Wild black-headed gulls (Larus ridibundus) as an environmental reservoir of Salmonella strains resistant to antimicrobial drugs

Salmonella were isolated from black-headed gulls (Larus ridibundus) in six locations in the Czech Republic from 1984 to 2005 (Chropyne and Nymburk in 1984-1986; Nove Mlyny, Bartosiovice, and Hodonin in 1991-1994; and Nove Myny, Bartosiovice, and Ostrava in 2005). Antimicrobial susceptibility was determined in 12 antimicrobial drugs using disk diffusion. Although 95% of Salmonella isolates (197 out of 207) were pansusceptible, the prevalences of resistance increased significantly from 1 (2%) out of 59 isolates in 1984-1986 and 3 (3%) out of 100 isolates in 1991-1994 to 6 (13%) out of 48 isolates in 2005. Furthermore, in 2005, two isolates were nalidixic acid-resistant and one isolate was multidrug-resistant Salmonella Typhimurium DT 104. These findings suggest that the occurrence of salmonellae in black-headed gulls depends to a large extent on the contamination where the gulls feed and possibly reflects the dissemination of these strains among farm animals and humans. Black-headed gulls may also become infected with resistant Salmonella and thus pose a potential risk of Salmonella contamination of surface water and animal feeds, and consequently dissemination.