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Infect. Immun., 06 1997, 2127-2135, Vol 65, No. 6
JR Butterton, ET Ryan, DW Acheson and SB Calderwood
A promoterless gene for the Shiga toxin 1 B subunit (stxB1) has been placed
under transcriptional control of the Vibrio cholerae heat shock gene htpG.
A chromosomal enterohemorrhagic Escherichia coli fragment containing eaeA
and 400 bp of upstream DNA was added to the construct, downstream of stxB1;
no transcription terminators were located between the two genes. The
plasmid construct was confirmed by DNA sequencing; in vitro
transcription-translation studies demonstrated expression of EaeA from the
plasmid. The htpGp-->stxB1, eaeA construct was inserted into lacZ on the
chromosome of Peru2, an El Tor V. cholerae strain with both attRS1
sequences and the entire cholera toxin genetic element deleted, and into
lacZ in JRB10, a Peru2 derivative that has a second copy of
htpGp-->stxB1 also inserted in the V. cholerae virulence gene irgA. Two
plasmid constructs, one containing stxB1 under the control of the tac
promoter and another containing htpGp-->stxB1,eaeA, were transformed
into Peru2. Expression of StxB1 by these constructs was quantified by
enzyme-linked immunosorbent assay and was highest in the plasmid construct
with stxB1 under the control of the tac promoter. Localization of EaeA to
the outer membrane of the vector strains was demonstrated both by Western
blotting and by immunofluorescence with an anti-EaeA antibody. A rabbit
model for colonization by V. cholerae was used to compare the immune
responses to the two heterologous antigens, StxB1 and EaeA, expressed by
these strains. Rabbits immunized with Peru2 transformed with a plasmid
carrying tac-->stxB1 developed neutralizing serum anti-StxB1
immunoglobulin G antibody responses. One of two rabbits immunized with a
strain carrying a chromosomal copy of eaeA developed a marked immune
response against EaeA. The plasmid construct containing
htpGp-->stxB1,eaeA was unstable, producing low levels of StxB1 in vitro
and not evoking anti-EaeA antibody responses in vivo following oral
immunization. Chromosomal insertion of eaeA may be preferred for future
expression of this antigen in V. cholerae vaccine constructs.
Copyright © 1997, American Society for Microbiology
Coexpression of the B subunit of Shiga toxin 1 and EaeA from enterohemorrhagic Escherichia coli in Vibrio cholerae vaccine strains
Infectious Disease Unit, Massachusetts General Hospital, Boston 02114, USA. ButtertonJ@A1.mgh.harvard.edu
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