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Grazing protozoa and the evolution of the Escherichia coli O157:H7 Shiga toxin-encoding prophage.

Steinberg KM, Levin BR - Proc. Biol. Sci. (2007)

Bottom Line: Why then does E. coli O157:H7 code for virulence determinants, like the Shiga toxins (Stxs), responsible for the morbidity and mortality of colonized humans?Here, we test the hypothesis that the carriage of the Stx-encoding prophage of E. coli O157:H7 increases the rate of survival of E. coli in the presence of grazing protozoa, Tetrahymena pyriformis.In the presence but not the absence of Tetrahymena, the carriage of the Stx-encoding prophage considerably augments the fitness of E. coli K-12 as well as clinical isolates of E. coli O157 by increasing the rate of survival of the bacteria in the food vacuoles of these ciliates.

View Article: PubMed Central - PubMed

Affiliation: Graduate Program in Population Biology, Ecology and Evolution, Emory University, Atlanta, GA 30322, USA. kmeltz@emory.edu

ABSTRACT
Humans play little role in the epidemiology of Escherichia coli O157:H7, a commensal bacterium of cattle. Why then does E. coli O157:H7 code for virulence determinants, like the Shiga toxins (Stxs), responsible for the morbidity and mortality of colonized humans? One possibility is that the virulence of these bacteria to humans is coincidental and these virulence factors evolved for and are maintained for other roles they play in the ecology of these bacteria. Here, we test the hypothesis that the carriage of the Stx-encoding prophage of E. coli O157:H7 increases the rate of survival of E. coli in the presence of grazing protozoa, Tetrahymena pyriformis. In the presence but not the absence of Tetrahymena, the carriage of the Stx-encoding prophage considerably augments the fitness of E. coli K-12 as well as clinical isolates of E. coli O157 by increasing the rate of survival of the bacteria in the food vacuoles of these ciliates. Grazing protozoa in the environment or natural host are likely to play a significant role in the ecology and maintenance of the Stx-encoding prophage of E. coli O157:H7 and may well contribute to the evolution of the virulence of these bacteria to colonize humans.

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Related in: MedlinePlus

Mixtures of E. coli C600 with and without the Stx2-encoding prophage, C600 and C600P, respectively, in the presence and absence of Tetrahymena. Means ±s.e. for two control (Tetrahymena-free) and six experimental (with Tetrahymena) cultures. (a) Change in ratio of C600P/C600 in the presence and absence of Tetrahymena. Open circles, with Tetrahymena; filled circles, without Tetrahymena. (b) Change in the total densities of bacteria and Tetrahymena in the culture shown in (a). Filled squares, total bacteria; open squares, Tetrahymena.
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fig1: Mixtures of E. coli C600 with and without the Stx2-encoding prophage, C600 and C600P, respectively, in the presence and absence of Tetrahymena. Means ±s.e. for two control (Tetrahymena-free) and six experimental (with Tetrahymena) cultures. (a) Change in ratio of C600P/C600 in the presence and absence of Tetrahymena. Open circles, with Tetrahymena; filled circles, without Tetrahymena. (b) Change in the total densities of bacteria and Tetrahymena in the culture shown in (a). Filled squares, total bacteria; open squares, Tetrahymena.

Mentions: As shown in figure 1a, there is no change in the ratio of C600P to C600 in the Tetrahymena-free controls but a nearly two order of magnitude increase in the ratio of C600P to C600 in the cultures with these grazing ciliates (p<0.002). The C600P/C600 ratio (figure 1a) increases when the density of Tetrahymena increases and levels off when there is no longer a change in the density of Tetrahymena.


Grazing protozoa and the evolution of the Escherichia coli O157:H7 Shiga toxin-encoding prophage.

Steinberg KM, Levin BR - Proc. Biol. Sci. (2007)

Mixtures of E. coli C600 with and without the Stx2-encoding prophage, C600 and C600P, respectively, in the presence and absence of Tetrahymena. Means ±s.e. for two control (Tetrahymena-free) and six experimental (with Tetrahymena) cultures. (a) Change in ratio of C600P/C600 in the presence and absence of Tetrahymena. Open circles, with Tetrahymena; filled circles, without Tetrahymena. (b) Change in the total densities of bacteria and Tetrahymena in the culture shown in (a). Filled squares, total bacteria; open squares, Tetrahymena.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2211389&req=5

fig1: Mixtures of E. coli C600 with and without the Stx2-encoding prophage, C600 and C600P, respectively, in the presence and absence of Tetrahymena. Means ±s.e. for two control (Tetrahymena-free) and six experimental (with Tetrahymena) cultures. (a) Change in ratio of C600P/C600 in the presence and absence of Tetrahymena. Open circles, with Tetrahymena; filled circles, without Tetrahymena. (b) Change in the total densities of bacteria and Tetrahymena in the culture shown in (a). Filled squares, total bacteria; open squares, Tetrahymena.
Mentions: As shown in figure 1a, there is no change in the ratio of C600P to C600 in the Tetrahymena-free controls but a nearly two order of magnitude increase in the ratio of C600P to C600 in the cultures with these grazing ciliates (p<0.002). The C600P/C600 ratio (figure 1a) increases when the density of Tetrahymena increases and levels off when there is no longer a change in the density of Tetrahymena.

Bottom Line: Why then does E. coli O157:H7 code for virulence determinants, like the Shiga toxins (Stxs), responsible for the morbidity and mortality of colonized humans?Here, we test the hypothesis that the carriage of the Stx-encoding prophage of E. coli O157:H7 increases the rate of survival of E. coli in the presence of grazing protozoa, Tetrahymena pyriformis.In the presence but not the absence of Tetrahymena, the carriage of the Stx-encoding prophage considerably augments the fitness of E. coli K-12 as well as clinical isolates of E. coli O157 by increasing the rate of survival of the bacteria in the food vacuoles of these ciliates.

View Article: PubMed Central - PubMed

Affiliation: Graduate Program in Population Biology, Ecology and Evolution, Emory University, Atlanta, GA 30322, USA. kmeltz@emory.edu

ABSTRACT
Humans play little role in the epidemiology of Escherichia coli O157:H7, a commensal bacterium of cattle. Why then does E. coli O157:H7 code for virulence determinants, like the Shiga toxins (Stxs), responsible for the morbidity and mortality of colonized humans? One possibility is that the virulence of these bacteria to humans is coincidental and these virulence factors evolved for and are maintained for other roles they play in the ecology of these bacteria. Here, we test the hypothesis that the carriage of the Stx-encoding prophage of E. coli O157:H7 increases the rate of survival of E. coli in the presence of grazing protozoa, Tetrahymena pyriformis. In the presence but not the absence of Tetrahymena, the carriage of the Stx-encoding prophage considerably augments the fitness of E. coli K-12 as well as clinical isolates of E. coli O157 by increasing the rate of survival of the bacteria in the food vacuoles of these ciliates. Grazing protozoa in the environment or natural host are likely to play a significant role in the ecology and maintenance of the Stx-encoding prophage of E. coli O157:H7 and may well contribute to the evolution of the virulence of these bacteria to colonize humans.

Show MeSH
Related in: MedlinePlus