CLINICAL MANIFESTATIONS IN RABBITS EXPERIMENTALLY INFECTED WITH ESCHERICHIA COLI O157:H7 ISOLATES OF DIFFERENT VIRULENCE GENE PROFILES

Abstract

Escherichia coli O157:H7 is a major cause of zoonotic food-borne infections transmissible from asymptomatic animals to humans following consumption of contaminated foods. Pathogenicity of E. coli O157:H7 is attributed to possession of virulence genes such as eaeA and stx responsible for intimate adhesion to enterocytes and production of cytolethal shiga toxins. The pathogenic potentials of five E. coli O157:H7 isolates of different virulence gene profiles recovered from the faeces of slaughter cattle was compared in rabbit model. Five groups (A-E) of five rabbits were each inoculated orally with 5 x 10⁹ colony forming units of an E. coli O157:H7 isolate possessing one of the virulence gene profiles: stx₁ / stx₂ / eaeA / hlyA (group A), stx₁ /stx₂ (B), stx₁ (C), stx₂ (D), and eaeA / hlyA (E). Group F (control) received sterile broth. The mean onset and duration of clinical manifestations varied significantly among the experimental groups being earliest and shortest in group infected with E. coli O157:H7 possessing stx₁ / stx₂ /eaeA / hlyA. Infected rabbits showed clinical signs including dullness, profuse non-bloody diarrhoea, weakness, anorexia and epistaxis starting from two days post infection (p.i.). Epistaxis was observed only in rabbits inoculated with isolates that possessed stx₂ either alone or in combination with other virulence genes. Mortality of 100% was recorded in isolates with stx₁ /stx₂ /eaeA / hlyA, stx₁ / stx₂ and stx_2­ and 60% with stx₁ and eaeA / hlyA.  Test organisms were detected in the faeces of inoculated animals as from two days p.i. and persisted in survivors for 19 to 30 days p.i. This study showed that E. coli O157:H7 isolates from cattle produced fatal illness in experimental rabbits and that virulence gene profile significantly influenced the onset, duration and severity of clinical manifestation of infection in the experimental animals.