Purpose: In this study, we evaluated the abilities of two phenotypic subtyping methods (phage typing and antimicrobial susceptibility) and three genotypic subtyping methods (PFGE, rep-PCR and MLST) to distinguish among a collection of S. enterica Enteritidis (S. Enteritidis) isolates that were collected from food and human sources.
Methods: We determined subtypes of Salmonella Enteritidis (S. Enteritidis) isolated from food products (n = 10) and human clinical samples (n = 10) between 2009 and 2010 in Seoul using five subtyping methods and evaluated the abilities of these subtyping methods. These methods included phage typing, antimicrobial susceptibility, PFGE, Rep-PCR and MLST methods. We compared the abilities of three different subtyping methods to distinguish S. enterica Enteritidis (S. Enteritidis) by calculation of Simpson's diversity index.
Results: Among the 20 isolates tested, there were six antimicrobial susceptibility patterns, three different phage types, four different PFGE profiles, seven Rep-PCR patterns and one MLST type. Food isolates were considerably more susceptible to antibiotics than human isolates. We were best able to discriminate among S. Enteritidis isolates using Rep-PCR, and obtained the highest Simpson’s diversity index of 0.82, while other methods produced indices that were less than 0.71. PFGE pattern appeared to be more related to antimicrobial resistance profiles and phage types of S.Enteritidis isolates than rep-PCR. MLST revealed identical alleles in all isolates at all seven loci examined, indicating no resolution.
Significance: The results of this study suggest that Rep-PCR provided the best discriminatory power for phenotypically similar S. Enteritidis isolates of food and human origins, while the discriminatory ability of MLST may be problematic due to the high sequence conservation of the targeted genes.