Infect Immun, February 1998, p. 856-861, Vol. 66, No. 2
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Cell-Specific Proteins Synthesized by
Salmonella typhimurium
Lisa
Burns-Keliher,*
Cheryl A.
Nickerson,
Brian J.
Morrow, and
Roy
Curtiss III
Department of Biology, Washington University,
St. Louis, Missouri 63130
Received 18 July 1997/Returned for modification 26 August
1997/Accepted 21 November 1997
 |
ABSTRACT |
Studies of the proteins synthesized by Salmonella
typhimurium during growth within tissue culture cells have
previously focused on a single cell type. In the present study we
examine the different protein patterns exhibited by S. typhimurium during growth within three different cell types
relevant to those it would encounter throughout the course of a natural
infection, including intestinal epithelial cells (Intestine-407),
macrophages (J774.A, rat bone marrow-derived macrophages, and
mouse bone marrow-derived macrophages), and liver cells (NMuLi).
Side-by-side comparisons reveal that S. typhimurium
responds to these different cellular environments with specific
patterns of protein synthesis unique to each cell type. The numbers of
proteins detected in each cell line are as follows: 142 proteins in
Intestine-407, of which 58 appear to be unique to growth within this
cell line; 413 proteins in J774.A, of which 157 appear to be unique;
260 proteins in rat bone marrow-derived macrophages, of which 40 appear
to be unique; 336 proteins in mouse bone marrow-derived macrophages, of
which 113 appear to be unique; and 183 proteins in NMuLi, of which 91 appear to be unique.
| |
TEXT |
Facultative anaerobes such as
Salmonella typhimurium respond dynamically to the particular
constraints of their diverse environments through the expression and/or
repression of groups of genes, each designed to confer a selective
advantage under specific environmental conditions (17, 22-24, 27,
28). This phenomenon is termed global regulation (9).
Studies have been done which delineate the groups of proteins
salmonellae synthesize while growing in culture under various
environmental conditions, as well as within cultured mammalian cells,
and not surprisingly, many of the genes involved in global regulation
also affect virulence of the organism (15, 16). Salmonellae
are able to attach to, invade (8), and survive within
eukaryotic cells (7). During the course of an infection, the
organism invades a number of different cell types, including the
intestinal epithelium (25, 26), various macrophages
(2), and deep tissues such as the liver and spleen (5,
6). The mechanisms which facilitate tropism toward such a broad
spectrum of host cells have not been specifically addressed. Although
numerous studies have been done on the intracellular protein synthesis
patterns of S. typhimurium in cultured cell lines, most
laboratories have limited their investigations to a single cell type
(1, 12) or occasionally to various cell lines representing a
single cell type (2). In an effort to address the extent to
which S. typhimurium is capable of responding to each unique
intracellular environment, protein synthesis was analyzed with a single
virulent SL1344 strain, 
3339, during growth within three distinct
cell types: intestinal epithelium, macrophages, and normal murine
liver. These cell types are representative of those which would be
encountered by S. typhimurium during the natural course of
infection. The different cell lines were all infected with S. typhimurium, and the intracellular protein synthesis patterns were
examined by two-dimensional (2-D) gel electrophoresis. The organism was
observed to synthesize proteins specific to each cell type examined,
presenting evidence that S. typhimurium dynamically responds
to each unique environment encountered during the establishment of
systemic infection.
Maintenance and growth conditions of the mammalian and bacterial
cells.
The three commercially available established cell lines
used for this study were all purchased from the American Type Culture Collection (ATCC), Rockville, Md. They include the human embryonic intestinal epithelial cell line Intestine-407 (Int-407; purchased as
ATCC CCL6 [11]), the murine macrophage-like cell line
J774.A (ATCC TIB67 [21]), and the murine normal liver
epithelial cell line NMuLi (ATCC CRL1638 [19]). These
cell lines were maintained in Eagle's minimal essential medium (Gibco
BRL, Gaithersburg, Md.) (EMEM) containing 10% fetal calf serum (FCS;
Sigma, St. Louis, Mo.) and 2 mM glutamine at 37°C in a 5%
CO2 environment. Working stocks were passaged every 3 to 5 days for up to 15 passages. Cells were seeded at 5 × 105/ml/well into six-well plates (Costar, Cambridge, Mass.)
and used the following day at near 95% confluency for purposes of the
labeling procedure.
