Antimicrobial susceptibility testing Susceptibility to a standard panel of antimicrobial agents http://www.danmap.org was determined by microbroth dilution and interpreted according to Clinical and Laboratory Standards Institute guidelines [32], except for ciprofloxacin (≥0.125 μg/mL was used as breakpoint). Phage typing Phage typing was performed by the National Food Institute, Technical University of Denmark according to the phage typing scheme developed by Callow [33] and extended by Anderson et al. [34]. Strains that react with phages, but have a profile not included in the phage selleck compound typing scheme, are denoted Reaction Does Not Conform (RDNC). DNA microarray The DNA microarray used
in this study was previously described [35]. A set of 281 gene-specific
57-60 mer oligonucleotide probes were designed using the program Array Designer 4.1 (Premier Biosoft, Palo Alto, CA, USA). The oligonucleotides were spotted on glass slides using a QArray Mini Arrayer (Genetix, New Milton, UK). Hybridized spots were visualized in a GenePix Selumetinib 4000B laser scanner (Axon, Foster City, CA). Each oligonucleotide allows the detection of the presence or absence of a characteristic sequence previously described in Salmonella. The microarray used gives no information on the location of a gene or target sequence and can only score its presence or absence. Uncertain array results were resolved by PCR using primers described previously [35]. Data analysis Analysis of the DNA microarray data was performed as previously described [35]. A comparison was made by importing array values, gene present or absent, into BioNumerics 5.1 (Applied Maths, Sint-Martens-Latem, Belgium) as character data. An Unweighted Pair Group Method with Arithmetic mean (UPGMA) dendrogram (Fig. 2) was calculated by simple matching of binary coefficients on the basis of a geneset consisting of all genes from the array except the serotyping markers and the resistance markers. Multiple-locus
variable-number of tandem-repeat analysis (MLVA) MLVA was performed as described previously [36] to ensure that the strains were likely to be epidemiologically unrelated. The MLVA repeats were calculated selleck inhibitor and named according to the method described recently [37]. Pulsed-field gel electrophoresis (PFGE) PFGE was carried out with XbaI restriction enzyme according to the Pulse-Net protocol [38], gels were analyzed in BioNumerics 5.1, and profiles were assigned by comparison to a database with known Danish profiles (see additional file 1: Xba I PFGE profiles of all isolates). Sequence typing Multilocus sequence typing (MLST) was carried out as previously described [39] and the alleles and the sequence types were assigned according to the MLST scheme on http://mlst.ucc.ie/mlst/mlst/dbs/Senterica/. Acknowledgements EL was partly funded by the Danish Research Council. We are grateful to the patients without whose kind participation this study would not have been possible.