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From commensal to pathogen: translocation of Enterococcus faecalis from the midgut to the hemocoel of Manduca sexta.

Mason KL, Stepien TA, Blum JE, Holt JF, Labbe NH, Rush JS, Raffa KF, Handelsman J - MBio (2011)

Bottom Line: While controversy remains regarding Bacillus thuringiensis toxin-induced killing, our laboratory previously found that under some conditions, the midgut microbiota is essential for B. thuringiensis toxin killing of Lymantria dispar (N.Acad.This work reconciles much of the apparently contradictory previous data and reveals that the M. sexta-E. faecalis system provides a model for mammalian sepsis.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut, USA.

ABSTRACT

Unlabelled: A dynamic homeostasis is maintained between the host and native bacteria of the gastrointestinal tract in animals, but migration of bacteria from the gut to other organs can lead to disease or death. Enterococcus faecalis is a commensal of the gastrointestinal tract; however, Enterococcus spp. are increasingly frequent causes of nosocomial infections with a high mortality rate. We investigated the commensal-to-pathogen switch undergone by E. faecalis OG1RF in the lepidopteran model host Manduca sexta associated with its location in the host. E. faecalis persists in the harsh midgut environment of M. sexta larvae without causing apparent illness, but injection of E. faecalis directly into the larval hemocoel is followed by rapid death. Additionally, oral ingestion of E. faecalis in the presence of Bacillus thuringiensis insecticidal toxin, a pore-forming toxin that targets the midgut epithelium, induces an elevated mortality rate. We show that the loss of gut integrity due to B. thuringiensis toxin correlates with the translocation of E. faecalis from the gastrointestinal tract into the hemolymph. Upon gaining access to the hemolymph, E. faecalis induces an innate immune response, illustrated by hemocyte aggregation, in larvae prior to death. The degree of hemocyte aggregation is dependent upon the route of E. faecalis entry. Our data demonstrate the efficacy of the M. sexta larval model system in investigating E. faecalis-induced sepsis and clarifies controversies in the field regarding the events leading to larval death following B. thuringiensis toxin exposure.

Importance: This study advances our knowledge of Enterococcus faecalis-induced sepsis following translocation from the gut and provides a model for mammalian diseases in which the spatial distribution of bacteria determines disease outcomes. We demonstrate that E. faecalis is a commensal in the gut of Manduca sexta and a pathogen in the hemocoel, resulting in a robust immune response and rapid death, a process we refer to as the "commensal-to-pathogen" switch. While controversy remains regarding Bacillus thuringiensis toxin-induced killing, our laboratory previously found that under some conditions, the midgut microbiota is essential for B. thuringiensis toxin killing of Lymantria dispar (N. A. Broderick, K. F. Raffa, and J. Handelsman, Proc. Natl. Acad. Sci. U. S. A. 103:15196-15199, 2006; B. Raymond, et al., Environ. Microbiol. 11:2556-2563, 2009; P. R. Johnston, and N. Crickmore, Appl. Environ. Microbiol. 75:5094-5099, 2009). We and others have demonstrated that the role of the midgut microbiota in B. thuringiensis toxin killing is dependent upon the lepidopteran species and formulation of B. thuringiensis toxin (N. A. Broderick, K. F. Raffa, and J. Handelsman, Proc. Natl. Acad. Sci. U. S. A. 103:15196-15199, 2006; N. A. Broderick, et al., BMC Biol. 7:11, 2009). This work reconciles much of the apparently contradictory previous data and reveals that the M. sexta-E. faecalis system provides a model for mammalian sepsis.

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Related in: MedlinePlus

The presence of B. thuringiensis toxin during E. faecalis feeding promotes larval death. Early-5th-instar larvae were force fed PBS, E. faecalis alone (Ef), B. thuringiensis toxin alone (Toxin), or E. faecalis and B. thuringiensis toxin together (Ef + Toxin). Larvae were given unmodified food ad libitum for the duration of the experiment. One experimental group was force fed PBS, and food was subsequently removed for the duration of the experiment (Starved). Larval deaths were recorded over time (n = 12/group, 1 representative experiment of 12).
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f2: The presence of B. thuringiensis toxin during E. faecalis feeding promotes larval death. Early-5th-instar larvae were force fed PBS, E. faecalis alone (Ef), B. thuringiensis toxin alone (Toxin), or E. faecalis and B. thuringiensis toxin together (Ef + Toxin). Larvae were given unmodified food ad libitum for the duration of the experiment. One experimental group was force fed PBS, and food was subsequently removed for the duration of the experiment (Starved). Larval deaths were recorded over time (n = 12/group, 1 representative experiment of 12).

Mentions: Ingested B. thuringiensis toxin promotes larval death (14), but the mechanism of killing following pore formation remains under debate. To test the effect of E. faecalis in the presence of B. thuringiensis toxin, we force fed or injected early-5th-instar larvae. E. faecalis and E. faecalis plus toxin induced rapid larval death at similar rates when injected (Fig. 2). Phosphate-buffered saline (PBS) induced no death when fed or injected, and E. faecalis induced no death when fed to larvae alone. Larvae fed B. thuringiensis toxin alone refused all food and died slowly over time from apparent starvation. Larvae fed toxin alone or PBS did not melanize. However, larvae fed E. faecalis plus toxin succumbed to a sepsis-like infection that resulted in rapid death. These data support the hypothesis that in the presence of B. thuringiensis toxin, E. faecalis translocates from the gut to the hemocoel and causes septic death.


