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Infection and Immunity, August 1999, p. 4260-4263, Vol. 67, No. 8
Department of Microbiology and
Immunology1 and Center for Vaccine
Development,2 University of Maryland School of
Medicine, Baltimore, Maryland 21201
Received 21 January 1999/Returned for modification 24 March
1999/Accepted 26 May 1999
The locus of enterocyte effacement (LEE) pathogenicity island of
enterohemorrhagic Escherichia coli (EHEC) O157:H7 possesses the same genes in identical order and orientation as the LEE of enteropathogenic E. coli (EPEC) O127:H6 but is unable to
form attaching and effacing (A/E) lesions or to secrete Esp proteins when it is cloned in an E. coli K-12 background. The A/E
phenotype could not be restored by trans complementation
with a variety of cloned EPEC LEE fragments, suggesting functional
and/or regulatory differences between the LEE pathogenicity islands of
EPEC O127:H6 and EHEC O157:H7.
The phenomenon known as attaching
and effacing (A/E) is observed in a family of pathogens that include
the prototypic A/E pathogen enteropathogenic Escherichia
coli (EPEC) as well as enterohemorrhagic E. coli
(EHEC), Citrobacter rodentium, and others (17).
The A/E lesion is characterized by the loss of host cell microvilli (effacement) and intimate attachment of the bacterium to the host membrane on a pedestal of polymerized cytoskeletal elements, notably actin (4, 8, 9). Formation of the A/E lesion is accompanied by a number of signal transduction events in the host cell, including activation of protein kinase C, induction of NF- All the genes necessary for A/E lesion formation by EPEC are encoded on
a pathogenicity island called the locus of enterocyte effacement (LEE)
(14, 15). In EPEC O127:H6, the LEE is a 35,637-bp element
containing 41 predicted open reading frames (ORFs) in at least 10 operons. These genes encode a type III protein translocation complex,
secreted proteins including EspA and Tir, the intestinal adhesin
intimin (encoded by eae), and 23 ORFs of undefined function (2, 10, 12). The LEE from EHEC O157:H7 strain EDL933 has also been recently cloned and sequenced and possesses all the genes
found in the EPEC LEE in the same organization (18). In general, the two LEE elements are 94% conserved at the amino acid level and differ by less than 2% in the regions encoding the protein translocation complex, although divergence of up to 34% is seen in
genes encoding proteins that are believed to interact with the host
(Fig. 1). The EHEC O157:H7 LEE also
encodes a cryptic prophage at one end that is not found in the EPEC
O127:H6 LEE. Analysis suggests that the prophage inserted into the LEE
after the island was already present on the chromosome and is unlikely to encode any known virulence function (18).
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Copyright © 1999, American Society for Microbiology. All rights reserved.
The Cloned Locus of Enterocyte Effacement from Enterohemorrhagic
Escherichia coli O157:H7 Is Unable To Confer the
Attaching and Effacing Phenotype upon E. coli
K-12
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B, and release of
interleukin-8 (reviewed in references 4, 8, and
17).

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FIG. 1.
LEE of EHEC O157:H7 and maps of clones of LEEs from EPEC
O127:H6(pCVD462) and EHEC O157:H7(pJAY1512). The degree of genetic
divergence in each ORF between the EPEC and EHEC LEEs is represented by
shading. R, EcoRI; M, MluI; Sm, SmaI;
K, KpnI.
The sequence divergence between the LEEs is reflected in differences in LEE-associated phenotypes. Unlike EPEC, EHEC O157:H7 does not produce a tyrosine-phosphorylated Tir (6) and requires 6 h to cause A/E lesions in an in vitro assay compared to the 3 h required for A/E formation by EPEC (11). EHEC and EPEC have different modes of pathogenesis and colonize different sites in the intestine, due at least in part to differences in intimin (17, 21). However, it is unclear to what extent the differences between EPEC and EHEC are due solely to differences in the LEE. EPEC and EHEC are known to differ at several other loci, including the large virulence-associated plasmid, pili, the Shiga toxin phage (which is absent in EPEC), and the Per regulator (absent in EHEC) (4, 5, 17). Recent work (3, 16, 20) has also demonstrated regulatory differences between EPEC and EHEC.
