Emergence of Salmonella Enteritidis outbreaks in broiler chickens in the Lebanon: epidemiological markers and competitive exclusion control

This study investigates the first emergence of Salmonella Enteritidis outbr eaks among chickens in the Lebanon and identifies the epidemiological marke rs of selected recovered Enteritidis strains. In addition, the authors eval uate a competitive exclusion approach to control infection in broiler chick ens by Enteritidis organisms which possess the prevalent identified markers . The basic procedure in this investigation involved recording signs and le sions in eleven broiler chicken flocks on eleven farms, and culturing liver s, spleens, and caeca of ten randomly selected birds per flock for Salmonel la isolation and serotyping. Furthermore, culturing for Salmonella and sero typing was attempted from the livers, spleens, caeca and oviduct swabs of t en hens in four broiler breeder flocks which provided hatching eggs for the broilers under study. The identification of epidemiological markers in rec overed S.Enteritidis included the determination of drug-resistance patterns and plasmid profiling. The competitive exclusion was evaluated by spraying the microflora on day-old broilers in the hatchery, followed by a controll ed oral challenge at three days of age, with 2.85 x 10(5) colony-forming un its of S. Enteritidis organisms per bird. Exclusion was evaluated by cultur ing for S. Enteritidis in anal swabs, spleens, livers, and caeca of individ ual challenged birds treated with the microflora and in untreated challenge d birds. A total of 112 invasive S.Enteritidis strains were recovered on eleven farm s from individual organs of broiler chickens with typical signs and lesions of salmonellosis. The prevalent resistance to drugs in such strains was to furaltadone and gentamycin, a marker identified in 93 strains (83%), recov ered from nine out of eleven farms. The same resistance pattern was present in S. Enteritidis strains recovered from breeders on one out of four farms . The prevalent plasmid profile in nine S. Enteritidis organisms selected r andomly from a pool of 93 strains tone per each of the nine broiler farms) was 14.1 kilobases (kb) and similar to 50.0 kb, a typical pattern to that i dentified in S.Enteritidis organisms recovered from oviducts of breeders on one out of four breeder farms. The exclusion significantly reduced cumulat ive mortality in birds of up to 45 days of age by 3.93%, in comparison to t hat observed in untreated challenged birds (P < 0.05). At 45 days of age, e xclusion resulted in a 15.6% reduction in the percentage infection rate by S.Enteritidis in spleens or livers and a 34.4% reduction in the percentage infection rate of the caeca (P < 0.05).