Beatrix Stessl | University of Veterinary Medicine Vienna (original) (raw)

Papers by Beatrix Stessl

The eradication of Listeria monocytogenes from food chains is still a great challenge for the foo... more The eradication of Listeria monocytogenes from food chains is still a great challenge for the food industry and control authorities since some clonal complexes (CCs) are either better adapted to food processing environments (FPEs) or are globally widespread. In this work, we focus on the in-house evolution of L. monocytogenes genotypes collected from a heavily contaminated FPE whose contamination pattern underwent a massive and yet unexplained change. At the beginning of the sampling in 2010, a high variety of most likely transient L. monocytogenes genotypes was detected belonging to sequence type (ST) 1, ST7, ST21, ST37. After several efforts to intensify the hygiene measures, the variability was reduced to L. monocytogenes ST5 that was dominant in the following years 2011 and 2012. We aimed to elucidate possible genetic mechanisms responsible for the high abundance and persistence of ST5 strains in this FPE. Therefore, we compared the genomes of six L. monocytogenes ST5 strains to the less frequently occurring transient L. monocytogenes ST37 and ST204 from the same FPE as well as the highly abundant ST1 and ST21 isolated in 2010. Whole genome analysis indicated a high degree of conservation among ST5 strains [average nucleotide identity (ANI) 99.93–99.99%; tetranucleotide correlation 0.99998–0.99999]. Slight differences in pulsed field gel electrophoresis (PFGE) patterns of two ST5 isolates could be explained by genetic changes in the tRNA-Arg-TCT prophages. ST5 and ST204 strains harbored virtually identical 91 kbp plasmids related to plasmid group 2 (pLM80 and pLMUCDL175). Interestingly, highly abundant genotypes present in the FPE in 2010 did not harbor any plasmids. The ST5 plasmids harbored an efflux pump system (bcrABC cassette) and heavy metal resistance genes possibly providing a higher tolerance to disinfectants. The pLM80 prototype plasmids most likely provide important genetic determinants for a better survival of L. monocytogenes in the FPE. We reveal short-term evolution of L. monocytogenes strains within the same FPE over a 3 year period and our results suggest that plasmids are important for the persistence of ST5 strains in this FPE.

Impacts • Campylobacter spp. were highly prevalent in Austrian broiler flocks during the sampling... more Impacts • Campylobacter spp. were highly prevalent in Austrian broiler flocks during the sampling in summer [80% (12 of 15) positive flocks] and harboured flock-specific genotypes. • Multilocus sequence typing (MLST) of C. jejuni revealed that the majority of isolates were assigned to globally distributed clonal complexes or had a strong link to the human interface. • Rapid test tools in combination with molecular epidemiology could support the Campylobacter spp. reduction even at primary production. Summary Campylobacter spp. are important causes of bacterial zoonosis, most often transmitted by contaminated poultry meat. From an epidemiological and risk assessment perspective, further knowledge should be obtained on Campylobac-ter prevalence and genotype distribution in primary production. Consequently, 15 Austrian broiler flocks were surveyed in summer for their thermophilic Campylobacter spp. contamination status. Chicken droppings, dust and drinking water samples were collected from each flock at three separate sampling periods. Isolates were confirmed by PCR and subtyped. We also compared three alternative methods (culture-based enrichment in Bolton broth, culture-independent real-time PCR and a lateral-flow test) for their applicability in chicken droppings. Twelve flocks were found to be positive for thermophilic Campylobacter spp. during the entire sampling period. Seven flocks (46.6%) were contaminated with both, C. jejuni and C. coli, five flocks harboured solely one species. We observed to a majority flock-specific C. jejuni and C. coli genotypes , which dominated the respective flock. Flocks within a distance <2 km shared the same C. jejuni genotypes indicating a cross-contamination event via the environment or personnel vectors. Multilocus sequence typing (MLST) of C. jejuni revealed that the majority of isolates were assigned to globally distributed clonal complexes or had a strong link to the human interface (CC ST-446 and ST4373). The combination of techniques poses an advantage over risk assessment studies based on cultures alone, as, in the case of Campylobac-ter, occurrence of a high variety of genotypes might be present among a broiler flock. We suggest applying the lateral-flow test under field conditions to identify 'high-shedding' broiler flocks at the farm level. Consequently, poultry farmers and veterinarians could improve hygiene measurements and direct sanitation activities, especially during the thinning period. Ultimately, real-time

