UNE-EN ISO 22610: 2007 - Test method to determine resistance to wet bacterial penetration - Cloths, gowns and clean air suits for surgical use as medical devices, for patients, clinical staff and equipment. The test requirements are indicated in the UNE-EN 13795-1 Standard (Surgical cloths and sheets. Requirements and test methods. Part 1: Surgical cloths and gowns).

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In many situations, bacteria carried by a liquid migrate through a material barrier in a wet state, such as the penetration of skin flora through a coating material. ISO 22610: 2018 standard specifies a test method, with associated test apparatus, to determine the resistance of a material to the penetration of bacteria carried by a liquid, when subjected to mechanical rubbing.

To perform the test, the sample of the material under test is placed on an agar plate. This material tested are 25 x 25 cm square pieces or with a diameter of approximatelly 25 cm. A donor carrier sheet contaminated with a culture of Bacillus atrophaeus is placed on the sample of the material under test with the contaminated side facing down and covered by a sheet of high density polyethylene. The three sheets (material under test, donor material sheet and cover sheet) are held together and stretched by two conical steel rings. An eccentric rotating finger acts on the three sheets, exerting a moving force for 15 minutes to bring the test specimen into contact with a small area of the agar surface.

Due to the combined effect of rubbing and liquid migration, bacteria can pass from the donor sheet through the test specimen to the agar surface. The pressure exerted in the assay is intended to simulate the type of pressure exerted by a surgeon´s elbow during a procedure and was specifically developed to measure bacterial penetration through reusable, single-use materials used during the surgical procedure.

Five replicates of each test material should be tested (5 pieces of 25 x 25 cm) or with a diameter of approximately 25 cm. For each of the pieces or replicas of the sample, this process is repeated with five plates of culture medium for 15 minutes using a freshly prepared donor for each test specimen, performing 5 concatenated tests to estimate penetration throughout the time. At the end of the process, the remaining bacterial load on the upper side of the test specimen and the bacterial load remaining on the donor material are examined in 2 more Petri dishes. As a consequence, 7 Petri dishes will be obtained for each of the 5 test replicates. The plates are incubated, and the CFUs are subsequently counted.

The results are expressed as a percentage (%) of penetration compared with the bacterial load initially inoculted on the donor. Bacterial counts are also used to calculate the barrier index (IB) which describes the fraction of the bacterial inoculum that has not penetrated the barrier material.

The UNE-EN 13795-1 Standard, states that both for surgical drapes and surgical gowns, for the critical areas of the product in standard performance products, the barrier index (IB) must be equal to or greater than 2.8. While for high performance products, the barrier index in critical areas should be equal to 6.0, the maximum achievable value that indicates no penetration.

The critical area of the product is the area most likely to contribute to the transfer of infectious agents to and from a wound, for example, the front and sleeves of surgical gowns. Demonstracting of wet microbial penetration is not required for other less critical areas of the product, where the pressure on them is considered to be lower and also the risks of penetration of blood and microbes by impact on the material.

Standard performance products are those that meet minimum requirements, while high performance products are those that meet high performance requirements for various products used in invasive surgical procedures. For example, high performance products are those used in procedures where exposure to fluids is expected to be high, a higher mechanical action, or longer surgical procedures can be expected.