Isolation of the LEE in a K-12 background will assist in the examination of LEE function in isolation from other EHEC genomic factors. McDaniel and Kaper (15) demonstrated that the cloned EPEC O127:H6 LEE was able to confer the A/E phenotype upon E. coli K-12, including the ability to secrete EspB and translocate Tir into host cells. Therefore, the EPEC LEE is sufficient for the A/E phenotype in E. coli K-12. Since the LEE has been demonstrated to be necessary for A/E lesions and Esp secretion in EHEC O157:H7 strains 85-170 (3) and 86-24 (7), we hypothesized that the cloned LEE from EHEC should also be able to mediate these functions in E. coli K-12. By cloning the EHEC LEE into K-12 we sought to confirm this hypothesis as well as to determine the extent that the differences between EPEC and EHEC are mediated solely by variations between the two LEE elements.
Cloning and mapping the EHEC LEE.
The EHEC O157:H7 LEE was
cloned from strain 85-170, which is a
stx variant of
strain 84-289. Both 85-170 and 84-289 secrete higher levels of Esp
proteins than do EDL933 and other EHEC strains (7), and we
have observed that they are also more active in the fluorescent actin
stain (FAS) assay. Prior to cloning, the chromosomal locus was mapped
by Southern blotting on digested 85-170 chromosomal DNA and probing
with the four EPEC LEE fragments identified as LEE A through D by
McDaniel et al. (14). The resulting restriction map (Fig. 1)
indicated that the LEE of 85-170 was indistinguishable from that of
O157:H7 strain EDL933 and similar to that of EPEC. The 85-170 LEE was
cloned following the procedure of McDaniel and Kaper (15).
Chromosomal DNA was partially digested with PspAI, an
isoschizomer of SmaI that generates cohesive ends, ligated
into the cosmid vector pCVD551, and transfected into HB101. Colonies
were probed with radiolabeled LEE probes A to D. One cosmid, pJAY1512,
contained a 37-kb DNA insert that hybridized to all four EPEC LEE
probes. Several partial LEE clones were also obtained. pJAY1512 was
mapped with restriction enzymes and LEE probes A through D (Fig. 1).
This process confirmed and extended the 85-170 LEE map obtained from
chromosomal Southern blotting. We found that the cosmid clone pJAY1512
did not contain the LEE-associated prophage found at the extreme end of
the EHEC LEE. In addition to pJAY1512, we also obtained the LEE clone
pLEEO157 (18) from F. Blattner.
pLEEO157 was derived from the chromosome of strain EDL933,
a wild-type EHEC O157:H7 strain, by a FLP recombinase-based method
(19) and has been entirely sequenced (18). It
contains the LEE prophage as well as genes flanking the LEE
(18).
Characterization of the cloned EHEC LEE functions.
Both
pJAY1512 and pLEEO157 in their respective E. coli K-12 host strains (Table 1)
were examined in the FAS assay for A/E lesion formation
(11). The FAS assay involves incubation of bacteria on a
HEp-2 cell tissue culture monolayer for 3 to 6 h during which time
the bacteria form A/E lesions on the surfaces of infected cells. The
addition of phalloidin-fluorescein isothiocyanate conjugate, which
binds to actin, allows visualization of actin condensed below the
bacteria in the A/E lesion. FAS test results were scored blindly by at
least one other independent observer and were repeated at least three
times. When the cloned EHEC LEE was tested in different K-12 genetic
backgrounds, including HB101, W3110, and DH5
, none of the resulting
strains was able to form A/E lesions (Table 1) or secrete Esp
proteins (results not shown). This finding contrasts with that for the
cloned EPEC LEE (Table 1).
|
eae mutant and
the resultant complemented strain colonized the intestine in a manner
characteristic of EPEC rather than of EHEC (21).
To test for complementation of pJAY1512 with cloned EPEC genes,
plasmids containing regions of the EPEC O127:H6 LEE were isolated to
ensure that entire operons within hypervariable regions were represented (Fig. 1 and Table 1). These plasmids were transformed into HB101(pJAY1512) and examined by the FAS assay. None of the resulting complemented strains exhibited FAS (Table 1). As a control,
we transformed pJAY1512 into CVD451, an escN mutant of EHEC
O157:H7 that is unable to form A/E lesions or to secrete Esp proteins
(7). The resultant strain, CVD451(pJAY1512), was positive in the 6-h FAS test, indicating that the EHEC LEE clone could
rescue the chromosomal escN mutation in an EHEC background.