Bone marrow-derived macrophages were prepared by culturing bone marrow
cells from femurs and tibias of either Sprague-Dawley rats (Harlan
Sprague Dawley, Indianapolis, Ind.) or BALB/c mice (Harlan Sprague
Dawley) following previously described procedures (2). Cells
were maintained in 75-cm2 flasks in Dulbecco's modified
Eagle medium (Gibco BRL) plus 10% FCS, 5% horse serum (Sigma, St.
Louis, Mo.), 10% conditioned medium from L929 cells (L-cells), 1 mM
glutamine, and 1% penicillin for 24 h in a 5% CO2
environment. Nonadherent bone marrow cells were removed after 24 h, spent medium was replaced, and the cells were incubated for an
additional 5 days. Prior to their use in infection experiments,
macrophages were scraped from the surface of the tissue culture flask;
resuspended in fresh Dulbecco's modified Eagle medium supplemented
with 10% FCS, 5% horse serum, and 10% L-cell-conditioned medium
(without antibiotics); and used to seed six-well tissue culture plates
at a concentration of 5 × 105/ml and used the
following day at 95% confluency.
The bacterial strain used in this study was S. typhimurium
3339, an animal-passaged isolate of the virulent SL1344 wild type (10). 3339 was first grown in Luria broth (13)
as an aerated overnight culture at 37°C. It was then inoculated at a
dilution of 1:100 into 30 ml of prewarmed EMEM and incubated statically overnight in a 5% CO2 atmosphere at 37°C. Titers in EMEM
were comparable to those obtained in Luria broth (1.9 × 108). The culture was centrifuged at 8,800 × g for 10 min and resuspended in 10 ml of fresh EMEM, and 1 ml per well was added to the monolayers at a multiplicity of infection
of approximately 100:1.
Labeling the proteins synthesized intracellularly by 3339.
Int-407, J774.A, and NMuLi cells were seeded at 5 × 105/ml and allowed to grow to near 95% confluency in
six-well plates. Primary macrophage cultures were plated as described
above. Monolayers were washed twice with prewarmed Hanks' balanced
salt solution, and each well received 1 ml of the 3339 suspension
described above at a multiplicity of infection of approximately 100:1.
All incubations were done in a 5% CO2 atmosphere at
37°C. Attachment and invasion were allowed to proceed for 2 h.
Supernatant fluid was then removed, the monolayers were washed three
times with Hanks' balanced salt solution, and fresh EMEM containing
gentamicin (100 µg/ml), cycloheximide (200 µg/ml), and
Tran35S Label (150 µCi/ml; specific activity, 1,092 Ci/mmol) (ICN Radiochemicals, Irvine, Calif.) was added. This labeling
solution contains a mixture of [35S]methionine and
[35S]cysteine. Control monolayers containing no bacteria
were also treated with cycloheximide and were maintained under the same conditions for each cell line. One milliliter of the remaining bacterial suspension was placed in a microcentrifuge tube and allowed
to incubate under the same conditions as the infected monolayers.
