laboratories (UK) Ltd (www. als-testing.co.uk) is one of the UK’s leading providers of food and drink testing services. With six accredited laboratories located across the country, they offer a comprehensive range of high quality, analytical testing services, including microbiological, nutritional, vitamins and minerals, pesticides and contaminants, allergens and speciation. They also provide clients with a wide range of consultancy services and technical support on food safety, labelling requirements, allergens management and sensory testing.