From commensal to pathogen: translocation of Enterococcus faecalis from the midgut to the hemocoel of Manduca sexta.

Mason KL, Stepien TA, Blum JE, Holt JF, Labbe NH, Rush JS, Raffa KF, Handelsman J - MBio (2011)

The presence of B. thuringiensis toxin during E. faecalis feeding promotes larval death. Early-5th-instar larvae were force fed PBS, E. faecalis alone (Ef), B. thuringiensis toxin alone (Toxin), or E. faecalis and B. thuringiensis toxin together (Ef + Toxin). Larvae were given unmodified food ad libitum for the duration of the experiment. One experimental group was force fed PBS, and food was subsequently removed for the duration of the experiment (Starved). Larval deaths were recorded over time (n = 12/group, 1 representative experiment of 12).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3101781&req=5

f2: The presence of B. thuringiensis toxin during E. faecalis feeding promotes larval death. Early-5th-instar larvae were force fed PBS, E. faecalis alone (Ef), B. thuringiensis toxin alone (Toxin), or E. faecalis and B. thuringiensis toxin together (Ef + Toxin). Larvae were given unmodified food ad libitum for the duration of the experiment. One experimental group was force fed PBS, and food was subsequently removed for the duration of the experiment (Starved). Larval deaths were recorded over time (n = 12/group, 1 representative experiment of 12).
Mentions: Ingested B. thuringiensis toxin promotes larval death (14), but the mechanism of killing following pore formation remains under debate. To test the effect of E. faecalis in the presence of B. thuringiensis toxin, we force fed or injected early-5th-instar larvae. E. faecalis and E. faecalis plus toxin induced rapid larval death at similar rates when injected (Fig. 2). Phosphate-buffered saline (PBS) induced no death when fed or injected, and E. faecalis induced no death when fed to larvae alone. Larvae fed B. thuringiensis toxin alone refused all food and died slowly over time from apparent starvation. Larvae fed toxin alone or PBS did not melanize. However, larvae fed E. faecalis plus toxin succumbed to a sepsis-like infection that resulted in rapid death. These data support the hypothesis that in the presence of B. thuringiensis toxin, E. faecalis translocates from the gut to the hemocoel and causes septic death.

Bottom Line: While controversy remains regarding Bacillus thuringiensis toxin-induced killing, our laboratory previously found that under some conditions, the midgut microbiota is essential for B. thuringiensis toxin killing of Lymantria dispar (N.Acad.This work reconciles much of the apparently contradictory previous data and reveals that the M. sexta-E. faecalis system provides a model for mammalian sepsis.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut, USA.

ABSTRACT

Unlabelled: A dynamic homeostasis is maintained between the host and native bacteria of the gastrointestinal tract in animals, but migration of bacteria from the gut to other organs can lead to disease or death. Enterococcus faecalis is a commensal of the gastrointestinal tract; however, Enterococcus spp. are increasingly frequent causes of nosocomial infections with a high mortality rate. We investigated the commensal-to-pathogen switch undergone by E. faecalis OG1RF in the lepidopteran model host Manduca sexta associated with its location in the host. E. faecalis persists in the harsh midgut environment of M. sexta larvae without causing apparent illness, but injection of E. faecalis directly into the larval hemocoel is followed by rapid death. Additionally, oral ingestion of E. faecalis in the presence of Bacillus thuringiensis insecticidal toxin, a pore-forming toxin that targets the midgut epithelium, induces an elevated mortality rate. We show that the loss of gut integrity due to B. thuringiensis toxin correlates with the translocation of E. faecalis from the gastrointestinal tract into the hemolymph. Upon gaining access to the hemolymph, E. faecalis induces an innate immune response, illustrated by hemocyte aggregation, in larvae prior to death. The degree of hemocyte aggregation is dependent upon the route of E. faecalis entry. Our data demonstrate the efficacy of the M. sexta larval model system in investigating E. faecalis-induced sepsis and clarifies controversies in the field regarding the events leading to larval death following B. thuringiensis toxin exposure.

Importance: This study advances our knowledge of Enterococcus faecalis-induced sepsis following translocation from the gut and provides a model for mammalian diseases in which the spatial distribution of bacteria determines disease outcomes. We demonstrate that E. faecalis is a commensal in the gut of Manduca sexta and a pathogen in the hemocoel, resulting in a robust immune response and rapid death, a process we refer to as the "commensal-to-pathogen" switch. While controversy remains regarding Bacillus thuringiensis toxin-induced killing, our laboratory previously found that under some conditions, the midgut microbiota is essential for B. thuringiensis toxin killing of Lymantria dispar (N. A. Broderick, K. F. Raffa, and J. Handelsman, Proc. Natl. Acad. Sci. U. S. A. 103:15196-15199, 2006; B. Raymond, et al., Environ. Microbiol. 11:2556-2563, 2009; P. R. Johnston, and N. Crickmore, Appl. Environ. Microbiol. 75:5094-5099, 2009). We and others have demonstrated that the role of the midgut microbiota in B. thuringiensis toxin killing is dependent upon the lepidopteran species and formulation of B. thuringiensis toxin (N. A. Broderick, K. F. Raffa, and J. Handelsman, Proc. Natl. Acad. Sci. U. S. A. 103:15196-15199, 2006; N. A. Broderick, et al., BMC Biol. 7:11, 2009). This work reconciles much of the apparently contradictory previous data and reveals that the M. sexta-E. faecalis system provides a model for mammalian sepsis.

Show MeSH
Related in: MedlinePlus