Environmental testing of food contact surfaces and other surfaces that workers might easily touch and then cross contaminate a product can help you quickly find gaps in your food safety program. If you read an earlier post I did on the subject, then you may remember that here at our tiny farmstead creamery, we do an APC on the milk used for each batch of cheese. This spring we made some changes in our general procedures that lead to increased bacteria counts in our milk. By using swab testing, we were able to pinpoint where the problem was originating- before the bacteria levels became too high.
We had made several changes on the dairy farm side of processing. First, we greatly shortened the time in which the milk goes from the body temperature of the animal to refrigeration temperatures. Second, we changed some of the cleaning products to more environmentally friendly variations. When I say “environmentally friendly” in this case I mean products that break down quickly into less harsh compound or elements and are therefore easier on a septic system – ours is an oversized domestic system that handles the waste water from our home, dairy, and creamery. Due to the heavy use of cleaning and sanitizing products, our septic tank was functioning at less than optimum and costing us quite a bit in maintenance.
Since rapid chilling of milk is one of the best ways to limit bacterial growth, our problem of rising bacteria counts meant that either the equipment was not being cleaned adequately, or that bacteria was being introduced – in large numbers – at another step in the process. I mentioned we are a very small farm, so it was quite easy to gather the entire team (myself, our daughter, and one intern) and go over the possibilities. After I completed a milking and what I felt was a thorough cleaning and sanitization of the equipment, I swabbed the inside of one of the sections that collects milk from the animal (called a “claw”). After plating and incubating the results showed many cfu’s, there should have been almost zero. (See the photo later)
Swab Testing: What You’ll Need
- Incubator- We use the small, inexpensive version sold by Nelson Jameson (about 90.00)
- 3M Petrifilm plates- Aerobic Plate Count and Coliform Count (70-80 cents each)
- Plate spreader (comes with Petrifilm plates)
- 3M Quick Swabs (about 1.40 each)
- Sharpie or other marker
- Once you have gathered your supplies, you can begin taking samples. It is a good idea to test far more surfaces in the beginning of a testing program than you may need to do on follow up tests – this will help establish a baseline of awareness. Once enough tests confirm that cleaning protocols (SSOP’s – sanitization standard operating procedures) are effective, you may be able to decrease the number of surfaces tested as well as the frequency.
Steps for Successful Swab Testing
- Using a sharpie or marker, write the source of the sample and date taken on the Quick Swab container.
- When you are ready to swab the surface, bend the neck of the liquid filled end of the Quick Swab so that the nutrient broth contained in the bulb flows into the end that contains the swab. Squeeze the bulb so that all of the solution is drained.
- Twist apart and remove the swab from the tube. Hold the tube so that the broth solution remains inside once the swab is removed.
- Rub the end of the swab, holding it at a slight angle so that the sides make some contact with the surface, on the desired area to be sampled. Rub the swab three times over an area of roughly 3-4 square inches.
- Return the swab to the broth and close the tube.
- Shake the tube for about 10 seconds to mix the sample into the broth.
- Remove the swab from the tube, squeezing it inside the neck of the tube to remove as much of the solution from the absorbent material as possible.
- Peel back the film on the sample plate (APC or other) and carefully pour the solution onto the center of the plate. It tends to run out very quickly and is tricky to do properly (as you might notice from the photo of the “claw” sample later in this article).
- Use the plate spreader to gently press the sample into the plate. Use the flat side for coliform plates and the recessed side for APC plates.
- Allow the plate to sit for about 1 minute so that the liquid sample will gel with the plate.
- Incubate as directed for the type of sample being run. (For APC it is 90F for 48 hours, for coliform plates incubate at 90F for 12 hours).
Coliform Plates- How are they Different, When and How to Use
When you open a pack of coliform count Petrifilm plates you will immediately notice two things that are different from the APC plates. First, they are red instead of white. Next, the plate is thicker and has a circular “well” that helps contain the sample of fluid, while the APC plates are flat. When you use the plastic plate spreader on a fluid sample on the APC plates, you use the side of the spreader that has a recessed area. When spreading a sample on a coliform plate, use the flat side of the spreader. Coliform plates are a little bit more expensive then the APC plates, at about 75-80 cents each. Coliform plates that differentiate between total coliforms and e. coli are even more costly at about 1.50 each. You can also purchase “rapid” count plates that will give you results in just a few hours.
So why should you choose to run a coliform sample over an APC sample? In general it is best to focus on coliforms when testing surfaces, especially those that might come in contact with raw or finished product. While other bacteria will always be present in a cheesemaking facility, coliforms are from fecal sources and should not be expected or tolerated on surfaces inside the processing area. If a total coliform count reveals no coliforms, then purchasing and using the more expensive e.coli specific plates is not strictly needed. (These policies should be determined by each facility in consultation with a food safety specialist, however. This article is based solely on our experiences here at our own farm)
A coliform plate is read differently than an APC plate. When you look at the incubated Petrifilm coliform plate, you may see multiple small, red dots, just like you do on the APC plate (although they are more difficult to see thanks to the red background color of the plate – which is intentional). Coliform cfu’s will also have a red dot, but it will be surrounded by a little ring of air – a gas pocket produced by the bacteria. Unfortunately (or fortunately depending on how you look at it) the samples I took for this article did not grow any coliforms. Perhaps I should have swabbed the milking parlor floor drain, which would no doubt have created quite a high count plate for you to see!
Lessons in Swabbing
Here at Pholia Farm, swab testing has helped us determine the frequency of cleaning door handles, light switches, and other hand contact surfaces as well as the efficiency of our cleaning protocols for the cheese vat, milk cans, and milking equipment. Thanks to this quick and easy test we were able to pinpoint the gap in our process – in this case inadequate cleaning products – and make immediate changes. In our case, we returned to our former CIP detergent and will be attempting to offset the damage to our septic system flora by regularly treating the system with beneficial bacteria treatments. Of course, the long term lesson is that there will always be something to try to improve and compromises made – whether that is in the use of chemicals that are not as “green” as we would like or in costs and time spent trouble shooting problems. Being a small cheesemaker also means being alert and adaptable, there is nothing boring about this career!
It is important to remind you that you may not provide testing or plate counts to others unless you are a certified professional working in a certified facility. When first developing a testing frequency protocol, it is advisable to include certified lab testing and consultation with a food safety professional.
Instructions: www.msu.edu/course/fsc/441/3mapc.html https://www.msu.edu/course/fsc/441/3mc&ec.html, and http://solutions.3m.com/wps/portal/3M/en_US/Microbiology/FoodSafety/industries/one/