LEE-encoded regulator (Ler) mutants elicit serotype-specific protection, but not cross protection, against attaching and effacing E. coli strains.
We previously showed that single dose orogastric immunization with an attenuated regulatory Lee-encoded regulator (ler) mutant of the rabbit enteropathogenic Escherichia coli (REPEC) strain E22 (O103:H2) protected rabbits from fatal infection with the highly virulent parent strain. In the current study we assessed the degree of homologous (serotype-specific) and heterologous (cross-serotype) protection induced by immunization with REPEC ler mutant strains of differing serotypes, or with a prototype strain RDEC-1 (O15:H-) which expresses a full array of ler up-regulated proteins. We constructed an additional ler mutant using RDEC-1 thus, permitting immunization with a ler mutant of either serotype, O15 or O103, followed by challenge with a virulent REPEC strain of the same or different serotypes. Consistent with our previous data, the current study demonstrated that rabbits immunized with a RDEC-1 ler mutant were protected from challenge with virulent RDEC-H19A (RDEC-1 transduced with Shiga toxin-producing phage H19A) of the same serotype. Rabbits immunized with RDEC-1 or E22 derivative ler mutants demonstrated significant increase in serum antibody titers to the respective whole bacterial cells expressing O antigen but not to the LEE-encoded proteins. However, immunization with the ler mutants of either E22 or RDEC-1 failed to protect rabbits from infections with virulent organisms belonging to different serotypes. In contrast, rabbits immunized with the prototype RDEC-1 were cross protected against challenge with the heterologous E22 strain as shown by normal weight gain, and the absence of clinical signs of disease or characteristic attaching and effacing (A/E) lesions. Immunization with RDEC-1 induced significantly elevated serum IgG titers to LEE-encoded proteins. We thus, demonstrated homologous protection induced by the REPEC ler mutants and heterologous protection by RDEC-1. The observed correlation between elevated immune responses to the LEE-encoded proteins and the protection against challenge with heterologous virulent REPEC strain suggests that serotype-non-specific cross protection requires the expression of, and induction of antibody to, LEE-encoded virulence factors.
Zhu
C
C
University of Maryland, School of Medicine, 685 West Baltimore Street, Baltimore, MD 21201, USA.
Feng
S
S
Yang
Z
Z
Davis
K
K
Rios
H
H
Kaper
J B
JB
Boedeker
E C
EC
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D001422:Bacterial Adhesion; D015153:Blotting, Western; D001835:Body Weight; D002432:Cecum / Q000382:microbiology / Q000473:pathology; D003106:Colon / Q000382:microbiology / Q000473:pathology; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D004926:Escherichia coli / Q000235:genetics / Q000276:immunology* / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000276:immunology / Q000517:prevention & control*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000276:immunology*; D022361:Escherichia coli Vaccines / Q000235:genetics / Q000276:immunology*; D005243:Feces / Q000382:microbiology; D006651:Histocytochemistry; D007082:Ileum / Q000382:microbiology / Q000473:pathology; D007074:Immunoglobulin G / Q000097:blood; D050505:Mutant Proteins / Q000235:genetics / Q000276:immunology; D011817:Rabbits; D015534:Trans-Activators / Q000235:genetics / Q000276:immunology*; D037521:Virulence Factors / Q000276:immunology
D000907:Antibodies, Bacterial; D029968:Escherichia coli Proteins; D022361:Escherichia coli Vaccines; D007074:Immunoglobulin G; C465556:Ler protein, E coli; D050505:Mutant Proteins; D015534:Trans-Activators; D037521:Virulence Factors