Antimicrobial Resistance and Phage Types of Salmonella Isolates from Healthy and Diarrheic Pigs in Korea

Objective: To investigate the serotypes, antimicrobial resistance, and phage types of Salmonella spp. isolated from healthy and diarrheic pigs in Korea. Materials and Methods: A total of 1072 fecal samples and mesenteric lymph nodes were collected from healthy (n = 641) and diarrheic (n = 431) pigs throughout Korea during 2006-2007. Salmonella isolates were tested for antimicrobial susceptibility and phage types. Results: A total of 204 Salmonella were isolated, and 3 and 9 serotypes were identified in the isolates from healthy and diarrheic pigs, respectively. Salmonella Typhimurium (38.9%), Salmonella Rissen (25.3%), and Salmonella Schwarzengrund (17.9%) were the most commonly observed serotypes in healthy pigs, while Salmonella Typhimurium (89.7%) in diarrheic pigs. A high frequency of resistance to antimicrobials, including tetracycline, sulfamethoxazole, and streptomycin, was observed in Salmonella isolates. In particular, Salmonella Typhimurium showed much higher rates of resistance than those of other serotypes, and most of Salmonella Typhimurium had resistance to more than four antimicrobials tested. Twelve definitive phage types (DTs) of Salmonella Typhimurium were identified, and the most commonly observed types were PT194 (15%) and PT203 (14%). Only 3% (4/133) of Salmonella Typhimurium were identified as DT104, and they all showed resistance to multiple drugs (>= 4). Conclusion and Applications: This is the first report on the prevalence of Salmonella status in Korean pig production system obtained from a nationwide survey. Our results show alarming rates of resistance and multiple resistances. This information can help select appropriate drug agents for empirical therapy of Salmonella Typhimurium infection. It may also be helpful to set the guidelines on prevention and control of this pathogen in swine production system.