Listeria monocytogenes in ready-to-eat (RTE) delicatessen foods: Prevalence, genomic characterization of isolates and growth potential

This study investigated Listeria monocytogenes prevalence and count in 132 ready-to-eat (RTE) delicatessen samples belonging to different categories (starters with/without mayonnaise pasta/rice-based courses, meat/fish-based main courses) produced by an Italian industry. Whole Genome Sequencing characterized the isolates to map the pathogen circulation. Moreover, the growth potential of L. monocytogenes in the most contaminated product was investigated by a challenge test. L. monocytogenes was detected in 23 samples, giving an estimated prevalence of 17.4 %. Starters with mayonnaise showed a very high prevalence (56.7 %), showing the role of the sauce in the diffusion of the pathogen within the plant. A total of 49 isolates were obtained; they belonged to two different serogroups, IIb and IIa, and were related to two clonal complexes (CCs) and sequence types (STs) (CC288-ST330 and CC121-ST717), suggesting the possible persistence and circulation of the pathogen within the plant. The results of the challenge test showed a limited ability to grow in the selected product thanks to the presence of lactic microflora.

Predictive factors of selective transarterial embolization failure in acute renal bleeding: a single-center experience

PURPOSE

Transarterial embolization of renal artery branches (RTE) is a minimally invasive procedure commonly performed in life-threatening renal bleeding of different etiologies. Despite the widespread use of RTE, no consensus guidelines are currently available. Our aim was to investigate clinical and technical efficacy and to identify potential predictors for clinical failure of this procedure.

METHODS

All the RTE procedures performed in our Interventional Radiology unit in last 10 years were retrospectively collected and analyzed. All selected patients underwent both pre-procedural computed tomography angiography (CTA) and post-procedural CTA within 30 days. Clinical success was considered as primary endpoint. Demographic, laboratory, and diagnostic findings predictive of clinical failure of RTE were identified.

RESULTS

Over a total of 51 patients enrolled, 27 (53%) were females and 33 (64.7%) had a renal bleeding of iatrogenic origin. Technical and clinical success was 100% and 80.4%, respectively. Hematoma volumes > 258.5 cm3 measured at CTA, higher pre- and post-procedural serum creatinine (Scr) levels, an increase in Scr value > 0.135 mg/dl after the procedure, a worse post-procedural estimated glomerular filtration rate (eGFR), a post-procedural reduction of eGFR < 3.350 ml/min, and a post-procedural reduction of platelet count (PLT) > 46.50 × 103/mmc showed a significantly higher rate of clinical failure.

CONCLUSION

RTE is a safe and effective procedure in the management of acute renal bleeding of various origins. Hematoma volume, Scr, PLT, and eGFR values were found to be predictive factors of poor clinical outcome and should be closely monitored.

A proteomic approach of the different environmental conditions of Listeria monocytogenes

 

Listeria monocytogenes is the ubiquitous food-borne pathogen which causes listeriosis, a disease with a high mortality rate, mostly transmitted through contaminated ready-to-eat foods. To better understand the systemic response of L. monocytogenes exposed at 3 environmental factors (T, pH and NaCl), the proteome of L. monocytogenes strain NRG 1749-2016, isolated from a meat product, was investigated to identify differences in the protein patterns of such pathogen. Four different conditions were carried out as follows: A) T 37 °C, pH 7.0, NaCl 0.5%; B) T 37 °C, pH 5.5, NaCl 7%; C) T 12° pH 7, NaCl 0.5%; D) T 12 °C, pH 5.5, NaCl 7%. The proteins belonging to cytosol (C1) and vesicles (C2) were isolated and purified by CelLytic B Cell Lysis Reagent and CelLytic IB Inclusion Body Solubilization Reagent according manufacturer's instructions. The analysis were conducted by SDS PAGE and Immunoblotting techniques. The protein concentrations were evaluated by Pierce BCA Protein Assay Kit. From preliminary results, the protein banding patterns generated by 1D SDS PAGE were found to be different at visual observation for C1 and C2, in A, B, C and D conditions. The presence of specific antigen-antibody immunocomplexes (Ag-Ab ICs) was identified by Immunoblotting, in C1 at 100, 60, 55, 35 and 25 kDa for all incubated conditions with a positive serum to L. monocytogenes. As regards C2, Ag-Ab ICs at 110 kDa were observed in A and B, Ag-Ab ICs at 80 kDa in C and D, Ag-Ab ICs at 60 kDa in A and D, while Ag-Ab ICs at 40 and 30 kDa in all conditions. The analysis of the proteome profiles shows an intra-strain variation in the protein patterns produced by L. monocytogenes during the adaptation at different environmental conditions. Further analysis will be carried out to better understand the systemic response of L. monocytogenes, in particular in order to characterize the immunogenic proteins highlighted by Immunoblotting and their role in the virulence expression of such pathogen.

