Genetic and Molecular Characterization of Conjugative R Plasmids Detected in Salmonella Strains Isolated from Humans and Feral Pigeons in the Same District

Abstract

A total of 24 conjugative R plasmids were isolated from 19 Salmonella typhimurium strains from human patients with acute diarrhea in Hiroshima City. Moreover, 6 R plasmids were detected in 4 S. typhimurium strains and 1 S. litchfield strain which were isolated from pigeon droppings collected at 3 parks of the city. Genetic properties of these R plasmids of human and pigeon origins were used as an epidemiologic marker to confirm the possibility of transmission of Salmonella between pigeons and humans. Incompatibility (Inc) group H1 (12 plasmids-50.0%) was most frequently detected among the 24 human plasmids, followed by IncIα (4-16.7%) and FII (1-4.2%). Three of the 6 plasmids of pigeon origin were classified into IncIα and 1 into H1. IncIα plasmids conferring resistance to streptomycin (Sm), sulfadimeth-oxine (Su) and tetracycline (Tc) with or without mercury resistance and IncH1 plasmids conferring resistance to chloramphenicol, kanamycin, Sm, Su and Tc with or without mercury resistance were detected in Salmonella strains of both human and pigeon origins. Half of the IncIα plasmids and all of the H1 plasmids described above were derived from parent S. typhimurium subserovar copenhagen strains with the same biovar, respectively. Five IncIα and two IncH1 R plasmids of human and pigeon origins were about 76.9 and 120 megadaltons in size, respectively, and the plasmid DNAs of each Inc group showed identical restriction pattern. On the basis of the distribution of the same R plasmids in particular or non-particular Salmonella strains from humans and pigeons, the possibility of association of pigeons with human salomonellosis was presumed.