Monocytogenes Sequence Type Research Articles

Draft genome sequences of Listeria monocytogenes strains of sequence type 1733 which constituted a pseudo-outbreak due to contaminated blood agar media.

We report genome sequences of Listeria monocytogenes sequence type (ST) 1733 from a 2013 pseudo-outbreak, where L. monocytogenes isolation from non-sterile sites (urine, wound, or abscess) was an artifact from contaminated sheep blood in the isolation media. Two ST1733 strains from wound and urine in 2005 are also reported.

The first case of detection of Listeria monocytogenes sequence types ST7, ST20, ST425 in wastewater during an investigation of water bodies in the Vologda region

Introduction. Listeria monocytogenes is an important human pathogen causing various forms of listeriosis, including foodborne infections, meningitis, neonatal sepsis, and abortion. Listeria are common all over the world.The purpose of the study was to conduct microbiological monitoring of L. monocytogenes in water reservoirs near livestock premises in the Vologda district of the Vologda region.Materials and methods. Bacterial cultures were isolated using two methods, titration and filtration, followed by analysis using methods of conventional bacteriology, serotyping, and species identification by instrumental procedures such as whole genome sequencing, and bioinformatic analysis.Results. Three isolates of L. monocytogenes and one isolate of Listeria innocua were isolated from 12 analyzed water samples (wastewater — 6, river water — 4, and storm water — 2 samples). whole genome sequencing of three L. monocytogenes strains attributed them to the evolutionary line II, and to three sequence types and two serogroups ST425(1/2a-3a), ST20(1/2a-3a), ST7 (4a-4c). The strains are shown to belong to multiple drug resistant ones conferring resistance to three functional groups of antibacterials such as tetracyclines, macrolides, and sulfonamides. Antibiotic resistance genes (fox, psp-like, lin,norB,sul), virulence Islands LIPI-1 and LIPI-2, and virulence genes inlABCJ, oatA, ami, gtcA, vip, and lisK in genomes of the strain were identified. Stress tolerance Island SSI-1 was identified in one strain.Conclusions. The data obtained indicate contamination of water sources near the livestock premises with L. monocytogenes strains possessing high pathogenic potentiality for outbreaks of listeriosis in humans. This shows the necessity of careful monitoring of water sources for the presence of the causative agent of listeriosis as well as the implementing of anti-epidemic measures.

Antimicrobial susceptibility, multilocus sequence typing, and virulence of listeria isolated from a slaughterhouse in Jiangsu, China

BackgroundListeria monocytogenes is one of the deadliest foodborne pathogens. The bacterium can tolerate severe environments through biofilm formation and antimicrobial resistance. This study aimed to investigate the antimicrobial susceptibility, resistance genes, virulence, and molecular epidemiology about Listeria from meat processing environments.MethodsThis study evaluated the antibiotic resistance and virulence of Listeria isolates from slaughtering and processing plants. All isolates were subjected to antimicrobial susceptibility testing using a standard microbroth dilution method. The harboring of resistant genes was identified by polymerase chain reaction. The multilocus sequence typing was used to determine the subtyping of the isolates and characterize possible routes of contamination from meat processing environments. The virulence of different STs of L. monocytogenes isolates was evaluated using a Caco-2 cell invasion assay.ResultsA total of 59 Listeria isolates were identified from 320 samples, including 37 L. monocytogenes isolates (62.71%). This study evaluated the virulence of L. monocytogenes and the antibiotic resistance of Listeria isolates from slaughtering and processing plants. The susceptibility of these 59 isolates against 8 antibiotics was analyzed, and the resistance levels to ceftazidime, ciprofloxacin, and lincomycin were as high as 98.31% (L. m 37; L. innocua 7; L. welshimeri 14), 96.61% (L. m 36; L. innocua 7; L. welshimeri 14), and 93.22% (L. m 35; L. innocua 7; L. welshimeri 13), respectively. More than 90% of the isolates were resistant to three to six antibiotics, indicating that Listeria isolated from meat processing environments had high antimicrobial resistance. Up to 60% of the isolates harbored the tetracycline-resistance genes tetA and tetM. The frequency of ermA, ermB, ermC, and aac(6′)-Ib was 16.95, 13.56, 15.25, and 6.78%, respectively. Notably, the resistant phenotype and genotype did not match exactly, suggesting that the mechanisms of antibiotic resistance of these isolates were likely related to the processing environment. Multilocus sequence typing (MLST) revealed that 59 Listeria isolates were grouped into 10 sequence types (STs). The dominant L. monocytogenes STs were ST5, ST9, and ST121 in the slaughtering and processing plant of Jiangsu province. Moreover, ST5 subtypes exhibited high invasion in Caco-2 cells compared with ST9 and ST121 cells.ConclusionThe dominant L. monocytogenes ST5 persisted in the slaughtering and processing plant and had high antimicrobial resistance and invasion characteristics, illustrating a potential risk in food safety and human health.

