Authors: Sana A. Khan, Steven Foley, Rossina Stefanova, Mohamed S. Nawaz, Carl E. Cerniglia, Ashraf A. Khan
A total of 47 Salmonella enterica ser. Typhimurium strains were isolated from patients and were analyzed for antibiotic susceptibility, virulence genes, plasmids, Multiple-locus Variable-number Tandem Repeat Analysis (MLVA) and Pulsed-field Gel Electrophoresis (PFGE). The composite analysis was based on equal weighting of PFGE restriction enzyme XbaI and MLVA data. Clustering for both data sets was performed using the unweighted pair group method with arithmetic mean (UPGMA). All the isolates were susceptible to gentamicin, kanamycin, nalidixic acid, and trimethoprim-sulfamethoxazole. Six isolates were resistant to ampicillin, one isolate to chloramphenicol, and another isolate to tetracycline. Sixteen virulence genes (sopB, pagC, pefA, spiA, msgA, tolC, spvB, spaN, invA, iroN, orgA, sifA, ipfC, prgH, sipB, and sitC), were screened by the polymerase chain reaction (PCR). All isolates were positive for ten genes: msgA, tolC, spaN, invA, iroN, sifA, ipfC, prgH, sipB, and sitC; and negative for the pefA gene. Seven strains carried one or more plasmids. Twenty-five MLVA patterns were detected among the 47 clinical isolates. The six most common patterns in the data set were all highly related with each other. Most of the patterns had been seen before in the PulseNet national MLVA database; however, patterns for seven of the isolates were new. Additionally, 14 isolates with 9 different MLVA patterns were deemed rare to the database (0.21%). Analysis of the PFGE and MLVA data as a composite dataset improved the discrimination between isolates compared to either data set alone, dividing the isolates into 29 different profiles. The highly discriminatory nature of MLVA, and its usefulness as a complementary technique for PFGE, were well illustrated in this study. There were 4 different XbaI PFGE restriction patterns. MLVA, PFGE, plasmid, antibiotic susceptibility, and virulence
gene analysis were useful and important tools to discriminate S. Ser. Typhimurium strains from clinical samples.