Assessing the Genetic Diversity of Austrian Corynebacterium diphtheriae Clinical Isolates, 2011 to 2019.

Diphtheria is a vaccine-preventable disease with a high potential for reemergence. One of its causative agents is Corynebacterium diphtheriae, with some strains producing diphtheria toxin. From 2011 to 2019, 57 clinical C. diphtheriae strains were isolated in Austria, either from the respiratory tract or from skin infections. The aim of this study was to investigate the genetic diversity of these C. diphtheriae isolates using whole-genome sequencing. Isolates were characterized by genome-wide comparisons using single nucleotide polymorphism analysis or core genome multilocus sequence typing and by searching sequence data for antimicrobial resistance genes and genes involved in diphtheria toxin production. The genetic diversity among the isolates was high, with no clear distribution over time or place. Corynebacterium belfantii isolates were separated from other strains and were strongly associated with respiratory infections (odds ratio [OR] = 57). Two clusters, limited in time and space, were identified. Almost 40% of strains carried resistance genes against tetracycline or sulfonamides, mostly from skin infections. Microbiological tests showed that 55% of isolates were resistant to penicillin but did not carry genes conferring ß-lactam resistance. A diphtheria toxin gene with no nonsynonymous mutation was found in three isolates only. This study showed that sequencing can provide valuable information complementing routine microbiological and epidemiological investigations. It allowed us to identify unknown clusters, evaluate antimicrobial resistance more broadly, and support toxigenicity results obtained by PCR. For these reasons, C. diphtheriae surveillance could strongly benefit from the routine implementation of whole-genome sequencing.

Large Nationwide Outbreak of Invasive Listeriosis Associated with Blood Sausage, Germany, 2018-2019.

Invasive listeriosis is a severe foodborne infection in humans and is difficult to control. Listeriosis incidence is increasing worldwide, but some countries have implemented molecular surveillance programs to improve recognition and management of listeriosis outbreaks. In Germany, routine whole-genome sequencing, core genome multilocus sequence typing, and single nucleotide polymorphism calling are used for subtyping of Listeria monocytogenes isolates from listeriosis cases and suspected foods. During 2018-2019, an unusually large cluster of L. monocytogenes isolates was identified, including 134 highly clonal, benzalkonium-resistant sequence type 6 isolates collected from 112 notified listeriosis cases. The outbreak was one of the largest reported in Europe during the past 25 years. Epidemiologic investigations identified blood sausage contaminated with L. monocytogenes highly related to clinical isolates; withdrawal of the product from the market ended the outbreak. We describe how epidemiologic investigations and complementary molecular typing of food isolates helped identify the outbreak vehicle.

Listeriosis outbreak likely due to contaminated liver pâté consumed in a tavern, Austria, December 2018.

In late December 2018, an outbreak of listeriosis occurred after a group of 32 individuals celebrated in a tavern in Styria, Austria; traditional Austrian food (e.g. meat, meat products and cheese) was served. After the celebration, 11 individuals developed gastrointestinal symptoms, including one case with severe sepsis. Cases had consumed mixed platters with several meat products and pâtés originating from a local production facility (company X). Human, food and environmental samples taken from the tavern and company X were tested for L. monocytogenes. Whole genome sequence-based typing detected a novel L. monocytogenes strain of serotype IVb, sequence type 4 and CT7652 in 15 samples; 12 human, two food and one environmental sample from company X with an allelic difference of 0 to 1. Active case finding identified two further cases who had not visited the tavern but tested positive for the outbreak strain. In total, 13 cases (seven females and six males; age range: 4-84 years) were identified. Liver pâté produced by company X was identified as the likely source of the outbreak. Control measures were implemented and since the end of December 2018, no more cases were detected.

High genetic diversity of Vibrio cholerae in the European lake Neusiedler See is associated with intensive recombination in the reed habitat and the long-distance transfer of strains.

Coastal marine Vibrio cholerae populations usually exhibit high genetic diversity. To assess the genetic diversity of abundant V. cholerae non-O1/non-O139 populations in the Central European lake Neusiedler See, we performed a phylogenetic analysis based on recA, toxR, gyrB and pyrH loci sequenced for 472 strains. The strains were isolated from three ecologically different habitats in a lake that is a hot-spot of migrating birds and an important bathing water. We also analyzed 76 environmental and human V. cholerae non-O1/non-O139 isolates from Austria and other European countries and added sequences of seven genome-sequenced strains. Phylogenetic analysis showed that the lake supports a unique endemic diversity of V. cholerae that is particularly rich in the reed stand. Phylogenetic trees revealed that many V. cholerae isolates from European countries were genetically related to the strains present in the lake belonging to statistically supported monophyletic clades. We hypothesize that the observed phenomena can be explained by the high degree of genetic recombination that is particularly intensive in the reed stand, acting along with the long distance transfer of strains most probably via birds and/or humans. Thus, the Neusiedler See may serve as a bioreactor for the appearance of new strains with new (pathogenic) properties.

