Research Article Molecular Epidemiology of Invasive Listeriosis due to Listeria monocytogenes in a Spanish Hospital over a Nine-Year Study Period, 2006–2014 Jaime Ariza-Miguel, 1 María Isabel Fernández-Natal, 2,3 Francisco Soriano, 4 Marta Hernández, 1 Beatrix Stessl, 5 and David Rodríguez-Lázaro 1,6 1 Instituto Tecnol´ ogico Agrario de Castilla y Le´ on, Valladolid, Spain 2 Department of Clinical Microbiology, Complejo Asistencial Universitario de Le´ on, Le´ on, Spain 3 Institute of Biomedicine (IBIOMED), University of Le´ on, Le´ on, Spain 4 Public Health, School of Physiotherapy ONCE, Madrid, Spain 5 Institute of Milk Hygiene, Milk Technology and Food Science, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine, Vienna, Austria 6 Microbiology Section, Department of Biotechnology and Food Science, Faculty of Sciences, University of Burgos, Burgos, Spain Correspondence should be addressed to Mar´ ıa Isabel Fern´ andez-Natal; ifernandeznatal@gmail.com and David Rodr´ ıguez-L´ azaro; rodlazda@gmail.com Received 18 April 2015; Revised 23 June 2015; Accepted 1 July 2015 Academic Editor: Milton O. Moraes Copyright © 2015 Jaime Ariza-Miguel et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We investigated the pathogenicity, invasiveness, and genetic relatedness of 17 clinical Listeria monocytogenes stains isolated over a period of nine years (2006–2014). All isolates were phenotypically characterised and growth patterns were determined. Te antimicrobial susceptibility of L. monocytogenes isolates was determined in E-tests. Invasion assays were performed with epithelial HeLa cells. Finally, L. monocytogenes isolates were subtyped by PFGE and MLST. All isolates had similar phenotypic characteristics (-haemolysis and lecithinase activity), and three types of growth curve were observed. Bacterial recovery rates afer invasion assays ranged from 0.09% to 7.26% (1.62 ± 0.46). MLST identifed 11 sequence types (STs), and 14 PFGE profles were obtained, indicating a high degree of genetic diversity. Genetic studies unequivocally revealed the occurrence of one outbreak of listeriosis in humans that had not previously been reported. Tis outbreak occurred in October 2009 and afected three patients from neighbouring towns. In conclusion, the molecular epidemiological analysis clearly revealed a cluster (three human cases, all ST1) of not previously reported listeriosis cases in northwestern Spain. Our fndings indicate that molecular subtyping, in combination with epidemiological case analysis, is essential and should be implemented in routine diagnosis, to improve the tracing of the sources of outbreaks. 1. Introduction Listeria monocytogenes is an emerging foodborne pathogen capable of infecting animals and humans. It is the leading cause of death in reported cases of food poisoning [1]. Te groups at highest risk of listeriosis are pregnant women, in whom this infection may cause late miscarriage or stillbirth, neonates, immunocompromised individuals, and the elderly, in whom it causes mostly septicaemia and meningoen- cephalitis [2, 3]. Te incidence of listeriosis has recently been reported to be higher among the elderly than in other groups [4, 5]. Te case-fatality rate is still increasing (20–30%) worldwide, despite antibiotic treatment [6, 7]. Noninvasive listeriosis is ofen associated with febrile gastroenteritis and sometimes with cutaneous forms, as observed in veterinary surgeons coming into direct contact with aborted foetuses from livestock [8, 9]. Te disease is usually vertically trans- mitted during pregnancy or acquired by the consumption of contaminated food, particularly fresh and ready-to-eat products that are not heated before consumption [10, 11]. Hindawi Publishing Corporation BioMed Research International Volume 2015, Article ID 191409, 10 pages http://dx.doi.org/10.1155/2015/191409