Labeling continued for 2 h, and the monolayers were then washed
three times with phosphate-buffered saline and lysed with 1 ml of 0.1%
sodium deoxycholate. Ten microliters was removed to calculate the
titer. The numbers of bacteria recovered from each cell type were
5.1 × 106 (J774.A), 4.2 × 106
(Int-407), 2.5 × 106 (rat bone marrow-derived
macrophages), 1.9 × 106 (mouse bone marrow-derived
macrophages), and 1.1 × 106 (NMuLi). The remaining
bacteria were collected by centrifugation in a microcentrifuge tube for
10 min at 8,800 × g. The 1-ml sample of control
bacteria was prepared in the same manner. Bacterial pellets were
resuspended in 40 µl of sample buffer I (SB-I; 0.3% [wt/vol]
sodium dodecyl sulfate, 200 mM dithiothreitol, 28 mM Tris-HCl, 22 mM
Tris base) and boiled for 5 min. The suspensions were treated with 4 µl of sample buffer II (SB-II; 24 mM Tris base, 476 mM Tris-HCl, 50 mM MgCl2, DNase [1 mg/ml], RNase A [0.25 mg/ml]),
chilled on ice for 10 min, and then treated with 160 µl of sample
buffer III (SB-III; 9.9 M urea, 4% Nonidet P-40, 2.2% preblended
ampholytes [pH 3 to 10 and 5 to 7], 100 mM dithiothreitol). Ten
microliters was removed from each sample to determine the counts per
minute. Samples were stored at 
70°C until analyzed by 2-D
electrophoresis. Noninfected control monolayers were washed three times
with phosphate-buffered saline, lysed with 0.5 ml of boiling-hot SB-I,
boiled further for 5 min, and then placed on ice for 5 min. Twenty-four
microliters of SB-II was added, and the sample was further chilled for
10 min. Samples were centrifuged at 8,800 × g for 10 min, the supernatant was removed, and the pellets were allowed to air
dry for 5 min. The pellets were resuspended in 240 µl of a 1:4
mixture of SB-I and SB-III and analyzed by 2-D electrophoresis. A
10-µl sample was removed to determine the counts per minute, and
these samples were loaded on the basis of the amount of protein
(approximately 100 µg). All of the bacterial samples were normalized
to 500,000 cpm, except those from NMuLi (50,000 cpm), for which the
total counts obtained were much lower. These experiments were repeated
three times for the Int-407, NMuLi, and J774.A cell lines and twice for
the mouse bone marrow-derived macrophages, each time with a single
culture of 3339 and simultaneous infection of the cell lines. The
rat bone marrow-derived macrophages were examined separately, and the
experiment was repeated twice. Samples from each trial were analyzed as
described below.
2-D electrophoresis of the intracellular proteins.
2-D
electrophoresis was performed essentially by the method of
O'Farrell (18), with some modifications. (All
reagents were obtained from Oxford Glycosystems, Bedford, Mass.; the
equipment used was the Millipore 2-D Investigator, which is now
available from ESA, Chelmsford, Mass.). Protein samples were loaded
onto 4.1% acrylamide tube gels for isoelectric focusing in the first dimension. The ampholytes used were in a preblended mixture with a pH
range of 3 to 10, reinforced in the pH 5 to 7 range. Isoelectric focusing was carried out for 18,000 V · h. The second dimension consisted of large-format (22- by 22-cm) 11.5% polyacrylamide slab
gels which were run for 6 h at a maximum voltage of 500. The 2-D
parameters described in this study allow detection of proteins having
pIs primarily within the 3.5 to 6.5 range and molecular masses of
approximately 14 to 100 kDa. Gels were fixed in a solution of
isopropanol-water-acetic acid (65:25:10 [vol/vol/vol]) for 30 min,
soaked in Amplify (Amersham International, Arlington Heights, Ill.) for
30 min, dried, and exposed to Kodak X-Omat AR X-ray film (Eastman Kodak
Co., Rochester, N.Y.) at 70°C. The number of bacteria obtained from
NMuLi cells was lower than that obtained from the others, as were the
counts obtained. We were able to load only 50,000 cpm for preparations
obtained from NMuLi cells, which resulted in the need for a longer
exposure time, 4 days. The gels from the rest of the samples were
exposed for 2 days. Samples of the uninfected,
cycloheximide-treated monolayers of each cell type were also run on 2-D
gels. These gels were exposed for the same length of time as the gels
containing the bacterial samples from that cell type. The
autoradiograms revealed no proteins, indicating that host cell protein
synthesis was inhibited throughout the time course of the assay (data
not shown).
Image acquisition and analysis of protein patterns.
A
description of the equipment and software used for image acquisition
and analysis has been given previously (4). We have used the
technique of 2-D polyacrylamide gel electrophoresis extensively in this
laboratory to analyze proteins synthesized by virulent strains of
S. typhimurium in response to diverse environmental conditions in vitro. These analyses have led to the development of a
database of proteins synthesized under an extensive range of growth
conditions (unpublished data), including intracellular environments
with a variety of cell lines and various stresses, including in vitro
conditions which represent some aspects of the macrophage intracellular
environment (heat shock, acid shock, detergent shock, nutrient
deprivation, and oxidative stress). This database was used as a source
of comparison for analysis of the present study.
