ISO 14698-1 and ISO 18593 standards describe the surface sampling best practices using contact plates. In a contact plate, the level of agar is slightly higher than the dish itself, and is applied on a surface during a defined time. This method seems very simple, and yet the experience shows that its repeatability depends on who does the sampling. To solve this issue, there are solutions!
A sampling is compliant through 2 important conditions, which warranty the repeatability and, as a result, the representativity of the final count.
The first condition is the pressure applied on the dish. From one laboratory technician to another, the pressure and the weight distribution are different. However, the micro-organisms recovery is linked to the application of the agar over the surface. If the pressure is not strong enough or not evenly distributed, some microorganisms will not be sampled because the agar will not be in contact on its full surface (example: bubble). On the other hand, if the pressure is too strong, the agar can be damaged, and the micro-organisms stressed. Even worse, the agar may slip on the surface, collecting more than usual, and giving random results.
The second condition is time. In the vast majority of laboratories, the technician counts up to 10 seconds. But if you and I, we count in our head up to 10, I am pretty sure we will not end at the same time. Contact time is also variable and will impact the recovery.
In conclusion, there is a simple thing to do to standardize your samplings: what if you use a bio-applicator?
A bio-applicator is a light device, choc-proof and easy to clean, made to standardize the surface samplings. It is made of a piston on which the dish can be quickly fixed, and applied on the surface. A soft push is enough to start a countdown, indicating the end of the sampling.
The graph below compares the recovery rate obtained following surface sampling with and without the Alliance Bio Expertise bio-applicator, performed by 3 different operators. The recovery rate is on average 8% higher when using a bio-applicator, and the variability of results between different operators is reduced by 9%.
The piston is calibrated to start the 10 seconds countdown only when a calibrated pressure is applied on it (not more, not less !). After this time, the device vibrates and flashes in red, indicating that the contact dish is ready for analysis. The sampling is standardized : sampling time is always the same, and so is the pressure, evenly distributed over the surface. And the agar is maintained on its sampling zone.
ABE offers the calibration before the shipment of your new device. After a year, it’s possible to send it back for maintenance and annual calibration if necessary, to ensure the metrology follow up of your applicators.
