Characterization of Listeria monocytogenes Strains Isolated During 2011–2013 from Human Infections in Switzerland

Listeria monocytogenes, an emerging foodborne pathogen, can cause in the population at risk severe infections that are associated with high case fatality rates. A total of 93 L. monocytogenes strains isolated from different patients in Switzerland from July 2011 to September 2013 were further characterized. Septicemia was reported for 74.2% of the patients, meningitis for 10.8%, and abortion for 3.2%. The majority of the strains belonged to serotype 1/2a (n=58) followed by serotype 4b (n=28), 1/2b (n=5), and 1/2c (n=2). The strains represented 35 multilocus sequence typing sequence types, 8 of which were designated for the first time. Sequence analysis of the inlA gene in the 35 sequence types showed that most of the strains encoded full-length proteins. Screening for Listeriolysin S showed the presence of this virulence factor in 29 of the 33 genetic lineage I strains. By using ApaI and AscI for pulsed-field gel electrophoresis, most strains showed distinguishable patterns.