Our analyses of the bacterial samples revealed that the fewest proteins
were synthesized within the epithelial cell lines Int-407 and NMuLi
(Table 1). There were 142 total
detectable proteins synthesized by 3339 during growth within the
Int-407 cell line (Fig.
1B). The most prominent
of these proteins was designated A1816, which represented 36% of the
total integrated intensity of all proteins combined. A1816 exhibited a
pI of 4.77 and a molecular mass of 20.5 kDa. The intracellular pattern
was compared to the pattern exhibited by 3339 grown in EMEM (Fig. 1A), and 66 proteins were found to be present under both conditions. Three of the common proteins were induced at threefold or higher levels
during intracellular growth. The remaining 76 proteins were synthesized
only during intracellular growth, and of this group, 58 appeared to be
synthesized only in response to the Int-407 intracellular environment
(Table 1).
View larger version (112K):
[in this window]
[in a new window]
View larger version (60K):
[in this window]
[in a new window]
|
FIG. 1.
2-D sodium dodecyl sulfate-polyacrylamide gel
electrophoresis and autofluorography of 3339 whole-cell proteins
synthesized in the presence of Tran35S Label. Circles show
representative proteins that are missing or reduced during
intracellular growth. Squares show representative proteins that are
enhanced or unique to intracellular growth. (A) Whole-cell proteins
synthesized by 3339 during growth within EMEM. (B) Whole-cell
proteins synthesized by 3339 during growth within Int-407 cells.
Protein A1816 is labeled. (C) Whole-cell proteins synthesized by
3339 during growth within NMuLi cells. Protein A1816 is labeled. The
arrow indicates a predominant protein, AX324, which is found only
during growth within NMuLi. (D) Whole-cell proteins synthesized by
3339 during growth within J774.A cells. Protein A1816 is labeled.
The heat shock proteins DnaK and GroEL are also labeled. (E) Whole-cell
proteins synthesized by 3339 during growth within rat bone
marrow-derived macrophages. Protein A1816 is not detected during growth
within these cells. (F) Whole-cell proteins synthesized by 3339
during growth within mouse bone marrow-derived macrophages.
|
|
There were 183 detectable proteins synthesized by 3339 when this
organism was grown within the NMuLi cell line (Fig. 1C); 87 of them
matched the pattern seen during growth within EMEM. The remaining 96 proteins were synthesized only during intracellular growth, and 91 of
them were found to be unique to growth within NMuLi cells (Table 1).
The most prominent protein synthesized solely within NMuLi cells was
designated AX324, which represented 12% of the total integrated
intensity. AX324 exhibited a pI of 4.83 and a molecular mass of 24.2 kDa. A1816, seen during growth within Int-407 cells, was also
synthesized within NMuLi cells. It represented 23.8% of the total
integrated intensity of all proteins combined.
The greatest number of proteins was synthesized within the macrophage
cells (Table 1). One possible explanation for this result is that de
novo synthesis of a larger set of proteins may be required for survival
and multiplication within these cells than within the epithelial cell
lines, which do not mount an actively antimicrobial response upon
invasion by bacteria. There were 413 proteins detected in the J774.A
cell line (Fig. 1D) (including A1816; 10% of total integrated
intensity), of which 163 matched the in vitro pattern (Fig. 1A). Of the
163 that matched the pattern in EMEM, 123 were induced at threefold or
higher levels during intracellular growth. There were 250 proteins
which were synthesized only during intracellular growth, 157 of which
appeared to be unique to the J774 environment (Table 1).
There were 260 proteins detected during growth within rat bone
marrow-derived macrophages, 161 of which matched the pattern seen in
EMEM. Of the remaining 99 proteins, 40 were unique to the rat bone
marrow-derived-macrophage environment (Fig. 1E; Table 1).
