Salmonella typhi Outer Membrane Proteins 
The outer membrane proteins (OMPs) of a variety 
of gram-negative bacteria have been shown to be 
immunogenic in various host systems, including S. 
typhi OMPs in humans. In this respect, Dr. Calva and 
his group, in collaboration with Dr. Guillermo 
Ruiz-Palacios and his colleagues (National Institute 
for Nutrition, Mexico City) have shown the useful- 
ness of OMP preparations for the rapid diagnosis of 
TF in patients from different parts of the world. 
Dr. Calva and his colleagues started their molecu- 
lar studies on S. typhi by isolating OMP genes with 
sequence similarity to three Escherichia coli OMP 
genes: ompC, ompF, and phoE. They determined 
that the S. typhi ompC gene codes for a major OMP 
whose expression is influenced by medium osmo- 
larity differently than that of its extensively studied 
counterpart in E. coli. Main variable regions within 
the 5. typhi ompC gene were defined, most of 
which appear to code for segments of the OmpC 
protein that are exposed to the cellular exterior, as 
assessed by comparative studies with other OMP se- 
quences. Topological studies are being performed 
by constructing chimeric genes, coding for OmpC 
proteins with a foreign epitope inserted into a partic- 
ular region, and then determining whether this epi- 
tope is exposed to the cell surface. Their current 
research also includes characterization of the ge- 
netic factors that influence ompC expression, such 
as the envZ and ompR genes. These factors, espe- 
cially those involved in the response to osmotic 
stress, could well form part of a global genetic cir- 
cuitry that controls a variety of genes, including 
some involved in pathogenesis. 
An ompF-like gene has been isolated and is under 
study in the laboratory. Unexpected features distin- 
guish it from E. coli ompF, such as coding for a 
protein of unusually different size, with another 
pattern of expression. The 5. typhi phoE gene is be- 
ing characterized. The search for and examination 
of other OMP genes with sequence similarities to 
ompC or ompF are current undertakings of Dr. 
Calva and his group. 
In terms of molecular phytogeny, the ompC gene 
is being used as a probe for genetic variation within 
the Salmonella genus by oligonucleotide hybridiza- 
tion and PCR (polymerase chain reaction) technol- 
ogy. Use is made of nucleotide sequence informa- 
tion corresponding to variable and conserved 
segments. In this manner the usefulness of ompC as 
a DNA probe for diagnostics is being assessed. 
Molecular Taxonomy of Campylobacter 
Campylobacter jejuni and C. coli are the two 
species of Campylobacter most frequently asso- 
ciated with human enteritis. Their genomes share 
extensive homology, although variable and con- 
served DNA sequences have not been comprehen- 
sively defined. The two species are differentiated 
mainly on the basis of a single biochemical test, and 
it is not clear whether they have different modes of 
pathogenesis. Dr. Calva's group has isolated two 
DNA probes for Campylobacter. One is specific for 
C. jejuni and C. coli, and the other allows distinc- 
tion between most isolates of these two species, by 
hybridizing preferentially with C. jejuni. Aside from 
their potential role in molecular epidemiology, the 
genes contained in both probes are being analyzed, 
since this presents a favorable opportunity to learn 
more about the uniqueness of these organisms. 
The molecular characterization of a Campylo- 
bacter cholera-like enterotoxin (CJT) has been un- 
dertaken in collaboration with Dr. Ruiz-Palacios and 
his colleagues, who were the first to describe the 
presence of CJT in some C. jejuni clinical isolates. 
These studies make possible future research on the 
function of CJT in the bacterial cell, and more pre- 
cise classification of the clinical isolates. 
Dr. Calva is Associate Professor and Chairman 
of the Molecular Biology Department at the Bio- 
technology Institute of the National Autonomous 
University of Mexico, Cuernavaca. 
Books and Chapters of Books 
Calva, E., Fernandez, M., and Puente, J.L. 1992. Mo- 
lecular biology of the Salmonella typhi outer 
membrane porins. In Typhoid Fever: Strategies 
for the 90's. Selected Papers from the First Asia- 
Pacific Symposium on Typhoid Fever (Pang, T., 
Koh, C.L., and Puthucheary, S.D., Eds.). Singa- 
pore: World Scientific, pp 24-29. 
Puente, J.L., Dobadilla, M., Arias, C, and Calva, E. 
1992. Genetic variation of the Salmonella ompC 
gene; a study on OmpC topology. In Typhoid 
Fever: Strategies for the 90's. Selected Papers 
from the First Asia-Pacific Symposium on Ty- 
phoid Fever (Pang, T., Koh, C.L., and Puthu- 
cheary, S.D., Eds.). Singapore: World Scientific, 
pp 59-63. 
Verdugo-Rodriguez, A., Santana, F.J., Puente, J.L., 
Calva, E., Lopez-Vidal, Y., and Ruiz-Palacios, 
G.M. 1992. Salmonella typhi outer membrane 
proteins in the diagnosis of typhoid fever. In Ty- 
phoid Fever: Strategies for the 90's. Selected 
Papers from the First Asia-Pacific Symposium 
on Typhoid Fever (Pang, T., Koh, C.L., and Puth- 
ucheary, S.D., Eds.). Singapore: World Scientific, 
pp 216-220. 
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