Function and distribution of the conjugative plasmid pLM1686 in foodborne Listeria monocytogenes in China

Listeria monocytogenes, a fatal foodborne pathogen has the extraordinary capacity to survive in harsh conditions and is a potential threat to public health. A novel 91 kb plasmid pLM1686 was found in the prevalent L. monocytogenes sequence type (ST) 87 strain in China. In this study, the function and distribution of pLM1686 were firstly investigated in L. monocytogenes. The results showed plasmid pLM1686 had self-transmissible ability and existed in various types of L. monocytogenes isolates belonging to two lineages (lineage I and II), four serotypes (1/2b, 3b, 1/2c and 1/2a) and four STs (ST87, ST59, ST9 and ST120). The wild strain LM1686 and transconjugant strain 10403SP1686 exhibited significantly higher growth rate and biofilm formation in Modification of Welshimer's medium (MWB), greater salinity tolerance, stronger cell invasion and higher cytotoxicity than plasmid-cured strain and reference strain 10403S. Moreover, plasmid curing caused the loss of cadmium resistance of strain, and the recipient strain acquired cadmium resistance after conjugation. Thus, pLM1686 would provide L. monocytogenes advantages of surviving in adverse environments.

Complete Genome Sequences of Three Clinical Listeria monocytogenes Sequence Type 8 Strains from Recent German Listeriosis Outbreaks.

We report here the closed genome sequences of three clinical Listeria monocytogenes strains of multilocus sequence typing (MLST) sequence type 8 (ST8). These strains are representatives of three separate listeriosis outbreak clusters (Alpha1, Pi4, and Sigma1) that affected Germany between 2012 and 2020.

Retrospective Use of Whole-Genome Sequencing Expands the Multicountry Outbreak Cluster of Listeria monocytogenes ST1247.

Listeria monocytogenes sequence type 1247 clonal complex 8 caused a prolonged multicountry outbreak in five EU countries: Denmark, Estonia, Finland, France, and Sweden. A total of 22 disease cases were identified with onset of symptoms between July 2014 and February 2019. Five patients died due to, or with, the disease. The retrospective analysis of L. monocytogenes isolate VLTRLM2013 revealed the presence of an outbreak-related strain (cgMLST type L2-SL8-ST1247-CT4158) in ready-to-eat fish product more than a year prior to the first outbreak-related cases. Reference outbreak strain and VLTRLM2013 strain were compared using core genome and whole-genome multilocus sequence typing analyses. Genomic level differences of the persistent L. monocytogenes strains associated with a prolonged multicountry foodborne listeriosis outbreak are described. It was concluded that the persistent nature of the multicountry outbreak-related L. monocytogenes strain VLTRLM2013 together with stress island, virulence, and antibiotic resistance genes could potentially be the determining factors for the extensive and prolonged outbreak affecting five European Union countries. Our results support the systematic application of whole-genome sequencing in food and public health surveillance and further encourages its wide adoption.

A Large-Scale Sequencing-Based Survey of Plasmids in Listeria monocytogenes Reveals Global Dissemination of Plasmids.

