Abstract
Disinfectants play an important role in controlling microbial contamination on hard surfaces in hospitals. The effectiveness of disinfectants in real life can be predicted by laboratory tests that measure killing of microbes on carriers. The modified Quantitative Disk Carrier Test (QCT-2) is a standard laboratory method that employs American Iron and Steel Institute (AISI) Type 430 stainless steel carriers to measure hospital disinfectant efficacy against Clostridium difficile spores. The formation of a rust-colored precipitate was observed on Type 430 carriers when testing a peracetic acid (PAA)-based disinfectant with the QCT-2 method. It was hypothesized that the precipitate was indicative of corrosion of the Type 430 carrier, and that corrosion could impact efficacy results. The objective of this study was to compare the suitability of AISI Type 430 to Type 304 stainless steel carriers for evaluating PAA-based disinfectants using the QCT-2 method. Type 304 is more corrosion-resistant than Type 430, is ubiquitous in healthcare environments, and is used in other standard methods. Suitability of the carriers was evaluated by comparing their impacts on efficacy results and PAA degradation rates. In efficacy tests with 1376 ppm PAA, reductions of C. difficile spores after 5, 7 and 10 minutes on Type 430 carriers were at least about 1.5 log10 lower than reductions on Type 304 carriers. In conditions simulating a QCT-2 test, PAA concentration with Type 430 carriers was reduced by approximately 80% in 10 minutes, whereas PAA concentration in the presence of Type 304 carriers remained stable. Elemental analyses of residues on each carrier type after efficacy testing were indicative of corrosion on the Type 430 carrier. Use of Type 430 stainless steel carriers for measuring the efficacy of PAA-based disinfectants should be avoided as it can lead to an underestimation of real life sporicidal efficacy. Type 304 stainless steel carriers are recommended as a suitable alternative.
Highlights
Disinfectants are used in hospitals, long-term care facilities, restaurants, hotels and homes to kill microorganisms that can cause serious illnesses [1]
Materials and methods Bacterial strain and spore preparation and purification The strain used throughout this study was C. difficile ATCC 43598 (American Type Culture Collection, Manassas, VA) because it is the strain specified in the QCT-2 method to support Environmental Protection Agency (EPA) registration
The final spore preparation was suspended in Phosphate Buffered Saline + 0.1% tween80 (PBS-T) and stored at -80 ̊C until used
Summary
Disinfectants are used in hospitals, long-term care facilities, restaurants, hotels and homes to kill microorganisms that can cause serious illnesses [1]. Regulatory authorities rely on the use of standard laboratory methods to predict the effectiveness of disinfectants under real life conditions. The United States Environmental Protection Agency (EPA) and the European Chemicals Agency (ECHA) require data from standard efficacy methods to regulate disinfectant products claiming to kill microbes of public health importance [2, 3]. Disinfectant efficacy may be evaluated by what are known as suspension or carrier methods. The basic steps of suspension methods are as follows: (i) preparation of the microbe test suspension, (ii) exposure to the disinfectant, (iii) neutralization or removal of the active antimicrobial agent, and (iv) enumeration of the surviving population. Carrier tests are useful for predicting the efficacy of disinfectants in specific, real life uses. The two most common carrier materials used in standard disinfection methods are glass and AISI Type 304 austenitic stainless steel (Table 1)
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