Ask a QC why every batch of cooked pie filling is tested for coliforms and the usual answer is that the customer specification says so, or that the previous QC set it up. Ask what a coliform count of 200 cfu/g proves and the room goes quiet. Most testing schedules are inherited, and an inherited schedule is hard to defend to an auditor. Getting indicator organisms vs index organisms straight is where the defence starts.
In short
- An indicator organism tells you about hygiene or process failure. Enterobacteriaceae in a cooked product is the usual example.
- An index organism suggests that a related pathogen may be present. E. coli points to faecal contamination, and Listeria species point to conditions that suit Listeria monocytogenes.
- Coliforms are defined by a lab test, Enterobacteriaceae are a whole family that includes Salmonella, and E. coli is a single species.
- An indicator only works where it should be absent or low when the process is right. Coliforms on raw salad tell you almost nothing.
- Pathogen testing of finished product verifies your controls. It cannot act as the control.
The distinction gets a full module, including a 37 minute lesson on indicator micro-organisms in food, in the Advanced Food Microbiology Course from ASC Food Safety Training (8 hours, online, R1 750). This post gives you enough to audit your schedule on Monday.
What is the difference between an indicator organism and an index organism?
An indicator organism is a group whose numbers reflect the hygienic condition of a food or the failure of a process, such as under-cooking or contamination after cooking. An index organism is one whose presence suggests that an ecologically related pathogen could also be present. The same organism can play either role, depending on the product.
Keeping the two apart forces you to say what question each test answers. An indicator asks whether the process and the cleaning worked. An index asks whether there is a route by which a pathogen could have arrived.
Both exist because pathogens are usually absent, and when present are few and patchy, so testing for them directly finds very little. Indicator and index groups are numerous and cheap to count, so you can trend them.
Before you add a test, write down what you will do when it fails. If you cannot, you do not need the test.
What is the difference between coliforms, Enterobacteriaceae and E. coli?
Coliforms, Enterobacteriaceae and E. coli are nested groups. Enterobacteriaceae is a large family of Gram negative rods that ferment glucose, and it includes Salmonella. Coliforms are the members of that family that ferment lactose under the conditions of the test, so the group is defined by the method and has no standing in taxonomy. E. coli is one species within the coliforms.
That nesting explains why many specifications for heat treated foods have moved from coliforms to Enterobacteriaceae. The coliform test misses the non lactose fermenters, Salmonella among them. The family count catches them all, which makes it the more sensitive alarm for a failed kill step or recontamination afterwards.
| Group | What it is | Role | Where it works | Where it misleads |
|---|---|---|---|---|
| Coliforms | Lactose fermenting Gram negative rods, defined by the test method | Hygiene indicator | Pasteurised milk, water, cooked products | Raw produce and raw meat, where they occur naturally. Misses Salmonella |
| Enterobacteriaceae | The whole family, including non lactose fermenters | Process hygiene indicator after a kill step | Cooked, pasteurised and dried products, and swabs from cleaned equipment | Raw foods, where a count is expected |
| E. coli | One species, with its main home in the gut of warm blooded animals | Index of faecal contamination | Ready to eat foods, fresh produce, water, raw meat hygiene | Says nothing about Listeria or other pathogens that do not come by the faecal route |
| Listeria species | The genus, including harmless species such as L. innocua | Index for L. monocytogenes | Environmental swabs in chilled ready to eat plants | Treated as a nuisance result because “it was only innocua” |
Most E. coli strains are harmless. The common enumeration method relies on an enzyme that E. coli O157 typically lacks, so a clean count tells you nothing directly about that organism. It tells you the faecal route looks closed, which is a different statement.
Why is Listeria spp. used as an index for Listeria monocytogenes?
Listeria species share much the same habits: cold, wet niches such as drains, floor wall junctions, hollow rollers and worn gaskets. If a swab finds any Listeria species, the conditions that allow L. monocytogenes to settle are present at that site. Testing for the genus gives more positives, and therefore more warning, than testing for the pathogen alone.
The classic mistake is relief. The lab reports Listeria innocua on a slicer frame, somebody says “not the dangerous one”, and the result is filed. Treat an index result as a finding about the site: water, food residue and time have come together in a niche the cleaning has not reached. After the 2017 to 2018 listeriosis outbreak in South Africa, few auditors will accept a plant that ignores genus level positives in high care.
Zones and the response to a positive are covered in our guide to environmental monitoring for Listeria. Technique is in the surface swabbing guide.
If you would struggle to explain the coliform table to your production manager, an auditor will notice too. Module 3 of this advanced food microbiology training course is the quickest fix we can offer. It covers the index of micro-organisms and indicator micro-organisms in food.
Start the Advanced Food Microbiology Course, R1 750
When does pathogen testing of finished product make sense?
Product pathogen testing makes sense as verification: a periodic check that controls already proven to work are still working. It also makes sense where law or a customer requires it, and for high risk ready to eat foods that support growth. It makes little sense as the main control, because sampling statistics are against you.