In summary, our data clearly suggest that the genetic differences
between EPEC and EHEC LEE elements are reflected phenotypically when
the LEE is cloned into an E. coli K-12 background. While the
cloned EPEC LEE was sufficient for A/E lesion formation and Esp
secretion in an E. coli K-12 host (15), a
similarly cloned LEE from EHEC was inactive in all these assays. This
result was confirmed with an independent EHEC LEE clone,
pLEEO157. This clone, which was derived from a different
O157:H7 strain in a different laboratory by a different methodology,
was also negative for the A/E phenotype as shown by the FAS test. The
inability of the EHEC LEE clone to mediate A/E lesion formation was not
due to an obvious defect in the cloning of the LEE or the inability of
the LEE in the native O157:H7 strain to mediate A/E lesions. The EHEC
LEE diverges from its EPEC counterpart in several genes, and these genes are a likely source of phenotypic differences between both the
wild-type organisms and their cloned LEEs (18). However, complementation of pJAY1512 with subclones representing the entire EPEC
LEE was unable to confer A/E lesion activity. Our data also exclude the
possibility that failure to form A/E lesions was due to failure to
initially associate with the cell, as transformation of HB101(pJAY1512)
with plasmids encoding adhesins resulted in increased adhesion but not
the A/E phenotype.
These data raise the question of whether only the LEE of EPEC O127:H6
strain E2348/69 is sufficient for A/E lesion formation in an E. coli K-12 background and would imply that the EHEC LEE requires a
factor in trans that is not present in E. coli
K-12. Recent work (3, 16, 20) has shown that EPEC and EHEC
have differences in regulation and also suggest that they may require different factors in trans, a topic which is currently being
investigated in our laboratory.
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ACKNOWLEDGMENTS |
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We thank Tim McDaniel for plasmids and advice, Fred Blattner for strain XL1-Blue (pLEEO157), and Maria S. Dubois and Leslie Wainwright for secreted protein preparations.
NIH grants AI21637 and AI41325 and the Ronald McDonald House charities supported this research.
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FOOTNOTES |
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* Corresponding author. Mailing address: Center for Vaccine Development, University of Maryland School of Medicine, 685 W. Baltimore St., Baltimore, MD 21201. Phone: (410) 706 2344. Fax: (410) 706 0182. E-mail: jkaper{at}umaryland.edu.
Editor: P. E. Orndorff
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REFERENCES |
|---|
|
|
|---|
| 1. | Baldini, M. M., J. B. Kaper, M. M. Levine, D. C. Candy, and H. W. Moon. 1983. Plasmid-mediated adhesion in enteropathogenic Escherichia coli. J. Pediatr. Gastroenterol. Nutr. 2:534-538[Medline]. |
| 2. | Elliott, S., L. A. Wainwright, T. McDaniel, B. MacNamara, M. Donnenberg, and J. B. Kaper. 1998. The complete sequence of the locus of enterocyte effacement (LEE) from enteropathogenic Escherichia coli E2348/69. Mol. Microbiol. 28:1-4[Medline]. |
| 3. | Elliott, S. J., V. Sperandio, J. Mellies, J. A. Girón, T. K. McDaniel, S. Hutcheson, and J. B. Kaper. Unpublished data. |
| 4. | Frankel, G., A. D. Philips, I. Rosenshine, G. Dougan, J. B. Kaper, and S. Knutton. 1998. Enteropathogenic and enterohemorrhagic E. coli: more subversive elements. Mol. Microbiol. 30:911-921[Medline]. |
| 5. | Gómez-Duarte, O. G., and J. B. Kaper. 1995. A plasmid-encoded regulatory region activates chromosomal eaeA expression in enteropathogenic Escherichia coli. Infect. Immun. 63:1767-1776[Abstract]. |
| 6. | Ismaili, A., D. J. Philpott, M. T. Dytoc, and P. M. Sherman. 1995. Signal transduction responses following adhesion of verocytotoxin-producing Escherichia coli. Infect. Immun. 63:3316-3326[Abstract]. |
| 7. | Jarvis, K. G., and J. B. Kaper. 1996. Secretion of extracellular proteins by enterohemorrhagic Escherichia coli via a putative type III secretion system. Infect. Immun. 64:4826-4829[Abstract]. |
| 8. | Kaper, J. B., S. J. Elliott, V. Sperandio, N. T. Perna, G. F. Mayhew, and F. R. Blattner. 1998. Attatching and effacing intestinal histopathology and the locus of enterocyte effacement, p. 163-182. In J. B. Kaper, and A. D. O'Brien (ed.), Escherichia coli O157:H7 and other Shiga-toxin-producing E. coli strains. ASM Press, Washington, D.C. |
| 9. | Kaper, J. B. 1998. EPEC delivers the goods. Trends Microbiol. 6:169-172[Medline]. |
| 10. | Kenny, B., R. DeVinney, M. Stein, D. J. Reinscheid, E. A. Frey, and B. B. Finlay. 1997. Enteropathogenic E. coli (EPEC) transfers its receptor for intimate adherence into mammalian cells. Cell 91:511-520[Medline]. |