There were 336 proteins detected during growth within mouse
bone marrow-derived macrophages, 144 of which matched the pattern seen for growth in EMEM (Fig. 1F). Of the remaining 192, 113 were observed to be unique to this cell line. Interestingly, the A1816 protein, previously seen only in the established cell lines, was detected by computer-assisted analysis during growth within this primary cell line, although at levels significantly lower than those in
the established lines. A1816 represented only 0.6% of the total
integrated intensity (Table 2). The
difference in protein pattern between the primary macrophages and the
immortalized cell line was not surprising, since it has been shown that
J774.A cells allow higher rates of intracellular survival than do
primary macrophage cultures (2, 29) and, subsequently, a
greater recovery of bacteria from this cell line as compared with the
primary macrophages, which could affect the number of detectable
proteins. An alternative explanation for this difference in protein
number may be that the timing involved in synthesis of proteins varies
among cell types, even among the different macrophages. It is possible
that the primary macrophages respond more rapidly than J774.A cells. In
order to see the entire repertoire of proteins made in each cell type
it would be necessary to perform studies of bacteria harvested at a
number of different time points in each cell line. However, even within
the time constraints of the present study, we were able to identify
proteins unique to each cell type and line.
Abshire and Neidhardt (1) observed the repression of 12 proteins and the induction of 22 proteins within four hours of phagocytosis in U937 cells. However, computer imaging and detection analysis revealed that 40 proteins were induced and 100 were repressed over the course of intracellular growth (1). The regulation of this larger number of proteins corresponds well with our own observations.
In addition to the identification of groups of proteins which were
uniquely associated with each cell line or primary cell culture,
several interesting patterns were observed. Nine proteins were
identified that were present under all conditions, both intra- and
extracellular (Table 1). A group of 27 proteins was synthesized only
within macrophages and the macrophage-like cell line J774.A. A
comparison to our database of proteins induced by in vitro stresses revealed that 2 of these 27 proteins appear to be completely unique to
the macrophage environment, since the synthesis of either of these
proteins was not observed to be induced by any of the stresses previously tested in our laboratory (unpublished data). An indication of the differences among the intracellular environments tested is
apparent in the fact that no proteins were identified that were
synthesized under all intracellular conditions, although a group of
five proteins was observed which were synthesized in all of the cell
lines except the liver cell line, NMuLi. This observation could be the
result of the lower number of bacteria and counts obtained from the
NMuLi cell line. It should also be kept in mind that there may be many
other proteins synthesized in such small amounts that we are unable to
detect them within the limits of this particular technique. Therefore,
the groups discussed here should be considered only as starting points
for further study and not as definitive lists of all cell-specific proteins synthesized by S. typhimurium.
Table 2 provides a comparison among cell types of two prominent
proteins, A1816 and C1807. A1816 was greatly induced almost exclusively
within the immortalized cell lines, with the exception of the mouse
bone marrow-derived macrophages. Although A1816 was synthesized within
these cells, its synthesis occurred at a significantly reduced level.
C1807 was seen to be enhanced under all intracellular conditions,
regardless of cell type.
It is evident from this study that the S. typhimurium SL1344
strain 3339 responded differently to each cell line which it invaded
or into which it was phagocytosed. A systematic study of cell-specific
responses has not been previously undertaken, although several
instances of differential response of salmonellae to specific cell
lines have been previously noted (1, 7). It has been
reported that S. typhimurium (ATCC 14028) heat shock proteins were prominently upregulated following phagocytosis by cells
of the murine macrophage-like cell line J774 (3), but these
same proteins were not upregulated by S. typhimurium SR-11 following phagocytosis by the human macrophage-like cell line U937
(1). In the present study the levels of the heat shock proteins DnaK and GroEL were upregulated within the J774.A cell line
(Fig. 1D) but were not seen to be significantly enhanced in either of
the primary cell cultures of mouse or rat bone marrow-derived macrophages.
The extent of variation within the SL1344 intracellular protein
patterns in this study indicates that the systems used for sensing
environmental conditions and regulating gene expression provide
Salmonella a reasonably high degree of complexity in
controlling its response to each specific intracellular environment.
S. typhimurium uses a series of two-component regulatory
systems to coordinately regulate genes in response to a diverse set of
environmental signals (14). It is reasonable to assume that
host cells possess unidentified factors which serve as signals to
induce the synthesis of proteins necessary for survival or
multiplication within those cells. These hypothetical signals may vary
considerably between different cell types, providing
Salmonella with the opportunity to specifically adapt to
each new environment, thereby increasing the likelihood for survival.
This view is certainly supported by the present comparative analysis of
the SL1344 protein synthesis patterns within a variety of different
cell types.
