Genotypic and phenotypic diversity of Salmonella enteritidis isolated from chickens and humans in Korea

Salmonella Enteritidis is the most common cause of salmonellosis in humans in South Korea. It has been recognized that the principal source of human infection with S. Enteritidis is chickens and their products such as meat and eggs. A total of 173 S. Enteritidis isolates from humans (65 isolates) and chickens or their products (108 isolates) were analyzed by antibiotic susceptibility assay, phage typing, and pulsed-field gel electrophoresis (PFGE). Drug resistance was found to streptomycin (32.3%), ampicillin (30.6%), nalidixic acid (30.1%), ticarcillin (30.1%), and tetracycline (28.3%). More than 70% of the isolates were found to be resistant to one or more antibiotics tested. The most frequent patterns of resistant isolates were resistance to nalidixic acid only (28.3%) and resistance to two antibiotics (four combinations; 20.2%). The most predominant phage type (PT) was PT1 (27.2%) followed by PT21 (20.8%) and PT4 (8.7%) in chicken and human isolates. Nineteen different PFGE patterns were found among the 173 isolates, and A1 was the most common PFGE pattern, followed by A6 (17.3%). Most S. Enteritis isolates (except two isolates with patterns B and C) showed similar PFGE patterns that differed by only a few bands. These results show that 2 or 3 subtypes of S. Enteritidis are shared to a large extent by humans and chickens. This implies the possibility of the spread of chicken S. Enteritidis to humans.