WHAT DOES CFU STAND FOR?

nomad Testers allow you to conduct simple, easy and fast CFU testing without the need for a lab or specialized equipment

CFU testing or colony-forming-unit testing is a method of testing for the number of microbes present in a given sample.

Each microbe in the original sample is trapped on a flat surface, given good and the right conditions to grow, and will form a colony on the test medium. Counting these colonies gives us a good idea of the total number of microbes alive the original sample.

 

NOMAD MAKES BACTERIAL ENUMERATION EASY AND FOOL-PROOF

With nomad Testers, on-site microbial testing is easy and fast, thanks to our self-contained samplers and easy-to-use comparison charts.

At Pinqkerton we understand that the safety and satisfaction of your consumers is your number one concern. You need to ensure that your end products are free from pathogens and contaminants. Our nomad testers are a simple way to test a sample of your product for bacteria, yeast and mould, and to test your processes, equipment and environment. Healthcare such as dental unit lines can benefit from regular microbial monitoring.

Most microorganisms naturally present in our environment will not pose a hazard or threat to your product or process unless they are present in excessive numbers. Whether your organisation has internal guidelines on accepted concentrations of different bacteria or not, regular colony-forming unit testing with nomad Testers can alert you to an increase in bacterial number and help catch a potential loss of control early. This can be particularly useful in processes such as water purification, to ensure your final product is of a high quality.

nomad Testers are based on membrane filtration, which causes trapped microorganisms to form distinct colonies, which allows you to accurately count and identify the different microbes that might be present. The swab provided in the nomad Tester kit allows you to test and monitor surfaces as well as liquids.

nomad Testers are used to count each colony formed by bacteria in the original sample. The number of colonies present on the tester indicates the number of individual bacteria trapped in the sample.

 

EXAMPLE OF COMPARISON CHART

Number of colony-forming units (CFU) in the original sample, indicating the number of culturable bacteria in the original sample

 

HOW TO USE NOMAD TESTERS :

QUICK-START GUIDE

 

HOW DO I COLLECT SAMPLES FOR
NOMAD MICROBIAL TESTER?

 

nomad Testers and kits are stand-alone devices suitable for testing a range of liquids and surfaces for bacteria, mould and yeast.


Learn how to prepare your sample for microbial enumeration testing with nomad!

 

COLLECTING DIFFERENT SAMPLES FOR COLONY-FORMING UNIT TESTING WITH NOMAD

The nomad Tester uses a 0.45µm membrane to filter the sample. That means that the sample needs to be a filterable liquid to be used in the tester.

However some products that you might want to test may not be filterable liquids!


Testing non-liquid substances

To test 'unfilterable' samples, you will need to suspend the substance to be tested in a measured amount of sterile liquid buffer, and then conduct a test on a sample of the buffer. Typically you should dilute the product at a ratio of 1:10, so for example for 10g / 10ml of product you would add 90ml of buffer solution.

Ready To Use sterile buffers and other expendables we mention in this section and below are available from all good lab supply distributors.

You can also use this method to collect microorganisms from surfaces.

Testing Surfaces

Moisten a sterile stick swap, fabric or sponge with buffer solution and use it to swab the surface to be tested. Then suspend the swab, fabric or sponge in a measured volume of sterile buffer solution, and proceed to test the buffer solution as you would any other liquid.

Most equipment, products and surfaces can be CFU tested using nomad testers with minimal preparation and no specialized or expensive equipment. If you do have access to appropriate equipment, feel free to use that. But if you don't, here are our tips and suggestions on how to test different media with minimal investment!


Once you've run your tests, learn how to interpret your testing data!


 

Which protocol would be right for my microbial test?

 

PRACTICAL TESTING EXAMPLES

 

Small solids

e.g. Stoppers and bungs

Immerse the sample in sterile buffer (e.g. 90-100ml), shake, collect 18ml of the suspension buffer for testing in a nomad Tester.

Consumables Required:
  • Appropriate nomad tester
  • Sterile peptone water
  • Sterile bag or pot large enough to hold buffer and solid

Semi-solids

e.g. Paste

Immerse the sample in sterile buffer (e.g. 90-100ml), blend (for example in a stomacher® bag), collect 18ml of the suspension buffer (top portion containing less suspended matter) for testing in a nomad Tester.

Consumables Required:
  • Appropriate nomad tester
  • Sterile peptone water
  • Sterile bag or pot large enough to hold buffer and solid (stomacher® bag for example)
  • Mini cocktail mixer with sterilized attachment (starting at 25€)

Hard to reach equipment

e.g. VENTILATION ducts

Moisten a sterile swab with sterile buffer, and swab the surface. Resuspend the swab in at least 18ml of buffer and shake. Test the 18ml of buffer in a nomad Tester.

Consumables Required:
  • Appropriate nomad Tester or Test Kit (which includes swab and buffer)
  • If using a tester: 20ml sterile peptone water + dry stick swab.
  • If using the Kit: none – everything is included.

Internal surfaces

e.g. PIPING

Flush / rinse the piping with water and then collect 18 ml of the rinse (e.g. CIP rinse) water for testing in a nomad Tester.

Consumables Required:
  • Red nomad Tester
  • Bucket for wasted 1-3 litre flush water collection

Large surface (>1 sq.m / 10 sq.ft)

e.g. walls, ceilings

Moisten a sterile sponge or fabric with sterile buffer, and swab the surface. Resuspend the swab in at least 18ml of buffer and shake. Test the 18ml of buffer in a nomad Tester.

Consumables Required:
  • Appropriate nomad Tester
  • Sterile sampling fabric or sponge (available Ready To Use from all good lab equipment suppliers)
  • 90ml sterile peptone water
  • Sterile bag or pot (capacity > 120ml)

Liquids in small containers

e.g. Bottled liquids

Directly pour 18ml of the liquid to be tested into a nomad sampling chamber.

