Plasmid profiles and resistance to antimicrobial agents among Salmonella enteritidis isolates from human beings and poultry in the midwestern United States.

In the study reported here, 121 Salmonella enteritidis isolates from human beings and 467 isolates from nonhuman sources were analyzed for plasmid pattern and susceptibility to a panel of antimicrobial agents commonly used as biologic markers. A significant (P < 0.05) number of isolates from nonhuman sources were resistant to beta-lactam antibiotics and tetracycline. Resistance to aminoglycosides, quinolones, and trimethoprim/sulfamethoxazole was uncommon. Of the 588 isolates, 445 (76%) were resistant to 2 or more antimicrobial agents. Sixty of 121 (50%) S enteritidis isolates from human beings were susceptible to all 12 antimicrobial agents, but 425 of 467 (91%) S enteritidis isolates from nonhuman sources expressed resistance to 1 or more of the antimicrobial agents used in the study. Analysis of plasmid profiles revealed that significantly (P < 0.05) more isolates from nonhuman sources had high molecular weight plasmids than did isolates from human beings. Isolates from ceca of chickens were associated with patterns of low molecular weight plasmids. Analysis of results of the study revealed similarities among S enteritidis from human beings and eggs, as determined on the basis of plasmid profiles and antibiotic susceptibility patterns, which may implicate eggs as one of the potential sources for infection of human beings. In addition, periodic monitoring of a substantial number of Salmonella isolates to detect drug resistance may be a prudent practice for use in revising the list of antimicrobial agents commonly used in human beings and other animals.