Molecular Characterization of Salmonella enteritidis Isolates from Maine Poultry and Poultry Farm Environments

Eighty-six Salmonella enteritidis isolates obtained during a surveillance program of poultry farms in Maine were subjected to phage-typing, plasmid profiling and fingerprinting, outer-membrane polypeptide analysis, and antimicrobial sensitivity testing. Isolates were obtained from a variety of sources, including poultry-farm environmental samples, chicken organ samples, human stool samples, cat feces, and live-trapped rats and mice. These isolates were compared with 21 S. enteritidis isolates originating outside of Maine. Phage types isolated in Maine included 13a (60%); 14b (29%); 23 (5%); 8 (2%); and 2 (2%). All S. enteritidis isolates from Maine carried plasmid DNA, and 97% of these isolates carried a 40.3-megadalton plasmid alone (6%) or in conjunction with several smaller plasmids (91%). All 52 phage-type 13a isolates harbored 40.3- and 3.0-megadalton plasmids. All 25 phage-type 14b isolates carried 3.3- and 1.3-megadalton plasmids, and 22 isolates also carried the 40.3-megadalton plasmid. All isolates displayed highly similar outer-membrane polypeptide profiles and were sensitive to a variety of antimicrobials commonly used against gram-negative organisms. The above data suggest that phage type and plasmid content may be related in the cases of phage-type 13a and 14b isolates, and that traditional plasmid-borne antimicrobial resistance determinants were not present in Maine isolates. Results also indicate that phage-typing can be a valuable epizootiological tool for monitoring the potential spread of these strains throughout the Northeast.