Chrysotile fibers penetrate Escherichia coli cell membrane and cause cell bursting by sliding friction force on agar plates.

A mixture (50 microl) consisting of Escherichia coli cells, chrysotile fibers, and 200 mM NaCl was added to 2% agar plates and spread with a plastic stir stick. An apparatus was developed to generate a sliding friction force on the surface of the plate by applying a fixed vertical reaction force to the stir stick while turning the plate. This operation was defined as chrysotile-exposure. The number of living cells, expressed as colony forming units, was reduced in proportion to the duration of chrysotile-exposure. The decrease in the number of living cells was greater following 120 s of chrysotile-exposure than crocidolite- or amosite-exposure. There was no decrease in the number of living cells exposed to chrysotile on 0.5% agar even after 120 s. The number of living cells after chrysotile-exposure decreased with increasing chrysotile concentration. Leakage of beta-galactosidase from cells increased with increasing duration of chrysotile-exposure. Transmission and scanning electron microscopy observation of E. coli revealed chrysotile penetration of the cell membrane. These results show that chrysotile fibers destroy cells by penetration. The driving force for the chrysotile penetration was the sliding friction force, as the number of living cells following chrysotile-exposure decreased with increasing exposure times, but did not decrease following chrysotile-exposure on a low concentration of agar, which provided cells with low sliding friction force.