Suitability of Methods to Determine Resistance to Biocidal Active Substances and Disinfectants—A Systematic Review

Abstract

Biocide resistance is an increasing concern. However, it is currently unknown if an elevated MIC value for an isolate correlates with a lower log10 reduction in suspension tests or carrier tests. The aim of this review was therefore to evaluate if isolates with a suspected tolerance to a biocidal active substance reveal an elevated MIC value and an impaired efficacy in suspension tests and carrier tests. A Medline search was done on 6 July 2022 using the following terms: “resistance biocidal MIC suspension” (16 hits), “resistance biocidal MIC carrier” (22 hits), “resistance biocidal suspension carrier” (41 hits), “tolerance biocidal MIC suspension” (1 hit), “tolerance biocidal MIC carrier” (4 hits) and “tolerance biocidal suspension carrier” (3 hits). Studies were included when a tolerance or resistance to the biocidal active substance or disinfectant was suspected and at least two of the three endpoints were evaluated in parallel in comparison to the control isolates. In three out of five studies, the elevated MIC values did not correlate with an impaired bactericidal efficacy against the biocide-tolerant isolates. In three out of five studies, an impaired activity in the suspension tests was described that correlated with an impaired efficacy in the carrier tests (peracetic acid-tolerant K. pneumoniae and glutaraldehyde-tolerant M. chelonae; the two other studies did not allow a comparison. Overall, the results from the suspension tests and tests under practical conditions allowed to determine a clinically relevant resistance.