Current Opinion in Food Science, 2015

Journal of Food Protection, Jun 1, 2011

Microbial diagnostic microarrays are tools for simultaneous detection and identification of micro... more Microbial diagnostic microarrays are tools for simultaneous detection and identification of microorganisms in food, clinical, and environmental samples. In comparison to classic methods, microarray-based systems have the potential for high throughput, parallelism, and miniaturization. High specificity and high sensitivity of detection have been demonstrated. A microbial diagnostic microarray for the detection of the most relevant bacterial food- and waterborne pathogens and indicator organisms was developed and thoroughly validated. The microarray platform based on sequence-specific end labeling of oligonucleotides and the phylogenetically robust gyrB marker gene allowed a highly specific (resolution on genus and/or species level) and sensitive (0.1% relative and 10(4) CFU absolute sensitivity) detection of the target pathogens. In initial challenge studies of the applicability of microarray-based food analysis, we obtained results demonstrating the questionable specificity of standardized culture-dependent microbiological detection methods. Taking into consideration the importance of reliable food safety assessment methods, comprehensive performance assessment is essential. Results demonstrate the potential of this new pathogen diagnostic microarray to evaluate culture-based standard methods in microbiological food analysis.

Foodborne pathogens and disease, Jan 7, 2016

Food illegally brought into the European Union, mainly in the personal luggage of travelers, repr... more Food illegally brought into the European Union, mainly in the personal luggage of travelers, represents a potential threat to consumers' health. The aim of this study was to investigate the presence of five pathogens in food brought into the European Union by Moldavian citizens as personal goods and illegally sold in Romania in the vicinity of the border. The occurrence of Staphylococcus aureus and Listeria monocytogenes was 7.5% and 8%, while Campylobacter spp., Escherichia coli O157:H7, and Salmonella spp. were absent in all samples. L. monocytogenes sequence type 2, 9, 121, and 155, highly prevalent among foodstuffs worldwide, was also present among isolates from ready-to-eat food illegally sold in Romania, even at the same date of sampling, indicating cross-contamination during food handling. S. aureus spa types t449, t304, and t524 were most often isolated from raw-milk cheeses contaminated with 10(3)-10(5) colony-forming units per gram, evidencing a contamination at herd l...

BioMed research international, 2015

We investigated the pathogenicity, invasiveness, and genetic relatedness of 17 clinical Listeria ... more 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. The 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 (β-haemolysis and lecithinase activity), and three types of growth curve were observed. Bacterial recovery rates after invasion assays ranged from 0.09% to 7.26% (1.62 ± 0.46). MLST identified 11 sequence types (STs), and 14 PFGE profiles 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. This outbreak occurred in October 2009 and ...

Meat Science, 2015

This study determined the colonisation scenario of Listeria monocytogenes in a newly-opened ready... more This study determined the colonisation scenario of Listeria monocytogenes in a newly-opened ready-to-eat meat processing facility using a combination of classical microbiology and molecular biology techniques. Samples (n=183), including food contact surfaces, non-food contact surfaces, raw materials and food samples, collected on four sampling occasions, were analysed for L. monocytogenes by the ISO 11290:1996 standard method and by real-time PCR applied to the second enrichment broth from the ISO method. No L. monocytogenes were detected on the first sampling occasion, but by the second sampling occasion a persistent clone had colonised the facility. Analysis of the second enrichment of the ISO method by real-time PCR was more sensitive for the detection of L. monocytogenes than the ISO method alone. In order to reduce the risk of cross contamination and the public health risk, awareness and proactive measures are required to control L. monocytogenes from the first days of production in a newly opened meat processing facility.

