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MICROBIOLOGICAL GROWTH AND SPOILAGE

By David Robbins

Tops popping off bottles, discolouration or turbidity of liquid products, filter blockages, gauge errors, self-heating of stored produce and unaccounted for pipe or tank perforations: these are just some of the effects of microbes when suitable conditions arise for them to grow and multiply. These undesirable effects are besides any potential health risks that can occur if pathogenic organisms also become established and people become exposed to them. When problems arise at a factory, or in an end product, the response may be significant, resulting in substantial loss associated with scrapping the product, recall campaigns, or even costly changes in production equipment. The cause of the problem might, however, not be accurately diagnosed or be attributed to other factors and the microscopic culprits never identified.

Bacteria, moulds and yeasts are ubiquitous in the environment and it is perhaps surprising that more problems do not occur given the ease with which they can grow. That micro-organisms do not cause more problems is due to the widespread use of preservative systems that prevent their growth and to the implementation of production methods that minimise the contamination of end products. The control measures can range from simple air-drying to the sophisticated nanometre-scale filtration and special building construction used in pharmaceutical plants. Many companies with a product susceptible to microbial spoilage will use a combination of techniques which might include the addition of biocides for preservation and gowning of personnel. When there are changes in production processes, responsible personnel or practices, unexpected problems can, however, arise which might, at first sight, have no rational cause.

A recent case with which Burgoynes was involved illustrates one such possibility. A contract cosmetics producer, with an established plant, began producing a new range of personal care products for an existing customer. The company had previously achieved good microbiological quality results for that customer’s current ranges and a long shelf-life for the new product could be anticipated with good microbiological quality control and with minimum levels of preservative. The minimum concentration of preservative was desired as the new formulation was marketed on the basis that it contained few additives.

Production began and stocks of the product were built up. However, while stocks were held at the warehouse, discolouration or coloured flecks began to appear in the bottles and some began to swell. Investigations into the cause began and the contamination was soon identified as being microbial in origin.

Considerable effort was subsequently expended in identifying the source of the organism as none of the raw materials appeared to contain micro-organisms and the source of contamination seemed elusive. One of the make-up components was a strong saline solution drawn from a tank that had been installed for more than ten years, yet the contamination could not have originated in that tank because microbes don’t grow in saline do they?

Eventually the tank was inspected, whereupon a build up of slime was found at the tidemark that was found to be largely bacterial in nature. The tank was made of a material that can be colonised by microbes and some types of bacteria, known as halophiles, can withstand levels of salinity usually inhibitory or lethal to other types of bug. The growth of the microbes was further assisted as freshwater is less dense than saline solution so fresh or less saline water was tending to accumulate towards the top of the tank and condensation forming inside the tank and running down the sides would result in sufficient water being available for microbes to grow at the interface. As the mineral saline solution was regarded as being incapable of supporting microbial growth, the tank was not routinely tested or inspected. Bacteria being shed from the slime, albeit it low numbers, were carried through with the saline into the end product. As the organisms were slow growing in routine media, they did not appear in the microbial quality checks carried out at the plant and owing to the relatively low level of additives in the formulation, their eventual growth was not prevented. 

The problems that arose with the introduction of a new formulation showed that the microbiological control at the plant was not as previously thought, that the techniques used in the in-house microbiology laboratory could be improved or supplemented and that the level of preservative for the new formulation was marginal. The colonisation of the saline tank illustrated the diverse range of habitats to which microbes can adapt and thrive, and that common assumptions should not be exempt from empirical review.

For further details please contact

David Robbins, Cardiff Office

 

 

 

 

 

 

 

categories: Microbiology