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The following information is provided to help clients interpret their testing results. This information should be seen as a guide only, as each product and process is different and unique to the various elements that go into producing it. For a detailed analysis and feedback on your specific product, please book a call back with one of our consultants HERE.
ND – not detected – for qualitative methods where there is a simple detected or not detected response
CFU – colony forming unit – used to estimate the number of viable bacteria or fungal cells in a sample, expressed in mL (for liquids) and g (solids)
CoA – Certificate of Analysis – a formal, controlled document showing the test method, sample name and test result, signed by an official signatory
Less than (<) – ISO 7218 (Microbiology of food and animal feedingstuffs — General requirements and guidance for microbiological examinations) sets out reporting guidelines:
When reporting a result where no organisms are detected, you cannot report zero, so would need to report <1 (in the case of liquids) or <10 (in the case of solids – due to a dilution taking place).
Subsequent dilutions would affect how the results were reported (for example, <100 or <1000).
Greater than (>) – a reported result of >x indicates that the number of viable organisms exceed the maximum amount that can be reported for that particular method (also can be expressed as TNTC – Too Numerous To Count)
E or ~ – Estimated – this is used if an actual count lies outside of the reportable range of results for a particular method.
For example, if a method has a reporting range from 50 – 500 and 40 cfus were counted, the result would be reported as 40E or ~40
Presumptive results are those where there is a two stage confirmatory process to a method and the first stage has indicated that this second stage is required.
A “presumptive” positive warning is issued to the client prior to the confirmation stage being undertaken
What the results mean
Food microbiology is a complex area, within which there is an element of uncertainty when it comes to interpreting results
The particulate nature of microorganisms and their ability to reproduce rapidly under favourable conditions has an impact on accuracy when it comes to testing.
Microbiological specifications for a range of food products have been established using robust scientific methods and captured in international standards and regulations where appropriate (Australian specifications are available in the Food Standards Code, Schedule 27 and in the FSANZ “Compendium of Microbiological Criteria for Food“.
For Qualitative methods (Detected or Not Detected), a positive (ie Detected) result in many cases means that the sample/batch is unacceptable and further action must be taken. The extent of the action will depend on a number of factors, including: regulatory requirements, industry standards, customer specifications and company HACCP plan.
Quantitative methods provide a count of microorganisms in a given amount of sample – for example, Standard Plate Count 150cfu/g.
What is acceptable here will also depend on specifications derived from a combination of the above factors.
For Environmental Monitoring, there is less guidance and no internationally recommended specifications. This is simply because all facilities are different, with different risks.
It is therefore crucial that, prior to any testing commencing, a thorough risk analysis is conducted, including sampling points, sampling frequency, target organisms, specifications, control measures and corrective actions.