The food-borne pathogen Listeria monocytogenes is known for its capacity to cope with multiple stress conditions occurring in food and food production environments (FPEs). Plasmids can provide benefits to their host strains, and it is known that various Listeria strains contain plasmids. However, the current understanding of plasmid frequency and function in L. monocytogenes strains remains rather limited. To determine the presence of plasmids among L. monocytogenes strains and their potential contribution to stress survival, a comprehensive dataset was established based on 1,921 published genomes from strains representing 14 L. monocytogenes sequence types (STs). Our results show that an average of 54% of all L. monocytogenes strains in the dataset contained a putative plasmid. The presence of plasmids was highly variable between different STs. While some STs, such as ST1, ST2, and ST4, contained few plasmid-bearing strains (<15% of the strains per ST), other STs, such as ST121, ST5, ST8, ST3, and ST204, possessed a higher proportion of plasmid-bearing strains with plasmids found in >71% of the strains within each ST. Overall, the sizes of plasmids analyzed in this study ranged from 4 to 170 kbp with a median plasmid size of 61 kbp. We also identified two novel groups of putative Listeria plasmids based on the amino acid sequences of the plasmid replication protein, RepA. We show that highly conserved plasmids are shared among Listeria strains which have been isolated from around the world over the last few decades. To investigate the potential roles of plasmids, nine genes related to stress-response were selected for an assessment of their abundance and conservation among L. monocytogenes plasmids. The results demonstrated that these plasmid genes exhibited high sequence conservation but that their presence in plasmids was highly variable. Additionally, we identified a novel transposon, Tn7075, predicted to be involved in mercury-resistance. Here, we provide the largest plasmid survey of L. monocytogenes to date with a comprehensive examination of the distribution of plasmids among L. monocytogenes strains. Our results significantly increase our knowledge about the distribution, composition, and conservation of L. monocytogenes plasmids and suggest that plasmids are likely important for the survival of L. monocytogenes in food and FPEs.

Unraveling the emergence and population diversity of Listeria monocytogenes in a newly built meat facility through whole genome sequencing

The food processing environments of a newly opened meat processing facility were sampled in ten visits carried out during its first 1.5 years of activity and analyzed for the presence of Listeria monocytogenes. A total of 18 L. monocytogenes isolates were obtained from 229 samples, and their genomes were sequenced to perform comparative genomic analyses. An increase in the frequency of isolation of L. monocytogenes and in the diversity of sequence types (STs) detected was observed along time. Although the strains isolated belonged to six different STs (ST8, ST9, ST14, ST37, ST121 and ST155), ST9 was the most abundant (8 out of 18 strains). Low (0 and 2) single nucleotide polymorphism (SNP) distances were found between two pairs of ST9 strains isolated in both cases 3 months apart from the same processing room (Lm-1267 and Lm-1705, with a 2 SNPs distance in the core genome; Lm-1265 and Lm-1706, with a 0 SNPs distance), which suggests that these strains may be persistent L. monocytogenes strains in the food processing environment. Most strains showed an in silico attenuated virulence potential either through the truncation of InlA (in 67% of the isolates) or the absence of other virulence factors involved in cell adhesion or invasion. Twelve of the eighteen L. monocytogenes isolates contained a plasmid, which ranged in size from 4 to 87 Kb and harbored stress survival, in addition to heavy metals and biocides resistance determinants. Identical or highly similar plasmids were identified for various sets of L. monocytogenes ST9 isolates, which suggests the clonal expansion and persistence of plasmid-containing ST9 strains in the processing environments of the meat facility. Finally, the analysis of the L. monocytogenes genomes available in the NCBI database, and their associated metadata, evidenced that strains from ST9 are more frequently reported in Europe, linked to foods, particularly to meat and pork products, and less represented among clinical isolates than other L. monocytogenes STs. It also showed that the ST9 strains here isolated were more closely related to the European isolates, which clustered together and separated from ST9 North American isolates.

Virulence characterization and comparative genomics of Listeria monocytogenes sequence type 155 strains