The obvious and significant differences in protein patterns presented
here provide a starting point for the elucidation of cell tropism in
Salmonella. Since many of these proteins are synthesized only during intracellular growth, they cannot be identified through comparisons with the SL1344 2-D reference map generated from in vitro-cultured bacteria (20). Therefore, the cell-specific
proteins A1816 (enhanced primarily in established cell lines) and AX324 (unique to growth within NMuLi) are currently being purified for microsequence analysis. It is hoped that the identification of these
proteins will lead to a better understanding of the responses of
S. typhimurium to the various intracellular environments
encountered during a systemic infection as well as to the
identification of proteins that may be necessary to establish that
infection.
| |
ACKNOWLEDGMENTS |
This work was supported by grant AI24533 from the National
Institutes of Health and an unrestricted grant from Bristol Myers Squibb.
We thank our colleagues for helpful discussions.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Department of
Biology, Campus Box 1137, Washington University, One Brookings Dr., St. Louis, MO 63130-4899. Phone: (314) 935-7186. Fax: (314) 935-7246. E-mail: burns{at}amonra.wustl.edu.
Editor: R. E. McCallum
| |
REFERENCES |
| 1.
|
Abshire, K. Z., and F. C. Neidhardt.
1993.
Analysis of proteins synthesized by Salmonella typhimurium during growth within a host macrophage.
J. Bacteriol.
175:3734-3743[Abstract/Free Full Text].
|
| 2.
|
Buchmeier, N. A., and F. Heffron.
1989.
Intracellular survival of wild-type Salmonella typhimurium and macrophage-sensitive mutants in diverse populations of macrophages.
Infect. Immun.
57:1-7[Abstract/Free Full Text].
|
| 3.
|
Buchmeier, N. A., and F. Heffron.
1990.
Induction of Salmonella stress proteins upon infection of macrophages.
Science
248:730-732[Abstract/Free Full Text].
|
| 4.
|
Burns-Keliher, L. L.,
A. Portteus, and R. Curtiss, III.
1997.
Specific detection of Salmonella typhimurium proteins synthesized intracellularly.
J. Bacteriol.
179:3604-3612[Abstract/Free Full Text].
|
| 5.
|
Conlan, J. W., and R. J. North.
1992.
Early pathogenesis of infection in the liver with the facultative intracellular bacteria Listeria monocytogenes, Francisella tularensis, and Salmonella typhimurium involves lysis of infected hepatocytes by leukocytes.
Infect. Immun.
60:5164-5171[Abstract/Free Full Text].
|
| 6.
|
Dunlap, N. E.,
W. B. Benjamin,
A. K. Berry,
J. H. Eldridge, and D. E. Briles.
1992.
A `safe-site' for Salmonella typhimurium is within splenic polymorphonuclear cells.
Microb. Pathog.
13:181-190[Medline].
|
| 7.
|
Finlay, B. B., and S. Falkow.
1989.
Salmonella as an intracellular parasite.
Mol. Microbiol.
3:1833-1841[Medline].
|
| 8.
|
Galan, J. E., and R. Curtiss, III.
1990.
Expression of Salmonella typhimurium genes required for invasion is regulated by changes in DNA supercoiling.
Infect. Immun.
58:1879-1885[Abstract/Free Full Text].
|
| 9.
|
Gottesman, S.
1984.
Bacterial regulation: global regulatory networks.
Annu. Rev. Genet.
18:415-441[Medline].
|
| 10.
|
Gulig, P. A., and R. Curtiss, III.
1987.
Plasmid-associated virulence of Salmonella typhimurium.
Infect. Immun.
55:2891-2901[Abstract/Free Full Text].
|
| 11.
|
Henle, G., and F. Deinhardt.
1957.
The establishment of strains of human cells in tissue culture.
J. Immunol.
79:54-59.
|
| 12.
|
Kusters, J. G.,
G. A. W. M. Mulders-Kremers,
C. E. M. van Doornik, and B. A. M. van der Zeijst.
1993.
Effects of multiplicity of infection, bacterial protein synthesis, and growth phase on adhesion to and invasion of human cell lines by Salmonella typhimurium.
Infect. Immun.
61:5013-5020[Abstract/Free Full Text].
|
| 13.
|
Luria, S. E., and J. W. Burrous.
