The starvation-survival of Escherichia coli in seawater was assessed by plate and epifluorescence counts, 3H-label decrease, cellular DNA concentrations, and metabolic activities. These assays were performed on two types of populations, adapted and non-adapted to seawater. The number of viable cells in the adapted population remained constant throughout starvation-survival in sterile seawater. In contrast, a significant decrease in the ability of the non-adapted E. coli to form colonies on plates following starvation-survival in sterile seawater was observed. However, this drop in viable counts was not mirrored by the epifluorescence counts and 3H-label, which did not show major changes for either population during the experiments, indicating maintenance of the number of cells. In addition, a significant increase in and subsequent maintenance of DNA content and thymidine incorporation was observed for both populations during starvation-survival in sterile seawater. The changes in cell-attached exoproteolytic activity and electron transport system activity showed that adapted and non-adapted E. coli cells maintain their metabolic potential. Cell-free exoproteolytic activity was drastically reduced in both populations. Adapted cells showed higher electron transport system activity and thymidine incorporation than non-adapted cells at the onset of starvation-survival. The effect of previous adaptation on E. coli starvation-survival, as assessed by plate counts and 3H-label decrease, was also observed in raw seawater. It seems from these data that the biological potential of E. coli cells suspended in sterile seawater has not been switched off or impaired seriously.
A rapid and direct fluorogenic assay was used to detect Escherichia coli in urine. Most clinical isolates of E. coli produce β‐glucuronidase, whereas almost all other enterobacteria lack the enzyme. Spectrofluorimetric assay of β‐glucuronidase, without previous induction, was performed on growing and starved uropathogenic E. coli in artificial urine. The presence of 103 cfu ml‐1 of E. coli in urine was detected by β‐glucuronidase activity in less than 1 h. These results indicate that β‐glucuronidase is a rapid, specific and sensitive indicator of the presence of E. coli in urine, and provide additional information on the biological state of the infecting bacterial population.
A kinetic model of colony formation was proposed by Hattori, based on a count of the colonies that appear on a plate in successive short intervals of time. In this model, three parameters (lambda, tr and N infinity) are defined, which reflect the ability of a bacterium to yield colonies and allow us to described the dynamics of bacterial populations in soil and of E. coli at different growth phases. In this paper we report a reparametrization of the kinetic model of colony formation, with the aim of facilitating more accurate calculation of lambda and tr. Moreover, we observed that during the starvation of E. coli and K. pneumoniae in urine, lambda can be used to assess survival, since this parameter clearly decreases during starvation. Retardation time values (tr) were similar in E. coli and K. pneumoniae throughout the starvation experimental period.
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