A study of bacterial culturability during bioaerosol challenge test using a test chamber

The bioaerosol challenge test using a chamber is performed to evaluate the specificity of air purifiers and samplers. Bacterial cells are exposed to various stresses in each step of the test and the detail of the influences by the stresses has been reported. These reports are very detailed but the change of the bacterial biological activity through the chamber test has not been referred yet. We followed the bacterial activity in each step through the practical bioaerosol challenge test for the specificity evaluation of an apparatus using Staphylococcus epidermidis and Escherichia coli, and tried to estimate the degree to which bacterial cells are stressed during the test by investigating bacterial culturability and the redox dye reduction activity. We used the ratio of the culturable or active cell number to the total cell number as a common indicator through the test step. According to the results, culturability of S. epidermidis and E. coli decreased to 98% and 93% of initial value by nebulization, respectively, but the culturability change of each bacterium was not significantly different. On the other hand, 54% of the cells in the original suspension used for nebulization lost their culturability after aerosolization in S. epidermidis. Furthermore we observed that culturability changed after a centrifugation wash cycle during sample preparation in E. coli, but not in S. epidermidis. We do not intend just to report the bacterial viability or culturability change in our system as one of the case studies in this paper. Bacterial biological activity cannot be controlled completely every time even if the cells are prepared by the same protocols. For the purpose of accurate evaluation, we will discuss the importance to mind that the cells which the tested apparatus is measuring in each step of the test are the cells which exist in what status of bacterial activity with showing our actual results through the chamber test. The actual evaluation systems for the specificity confirmation of apparatuses will be commonly established based on the reported basic information. The difference of opinion about the bacterial activity through the chamber test could lead to misjudgment of the specificity of a tested apparatus.

Research highlights
► Bioaerosol challenge test is performed to evaluate air samplers and purifiers.
► Bacterial status in each step of the test has been reported.
► Here we followed the change of bacterial status through the practical chamber test.
► Based on the results, we discussed the activity change for the evaluation test.
► We need a common opinion about it for the accurate evaluation.