ASSOCIATION OF SIX SELECTED PATHOGENICITY GENES OF Escherichia coli WITH GROSS AND HISTOPATHOLOGICAL LESIONS IN BROILER CHICKENS FROM FIELD CASES

The poultry meat produced in Pakistan is 28% of the total meat production in the country. There is a wide range of infectious diseases which affect the productive performance of the birds (Ahmad et al., 2012). Among infectious diseases, bacterial diseases are of high significance. These causes significant losses in the poultry industry in terms of high morbidity, mortality, decreased egg production and hatchability (Alexander, 2000). Among the bacterial diseases, colibacillosis is one of the important disease of poultry, producing lesions in different systems of the body (Rodrigue et al., 2005) and one of the main causes of economic losses in the broiler industry (Biswas et al., 2006). The disease is caused by avian pathogenic Escherichia coli (APEC) (Delicato et al., 2003) and the infections are widely reported in the poultry sector across the globe every year with mortality ranging from 5 – 55 % (Gomes et al., 2005). This E. coli is normally present in the intestinal tract of the birds, but 10 to 15% strains have the potential to cause the disease. This disease mostly occurs secondary to the primary infection like viral infections or mycoplosmosis and poor management. The main clinical signs include depression, anorexia, dullness, high body temperature, difficulty in breathing and whistling (Anjum, 1997). It produces lesions such as air sacculitis, peritonitis, perihepatitis, pericarditis, osteomyelitis, synovitis or omphalitis (Kumar et al., 2013). There are different virulence factors which lead to the development of lesions, especially in body tissues other than intestine. The described virulence factors for APEC, so far, are hemolysin, adhesins, iron-acquisition systems, antibactericidal factors and toxins (Ewers et al., 2004). By using molecular techniques such as PCR, it is now possible to characterize virulence genes (iucD, papC, tsh, fimC, iss and irp2) (Ewers et al., 2004). The fimC and papC are fimbria related virulence genes. The fimC play an important role in the adhesions of bacteria to the respiratory tract of the host and papC for adhesions to the internal organs of the host. The iucD and irp2 are iron-acquisition system virulence factors which play a role by removal of iron from the host cells and enhances the multiplication and growth of the bacteria. The tsh is a heamolysin virulence factor which causes destruction of the erythrocytes and iss gene plays an important role in the protection of bacteria against the bactericidal activity of the host. The APEC strains have the potential of zoonotic risk (Ewers et al., 2004). Although, a couple of studies have been reported in Pakistan on colibacillosis in broilers, but the application of molecular techniques for the isolation of virulent genes has still not been carried out. So, the present study was planned to detect the virulence genes in APEC in local isolates and to find an association of six selected genes with gross and histopathological lesions in broilers. Pak. J. Agri. Sci., Vol. 55(2), 433-440; 2018 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI:10.21162/PAKJAS/18.5616 http://www.pakjas. com.pk