1957.
Hybridization between Escherichia coli and shigella.
J. Bacteriol.
74:461-476[Free Full Text].
|
| 14.
|
Mekalanos, J. J.
1992.
Environmental signals controlling expression of virulence determinants in bacteria.
J. Bacteriol.
174:1-7[Free Full Text].
|
| 15.
|
Miller, J. F.,
J. J. Mekalanos, and S. Falkow.
1989.
Coordinate regulation and sensory transduction in the control of bacterial virulence.
Science
243:916-922[Abstract/Free Full Text].
|
| 16.
|
Miller, S. I.,
A. M. Kukral, and J. J. Mekalanos.
1989.
A two-component regulatory system (phoP-phoQ) controls Salmonella typhimurium virulence.
Proc. Natl. Acad. Sci. USA
86:5054-5058[Abstract/Free Full Text].
|
| 17.
|
Neidhardt, F. C.,
R. A. VanBogelen, and V. Vaughn.
1984.
The genetics and regulation of heat shock proteins.
Annu. Rev. Genet.
18:295-329[Medline].
|
| 18.
|
O'Farrell, P. H.
1975.
High resolution two-dimensional electrophoresis of proteins.
J. Biol. Chem.
250:4007-4021[Abstract/Free Full Text].
|
| 19.
|
Owens, R. B.,
H. S. Smith, and A. J. Hackett.
1974.
Epithelial cell cultures from normal glandular tissue of mice.
J. Natl. Cancer Inst. (Bethesda)
52:1375-1378.
|
| 20.
|
Qi, S.-Y.,
A. Moir, and C. D. O'Connor.
1996.
Proteome of Salmonella typhimurium SL1344: identification of novel abundant cell envelope proteins and assignment to a two-dimensional reference map.
J. Bacteriol.
178:5032-5038[Abstract/Free Full Text].
|
| 21.
|
Ralph, P., and I. Nakoinz.
1975.
Phagocytosis and cytocytosis by a macrophage tumour and its cloned cell line.
Nature
257:393-394[Medline].
|
| 22.
|
Smith, M. W., and F. C. Neidhardt.
1983.
Proteins induced by anaerobiosis in Escherichia coli.
J. Bacteriol.
154:336-343[Abstract/Free Full Text].
|
| 23.
|
Smith, M. W., and F. C. Neidhardt.
1983.
Proteins induced by aerobiosis in Escherichia coli.
J. Bacteriol.
154:344-350[Abstract/Free Full Text].
|
| 24.
|
Spector, M. P.,
A. Aliabadi,
T. Gonzalez, and J. W. Foster.
1986.
Global control in Salmonella typhimurium: two-dimensional electrophoretic analysis of starvation-, anaerobiosis-, and heat shock-inducible proteins.
J. Bacteriol.
168:420-424[Abstract/Free Full Text].
|
| 25.
|
Takeuchi, A.
1967.
Electron microscopic studies of experimental Salmonella infection. I. Penetration into the intestinal epithelium by Salmonella typhimurium.
Am. J. Pathol.
50:109-136[Medline].
|
| 26.
|
Takeuchi, A., and H. Sprinz.
1967.
Electron-microscope studies of experimental Salmonella infection in the preconditioned guinea pig. II. Response of the intestinal mucosa to the invasion by Salmonella typhimurium.
Am. J. Pathol.
51:137-161.
|
| 27.
|
Walker, G. C.
1984.
Mutagenesis and inducible responses to deoxyribonucleic acid damage in Escherichia coli.
Microbiol. Rev.
48:60-93[Free Full Text].
|
| 28.
|
Wanner, B. L., and R. McSharry.
1982.
Phosphate-controlled gene expression in Escherichia coli K-12 using Mud1-directed lacZ fusions.
J. Mol. Biol.
158:347-363[Medline].
|
| 29.
|
Wilmes-Riesenberg, M. R.,
B. Bearson,
J. W. Foster, and R. Curtiss, III.
1995.
The role of the acid tolerance response in the virulence of Salmonella typhimurium.
Infect. Immun.
64:1085-1092[Abstract].
|
Infect Immun, February 1998, p. 856-861, Vol. 66, No. 2
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
Top
Abstract
Text
