Whole genome sequencing as a tool to investigate a cluster of seven cases of listeriosis in Austria and Germany, 2011-2013

Clin Microbiol Infect. 2014 May;20(5):431-6. doi: 10.1111/1469-0691.12638. Epub 2014 Apr 28.


A cluster of seven human cases of listeriosis occurred in Austria and in Germany between April 2011 and July 2013. The Listeria monocytogenes serovar (SV) 1/2b isolates shared pulsed-field gel electrophoresis (PFGE) and fluorescent amplified fragment length polymorphism (fAFLP) patterns indistinguishable from those from five food producers. The seven human isolates, a control strain with a different PFGE/fAFLP profile and ten food isolates were subjected to whole genome sequencing (WGS) in a blinded fashion. A gene-by-gene comparison (multilocus sequence typing (MLST)+) was performed, and the resulting whole genome allelic profiles were compared using SeqSphere(+) software version 1.0. On analysis of 2298 genes, the four human outbreak isolates from 2012 to 2013 had different alleles at ≤6 genes, i.e. differed by ≤6 genes from each other; the dendrogram placed these isolates in between five Austrian unaged soft cheese isolates from producer A (≤19-gene difference from the human cluster) and two Austrian ready-to-eat meat isolates from producer B (≤8-gene difference from the human cluster). Both food products appeared on grocery bills prospectively collected by these outbreak cases after hospital discharge. Epidemiological results on food consumption and MLST+ clearly separated the three cases in 2011 from the four 2012-2013 outbreak cases (≥48 different genes). We showed that WGS is capable of discriminating L. monocytogenes SV1/2b clones not distinguishable by PFGE and fAFLP. The listeriosis outbreak described clearly underlines the potential of sequence-based typing methods to offer enhanced resolution and comparability of typing systems for public health applications.

Keywords: Foodborne infections; Listeria; listeriosis; outbreaks; typing; whole genome sequencing; zoonoses.

MeSH terms

  • Aged
  • Aged, 80 and over
  • Alleles
  • Austria / epidemiology
  • Bacterial Typing Techniques / methods*
  • Cheese / microbiology
  • Disease Outbreaks
  • Female
  • Food Microbiology
  • Genome, Bacterial*
  • Germany / epidemiology
  • Humans
  • Infant, Newborn
  • Listeria monocytogenes / classification
  • Listeria monocytogenes / genetics*
  • Listeria monocytogenes / isolation & purification
  • Listeriosis / epidemiology*
  • Listeriosis / microbiology*
  • Meat Products / microbiology
  • Multilocus Sequence Typing*
  • Serogroup
  • Software