A novel technique for the study of bacterial cell mechanical properties

A micromanipulation method is described for measuring the bursting forces of bacteria and relating them to cell size. At a compression speed of 6.2 μm s^-1, bursting forces of three samples of rapidly growing Staphylococcus epidermis from a batch culture varied from 3 to 34 μN with an average value of 13.8μN (standard error 0.8 μN). Escherichia coli grown in continuous culture at a specific growth rate of 0.5 h^-1 had bursting forces varying from 1 to 9 μN with an average value of 3.6 μN (standard error 0.4μN). In squeeze-hold experiments, force relaxation was observed, which was attributed to water loss from the cells, or viscoelasticity, or both. At high compression speed, such as 6.2 μm s^-1, this relaxation could be neglected. Micromanipulation strength measurements might be used in studies of cell mechanical disruption and of the dependence of cell strength on cell physiology.