In the field of microbiology, the efficacy of a biocidal active can be represented by different quantities. Often used are the minimum inhibitory concentration (i.e. “MIC”), which measures the minimum concentration of biocide above which the growth of a bacterial population is inhibited; and the minimum bactericidal concentration (“MBC”) beyond which bacteria are killed. Different actives are usually ranked against these quantities and different bacteria and fungi, to reflect how efficient and broad they are as antibacterial agents.<br/>Bleach and alcohol are generally used as the first measure to control bacterial growth; they are cheap, available and easy to implement at industrial levels. Their mechanism, based on oxidation, leaves nothing to the imagination: efficacy is directly related to the dose added. On the other hand, the use of more complex molecules, such as quaternized surfactants, which belong to the field of Soft Matter, had led to fascinating questions that only such objects could pose. Of particular interest is the way by which biocidal efficacy relates to all thermodynamic aspects of such actives being surfactants which can self-assemble, lower surface/interfacial tensions… Unlike bleach or short-chain alcohols, surfactants present several different attributes of thermodynamic origin, which may impact (positively or negatively) their efficiency as biocides: a critical micellar concentration (“CMC”) or concentration under which surfactants exist as “unimers”, and as micelles above; a the micelle aggregation number, i.e. the number of surfactant unimers involved in a single micelle; a micelles of particular shape. To be efficacious, must cationic surfactants be in a free “unimer” state, or present as micelles? Do MBCs need to be above or below the CMC, as a general rule, or is it more complex than that? Another question of interest lies in the membrane activity of such surfactants. While it is well accepted that they kill bacteria by contact, disrupting the cell membrane as soon as they touch it, numerous questions remain to be answered. How do their structures affect the bacteria membrane disruption? What is the contact time impact on their biocidal activity? Can the same quaternary ammonium surfactant be involved in consecutive bacterial death? We will provide different examples of cases where such questions, at the interface between soft matter and biology, pose a challenge for the scientist.<br/>

Bacterial interactions with quaternary ammonium surfactants

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.