Susceptibility of clinical isolates of Bordetella pertussis to chemicals

The aim of study: To test clinical isolates of Bordetella pertussis from the National Reference Laboratory for Pertussis and Diphtheria for susceptibility to commonly available disinfectants. Another aim was to determine the concentration and exposure time for each chemical under real conditions of use and possibly to detect the emergence of resistance to disinfectants among 34 strains of B. pertussis referred to the National Reference Laboratory for Pertussis and Diphtheria in 2014 and 2015. Material and methods: A total of 34 clinical isolates of Bordetella pertussis were tested for susceptibility to chemical disinfectants by three different methods. The microsuspension method was used for the primary screening, and the tests were carried out without protein contamination. Further testing was conducted in accordance with standard EN 14885, where the test procedure consists of several steps. Step 1 involves quantitative suspension methods (Phase 2, Step 1), and step 2 uses methods designed for practice (Phase 2, Step 2). The quantitative suspension method modified according to EN 13727+A2 was used in step 1 to confirm bactericidal activity of the test products under the dirty conditions. In step 2, clinical isolates were tested using a quantitative carrier test method under the dirty conditions modified according to EN 14561. Based on this standard, the real conditions of product use are simulated. Four disinfectants differing in composition and intended use were tested. Results: Disinfectant No. 1 showed bactericidal activity at a concentration of 0.5% after 2 min of exposure in the case of immersion or at a concentration of 5% after 2 min of exposure when treated by wiping. Disinfectant No. 2 was active at a concentration of 0.1% after 2 min of exposure or at a concentration of 1% after 2 min of exposure, respectively. Disinfectant No. 3 did not show bactericidal activity even at a concentration of 100% after 5 min of exposure. Disinfectant No. 4 showed bactericidal activity at a concentration of 10% after 5 min of exposure or at a concentration of 30% after 2 min of exposure. Conclusions: None of the strains tested was resistant. Using the methods that simulate the real conditions of use of disinfectants Nos. 1 and 2, it was possible to determine the concentration and exposure time needed to achieve disinfection of surfaces under the dirty conditions. Disinfectants Nos. 3 and 4 are not primarily intended for the treatment of surfaces but for the treatment of the skin and mucous membranes. The results obtained with the latter two products are interesting but inconclusive as the real conditions of their use were not simulated accurately.