Characterization of extended-spectrum beta-lactamase-producing Salmonella typhimurium by phenotypic and genotypic typing methods

Abstract

During 1994, 10 isolates of extended-spectrum beta-lactamase-producing Salmonella typhimurium were recovered from children transferred to our hospital from two different centers. Two additional isolates were recovered from two nurses from one of these centers. The aim of this study was to determine if there is any relationship between these isolates. The characterization was done by phenotypic and genotypic methods: biotyping, phage typing, antibiotic susceptibility pattern determination, plasmid analysis, ribotyping (by the four endonucleases EcoRI, SmaI, BglII, and PvuII), pulsed-field gel electrophoresis (PFGE) of genome macrorestriction patterns with XbaI, and randomly amplified polymorphic DNA (RAPD) pattern determination (with the three primers 217 d2, B1, and A3). The same biotype, the same serotype, and an identical antibiotype were found. All isolates were resistant to oxyimino-beta-lactams, gentamicin, tobramycin, and sulfamethoxazole-trimethoprim. All isolates showed an indistinguishable pattern by ribotyping and very similar patterns by PFGE and RAPD. The overall results indicated the spread of a closely related strain of S. typhimurium in children and nurses.

FIG. 1

Ribotyping profiles after digestion by EcoRI of S. typhimurium isolates S124, S1 to S12, and type strain ATCC 43971. Lane M contains molecular size markers.

FIG. 2

PFGE patterns of XbaI-digested genomic DNA obtained from S. typhimurium isolates S1, S2, S3, S4, S5, S6, S7, S8, S11, S12, S9, and S10. Lane M contains molecular size markers.

FIG. 3

RAPD patterns of S. typhimurium isolates with primer B1 (5′GTTCGCC3′). Strains include type strain ATCC 43971, S124, and S1 to S12. Lane M contains molecular size markers.