Comparison of five molecular subtyping methods for differentiation of Salmonella Kentucky isolates in Tunisia.

Salmonellosis is one of the most common causes of food-borne infection worldwide. In the last decade, Salmonella enterica serovar Kentucky has shown an increase in different parts of the world with the concurrent emergence of multidrug-resistant isolates. These drug-resistant types spread from Africa and the Middle East to Europe and Asia. Although S. Kentucky serovar is of potential human relevance, there is currently no standardized fingerprinting method for it, in Tunisia. In the present study, a collection of 57 Salmonella Kentucky isolates were analyzed using plasmid profiling, pulsed-field gel electrophoresis (PFGE), ribotyping, enterobacterial repetitive intergenic consensus (ERIC) fingerprinting, and Random Amplification of Polymorphic DNA. Plasmid profiling showed a discriminatory index (D) of 0.290, and only 9 out of 57 (16%) isolates carried plasmids, which represents a limitation of this technique. Fingerprinting of genomic DNA by PFGE and ribotyping produced 4 and 5 patterns, respectively. Distinct PFGE patterns (SX1, SX2, SX3, and SX4) were generated for only 28 strains out of 57 (49.1%) with a D value of 0.647. RAPD fingerprinting with primers RAPD1 and RAPD2 produced 4 and 20 patterns, respectively. ERIC fingerprinting revealed 14 different patterns with a high discriminatory index (D) of 0.903. When the methods were combined, the best combination of two methods was ERIC-2 with RAPD2. These results indicates that a single method cannot be relied upon for discriminating between S. Kentucky strains, and a combination of typing methods such ERIC2 and RAPD2 allows further discrimination.

Genotypic diversity, antibiotic resistance and bacteriocin production of enterococci isolated from rhizospheres.

This study aimed to identify and to characterize rhizospheric-derived enterococci. The results showed the prevalence of Enterococcus faecium species (97%) vs. Enterococcus durans (3%). Susceptibility testing for antibiotics showed a low percentage of resistance to erythromycin (3.2%) and tetracycline (11.2%), and intermediate resistance to vancomycin (6.5%). Nevertheless, a high proportion of bacteriocin production was recorded. Furthermore, PCR detection of antibiotic resistance and bacteriocin production-encoding genes was investigated. Pulsed-field gel electrophoresis typing (PFGE) showed a great variability of enterococci in the rhizosphere. Moreover, mutilocus-sequence-typing analysis (MLST) revealed the identification of three new sequence types (STs), which were registered as ST613, ST614 and ST615.