Frontiers in Microbiology, 2015

Campylobacteriosis is the leading zoonosis in the European Union with the majority of cases attri... more Campylobacteriosis is the leading zoonosis in the European Union with the majority of cases attributed to Campylobacter jejuni. Although the disease is usually self-limiting, some severe cases need to be treated with antibiotics, primarily macrolides and quinolones. However, the resistance to the latter is reaching alarming levels in most of the EU countries. To shed light on the expansion of antibiotic resistance in central Europe, we have investigated genetic similarity across 178 ciprofloxacin-resistant C. jejuni mostly isolated in Slovenia, Austria and Germany. We performed comparative genetic similarity analyses using allelic types of seven multilocus sequence typing housekeeping genes, and single nucleotide polymorphisms of a quinolone resistance determining region located within the DNA gyrase subunit A gene. This analysis revealed high genetic similarity of isolates from clonal complex ST-21 that carry gyrA allelic type 1 in all three of these central-European countries, suggesting these ciprofloxacin resistant isolates arose from a recent common ancestor and are spread clonally.

BioMed Research International, 2015

Improving the Safety and Quality of Milk, 2010

Methods in molecular biology (Clifton, N.J.), 2014

Nucleotide sequence-based methods focusing on the single nucleotide polymorphisms (SNPs) of Liste... more Nucleotide sequence-based methods focusing on the single nucleotide polymorphisms (SNPs) of Listeria monocytogenes housekeeping genes facilitate the rapid and interlaboratory comparison on open accessible databases, such as the multilocus sequence typing (MLST) databases that are available. MLST has advantages over other methods as it can reconstruct ancestral and evolutionary linkage between L. monocytogenes isolates. MLST detects all genetic variations within the amplified housekeeping gene that accumulate slowly. This chapter describes how to undertake MLST.

Applied and environmental microbiology, 2014

Soil and water are suggested to represent pivotal niches for the transmission of Listeria monocyt... more Soil and water are suggested to represent pivotal niches for the transmission of Listeria monocytogenes to plant material, animals, and the food chain. In the present study, 467 soil and 68 water samples were collected in 12 distinct geological and ecological sites in Austria from 2007 to 2009. Listeria was present in 30% and 26% of the investigated soil and water samples, respectively. Generally, the most dominant species in soil and water samples were Listeria seeligeri, L. innocua, and L. ivanovii. The human- and animal-pathogenic L. monocytogenes was isolated exclusively from 6% soil samples in regions A (mountainous region) and B (meadow). Distinct ecological preferences were observed for L. seeligeri and L. ivanovii, which were more often isolated from wildlife reserve region C (Lake Neusiedl) and from sites in proximity to wild and domestic ruminants (region A). The higher L. monocytogenes detection and antibiotic resistance rates in regions A and B could be explained by the ...

International Journal of Food Microbiology, 2014

The aim of this study was to analyze the changing patterns of Listeria monocytogenes contaminatio... more The aim of this study was to analyze the changing patterns of Listeria monocytogenes contamination in a cheese processing facility manufacturing a wide range of ready-to-eat products. Characterization of L. monocytogenes isolates included genotyping by pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). Disinfectant-susceptibility tests and the assessment of L. monocytogenes survival in fresh cheese were also conducted. During the sampling period between 2010 and 2013, a total of 1284 environmental samples were investigated. Overall occurrence rates of Listeria spp. and L. monocytogenes were 21.9% and 19.5%, respectively. Identical L. monocytogenes genotypes were found in the food processing environment (FPE), raw materials and in products. Interventions after the sampling events changed contamination scenarios substantially. The high diversity of globally, widely distributed L. monocytogenes genotypes was reduced by identifying the major sources of contamination. Although susceptible to a broad range of disinfectants and cleaners, one dominant L. monocytogenes sequence type (ST) 5 could not be eradicated from drains and floors. Significantly, intense humidity and steam could be observed in all rooms and water residues were visible on floors due to increased cleaning strategies. This could explain the high L. monocytogenes contamination of the FPE (drains, shoes and floors) throughout the study (15.8%). The outcome of a challenge experiment in fresh cheese showed that L. monocytogenes could survive after 14 days of storage at insufficient cooling temperatures (8 and 16°C). All efforts to reduce L. monocytogenes environmental contamination eventually led to a transition from dynamic to stable contamination scenarios. Consequently, implementation of systematic environmental monitoring via inhouse systems should either aim for total avoidance of FPE colonization, or emphasize a first reduction of L. monocytogenes to sites where contamination of the processed product is unlikely. Drying of surfaces after cleaning is highly recommended to facilitate the L. monocytogenes eradication.