Key messages

Understand how L. monocytogenes adapts physiologically to different environmental factors. Development of new detection method of L. monocytogenes and prevention strategies for listeriosis outbreaks.

Fast WGS source attribution of Listeria monocytogenes outbreak in a sheep flock in Abruzzo region

Background

Listeriosis is a life-threatening disease in human as well as animals, cows and sheep are the most sensible to the disease. Correlation to feed is well documented (silage). Some clonal complexes (CCs) are more virulent than others and frequently involved in animal and human listeriosis. Whole genome sequencing (WGS) and in silico CCs identification and core genome multilocus sequence typing (cgMLST) determination are the best way to characterize isolates and confirm connection between clinical strains and source of contamination. This work aimed to demonstrate the advantages of using WGS to find the source of Listeria monocytogenes (Lm), causing an outbreak in an ovine farm in Abruzzo region.

Methods

Lm was detected according to ISO 11290-1:2017. Serogroup was determined by multiplex PCR. WGS data were obtained using Illumina platform. Sequences were used to assess CCs and cgMLST according to BIGSdb Pasteur platform. Two brain samples and 1 lymph node from 2 sheep, one sample of silage (15 analytical portion), and 1 sample of hay were tested.

Results

Lm was detected in all animal specimens and in 2 analytical portions of feed (silage) tested. Out of 35 colonies detected 28 were identified as Lm (27 serogoup IVb and 1 sample of silage serogroup IIa). Five colonies were selected for WGS (one from each animal brain, one from the lymph node and one from each positive analytical portion of silage), among them only one colony from the silage showed the same CC of the strains isolated from sheep (CC1). cgMLST revealed no allelic distances between these strains.

Conclusions

CC1 is the main virulent clone among Lm isolates often involved in human and animal outbreak. Feed may be a vehicle for Lm and could be the outbreak source. Cases ceased after removing the silage. Use of WGS is a definitive help in source attribution when feed is available and the sampling is done in a correct manner.

Key messages

Silage can be cause of listeriosis in livestock. WGS can improve source attribution of outbreaks detecting the relatedness of the strains and improving the epidemiological investigation in case of outbreak.

Shiga-toxin producing Escherichia coli detection in samples from Abruzzo and Molise regions, Italy

Background

Top five serogroups (O157, O111, O26, O103 and O145) of Shiga-toxin producing Escherichia coli (STEC) represent the third most important increasing zoonosis reported in European Union. The ISO methods of analysis, used in foods and environmental samples, quite often does not confirm the molecular detection of STEC genes (stx1 and stx2) in enrichment broth. The aim of this study was to summarize the results of the tests carried out at Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise in the last six years (2016-2021), comparing genes detection in enrichment broth and in colonies grown on agar plates.

Methods

Along the 2016-2021, a total of 1716 foods and environmental samples from Abruzzo and Molise regions were tested, according to ISO/TS 13136:2012.

Results

Out of 1716 samples, 16 (0.9%) shown presumptive positive presence of STEC (stx1 and/or stx2) in broth. In spite of that, the presence of STEC (positive colonies for stx1 and/or stx2) was confirmed only in 4 out of 16 samples (one sample of cheese and 3 of minced meat). Then, eae gene was found in 54 samples in broth and only in 3 samples from colonies, during a foodborne outbreak investigation. Serogroup specific targets were detected in 6 broth samples (O26, O145 and O157) and confirmed in colonies only in 2 minced meat samples (O157).

Conclusions

STEC are a heavy hazard for the consumers and the number of cases is slightly increasing since 2015. Our results highlight a low number of presumptive positive samples and even lower number of STEC detection obtained with the ISO classical method. Furthermore, detection of the target genes in broth was rarely confirmed after plating, highlighting a weak point of the analytical method that needs to be investigated. Efforts are necessary to improve the method and the STEC confirmation from colonies. Immunomagnetic beads targeting the top five serogroups and digital PCR could help in increasing the recovery rate of cultivable STEC.