Consumables Required:
  • Appropriate nomad Tester

Liquids in large containers (too heavy to lift)

e.g. Liquids in barrels or kegs

Collect 18ml of liquid for testing using a sterile sampling stick. Test the 18ml of sample in a nomad Tester.

Consumables Required:
  • Appropriate nomad Tester
  • Sterile sampling stick 20ml (can be purchased as single-use item).

A body of water

e.g. River, Lake

Immerse the nomad chamber into the body of water with a slow swinging movement, the chamber opening facing forward, to collect an 18ml sample. The chamber is initially top-filled, simple briefly tilt it at a 45˚ angle to set the sample level to the 18ml mark. Test in a nomad tester.

Consumables Required:
  • Appropriate nomad Tester

Small soft/flat-ish surfaces

e.g. Fingers

Hydrate the nomad tester pad with 1ml of sterile liquid (e.g. sterile water). Roll the finger or surface on the filter surface.

Consumables Required:
  • Appropriate nomad tester or test kit
  • If using a Tester: 1ml sterile water or buffer solution + transfer pipette
  • If using a Test Kit, everything is included

Non-water miscible emulsions

e.g. cosmetics

Disperse the sample in solubilizing solution then dilute in buffer to break the emulsion. Collect 18 ml of the solution for testing in a nomad Tester.

Consumables Required:
  • Appropriate nomad Tester or Test Kit
  • Surfactant e.g. polysorbate 80
  • Buffer or diluent
  • Sterile pot or bag

Other hard-to-filter products

e.g. Meat, cheese, fruit pulp, emulsions

These may require a specific sample preparation step such as letting the solids settle by decanting or mesh filtration.

Want to find our more about how nomad can help your business?


GETTING CONSISTENT RESULTS

Results, means and standard deviations are influenced by sampling and preparation protocols and sample size.

To maintain consistent and meaningful results:

  • Define and record your sampling method, and reproduce it accurately each time you test
  • Prefer larger sample sizes over smaller ones as they give more consistent and representative results. In the case of surface swabbing, multiple smaller samples may be preferable to swabbing a single area thoroughly.

Learn more about the science behind nomad.

FURTHER READING

  • ISO 6887-1 : Preparation of test samples, initial suspension and decimal dilutions for microbiological examinationCovers sample preparation of frozen, hard, dry, dehydrated, low moisture, liquid and non-visqous, acidic, high-fat products and surfaces
  • Corry, Janet & Jarvis, Basil & Hedges, Alan. (2010). Minimising the between-sample variance in colony counts on foods. Food microbiology. 27. 598-603. 10.1016/j.fm.2010.02.002.
  • ISO 21149 : Cosmetics - Enumeration and detection of aerobic mesophilic bacteriaCovers sample preparation for water-miscible and water-immiscible products

INCUBATION

 

Most tests with red or yellow nomad Testers will give satisfactory result when incubated at room temperature.

With blue nomad Testers, an incubation temperature of 35°C / 95 °F is important.

Most egg/chicken incubators, available fur purchase online starting at 50€, can be set for these temperatures, and will do the job while limiting investment.

Contact your local distributor for guidance on the most suitable consumable and equipment.

Learn more about the different features of nomad.

 

HAVE A QUESTION?            WE CAN HELP!


Need help with setting control thresholds, interpreting microbial counts and adapting your processes, mapping your environment, designing a control plan

or anything else?

COUNTING THE NUMBER OF BACTERIAL COLONIES ACCURATELY

 

nomad devices provide a simple and easy method of counting bacterial, yeast and mould colonies with no need for specialized equipment.

 

Colonies growing on the filter surface should counted as individual organisms. The count of these colonies gives you your CFU count.


For most samples, the count per ml is the generally accepted system for recording your results. Therefore, for non-diluted samples, the number of colonies observed on the filter will be the number recorded (as sample count/ml).


For diluted samples, you should multiply the count by the dilution factor.


In recording your count with the blue Tester for coliforms, count only the blue colonies. Coliform and faecal coliforms (blue Testers) are always reported as the number per 100 ml of liquid sample and the count should be multiplied by 100.

TAKING MULTIPLE READINGS

Some populations of microorganisms grow faster than others.


When a micro-organism is trapped from the environment where it was living to be incubated on a test device, it will need to adapt its metabolism to the new conditions (change in temperature, nutrients, ..) before it starts multiplying.  Moreover, if the microorganisms are stressed by a heat or chemical treatment or starvation, the lag phase before they multiply may last up to a couple of days.


When testing a new sample we don't know how long it will take for the microbes on the filter to appear visibly.


To get a more accurate count, it's a good idea to take an extra reading two thirds of the way through the incubation time, and another one-third of the recommended incubation time after you take the final reading.


Thanks to these extra readings you will be able to:

  • better count slow-growing populations whose colonies are difficult to see and count after a normal incubation period
  • reduce unsure counts resulting from the fact that some fast-growing colonies overlap, join or merge with others.

In the following illustration, the observations are done on a Red Total Count Tester incubated at room temperature.

As you can see, at the end of the the recommended incubation period, a mould has grown quickly and overgrown a nearby bacteria colony, which might have been missed had we not taken the first reading.


In addition, in the second reading, a small colony has appeared on a grid-line which might have been overlooked had it not been for the third reading.


After three separate readings we know that the final count is 8, even though 8 individual colonies are not easy to observe on any of the individual readings. It can be a good idea to use a marker pen and put a dot over each colony on the tester chamber to facilitate counting over multiple readings.


Once you know the optimum incubation duration for a given temperature, you may reduce your counts to just one or two observations.


Learn more about how using nomad testers as part of a microbial monitoring program can help your business.

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