Dynamics of Vibrio cholerae abundance in Austrian saline lakes, assessed with quantitative solid-phase cytometry.

In order to elucidate the main predictors of Vibrio cholerae dynamics and to estimate the risk of Vibrio cholera-related diseases, a recently developed direct detection approach based on fluorescence in situ hybridization and solid-phase cytometry (CARD-FISH/SPC) was applied in comparison to cultivation for water samples from the lake Neusiedler See, Austria and three shallow alkaline lakes over a period of 20 months. Vibrio cholerae attached to crustacean zooplankton was quantified via FISH and epifluorescence microscopy. Concentrations obtained by CARD-FISH/SPC were significantly higher than those obtained by culture in 2011, but were mostly of similar magnitude in 2012. Maximum cell numbers were 1.26 × 10(6) V. cholerae per L in Neusiedler See and 7.59 × 10(7) V. cholerae per L in the shallow alkaline lakes. Only on a few occasions during summer was the crustacean zooplankton the preferred habitat for V. cholerae. In winter, V. cholerae was not culturable but could be quantified at all sites with CARD-FISH/SPC. Beside temperature, suspended solids, zooplankton and ammonium were the main predictors of V. cholerae abundance in Neusiedler See, while in the shallow alkaline lakes it was organic carbon, conductivity and phosphorus. Based on the obtained concentrations a first estimation of the health risk for visitors of the lake could be performed.

Ongoing outbreak of invasive listeriosis, Germany, 2012 to 2015.

Listeriosis patient isolates in Germany have shown a new identical pulsed-field gel electrophoresis (PFGE) pattern since 2012 (n = 66). Almost all isolates (Listeria monocytogenes serotype 1/2a) belonged to cases living in southern Germany, indicating an outbreak with a so far unknown source. Case numbers in 2015 are high (n = 28). No outbreak cases outside Germany have been reported. Next generation sequencing revealed the unique cluster type CT1248 and confirmed the outbreak. Investigations into the source are ongoing.

Draft Genome Sequences of Six Corynebacterium ulcerans Strains Isolated from Humans and Animals in Austria, 2013 to 2019.

Corynebacterium ulcerans is an emerging pathogen responsible for severe diseases in humans and animals. Here, we present the draft genome of six C. ulcerans strains isolated in Austria. These draft genomes have 2,446,822 to 2,551,141 bp encoding 57 to 60 RNAs.

Clostridium difficile: a new zoonotic agent?

Clostridium difficile is mainly considered a nosocomial pathogen associated with diarrhea and pseudomembranous colitis in hospitalized patients. Austrian hospitals reported 2761 cases of C. difficile infection (including 277 lethal outcomes) in 2007, compared with 777 cases (including 54 lethal outcomes) in 2003. The occurrence of community-acquired C. difficile infection is also increasingly reported. Recent studies have shown the occurrence of C. difficile in food and animals. The aim of the present study was to determine the occurrence of C. difficile in food and animals in Austria. Between March and July 2008, gut or fecal samples from 67 cows, 61 pigs and 59 broiler chickens were collected at Austrian abattoirs. Between February and April 2008 meat samples (51 beef [25 ground], 27 pork [17 ground] and 6 samples of chicken meat) were purchased at retail outlets. Of the 187 samples tested, eight yielded C. difficile: in cows 3/67 samples (4.5%) were positive, in pigs 2/61 (3.3%), in broiler chickens 3/59 (5%). Six of the eight isolates yielded toxigenic C. difficile (toxins A and B): 2/67 (3%) cow samples, 2/61 (3.3%) pig samples, 2/59 (3.4%) chicken samples. Genes for the binary toxin were detected in one of the two pig isolates, a PCR ribotype 126 strain. None of the 84 meat samples yielded C. difficile. The results of this Austrian study suggest that animal reservoirs are possible sources, via food, of human C. difficile infection.

Epidemiology of listeriosis in Austria.