Key messages

The presumptive positive samples for STEC genes in foodstuffs from the Abruzzo and Molise regions are quite rare, even lower is the number of confirmed colonies by agar plate isolation. Specific immunomagnetic beads for the top five STEC serogroups could improve the method and the STEC colonies detection, increasing the recovery rate of cultivable strains.

Genomic persistence of Listeria monocytogenes strains in dairy and meat processing plants in Italy

Background

Persistence of Listeria monocytogenes (Lm) in food processing plants (FPP) is still considered the major source of food contamination during processing. Correlations among different Lm strains and evaluation of the isolates persistence in FPP environments is an essential tool to improve food safety. The aim of this study was to investigate the genomic characteristics of persistent Lm strains (e.g. Metal and Detergent Resistance, SSIs and genomic island).

Methods

Totally 221 strains isolated from 10 FPP in the Abruzzo and Molise regions, Italy, were enrolled (4 of dairy products FPP - DP - and 6 of meat products FPP - MP). Sampling was performed in 6 sessions, from March 2017 to May 2018. Strains were sequenced using Illumina platform. The CCs, cgMLST analysis and Metal and Detergent Resistance, SSIs and genomic island (GI) detection was carried using the Pasteur scheme.

Results

Results returned 13 CCs and 2 singletons. cgMLST clustering showed two persistent clusters DP and 9 clusters in MP. In DP CC3 and CC9 were persistent. While in MP CC5, CC8, CC9, CC37, CC121 and CC155. The presence of SSI-1, was detected in 100% of the persistent strains from DP and 80% from MP, in particular in all strains of CC155, CC5, CC8 and CC9. In CC121 and CC37 it was absent. The presence of loci of Lm GI3, was in 100% of persistent strains of DP and in 52.3% of MP plant, in particular in 100% of CC121, CC8, CC5 and 16.3% of CC9. The 100% of CC121 in DP and MP plant harboured Tn6188 and SSI-2. The inlA PMSC mutations were detected in 100% of CC9 and CC121 strains.

Conclusions

The persistence of strains inside FPP was confirmed using NGS data, most of the strains were characterised by the presence of genes involved in resistance and adaptation. NGS is confirmed to be a powerful tool to study Lm persistence in FPP, looking also at strains' ecology.

Key messages

Most of persistent strains showed genes involved in resistance and adaptation in the food processing environment. NGS could help in facing Lm persistence in food producing plants giving new insights on the genomic characteristics of persistent strains.

Genotyping of Listeria monocytogenes strains in Italian food-processing environments

Background

In 2019, case fatality from Listeria monocytogenes (Lm) was higher than the previous years confirming Lm as a major public health problem. Food is the main source of Lm infection and cross-contamination from the food-processing environment (FPEs) is the most common route of contamination. The aim of this work was to characterize FPEs Lm strains collected from the National Reference Laboratory (NRL) for Lm in order to evaluate circulating clonal complexes (CCs) and their environmental adaptation.

Methods

NRL Lm database actually consists of 798 FPEs sequenced strains. In silico MLST was evaluated. Sequences related to prevalent CCs were further investigated using Pasteur's cgMLST scheme and detecting metal and detergent resistance genes and stress survival islet (SSI).

Results

MLST identified 25 CCs and 4 singleton. Nine isolates gave inexact match with existing alleles and were not classified. CC9 (17.4%) and CC121 (14.2%) were the prevalent clones. CC9 cgMLST analysis revealed a relatedness among strains isolated from the same establishment type (meat or dairy), even if sampled in different regions. Indeed, CC121 cgMLST clustering analysis was strictly associated to the point of sampling. Regarding stress adaptation genes, SSI1 and brcABC genes were detected in 100% and 2.9% of the CC9 strains, respectively. Meanwhile, SSI2 and transposon Tn6188 were detected, respectively, in 100% and 97.3% of CC121 strains.

Conclusions

Results confirmed, in Italian FPEs, prevalence of hypovirulent Lm strains, as previously observed in Italian food. Tested isolates highlighted adaptation to low pH and high salt concentration (SSI1 genes for CC9), to alkaline and oxidative stress (SSI2 genes for CC121) and benzalkonium chloride tolerance (Tn6188 in CC121) resulting in a best survival under stress conditions. Interestingly, CC9 clustering denoted allelic proximity among strains isolated in different Italian regions paying attention to clones spreading at national level.

