Response of populations of human faecal bacteria to viscosity in vitro

The effects of viscosity on cultures of human faecal bacteria in vitro were studied. The composition of the microbial populations which developed during in vitro incubation were affected by viscosity. The proportion of Bacteroides species was decreased at high viscosities and it is concluded that the 'viscotolerance' of a bacterial population contributes towards its composition. Viscosity alters the enzyme activity of cultures. Cell-associated total, and specific, β-galactosidase activities of cultures of human faecal bacteria were decreased at high viscosity.