Production of fimbrial adhesins K99 and F41 by enterotoxigenic Escherichia coli as a function of growth-rate domain

Abstract

The production of fimbrial adhesins K99 and F41 by enterotoxigenic Escherichia coli has been measured in steady-state chemostat experiments at various specific growth rates (μs) and in a recycling fermentor across a range of μ values falling to <0.004 h-1. It has been demonstrated that the production of K99 and F41 fimbriae is correlated with μ both in aerobic and anaerobic chemostat experiments. A significant production of fimbriae was only detected at μ values higher than 0.2 h-1. This behavior was further examined by culturing the bacteria in a recycling fermentor with complete biomass retention. It could be shown that the production of K99 and F41 fimbriae only occurred during balanced growth, with a high biomass yield at μ values higher than 0.04 h-1 corresponding to mass doubling times (t(d)) of less than 17 h. The production of both fimbriae halted during balanced growth with a lower biomass yield (at μ values between 0.012 and 0.04 h-1 corresponding to t(d) values between 17 and 58 h) and unbalanced stringent growth (at μ values lower than 0.012 h-1 or t(d) values higher than 58 h). The external pH of the medium greatly influenced the production of both K99 and F41 fimbriae. At pH values lower than 7, the production of fimbriae was strongly inhibited. Also, at pH values higher than 7, a decrease in production was observed. The consequences of the observed phenomena for the pathogenic behavior of this E. coli strain are discussed.