A total of 150 human cases of listeriosis (case definition based on isolation of Listeria monocytogenes from normally sterile material) were reported in Austria between 1997 and 2007. Of these, 14 cases (9.3%) were pregnancy-associated (mother/child illness considered as a single case) with a mean age of 29.3 years (median: 26.5; range 24-36). Among the non-pregnancy-associated cases (n = 136), 75 were male (55.2%) and 61 female (44.9%); patients in this group had a mean age of 64.3 years (median: 66.2; range 1-93). The average incidence of listeriosis in Austria in the period studied was 0.168 cases per 100,000 population. The majority of cases (90.7%) were caused by systemic infection, only 9.3% of cases were local infections. Among non-pregnancy-associated cases the fatality rate was 28.7% (39/136) and among the pregnancy-associated cases 35.7% (5/14: miscarriage x3, stillbirth x1, and one death in a newborn within 15 days of birth). Serotyping results for the 150 isolates revealed serovar (SV) 4b: 54%, SV 1/2a: 31.3%, SV 1/2b: 10%, SV 1/2c: 2.7%, 4d: 1.3% and SV 3a: 0.7%. Predisposing risk factors were determined for 131 of the 150 cases: age > or = 65 years (n = 73), pregnancy (n = 14) and 44 cases of carcinoma, blood malignancies, autoimmune diseases and status post solid organ transplants (7 patients had more than one underlying illness). During the period studied, the incidence of listeriosis doubled, despite a drastic reduction in the frequency of pregnancy-associated cases.

An outbreak of febrile gastroenteritis associated with jellied pork contaminated with Listeria monocytogenes.

In September 2008, the Austrian Agency for Health and Food Safety (AGES) learned of an outbreak of diarrheal illness that included a 71-year-old patient hospitalized for gastroenteritis with a blood culture positive for Listeria monocytogenes. Three stool specimens provided by seven of 19 persons attending a day trip to a foreign city, including a final break at an Austrian tavern, yielded L. monocytogenes. All isolates were of serovar 4b and had fingerprints indistinguishable from each other. A cohort study revealed that the outbreak of gastroenteritis occurred among 16 persons who had eaten dinner at the wine tavern on September 6. Of the 15 persons who ate from platters of mixed cold-cuts, 12 (80%) developed symptoms of febrile gastroenteritis within 24-48 h. The median age of those who became ill was 62 years. A 72-year-old patient recovered from gastroenteritis but was hospitalized with bacterial meningitis on day 19 after the dinner. The epidemiological investigation identified the consumption of mixed cold-cuts (including jellied pork) at the wine tavern as the most likely vehicle of the foodborne outbreak (P = 0.0015). This hypothesis was confirmed by microbiological investigation of jellied pork produced by the tavern owner on September 3. L. monocytogenes was isolated from leftover food in numbers of 3 x 10(3)-3 x 10(4) colony forming units/g and was indistinguishable from the clinical outbreak isolates. Symptoms reported by the 12 patients included unspecified fever (12x), diarrhea (9x), headache (5x), vomiting (4x), body aches (2x) and sore throat (1x). Active case finding identified one case of rhombencephalitis (female, age 48) among another group of four guests, among whom only the patient and her asymptomatic husband had eaten jellied pork on September 6. This is the first outbreak of L. monocytogenes-associated gastroenteritis reported in Austria. The occurrence of a secondary case of meningitis (diagnosed on day 19 after consumption of jellied pork) indicates a significant risk of systemic listeriosis among elderly patients with febrile gastroenteritis caused by L. monocytogenes; antibiotic therapy should therefore be considered in such cases of documented listerial gastroenteritis.

Isolate-Based Surveillance of Listeria monocytogenes by Whole Genome Sequencing in Austria.