BackgroundListeria (L.) monocytogenes strains show a high diversity regarding stress tolerance and virulence potential. Genome studies have mainly focused on specific sequence types (STs) predominantly associated with either food or human listeriosis. This study focused on the prevalent ST155, showing equal distribution among clinical and food isolates. We evaluated the virulence potential of 20 ST155 strains and performed comparative genomic analysis of 130 ST155 strains isolated from food, food processing environments and human listeriosis cases in different countries and years.ResultsThe in vitro virulence assays using human intestinal epithelial Caco2 and hepatocytic HEPG2 cells showed an impaired virulence phenotype for six of the 20 selected ST155 strains. Genome analysis revealed no distinct clustering of strains from the same source category (food, food processing environment, and clinical isolates). All strains harbored an intact inlA and inlB locus, except four strains, which had an internal deletion in the inlA gene. All strains harbored LIPI-1, but prfA was present in a longer variant in six strains, all showing impaired virulence. The longer PrfA variant resulted in lower expression of inlA, inlB, and prfA, and no expression of hly and actA.Regarding stress-related gene content, SSI-1 was present, whereas qacH was absent in all strains. 34.6% of the strains harbored a plasmid. All but one ST155 plasmids showed high conservation and harbored cadA2, bcrABC, and a triphenylmethane reductase.ConclusionsThis study contributes to an enhanced understanding of L. monocytogenes ST155 strains, being equally distributed among isolates from humans, food, and food processing environments. The conservation of the present genetic traits and the absence of unique inherent genetic features makes these types of STs especially interesting since they are apparently equally adapted to the conditions in food processing environments, as well as in food as to the human host environment. However, a ST155-specific mutation resulting in a longer PrfA variant impaired the virulence potential of several ST155 strains.

Draft Genome Sequence of a Multicountry Outbreak-Related Listeria monocytogenes Sequence Type 1247 Strain, VLTRLM2013.

We sequenced the genome of a multicountry outbreak-related Listeria monocytogenes sequence type 1247 strain (VLTRLM2013) that was isolated from a vacuum-packaged sliced salted salmon product of an Estonian fish-processing company that was obtained from an Estonian retail outlet in 2013.

Nosocomial cross-infection of hypervirulent Listeria monocytogenes sequence type 87 in China.

BackgroundTo investigate the epidemiological and phenotypic characteristics and molecular relatedness of L. monocytogenes, which were cultured from the blood and cerebrospinal fluid (CSF) samples isolated from two neonates.MethodsIn the present case study, two infected neonates were interviewed and epidemiological investigation performed. The phenotypic characteristics and molecular relatedness of L. monocytogenes was characterized by serotyping, pulsed-field gel electrophoresis and whole-genome sequencing (WGS).ResultsThe field investigation found that the two neonates were born in the same hospital (Hospital B) and admitted to the neonatal department through different channels within half an hour by different nurses, where they were weighed and placed in different but adjacent incubators. Then they were cared for by the same group of nurses that evening. It is worth noting that there was no record of sanitation of the neonatal incubator of neonate-1. The serotype of the two isolated L. monocytogenes were 1/2b, with an indistinguishable pulsotypes and were sequence type (ST) 87. WGS showed that there were no core SNP differences identified. In order to explore the genomic traits associated with L. monocytogenes virulence genes, we identified the Listeria pathogenicity island 4 and found that the genome was devoid of any stress islands. There are no positive results from the environmental samples. Considering the genomic data together with epidemiological evidence and clinical symptoms, insufficient surface cleaning along with the nursing staff caring for these neonates was considered as cross-infection factors.ConclusionsTo our knowledge, this is the first report of a nosocomial cross-infection of L. monocytogenes ST87 between two neonates, which carries the recently identified gene cluster expressing the cellobiose-family phosphotransferase system (PTS-LIPI-4) between two neonates. The test results of environmental samples in the hospital indicate that strict sterilization and patient isolation measures cannot be emphasized enough in neonatal nursing.

Multi‐country outbreak of Listeria monocytogenes sequence type 6 infections linked to ready‐to‐eatmeat products – 25 November 2019

Multi‐country outbreak of Listeria monocytogenes sequence type 6 infections linked to ready‐to‐eatmeat products – 25 November 2019

Distribution and Persistence of Listeria monocytogenes in a Heavily Contaminated Poultry Processing Facility

