Improvement of Methods for Assessing Resistance of Microorganisms to Disinfectants within the System of Sanitary and Bacteriological Testing of Environmental Objects in Health Facilities

Introduction: Monitoring the resistance of microorganisms to disinfectants used in healthcare facilities helps prevent or mitigate risks of the spread of infectious agents in the indoor environment. At the same time, microbiological laboratories face difficulties related to the lack of a ready form of a neutralizer to be used during testing of environmental objects to eliminate the effect of residual amounts of disinfectants on microbial cells.

Objective: To improve the method of assessing resistance of microorganisms to disinfectants using agar with neutralizing components.

Materials and Methods: We used the Dey-Engley neutralizing agar with 1.0 % dextrose, 0.5 % casein peptone, 0.25 % yeast extract, 0.7 % lecithin, 0.6 % sodium thiosulfate, and 0.5 % twin-80 as an agar with neutralizing components. The effectiveness of neutralization of quaternary ammonium compounds, aldehydes, active chlorine and oxygen-based compounds was evaluated in relation to S. aureus ATCC 6538P and E. coli ATCC 10536. Plastic surfaces (bottoms of 12- well plates) were used as test objects. A total of 122 tests were conducted with various solutions of disinfectants in the concentrations recommended by the instructions for use. Test results were then analyzed using Microsoft Office Excel 2016.

Results: The effectiveness of neutralizing residual amounts of disinfectants based on quaternary ammonium compounds using the Dey-Engley neutralizing agar was 95.18 ± 3.2 %; aldehydes – 98.1 ± 2.1 %; active chlorine-based compounds – 93.6 ± 2.4 %, and active oxygen-based compounds – 71.4 ± 5.5 %. When validating the applied technique, we observed no deviations of test results from the established acceptance criteria relative to the approved methodology for assessing sensitivity of microorganisms to disinfectants.

Conclusions: The study results indicate that it is possible to use the Dey-Engley neutralizing agar in a technique for determining resistance of microorganisms to disinfectants. The advantages of the proposed method include standardization of the process and reduction of material and time costs.

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