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Abstract
Bacteriological examination of a total of 300 chickens revealed that 235 cases were harbored bacterial strains affecting the respiratory tracts of chickens with an incidence of 78.33%.
Out of 300 cases, 212 and 23 cases were positive for single and mixed infection with an incidence of 70.67% and 7.67%, respectively.
The bacterial species isolated from the examine cases (300) were predominantly, E. coli (125 isolates), P. aeruginosa (64 isolates), Kl. pneumoniae subsp. pneumoniae (29 isolates), P. mirabilis (16 isolates), S. aureus (14 isolates) and Streptococcus species (10 isolates).
The most prevalent E. coli serogroups recovered from diseased chickens with respiratory manifestations were O78 and O1 with an incidence of 19%, 7.33%, respectively, followed by O2 (4%), O8 (3.33%), O25 (2.67%) and O119 (2%) while 10 isolates (3.33%) could not be serotyped by the available antisera.
E. coli, P. aeruginosa, P. mirabilis and S. aureus were recovered mainly from air sac samples (27%, 10.67%, 3.67% and 2%, respectively). Meanwhile, Str. avium and Str. zooepidemicus were recovered mainly from lung samples (1.33% and 0.67%, respectively). Kl. pneumoniae subsp. pneumoniae were recovered mainly from both lung and tracheal samples (3.33% of each).
The isolated E. coli serogroups were examined for the following virulence factors: Congo red binding assay, haemolytic activity, haemagglutination activities (haemagglutination and mannose resistance haemagglutination) and serum resistance tests (survival or growth in serum). The serogroups O78 and O1 were the most virulent isolates. Only serogroups O78 and O1 showed Congo red binding activity with an incidence of 68.7%. None of the isolates showed haemolytic activity while, all serogroups showed mannose resistance activity with chicken erythrocytes with an incidence of 100%. Also, all serogroups except serogroup O25 was able to survive and grow in serum with an incidence of 93.54% for each.
Concerning with detection of the virulence of P. aeruginosa it was found that, 58 isolates (90.63%) were β- haemolytic onto blood agar, while only 6 isolates (9.37%) were non haemolytic. All isolates produced exotoxins which have bactericidal effect on the other microorganisms.