CHARACTERIZATION OF 2 VIRULENCE PROTEINS SECRETED BY RABBIT ENTEROPATHOGENIC ESCHERICHIA-COLI, ESPA AND ESPB, WHOSE MAXIMAL EXPRESSION IS SENSITIVE TO HOST BODY-TEMPERATURE

Enteropathogenic Escherichia coli (EPEC) and rabbit EPEC (RDEC-1) caus e unique histopathological features on intestinal mucosa, including at taching/effacing (A/E) lesions. Due to the human specificity of EPEC, RDEC-1 has been used as an animal model to study EPEC pathogenesis. At least two of the previously identified FPEC-secreted proteins, EspA a nd EspB, are required for triggering host epithelial signal transducti on pathways, intimate adherence, and A/E lesions. However, the functio ns of these secreted proteins and their roles in pathogenesis have not been characterized. To investigate the function of EspA and EspB in R DEC-1, the espA and espB genes were cloned and their sequences were co mpared to that of EPEC O127, The EspA proteins showed high similarity (88.5% identity), while EspB was heterogeneous in internal regions (69 .8% identity). However, RDEC-1 EspB was identical to that of enterohem orrhagic E. coli serotype O26. Mutations in RDEC-1 espA and espB revea led that the corresponding RDEC-1 gene products are essential for trig gering of host signal transduction pathways and invasion into HeLa cel ls. Complementation with plasmids containing FPEC espA or/and espB gen es into RDEC-1 mutant strains demonstrated that they were functionally interchangeable, although the FPEC proteins mediated higher levels of invasion. Furthermore, maximal expression of RDEC-1 and EPEC-secreted proteins occurred at their respective host body temperatures, which m ay contribute to the lack of EPEC infectivity in rabbits.