We studied the colonization and distribution of Listeria monocytogenes in a heavily contaminated poultry processing plant over a 1-year period. A total of 180 nonfood contact surfaces, 70 food contact surfaces, 29 personnel, and 40 food samples were analyzed. L. monocytogenes isolates were subtyped by PCR serotyping, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing. L. monocytogenes was detected in samples collected at every visit to the plant, and 43.8% (visit 4) to 65.6% (visit 7) of samples were positive, for an overall prevalence of 55.2%. The deboning area had the highest prevalence of positive samples (83.3%), and the processing area had the highest diversity of PFGE types. Ninety percent of the final products were positive for L. monocytogenes. Most of the isolates belonged to well-known persistent L. monocytogenes sequence types (ST9 and ST121). This study illustrates a well-established L. monocytogenes contamination problem in a poultry processing plant associated with a generalized failure of the food safety system as a whole. These findings reflect the potential for L. monocytogenes contamination when the food safety and quality management system is unsatisfactory, as described in the present study. It is essential to revise food safety and quality management systems to eliminate L. monocytogenes from food processing facilities, to control the entrance of sporadic sequence types, and to prevent L. monocytogenes spread within such facilities, especially in those premises with higher L. monocytogenes prevalence in the environment and final food products.

Rapid detection of Listeria monocytogenes sequence type 121 strains using a novel multiplex PCR assay

Listeria monocytogenes is a hazardous foodborne causative agent, commonly found in foods and food production environments. The persistent contamination of L. monocytogenes sequence type (ST) 121 in food production environments is one of the challenging issues. The objective of this study was to develop a multiplex PCR for identification of L. monocytogenes ST121 strains. A total of 50 specific candidate genes of ST121 were screened by the comparative genomics approach. A novel multiplex PCR for ST121 identification, which comprised of ST121 strain-specific primers (LM6179_0609 and LM6179_0171) and L. monocytogenes-specific primers (prfA), was designed. The specificity of this multiplex PCR was robustly verified by other STs of L. monocytogenes and non-L. monocytogenes strains. The detection limit of the multiplex PCR was 253 fg/μL genomic DNA. This multiplex PCR could avoid the interference of L. monocytogenes ST9, ST8, ST87, and ST155 in different ratios, which are common contaminants in food items. In addition, this multiplex PCR method could successfully detect 2.5 × 104–2.5 × 100 cfu/10 mL of L. monocytogenes ST121 in artificially contaminated milk after 4–12 h enrichment. These results suggested that the newly developed multiplex PCR in this study offers a promising approach for specific, rapid, and accurate detection of L. monocytogenes ST121 strains.

Multi‐country outbreak of Listeria monocytogenes clonal complex 8 infections linked to consumption of cold‐smoked fish products

A prolonged multi-country outbreak of 22 listeriosis cases caused by Listeria monocytogenes sequence type (ST) 1247, clonal complex (CC) 8 has been identified through whole genome sequencing (WGS) in five EU countries: Denmark (9 cases), Estonia (6), Finland (2), France (1) and Sweden (4). Five patients have died due to, or with, the disease. The first case had symptom onset in July 2014 in Estonia, and the most recent case occurred in Denmark in February 2019. Eight patients, out of twelve for whom a food consumption history was available, confirmed the consumption of cold-smoked fish products.L. monocytogenes food isolates, matching the human outbreak strain by WGS, were detected at wholesale and retail level in four countries (i.e. France, Denmark, Italy and Sweden) from 13 batches of cold smoked or gravad salmon and from six batches of cold smoked trout products. Traceability information of the contaminated batches pointed to the Estonian processing Company A as the single common manufacturer of these fish products. The raw fish was received from suppliers in Norway and Finland. Environmental investigations and food testing at the Estonian processing plant showed the presence of L. monocytogenes that matched the outbreak strain in two samples on the processing line and in four batches of the final product.The presence of L. monocytogenes matching the outbreak strain over several years in the fish products suggests the persistence of the microorganism at the Estonian company's premises. Further investigation is needed to identify points of (cross-)contamination in the food processing plant. Control measures were implemented in Estonia, Denmark, France and Italy following the RASFF (Rapid Alert System for Food and Feed) notifications, but until the source of infection has been identified and controlled, new invasive listeriosis cases associated with this event may still occur.