When it earns its place
Chilled ready to eat foods with a long shelf life, products for vulnerable consumers, and dried powders in which Salmonella can survive for months. Codex guidance on Listeria monocytogenes in ready to eat foods sets criteria according to whether the food supports growth. New suppliers, new lines and the weeks after an incident also justify more product testing.
When it is money badly spent
Testing one 25 g sample per batch for Salmonella in a fully cooked product and calling it positive release. If one pack in a hundred is contaminated, a single sample misses it 99 times in 100. The same money spent on Enterobacteriaceae counts after the cook step and on environmental swabs will find a developing problem far sooner. What the certificates mean is in how to read a food microbiology lab report.
How do you choose the right organisms to test for your product?
To choose test organisms for a product, start from the hazard analysis and the process, never from the lab’s price list. Decide which failures you need to detect, pick the organism group that would reveal each one in that food, set a limit with a planned action, and drop any test that would not change a decision.
1
List the failures. Under-cooking, slow cooling, post cook contamination, poor cleaning, temperature abuse.
2
Match an organism. It must be absent or low when the process is right, and appear when the failure happens.
3
Choose the sampling point. Straight after the step you are checking. End of shelf life testing answers a different question.
4
Set limit and action. An alert level from your own baseline, a reject level, and a named person who acts on each.
5
Review every year. Drop tests that have never changed a decision. Add them where complaints show a blind spot.
Worked example
Mzansi Fresh Meals, the fictional ready meal plant ASC uses as a training case, inherited a schedule that ran the same suite, coliforms included, on cooked chicken curry and on the raw coleslaw side. On the curry, Enterobacteriaceae sampled after the blast chiller is a sharp check on the cook and on post cook handling. On the coleslaw, the coliform count was always high and always ignored. The reworked schedule puts E. coli and L. monocytogenes on the coleslaw, the realistic concerns for raw cabbage over a chilled shelf life, and moves the saved budget to drain and conveyor swabs.
Where the hazard analysis names a spore former or toxin producer, such as Bacillus cereus in cooked rice or Staphylococcus aureus in hand assembled products, it may deserve a line too. And the numbers only help if you know how much they wobble: see measurement uncertainty in food microbiology results.
What does the Advanced Food Microbiology Course cover, and what does it cost?
The Advanced Food Microbiology Course from ASC Food Safety Training is an 8 hour online course that costs R1 750. Its five modules are micro-organisms in a food handling environment, growth and reproduction, indicator organisms, sampling, enumeration and testing, and food quality and safety in microbiology. Module 4 then covers sampling and reading what the lab sends back.
Course facts
| Course | Advanced Food Microbiology Course. Provider: ASC Food Safety Training. Instructor: Mthokozisi Nkosi |
|---|---|
| Level | Advanced, the third step in the ASC microbiology ladder |
| Time | 8 hours |
| Price | R1 750 |
| Format | Online, self paced, lifetime access |
| Assessment | An assessment for each module, then a final assessment |
| Certificate | Certificate of completion |
| What you will be able to do | Say what each test on your schedule proves, identify and analyse pathogens and spoilage organisms, and evaluate growth, contamination and control |
| Who it is for | QCs, QA managers, food technologists and HACCP team leaders who set or defend a microbiological testing schedule |
Enrol in the Advanced Food Microbiology Course, R1 750
Questions people ask before they enrol
How long does it take, and what does it cost?
The course is 8 hours and costs R1 750, paid by card or EFT through PayFast. It is online and self paced with lifetime access, so you can return to the indicator organisms module whenever a specification comes up for review.
I am not a microbiologist. Is the advanced course too much for me?
It is the third step in a ladder. If microbiology is new to you, Introduction to Food Microbiology at R1 195 and the Intermediate course at R1 450 come first. If you already work with lab results, you can go straight in.
How am I assessed, and do I get a certificate?
Every module has its own assessment, so you are tested on indicator organisms while the material is fresh. A final assessment follows the fifth module, and you receive a certificate of completion for your training file.
Does the course apply to my type of product?
Module 5 covers micro-organisms affecting food quality by product type. The indicator and index reasoning in module 3 is the same in a dairy, a bakery, a ready meal plant or a kitchen supplying spaza shops. Only the organisms chosen differ.
Can I enrol from outside South Africa?
Yes. The course is delivered fully online. The price is in rand, and the course page shows an indicative USD, EUR and GBP equivalent. Payment settles in rand, and your bank handles the conversion.
A testing schedule you can explain line by line is worth more in an audit than a thicker file of certificates. One audit finding against a schedule nobody can defend, or one more year of paying for tests that never change a decision, costs more than R1 750. Enrol in the Advanced Food Microbiology Course from ASC and get the reasoning in 8 hours. To see where it sits among our other microbiology courses, start at the food microbiology training hub.
Codex texts are published by the Codex Alimentarius Commission. This course is an independent training product and is not approved or endorsed by Codex, any regulator or any certification body.