{'fraction_non_alphanumeric': 0.03768967205090553, 'fraction_numerical': 0.003915810083210965, 'mean_word_length': 5.701639344262295, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Concentration: a major factor in studying biocidal action.

Several factors are known to influence the activity of the active ingredients in antiseptics, disinfectants and preserved products (collective term used hereafter: biocides).1,2 These include the period of contact with micro-organisms, presence of interfering materials (e.g., organic or inorganic soils), formulation effects, temperature of contact and the nature and type of target micro-organisms. In this last category, for example, due consideration must be given to intrinsic, adaptive and acquired mechanisms of tolerance to biocides observed in bacterial spores, mycobacteria, other Gram-positive bacteria, viruses, yeasts and moulds.3,4 In addition, the efficacy of antimicrobial products depends on, and varies significantly with, formulation effects, which can often enhance activity despite the presence of lower levels of the biocide.3,4 All these factors are important in evaluating the modes of action of, and mechanisms of resistance to, biocides and are often regrettably overlooked. An example is the effect of concentration, which is particularly important in assessing the clinical significance of varying microbial tolerances to biocides. Most biocides are formulated for optimal, broad-spectrum antimicrobial activity at high concentrations for direct use on an inanimate (‘disinfectant’), or living (‘antiseptic’), surface; therefore concentration has obvious practical and clinical implications, as discussed below. The relationship between concentration and antimicrobial activity of biocides alone is not a simple one. If activity is represented by the concentration exponent (η), it can be shown mathematically that biocides with a high η-value, e.g., alcohols and phenolic compounds, are affected markedly by changes in concentration (or dilution), whereas those with a low η-value, e.g., organomercurials and formaldehyde, are influenced to a lesser extent.5 Furthermore, Hugo and Denyer6 have observed a possible relationship between the η-value and the