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Listeria mono and tolerance to QAC’s

by Gareth Lloyd-Jones: 26 March 2018
Post the Listeria Symposium in Johannesburg South Africa, hosted by Food Focus, a research paper compiled by students from the University of Stellenbosch, has been doing the rounds, after these findings were presented at the symposium. The study isolated Listeria (LM) in 9 salmon and meat facilities in Norway to investigate the prevalence of Quaternary Ammonium Compound (QAC) specific tolerance levels as well as the genes that code for such tolerance. When read at face value, the findings, which indicated a tolerance of the specific LM strain to QAC’s has caused a bit of panic throughout the SA food industry, which is understandable, as QAC are widely used for cleaning and disinfection. I have been inundated with messages and queries requesting clarity on the situation and decided to put together a short response on this matter.

Let me start by saying that academic research is an important element of any industry and each piece of research contributes to or confirms the body of knowledge of that specific area of expertise. Individual research needs to be read in the context of all the other knowledge and specific attention should be given to the research in terms of its scope, delimitations and the findings, recommendations and conclusions. We should not be overly vociferous until such context has been considered and critically evaluated, to an extent that we potentially overreact to a situation whether necessary or not.

I am not a scientist, but have enough critical thought ability to read such research in the required context and would like to position some observations and thought around this particular research and the implications and potential actions that can be considered, albeit in more layman terms.

The following noteworthy observations can be considered:

  1. The QAC used in the investigation was Benzalkonium Chloride (a single chain QAC). There are many different types of QACs (double chain, blends of different chains etc).
  2. QAC tolerant Listeria was found and their sensitivity to varying levels of the specific QAC was determined in suspension and biofilms.
  3. Listeria with QAC tolerance was found to tolerate low levels of Benzalkonium Chloride (such as in rinse water) (30 to 40ppm QAC) but could not survive a lethal dose (100ppm+) of Benzalkonium Chloride (whether in suspension or biofilms).
  4. Low levels were found in rinse water ( 1 – 15ppm QAC) and the concern is that if rinse water stands around long enough, it will allow proliferation of QAC tolerant Listeria over the non-tolerant variety.

Possible measures to ensure the QAC tolerant variety does not survive are:

  1. Use of alternate disinfectants, possibly weekly – oxidizing (Peracetic acid Sanitizer and a QAC) or as a weekly acid wash.
  2. Vary the QAC, use a double chain QAC (EG: Eco-San TCQ – Didecyl Dimethyl Ammonium Chloride) or Dual chain QAC (Blend of Single & Double Chain QAC’s)-EG: Eco-San QC80.
  3. Ensure that Chemical Concentration Verification (CCV) is maintained in the recommended range (For example 3% = 2100 ppm ( 20 times higher than lethal dose).
  4. Rinse Food-contact surfaces well after use and before production.
  5. Where QAC is rinsed from Food contact surfaces, a thorough rinse is required.
  6. Do not rinse non-food contact and peripheral areas.
  7. Keep food processing areas as dry as practically possible.

Hope this assists and gives some clarity on the matter.
Gareth Lloyd-Jones

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