Assessing the activity of microbicides against bacterial spores: knowledge and pitfalls

Abstract

Summary Bacterial endospores (spores) have a higher intrinsic resistance to microbicides as compared to other microbial forms, most likely due to their impermeable outer layers and low water content. Though structural differences between the spores of various bacterial species may account for observed variations in their resistance to microbicides, flaws in methods for testing the sporicidal activity of microbicides often exaggerate the differences. This has major implications when considering the selection of one or more surrogates to assess microbicides against clinically relevant spore‐formers such as Clostridium difficile. The mounting significance of Cl. difficile as a pathogen is leading to a corresponding increase in the number of commercially available microbicidal formulations claiming activity against its spores without proper differentiation between the product's sporistatic and sporicidal actions. In this review we critically assess the situation and the implications of product claims on the field use of microbicidal products.

Impact of standard test protocols on sporicidal efficacy

“…This is in accordance with our knowledge of sporicides and non-sporicides. 1,2,5 Our study however showed that neutralisation validation data needs to be closely examined. We observed that the normal data reporting as described in standard tests was insufficient to demonstrate that the DDAC or amines were neutralised appropriately.…”

“…1,2,4 The mechanisms leading to a sporistatic or sporicidal effect have recently been reviewed. 5 The structure of the endospores explains their resistance to biocidal products, notably the presence of spore coats, small acid soluble proteins (SASPs), a highly compressed spore membrane and low water content. 3 To measure the efficacy of sporicides against specific bacterial endospores a number of standard sporicidal tests are available.…”

“…The neutralisation of the biocide/biocidal products is also important to determine their sporicidal effect, 4 but is not always effective potentially leading to inappropriate product claims. 5,9 Empirically only a small number of biocides principally oxidising and alkylating agents have been shown to be sporicidal. 1,2,3,7 This study aims to compare the activity of a number of biocides/biocidal products against Bacillus subtilis (the standard strain in EN tests) and C. difficile using a number of standard test protocols commonly used in Europe and the USA.…”

Application of High Pressure with Homogenization, Temperature, Carbon Dioxide, and Cold Plasma for the Inactivation of Bacterial Spores: A Review

“…In this review, we discuss the efficacy of these 4 novel technologies for spore inactivation and their possible applications to food products in order to ensure food sterilization. Some reviews have already discussed spore inactivation by other processing technologies, such as irradiation (Doona and others ), application of microbiocides (Leggett and others ; Leggett and others ), among others. However, in this review, special attention was given to the state of the art of spore inactivation using the 4 technologies cited above, with a focus on food sterilization.…”

Evaluating the Sporicidal Activity of Disinfectants against Clostridium difficile and Bacillus amyloliquefaciens Spores by Using the Improved Methods Based on ASTM E2197-11

“…Commercial sporicidal formulations have been constantly increased due to the emergence of C. difficile infection, as significant nosocomial disease. Current disinfectant products, e.g., oxidizing agents (hydrogen peroxide) and chlorine-releasing agents (sodium hypochlorite, sodium dichloroisocyanurate) ( 13 – 15 ), are continually being improved and new ones are being developed ( 16 – 20 ).…”