Key messages

Listeria monocytogenes CC9 and CC121 prevalence in Italian establishment confirms environment is the main route of food contamination at production level. Prevalent food-processing environmental Italian Listeria monocytogenes strains denotes adaptation to environmental stress and clones spreading at national level.

Antimicrobial resistance of Listeria monocytogenes human strains and correlation to genomic data

Background

Studies checking antimicrobial resistance (AMR) of Listeria monocytogenes (Lm) are ongoing, coupled with disease surveillance. Lm resistant strains are reported and are increasing. The aim of the work was to investigate AMR of clinical strains of Lm collected from nine regions (mostly in Lombardy and Marche regions) from 2008 to 2020.

Methods

The dataset consisted of 233 Lm human strains collected from nine regions during the period 2008-2020. All the strains were tested using Sensititre™ Haemophilus Plate (Thermo Scientific, Milano, Italy). Results were expressed according to EUCAST breakpoints for Lm, S. pneumoniae and E. faecalis. Resistant strains were sequenced using Illumina platform, ABRicate was used to predict antimicrobial resistance genes and plasmids.

Results

Most of the strains were detected in Lombardy and Marche. The MIC results showed that 11 out of 233 strains were resistant, one to ampicillin, four to tetracycline and six to clarithromycin. Analysing the sequences, all the resistant strains showed to have a common antimicrobial resistant pattern (mprF, norB, FosX, (MLS)lin, lin and lmo0919). Genomic determinants for ampicillin and clarithromycin resistance were not detected. Indeed, only in 3 out of 4 resistant strains tetM was found. Meanwhile, plasmids were detected in 7 strains.

Conclusions

The distribution of the strains considered in this work did not reflect the real epidemiological situation in Italy, because their origin was mostly from two regions. The emergence of AMR also for Lm needs to be considered. Moreover, official breakpoints for Lm are not defined and to date limited to five antimicrobials excluding clarithromycin and tetracycline, where the pathogen showed resistance. Finally, the incongruence between phenotypic and genomic data suggests that the mechanisms involved in the resistance is not fully known especially for ampicillin. Further investigations are needed to improve the knowledge on Lm AMR.

Key messages

Monitoring AMR of Listeria monocytogenes is crucial, only effective drug in clinical cases should be used. Further investigations are needed to explore the mechanisms involved in antimicrobial resistance of Listeria monocytogenes.

Listeria monocytogenes clones in Italian food products: virulence and environmental adaptation

Background

Food is the main source of Listeria monocytogenes (Lm) infection. Lm is a highly heterogeneous species composed of hypervirulent and hypovirulent clones. Understanding the distribution of Lm clonal complexes (CCs) in different food categories has strong implications for risk assessment. The aim of this work was to analyse collection of Lm strains of National Reference Laboratory (NRL Lm) in order to assess link between genetic profile and matrices and the level of pathogenicity of circulating strains based on CCs.

Methods

NRL Lm database actually consists of 906 sequenced strains isolated in 10 years from 5 food compartments (meat, fish, dairy, vegetables and composite dishes). Epidata were analysed to remove redundant strains based on the same epidemiological description. After that, WGS data from 465 Lm strains were investigated. In silico MLST was defined and Roary 3.12.0 was used to obtain a pan-genome profile. Genes were later uploaded to Pasteur Institute platform for characterization.

Results

In silico MLST identified 36 CCs and 6 singleton. CC9 (23.0%), CC8 (15.3%) and CC121 (13.3%) were the prevalent CCs. In particular, CC9 was present in 35.2% of meat samples and CC8 in 25.8% of fish samples. Pan genome profile revealed high prevalence (&gt;98%) of genes related to biofilm formation and resistance to environmental stress in CC9 strains and genes involved in tolerance to quaternary ammonium compounds in CC121 strains.

Conclusions

Results, in particular for meat products, confirmed in Italy, the prevalence of hypovirulent Lm strains previously observed at European Union level. The high presence of stress resistance and disinfectant tolerance genes in these strains could make them able to persist in food-production environment and should be taken into account evaluating the health hazards. In fish product is also relevant the prevalence of CC8 strains which are potentially highly pathogenic and have been responsible of recent European multi country outbreak.

Key messages

Pangenome of Listeria monocytogenes isolated from Italian food revealed high presence of disinfectant tolerance and stress resistance genes in meat products and virulence genes in fish products. Listeria monocytogenes CC9 and CC121 prevalence in Italian meat product confirms occurrence of hypovirulent strains detected at European Union level.