Listeria monocytogenes (L. monocytogenes) is a ubiquitous organism that can easily enter the food chain. Infection with L. monocytogenes can cause invasive listeriosis. Since 2014, in Austria, L. monocytogenes isolates from human and food/food-associated samples have been provided on a mandatory basis by food producers and laboratories to the National Reference Laboratory. Since 2017, isolates undergo routinely whole genome sequencing (WGS) and core genome Multilocus Sequence Typing (cgMLST) for cluster analyses. Aims of this study were to characterize isolates and clusters of 2017 by using WGS data and to assess the usefulness of this isolate-based surveillance for generating hypotheses on sources of invasive listeriosis in real-time. WGS data from 31 human and 1744 non-human isolates originating from 2017, were eligible for the study. A cgMLST-cluster was defined as two or more isolates differing by ≤10 alleles. We extracted the sequence types (STs) from the WGS data and analyzed the food subcategories meat, fish, vegetable and diary for associations with the ten most prevalent STs among food, through calculating prevalence ratios (PR) with 95% confidence intervals (CI). The three most frequent STs among the human isolates were ST1 (7/31; 22.6%), ST155 (4/31; 12.9%) and ST451 (3/31; 9.7%) and among the non-human isolates ST451 (614/1744; 35.2%), ST8 (173/1744, 10.0%) and ST9 (117/1744; 6.7%). We found ST21 associated with vegetables (PR: 11.39, 95% CI: 8.32-15.59), ST121 and ST155 with fish (PR: 7.05, 95% CI: 4.88-10.17, PR: 3.29, 95% CI: 1.86-5.82), and ST511, ST7 and ST451 with dairy products (PR: 8.55, 95% CI: 6.65-10.99; PR: 5.05, 95% CI: 3.83-6.66, PR: 3.03, 95% CI: 2.02-4.55). We identified 132 cgMLST-clusters. Six clusters contained human isolates (ST155, ST1, ST101, ST177, ST37 and ST7) and for five of those cgMLST-based cluster analyses solely was able to hypothesize the source: an Austrian meat processing company, two Austrian cheese manufacturers and two vegetable processing companies, one based in Austria and the other in Belgium. Determining routinely STs in food isolates by WGS allows to associate STs with food products. Real-time WGS of L. monocytogenes isolates provided mandatorily, proved to be useful in promptly generating hypotheses on sources of invasive listeriosis.

Whole genome sequencing reveals resemblance between ESBL-producing and carbapenem resistant Klebsiella pneumoniae isolates from Austrian rivers and clinical isolates from hospitals.

In 2016, the Austrian Agency for Health and Food Safety started a pilot project to investigate antimicrobial resistance in surface water. Here we report on the characterisation of carbapenem resistant and ESBL-producing K. pneumoniae isolates from Austrian river water samples compared to 95 clinical isolates recently obtained in Austrian hospitals. Ten water samples were taken from four main rivers, collected upstream and downstream of major cities in 2016. For subtyping and comparison, public core genome multi locus sequence typing (cgMLST) schemes were used. The presence of AMR genes, virulence genes and plasmids was extracted from whole genome sequence (WGS) data. In total three ESBL-producing strains and two carbapenem resistant strains were isolated. WGS based comparison of these five water isolates to 95 clinical isolates identified three clusters. Cluster 1 (ST11) and cluster 2 (ST985) consisted of doublets of carbapenem resistant strains (one water and one clinical isolate each). Cluster 3 (ST405) consisted of three ESBL-producing strains isolated from one water sample and two clinical specimens. The cities, in which patient isolates of cluster 2 and 3 were collected, were in concordance with the water sampling locations downstream from these cities. The genetic concordance between isolates from river water samples and patient isolates raises concerns regarding the release of wastewater treatment plant effluents into surface water. From a public health perspective these findings demand attention and strategies are required to minimize the spread of multiresistant strains to the environment.

Whole Genome Sequencing Based Surveillance of L. monocytogenes for Early Detection and Investigations of Listeriosis Outbreaks.

In Austria, all laboratories are legally obligated to forward human and food/environmental L. monocytogenes isolates to the National Reference Laboratory/Center (NRL) for Listeria. Two invasive human isolates of L. monocytogenes serotype 1/2a of the same pulsed-field gel electrophoresis (PFGE) pattern, previously unknown in Austria, were cultured for the first time in January 2016. Five further human isolates, obtained from patients with invasive listeriosis between April 2016 and September 2017, showed this PFGE pattern. In Austria the NRL started to use whole-genome sequencing (WGS) based typing in 2016, using a core genome MLST (cgMLST) scheme developed by Ruppitsch et al. 2015, which contains 1701 target genes. Sequence data are submitted to a publicly available nomenclature server (Ridom GmbH, Münster, Germany) for allocation of the core genome complex type (CT). The seven invasive human isolates differed from each other with zero to two alleles and were allocated to CT1234 (declared as outbreak strain). Among the Austrian strain collection of about 6,000 cgMLST-characterized non-human isolates (i.e., food/environmental isolates) 90 isolates shared CT1234. Out of these, 83 isolates were traced back to one meat processing-company. They differed from the outbreak strain by up to seven alleles; one isolate originated from the company's industrial slicer. The remaining seven CT1234-isolates were obtained from food products of four other companies (five fish-products, one ready-to-eat dumpling and one deer-meat) and differed from the outbreak strain by six to eleven alleles. The outbreak described shows the considerable potential of WGS to identify the source of a listeriosis outbreak. Compared to PFGE analysis, WGS-based typing has higher discriminatory power, yields better data accuracy, and allows higher laboratory through-put at lower cost. Utilization of WGS-based typing results of human and food/ environmental L. monocytogenes isolates by appropriate public health analysts and epidemiologists is indispensable to support a successful outbreak investigation.

