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Biofilms: ‘the elephant in the QA room’

Dedicated biofilm detection and control should be enlisted and instilled as a fundamental and non-negotiable requirement for really effective QA programs, argues SA food safety consultant, Dr Robin Kirkpatrick. 

As if the large basket of challenges to optimal quality assurance were not already daunting, there is another key one to consider: the proverbial ‘elephant in the room’ – the continuous risk of the ‘behind-the-scenes’ microbial contamination of consumer products from ‘unseen’ bacterial biofilms.

Multiple reports confirm that factory personnel, raw ingredients, packaging materials and ventilation systems are all contributing factors for microbial contamination of finished products.

However, it is not these incidental causes of microbial spoilage, but rather the persistence of sources of contamination from biofilms that require dedicated attention.

It is widely recognised that upward of 90% of the bacteria in the environment currently exist in water-borne biofilms.

These same microbes exist and survive in the biofilm ‘slime layer’ which continuously sheds both spoilage and potentially pathogenic microbes into the equipment and water supplies in the food-beverage processing environment.

Almost all of these biofilm-associated bacteria have deliberately adapted to a wide range of adverse conditions to ensure their survival. These include metabolically dormant and spore forms which are tolerant, or at worst resistant to high temperatures, changes in pH, as well as the chemicals which form part of cleaning and disinfecting procedures. 

It is important to note that biocidal activity of most of the disinfecting agents requires that the target microbe must be metabolically active for the chemical to gain access to the target activity site within the microbe.

The dormant microbial growth form is thus in all likelihood already tolerant in some measure to the chemical agent as applied – this even before one examines the specific resistance mechanisms that the biofilm associated bacteria continue to develop. 

It is widely reported in the scientific literature that the recommended dosages and exposure times of the chemicals required for the control of the various microbe species in the industry are derived from laboratory-based trials.

But it can be suggested that these lab studies and ensuing ‘commercial use-recommendations’ are artificial and do not represent the ‘real world’ conditions which allow microbial biofilms to take hold and create a persistently contaminating environment.  

Under optimal conditions, biofilms can form within 2-4 hours and can start shedding bacteria into passing water streams within 2-4 days of initial contamination. Under optimal growth conditions, a colony of E coli bacteria can double in size within 20 minutes!

Despite this fact, QA personnel and labs responsible for food safety testing, rely on the microbial sampling from post-cleaning surface swabs and rinse water samples that, at best, represent a miniscule percentage of the freely available environmental bacteria.

What environmental conditions allow microbial biofilms to take hold?

Free-floating bacteria will not multiply and grow into mature biofilms without the required contact surface to adhere to, and a continuous supply of nutrients and oxygen.

These are the fundamental building blocks that are required to support a highly adaptable population of diverse microbes to gain a foothold and to grow into a self-sustaining source for further downstream contamination.

As biofilms mature, they become progressively self-sustaining and develop a vast array of defence mechanisms which progressively protect the embedded microbes from the adverse effects of cleaning and disinfecting chemicals.  

The importance of optimal cleaning and the absolute requirement for the removal of the ingredient and final product residues from processing equipment cannot be overstressed.

Aside from being a source of food allergens, these same residues of incomplete cleaning provide the nutrients that bacteria rely on to grow and multiply.

Biofilm detection

The use of rapid testing methods to verify factory cleaning is widespread. Foremost amongst these rapid tests is the ATP test which is geared towards the detection of microbial DNA.

While the level of test sensitivity is supported by lab-based studies, the relatively miniscule sample sizes of either surface swabs or water samples are not representative of the full production or water supply scenario.

Consider listeria

By way of example, let’s interrogate the recent listeria outbreak in SA and the fatal consequences for the unsuspecting consumer population. In good faith the consumers procured products that had been released for consumption as being both quality and safety assured.

It is well documented that Listeria relies on biofilms to survive in factories for extended period of time (years). Given the natural propensity of Listeria to form biofilms, it is self-evident that the pathogens will become established in unseen biofilms that will cause the persistent contamination of finished products over an extended period.

It’s all well and good to have a ‘zero tolerance’ policy for Listeria contamination in ‘Ready to Eat (RTE)’ products (USDA, FDA), but how exhaustive must the testing of finished products be in order to exclude the presence of the pathogen and assure the safety of consumers?

A better, easier biofilm detector

Given that the biofilm matrix is predominantly composed of water (90%) and organic polymers, the presence of sufficient microbial DNA for detection in post-CIP samples is thus highly unlikely to be representative of the sanitary status of the total production environment.   

Given the low concentrations of microbial DNA or metabolically inactive bacteria in the sampling water stream, there’s strong rationale for a more appropriate and cost-effective solution: namely to test for the presence of the organic polysaccharide matrix which constitutes the majority of the biofilm “footprint” as the indicator of microbial contamination.

Quality Assurance = ‘what gets measured gets improved’

How well can your QA team answer these difficult questions?

  • Where do the bacteria on surface swabs and in-water samples come from?
  • Why do bacteria persist despite rigorous cleaning activities?
  • Are you specifically testing for the presence of quality-destructive biofilms or merely testing for free-floating bacteria that might be in the sampled taken?
  • Are your existing QA protocols sufficiently robust to address the persistent risks of biofilm-related contamination and subsequent consumer health and safety?
  • Are your protocols a ‘band-aid’ that fails to address an underlying problem of persistent infections?

In conclusion, here’s a repeat of the opening paragraph: dedicated biofilm detection and control should be enlisted and instilled as a fundamental and non-negotiable requirement for really effective QA programs.

Article by Dr Robin Kirkpatrick, developer of Carbotect, a reliable measure to detect biofilm substrate before microbial contamination arises.

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