Single-Use System Integrity I: Using a Microbial Ingress Test Method to Determine the Maximum Allowable Leakage Limit (MALL)

Abstract

An aerosol microbial ingress test was specifically designed and used to create a predictive model in order to determine the maximum allowable leakage limit (MALL) of single-use systems (SUSs). The MALL is defined as the greatest leak size that does not pose any risk to the product. The procedure involved taking test samples of film material from single-use bags. As test samples, an ethylene vinyl acetate multilayer film (300 μm thick) and a polyethylene multilayer film (400 μm thick) were cut into 50 mm patches. Artificial defects of 1-100 µm were laser-drilled in the middle of each film patch. The patch was assembled on a holder and properly sealed. The test units were filled aseptically with culture media and placed inside an aerosol chamber. Various pressures were applied to the test unit to simulate the constraints that single-use systems may be subject to under real-world conditions. After an aerosolization cycle with spores of Bacillus atrophaeus , a minimum concentration of 10 6 CFU/cm 2 was reached on the film surface. The test units were incubated for 14 days at 30°C-35°C and visually inspected for bacterial ingress. Thirty samples per defect size were tested. Logistic regression was used to indicate the MALL for a single-use system according to the required risk level. With this method, the probability of the occurrence or absence of ingress for a specific defect size was reported according to the experimental data. In addition to physical parameters, such as the pr…