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Indian Journal of Comparative Microbiology, Immunology and Infectious Diseases
Year : 2009, Volume : 30, Issue : 2
First page : ( 95) Last page : ( 100)
Print ISSN : 0970-9320. Online ISSN : 0974-0147.

Studies on virulence factors associated with pathogenicity in Avian Escherichia coli

Singh S.D.*, Mahender M., Dhama K.

Avian Diseases Section, Division of Pathology, Indian Veterinary Research Institute, Izatnagar-243 122 (U.P.).

*Corresponding Author: sdsingh2005@rediffmail.com

Abstract

A total of 51 strains of E. coli were isolated from heart blood, yolk, airsacs, liver and diarrhoeic faeces of ailing/dead birds suspected for colibacillosis/colisepticemia. These isolates were characterized on the basis of morphology, cultural characteristics, biochemical tests and serotyping. Further these strains were studied for some of the virulence factors commonly found in pathogenic E. coli and associated with the pathogenicity. The characteristics exhibited by virulent strains of E. coli were most of the avian E. coli did not produce hemolysin on sheep blood agar and found to be non-hemolytic while three isolates produced enterohemolysin and only one isolate produced β-hemolysin. Haemagglutination assay revealed that only eleven isolates agglutinated chicken erythrocytes and out of these, ten isolates showed MSHA while one isolate showed MRHA. Regarding serum resistance, 31 (60.78%) showed resistance to normal serum of rabbits and chickens, six of which showed intermediate resistance. CR dye uptake was found to be a good prediction of virulence, but the test is controversial. The system of iron uptake, mediated by aerobactin siderophores was observed in 30 (58.82%) stains in the present study, eight of which were considered of intermediate production., Colicin V production mediated by Col V plasmids was shown to be an important characteristic because all the 31 colicinogenic strains studied were pathogenic for 1-day-old chicks. By using PCR, the ‘tsh’ gene has been detected in 11 E. coli isolates and a positive correlation was found between ‘tsh’ gene and in- vivo pathogenicity. Heat-labile toxin (Lt) in 22 E. coli isolates and verotoxin (VT) in 2 E. coli isolates have been detected causing invasion for CEF and VERO cells. Multiple antibiotic resistance (MAR) among different E. coli isolates of poultry has been found and most of the isolates were found sensitive for Ciprofloxacin and Norfloxacin only.

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