Characterization of a community-acquired-MRSA USA300 isolate from a river sample in Austria and whole genome sequence based comparison to a diverse collection of USA300 isolates.

The increasing emergence of multi-resistant bacteria in healthcare settings, in the community and in the environment represents a major health threat worldwide. In 2016, we started a pilot project to investigate antimicrobial resistance in surface water. Bacteria were enriched, cultivated on selective chromogenic media and species identification was carried out by MALDI-TOF analysis. From a river in southern Austria a methicillin resistant Staphylococcus aureus (MRSA) was isolated. Whole genome sequence analysis identified the isolate as ST8, spa type t008, SCCmecIV, PVL and ACME positive, which are main features of CA-MRSA USA300. Whole genome based cgMLST of the water isolate and comparison to 18 clinical MRSA USA300 isolates from the Austrian national reference laboratory for coagulase positive staphylococci originating from 2004, 2005 and 2016 and sequences of 146 USA300 isolates arbitrarily retrieved from the Sequence Read Archive revealed a close relatedness to a clinical isolate from Austria. The presence of a CA-MRSA USA300 isolate in an aquatic environment might pose a public health risk by serving as a potential source of infection or a source for emergence of new pathogenic MRSA clones.

Impact and Time Course of Clostridium difficile Colonization in Very Low Birth Weight Infants.

BACKGROUND: Clostridium difficile is a gram-positive, anaerobic spore-forming, toxin-producing bacillus, which is one of the most common causes for health care-associated infections. High colonization rates in clinically asymptomatic neonates and infants have been described, although most studies go back to the early 1980 and 1990s, and were carried out in term and late preterm infants. OBJECTIVES: The aim of our study was to determine both the impact and time course of C. difficile colonization in a cohort of very low birth weight infants (VLBWI) in an era of PCR-based technologies for diagnosis. METHODS: Stool samples of VLBWI were analyzed for the presence of C. difficile strains in regular intervals during the hospital stay by PCR ribotyping. Analysis was continued throughout the first 2 years of life. RESULTS: A 32% C. difficile colonization rate during the first 2 years of life and an in-hospital colonization rate of 8% was found in a cohort of 190 VLBWI. C. difficile colonization occurred mainly in the first 6 months of life, which was similar to term neonates. In-hospital colonization accounted for only a small percentage of cases with no detection of hypervirulent strains. Also, C. difficile colonization was not related to an adverse outcome in this VLBWI cohort. Oral lactoferrin of bovine origin and treatment with piperacillin/tazobactam were negatively correlated with C. difficile colonization in our study. CONCLUSIONS: C. difficile colonization in our cohort of VLBWI was significantly lower than has been described in the literature and was not related to an adverse outcome.

Draft Genome Sequences of Interpatient and Intrapatient Epidemiologically Linked Neisseria gonorrhoeae Isolates.

Neisseria gonorrhoeae is the causative agent of gonorrhea and was identified by the World Health Organization as an urgent public health threat due to emerging antibiotic resistance. Here, we report 13 draft genome sequences of N. gonorrhoeae isolates derived from two epidemiologically linked cases from Austria.

Occurrence of Vibrio cholerae serogroups other than O1 and O139 in Austria.

From 2000 to 2005, 13 infections due to non-O1/non-O139 Vibrio cholerae were documented in Austria. Twelve patients (8 years to 65 years old; 7 male) had symptomatic infections: diarrhea x 5, otitis x 6, septicemia once. All 5 patients who acquired their infections abroad, suffered from diarrhea. The 8 persons without travel history outside of Austria had otitis media (n = 4) or otitis externa (n = 2); the lethal case of septicemia affected a fisherman with underlying malignancy. One isolate was from an asymptomatic child. Detailed data on travel history inside Austria was available for 5 of these 8 patients: all 5 had visited or lived near Austria's largest lake. The concentration of salt in this westernmost steppe lake in Europe is approximately one-twentieth of that of sea water. Why otitis and not diarrhea is the dominating manifestation of non-O1/non-O139 infection acquired in Austria remains to be elucidated. We hypothesize that diarrhea due to Vibrio cholerae serogroups other than O1 and O139 acquired in Austria may simply be unrecognized by the standard operating procedures employed in clinical microbiology laboratories. Testing for Vibrio cholerae is not considered necessary for domestically acquired diarrhea. Only in patients who acquired diarrhea abroad, do physicians sometimes consider cholera as a differential diagnosis, thereby prompting the laboratory to use thiosulfate citrate bile salt sucrose (TCBS) agar plates.

