Microbiological quality control for medical grade honey

There is a risk of introducing micro-organisms into wounds, especially botulism, if honey is used as a dressing (Molan and Allen, 1996). The risk can be avoided by sterilisation. Gamma irradiation is one of the more common sterilisation methods in the wound dressing industry and it was found that gamma irradiation does not affect the antibacterial activity of honey (Molan and Allen, 1996). An international Medical Device ingredient microbiological requirement for manufacturing is a total plate count (TPC) of less than 500 colony forming units (cfu) per gram (g). The microbiological specification is required to meet a pre-sterilisation (gamma irradiation) requirement, ensuring the sterilisation process is always successful; thereby eliminating the risk of introducing microorganisms into wounds from honey dressings.

Primary microbiological contamination sources for honey include pollen, the digestive tracts of honey bees, dust, air, earth and nectar. The secondary contamination sources (processing, after harvest) include air, water, human/honey handlers, honey extraction and processing equipment and buildings (Snowdon, 1999; Snowdon and Cliver, 1996). Due to the natural physical properties of honey that serve to inhibit microbial growth — ie. low moisture (less than 21%), low water activity (Aw 0.5–0.6) and acidic environment (pH 3.4–6.1), the microbes of concern are from contamination; especially from post-harvest handling (Snowdon and Cliver, 1996).

Commonly found microbes in honey are osmophilic or sugar tolerant yeasts, moulds and spore-forming bacteria. Our medical grade honey processing system has been validated to ensure any existing yeast and mould cells, if present, are destroyed effectively, without damaging any honey quality aspects. However, removal of contaminated spore-forming bacteria (eg. from the genus Bacillus) in honey is not easy; the bacterial load does not reduce during storage, unlike other certain vegetative cells that have been known to decrease after time in honey, due to its antimicrobial properties that discourage the growth or persistence of many micro-organisms (Snowdon and Cliver, 1996). The honey supply programme, which is being managed very successfully, focuses on the prevention of possible spore-forming bacterial contamination.

Due to strict hygiene control from honey collection to honey extracting and processing, possible contamination of micro-organisms (eg. coliform bacteria and pathogenic bacteria such as Staphylococcus, Salmonella and Clostridium species) that indicate poor sanitary quality of honey has not been an issue for the medical grade honey supply programme. Strict packaging standards and storage conditions for extracted honey have also helped in the prevention of possible microbial increases during storage.

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