Food Control, 2015

Listeria monocytogenes enters the food processing facility via environment, or contaminated raw m... more Listeria monocytogenes enters the food processing facility via environment, or contaminated raw materials. To increase the understanding of L. monocytogenes environmental contamination in the meat and dairy food sector, six European scientific institutions sampled twelve food processing environments (FPEs) in a harmonized methodological approach. The selection of six previously assumed uncontaminated (UC) FPEs and six contaminated (C) FPEs was based on the L. monocytogenes occurrence information originating from the time prior to the current study. An aim of the study was to highlight, that FPEs regarded for years as uncontaminated, may also become L. monocytogenes contaminated and repeated environmental sampling could help to identify the potential sources of contamination.

Zoonoses and Public Health, 2014

The aim of this study was to determine the prevalence of Listeria spp. and Listeria monocytogenes... more The aim of this study was to determine the prevalence of Listeria spp. and Listeria monocytogenes (L. monocytogenes) in urban public lavatories and on shoe soles of facility patrons in a European capital city. More than 91% of all municipal public lavatories in Vienna close to public hubs were included in this study. Overall, 373 swab samples of public lavatories and shoes of facility patrons were enriched, according to ISO 11290-1. Listeria monocytogenes isolates were subtyped using pulsed-field gel electrophoresis. A total of 24 samples were positive for Listeria spp., yielding an overall prevalence of 6.4% (24/373). Listeria monocytogenes was found in 2.1% (8/373) of all samples. Swabs from lavatories in parks, container lavatories and lavatories at markets had the highest prevalences of 20.7% (6/29), 20% (2/10) and 12.5% (1/8) Listeria spp., respectively. These detection rates were statistically significantly higher than those associated with lavatories in shopping centres (P = 0.003, P = 0.002, P = 0.02) and at public transport locations (P = 0.0004, P = 0.005, P = 0.02). Shoes sampled at Christmas markets showed the highest Listeria spp. and L. monocytogenes prevalences of 80% (4/5) and 40% (2/5), respectively. With regard to shoe type, Listeria spp. detection rates were 14.3% (3/21; winter boots), 13.3% (2/15; hiking boots), sport shoes (5.9%; 2/34) and brogues (5.1%; 4/79). No Listeria spp. were found on shoe soles that had smooth treads (0/76), while Listeria spp. were detected on 19.5% (8/41) of medium depth tread shoe types and on 9.4% (3/32) of deep tread shoes. These data suggest that soil environment is still one of the most important reservoirs for the foodborne pathogen L. monocytogenes.

Journal of Food Protection, 2011

Journal of Applied Microbiology, 2009

Food Analytical Methods, 2012

A newly designed TaqMan® probe and an internal amplification control were implemented in a conven... more A newly designed TaqMan® probe and an internal amplification control were implemented in a conventional PCR system targeting the major fimbrial subunit encoding gene fimA. This assay has an inclusivity and exclusivity of 100 % (n 0126). The limit of detection (LOD) and the absolute quantification limit, both determined by advanced Poisson analyses, were three bacterial cell equivalents per quantitative real-time PCR reaction. The fimA assay achieved 100 % accuracy and performed very robustly, producing reproducible, reliable data for quantification of Salmonella spp., even at the LOD.

Applied and Environmental Microbiology, 2011

Listeria monocytogenes strains (n ‫؍‬ 117) were screened for the presence of stress survival isle... more Listeria monocytogenes strains (n ‫؍‬ 117) were screened for the presence of stress survival islet 1 (SSI-1). SSI-1 ؉ strains (32.5%) belonged mainly to serotypes 1/2c, 3b, and 3c. All sequence type 121 (ST-121) strains included (n ‫؍‬ 7) possessed homologues to Listeria innocua genes lin0464 and lin0465 instead of SSI-1.

Rapid Detection, Characterization, and Enumeration of Foodborne Pathogens, 2011