Determination of the apparent volume of bacteria using example of E. coli strain producing Dr fimbriae

The apparent volume of solute, V ϕ , is a meaningful physicochemical parameter that reflects not only its intrinsic volume, but also how solute interacts with the solvent and alters its structure in the immediate vicinity. In this study, we applied a densitometric method analogous to the determination of apparent molar volume for low-molecular-weight substances to measure V ϕ of bacteria. Two Escherichia coli strains were analyzed: control strain and genetically modified strain expressing Dr fimbriae, surface structures characteristic of uropathogenic E. coli . The measured V ϕ values showed clear differences between the strains, highlighting the role of surface structures and hydration effects. The obtained V ϕ values for the fimbriated strain were nearly twice as high as those for the control strain. The proposed method of measurement has not been previously applied to such systems. It is user-friendly and requires relatively simple instrumentation. By enabling quantification of solvation effects, it may potentially support the development of new antibacterial strategies targeting hydration-related interactions. • Apparent volumes of solutes provide insight into solvation effects. • Densitometry, routinely used for small molecules, is applied here to bacterial cells. • The method enables non-invasive determination of volumetric properties of E. coli. • Fimbriae-producing E. coli show higher apparent volumes than control strain. • Findings support development of hydration-targeting antimicrobial strategies.