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Microbial contamination

A fresh look at microbial contamination

By Phil Voysey - 24 November 2016

One of my early experiences as a food microbiologist was a visit I paid to a bread bakery that was having problems with a salmon-pink-coloured mould growing on their product. While the pink mould was very distinctive on the bread, the company was unable to identify the source of the problem in the bakery. I took a look around the production area and quickly spotted the source of the mould - the normally cream-coloured slicer comb had taken on a pink-coloured tint. Because the 'pink transition' had been slow, no-one had noticed the colour change. Analysis of the mould samples back in our labs identified Chrysonilia sitophila as the culprit. We gave advice on how best to clean the slicer comb and the problem was resolved.

Helpful advice

Many of the microbiology enquiries we receive that relate to manufacturing on-site issues are similar to this example, in that it's difficult or impossible to resolve the problem via email or over the phone. In some cases the enquirer doesn't know what information is important for us microbiologists to best help them. It can often save a lot of time and expense if a microbiologist can pay your factory a visit.

Factory visits don't have to be just about troubleshooting or problem solving per se. Sometimes all that is needed is for an experienced pair of eyes to take a fresh look at the factory and make comments and suggestions. Often a tour around a facility and chat about what is going on can easily lead to confirmation of a client's suspicions, and/or give weight to press for improvements on site.

On-site essentials

Sometimes microbiological contamination issues do occur in products. In these cases a visit to the production facility can be essential to best advise on what to do. For example, we got called in to assist when the food poisoning organism Listeria monocytogenes was isolated from a facility producing sandwiches. Time spent with the client observing processes and carrying out a programme of swabbing of the factory environment revealed that utensils coming into contact with the sandwich fillings were in turn indirectly coming into contact with cleaning equipment which was transferring contamination. Molecular identification of the strains of Listeria monocytogenes (and other species of Listeria), isolated from the factory environment as well as those isolated from the product, revealed a highly contaminated drain as the source. The drain was replaced, and this solved the problem.

On-site visits can also help if one of your product’s shelf life has markedly reduced recently. Many factors can potentially reduce shelf life, such as:



Often all that is required to solve an issue is a fresh, but experienced pair of eyes - knowing what to look for and where. The chances are that we have helped another food manufacturing site with a similar problem.

For further information or to arrange a factory visit please contact:


Phil Voysey: +44 (0)1386 842069 Phil.Voysey@campdenbri.co.uk