Characteristics of the e.coli strains isolated from chickens

In chickens, colibacillosis refers to any local or systemic infection produced by Escherichia coli (APEC) and it's economically worldwide impact is measured in the morbidity and mortality rates of affected birds. This is an acute and often systemic disease. Colibacillosis is a complex syndrome, starting from the respiratory mucous characterized by multiple organ lesions with airsacculitis and associated pericarditis, perihepatitis and peritonitis being most typical. The E.coli infection is generally associated with other factors, as mycoplasmas, viruses and/or environmental factors. However, management approaches based only on protecting poultry against the predisposing conditions have limited effect for the disease control. Antimicrobial drugs remain important in reducing both incidence and mortality associated with this disease, but there is increasing evidence that (APEC) is becoming more resistant to antimicrobial agents. A vaccine-based approach for the control remain highly desirable. Currently available vaccines are not totally effective, mainly because of the diversity of APEC strains. Currently E. Coli serotypes O1:K1, O2:K1 and O78:K80 are recognized as the most prevalent, however the number of serotypes is increasing. The APEC isolates vary profoundly in virulence. Virulent factors are encoded by at least 12 virulence genes, located either in the bacterial genome or in plasmids. Many studies demonstrated that virulence factors are rarely all present in the same isolate, their frequencies in clinical isolates is varying. This all indicates that APEC strains are a heterogeneous group. The virulence genes can be transmitted among APEC strains and can be detected using the PCR multiplex technique fastening the diagnosis on bacterial colonies or on samples from organs. For the development of effective vaccines, virulence genes studies are also important. These genes code for adhesins (F1-, P-fimbriae), iron acquisition systems (aerobactin, yersiniabactin), hemolysins (hemolysinE, temperature sensitive hemagglutinin), resistance to the bactericidal effects of serum and phagocytosis (outer membrane protein, iss protein, lipopolysaccharide, K/1), capsule and colilcin production) as well as toxins and cytotoxins (heat stable toxin, cyto-/verotoxin and flagella toxin). The limited knowledges on pathogenicity and immunogenicity of APEC infections urges further experimental studies. APEC share specific virulence factors with humans E.coli, their zoonotic potential is under consideration