| 11. |
Knutton, S.,
T. Baldwin,
P. H. Williams, and A. S. McNeish.
1989.
Actin accumulation at sites of bacterial adhesion to tissue culture cells: basis of a new diagnostic test for enteropathogenic and enterohemorrhagic Escherichia coli.
Infect. Immun.
57:1290-1298 |
| 12. | Knutton, S., I. Rosenshine, M. J. Pallen, I. Nisan, B. C. Neves, C. Bain, C. Wolff, G. Dougan, and G. Frankel. 1998. A novel EspA-associated surface organelle of enteropathogenic Escherichia coli involved in protein translocation into epithelial cells. EMBO J. 17:2166-2176[Medline]. |
| 13. |
Labigne-Roussel, A. F.,
D. Lark,
G. Schoolnik, and S. Falkow.
1984.
Cloning and expression of an afimbrial adhesin (AFA-I) responsible for P blood group-independent, mannose-resistant hemagglutination from a pyelonephritic Escherichia coli strain.
Infect. Immun.
46:251-259 |
| 14. |
McDaniel, T. K.,
K. G. Jarvis,
M. S. Donnenberg, and J. B. Kaper.
1995.
A genetic locus of enterocyte effacement conserved among diverse enterobacterial pathogens.
Proc. Natl. Acad. Sci. USA
92:1664-1668 |
| 15. | McDaniel, T. K., and J. B. Kaper. 1997. A cloned pathogenicity island from enteropathogenic Escherichia coli confers the attaching and effacing phenotype on E. coli K-12. Mol. Microbiol. 23:399-407[Medline]. |
| 16. | Mellies, J., S. J. Elliott, V. Sperandio, M. S. Donnenberg, and J. B. Kaper. The Per regulon of enteropathogenic Escherichia coli: identification of a regulatory cascade and a novel transcriptional activator, the locus of enterocyte effacement (LEE)-encoded regulator (Ler). Mol. Microbiol., in press. |
| 17. |
Nataro, J. P., and J. B. Kaper.
1998.
Diarrheagenic Escherichia coli.
Clin. Microbiol. Rev.
11:142-201 |
| 18. |
Perna, N. T.,
G. F. Mayhew,
G. Pósfai,
S. J. Elliott,
M. S. Donnenberg,
J. B. Kaper, and F. R. Blattner.
1998.
Molecular evolution of a pathogenicity island from enterohemorrhagic Escherichia coli O157:H7.
Infect. Immun.
66:3810-3817 |
| 19. |
Pósfai, G.,
M. D. Koob,
H. A. Kirkpatrick, and F. R. Blattner.
1997.
Versatile insertion plasmids for targeted genome manipulations in bacteria: isolation, deletion, and rescue of the pathogenicity island LEE of the Escherichia coli O157:H7 genome.
J. Bacteriol.
179:4426-4428 |
| 20. | Sperandio, V., J. L. Mellies, W. Nguyen, and J. B. Kaper. Regulation by Quorum sensing of genes encoding the type III secretion system in enterohemorrhagic E. coli O157:H7. Submitted for publication. |
| 21. | Tzipori, S., F. Gunzer, M. S. Donnenberg, L. de Montigny, J. B. Kaper, and A. Donohue-Rolfe. 1995. The role of the eaeA gene in diarrhea and neurological complications in a gnotobiotic piglet model of enterohemorrhagic Escherichia coli infection. Infect. Immun. 63:3621-362[Abstract]. |
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