Draft Genome Sequence of a Vancomycin-Resistant and Vancomycin-Dependent Enterococcus faecium Isolate.

Vancomycin-resistant enterococci have emerged as major nosocomial pathogens worldwide. While antimicrobial pressure promotes nosocomial colonization with these enterococci, prolonged exposure to vancomycin may foster the transition from vancomycin resistance to vancomycin dependence. Here, we report the draft genome sequence of a vancomycin-dependentEnterococcus faeciumisolate showing partial teicoplanin dependence.

High Rates of Treatment Success in Pulmonary Multidrug-Resistant Tuberculosis by Individually Tailored Treatment Regimens.

RATIONALE: We evaluated whether treatment outcomes for patients with multidrug-resistant and extensively drug-resistant tuberculosis can be substantially improved when sufficient resources for personalizing medical care are available. OBJECTIVES: To describe the characteristics and outcomes of patients with pulmonary multidrug-resistant tuberculosis at the Otto Wagner Hospital in Vienna, Austria. METHODS: We conducted a retrospective single-center study of patients initiated on treatment for multi-drug resistant tuberculosis between January 2003 and December 2012 at the Otto Wagner Hospital, Vienna, Austria. The records of patients with multidrug-resistant tuberculosis were reviewed for epidemiological, clinical, laboratory, treatment, and outcome data. MEASUREMENTS AND MAIN RESULTS: Ninety patients with pulmonary multidrug-resistant tuberculosis were identified. The median age was 30 years (interquartile range, 26-37). All patients were of non-Austrian origin, and 70 (78%) came from former states of the Soviet Union. Thirty-nine (43%) patients had multidrug-resistant tuberculosis; 28 (31%) had additional bacillary resistance to at least one second-line injectable drug and 9 (10%) to a fluoroquinolone. Fourteen (16%) patients had extensively drug-resistant tuberculosis. Eighty-eight different drug combinations were used for the treatment of the 90 patients. Surgery was performed on 10 (11.1%) of the patients. Sixty-five (72.2%) patients had a successful treatment outcome, 8 (8.9%) defaulted, 3 (3.3%) died, 8 (8.9%) continued treatment in another country and their outcome was unknown, and 6 (6.7%) were still on therapy. None of the patients experienced treatment failure. Treatment outcomes for patients with extensively drug-resistant tuberculosis were similar to those of patients with multidrug-resistant tuberculosis. CONCLUSIONS: High rates of treatment success can be achieved in patients with multidrug-resistant and extensively drug-resistant tuberculosis when individually tailored treatment regimens can be provided in a high-resource setting.

Whole genome sequence-based serogrouping of Listeria monocytogenes isolates.

Whole genome sequencing (WGS) is currently becoming the method of choice for characterization of Listeria monocytogenes isolates in national reference laboratories (NRLs). WGS is superior with regards to accuracy, resolution and analysis speed in comparison to several other methods including serotyping, PCR, pulsed field gel electrophoresis (PFGE), multilocus sequence typing (MLST), multilocus variable number tandem repeat analysis (MLVA), and multivirulence-locus sequence typing (MVLST), which have been used thus far for the characterization of bacterial isolates (and are still important tools in reference laboratories today) to control and prevent listeriosis, one of the major sources of foodborne diseases for humans. Backward compatibility of WGS to former methods can be maintained by extraction of the respective information from WGS data. Serotyping was the first subtyping method for L. monocytogenes capable of differentiating 12 serovars and national reference laboratories still perform serotyping and PCR-based serogrouping as a first level classification method for Listeria monocytogenes surveillance. Whole genome sequence based core genome MLST analysis of a L. monocytogenes collection comprising 172 isolates spanning all 12 serotypes was performed for serogroup determination. These isolates clustered according to their serotypes and it was possible to group them either into the IIa, IIc, IVb or IIb clusters, respectively, which were generated by minimum spanning tree (MST) and neighbor joining (NJ) tree data analysis, demonstrating the power of the new approach.