Cost estimation of listeriosis (Listeria monocytogenes) occurrence in South Africa in 2017 and its food safety implications

Periodic outbreaks of foodborne pathogens have resulted in food safety concerns, due to health implications and cost consequences. Occurrence of Listeria monocytogenes in foods and listeriosis have been reported in developed countries; however, documentation of listeriosis in South Africa is limited. In 2017–2018, Listeria was reported on polony (processed deli meat) and listeriosis was observed in South Africa (L. monocytogenes sequence type 6 (ST-6) was identified as the causal agent for listeriosis). Due to its potential effects, we conducted cost estimates to assess the implications of listeriosis outbreak with respect to illnesses, hospitalizations and deaths, and productivity losses. Cost estimates were computed on publicly available data by using USDA-ERS cost computation model for Listeria. Listeriosis had significant impacts, as mortality of 204 individuals with confirmed listeriosis cases was reported, with infants having the highest percent of fatalities (42%). The cost valuation of fatality cases was over US$ 260 million. Hospitalization costs associated with one-month recovery from listeriosis were estimated at US$ 10.4 million. Productivity losses attributed to listeriosis for humans and export value losses for food processors were in excess of US$ 15 million. Increase of food safety measures in South Africa could reduce foodborne disease outbreaks. Pre-emptive pathogen detection, sanitary procedures and bacterial inactivation can enhance control of L. monocytogenes in food processing environments.

Multi‐country outbreak of Listeria monocytogenes sequence type 8 infections linked to consumption of salmon products

A multi-country outbreak of 12 listeriosis cases caused by Listeria monocytogenes sequence type (ST) 8 has been identified through whole genome sequencing (WGS) analysis in three EU/EEA countries: Denmark (6 cases), Germany (5) and France (1). Four of these cases have died due to or with the disease. It is likely that the extent of this outbreak has been underestimated since the outbreak was identified through sequencing and only a subset of the EU/EEA countries routinely use this advanced technique to characterise L. monocytogenes isolates. The first case was sampled in October 2015 in Denmark and the most recent case was reported in May 2018 in Germany. In August 2017, Denmark identified the first cluster of cases, which was investigated and linked to the consumption of ready-to-eat cold-smoked salmon produced in Poland. Control measures were implemented and the Member States and competent authorities were informed. In October 2017, France reported the identification of a matching L. monocytogenes strain in food isolates from marinated salmon originating from the same Polish processing company as identified in the Danish outbreak investigation. This supports the hypothesis that contamination may have occurred at the processing company in Poland. However, due to the lack of WGS data on the isolates found in the environmental and food samples taken at the Polish processing plant, it is not possible at present to confirm the contamination with the L. monocytogenes ST8 outbreak strain at the suspected Polish plant. Moreover, until detailed information on the Norwegian primary producers of the salmon used in the contaminated batches is reported and assessed, possible contamination at primary production level cannot be excluded either. Although control measures were implemented following the Danish outbreak investigation in September 2017, the identification of the same strain in a salmon product in France and a new human case in Germany suggest that the source of contamination is still active and contaminated products have been distributed to other EU countries than Denmark. Until the source of infection has been eliminated, new invasive listeriosis cases may still occur. Pregnant women, the elderly and immunocompromised individuals are at increased risk of invasive listeriosis, which is associated with severe clinical course and potentially death.

Characterization of a Listeria monocytogenes meningitis mouse model

BackgroundListeria monocytogenes is a common cause of bacterial meningitis. We developed an animal model of listerial meningitis.MethodsIn survival studies, C57BL/6 mice received intracisternal injections with different L. monocytogenes sequence type 1 (ST1) colony forming units per milliliter (CFU; n = 48, 105, 106, 107, 108, and 109 CFU/ml). Second, mice were inoculated with 108 CFU/ml ST1 and sacrificed at 6 h and 24 h (n = 12/group). Outcome parameters were clinical score, CFUs, cyto- and chemokine levels, and brain histopathology. Third, 84 mice were inoculated (109 CFU/ml ST1) to determine optimal antibiotic treatment with different doses of amoxicillin and gentamicin. Fourth, mice were inoculated with 109 CFU/ml ST1, treated with amoxicillin, and sacrificed at 16 h and 24 h (n = 12/group) for outcome assessment. Finally, time point experiments were repeated with ST6 (n = 24/group).ResultsMedian survival time for inoculation with 108 and 109 CFU/ml ST1 was 46 h and 40 h; lower doses of bacteria led to minimal clinical signs of disease. Brain levels of IL-6, IL-17A, and IFN-γ were elevated at 24 h, and IL-1β, IL-6, IL-10, IFN-γ, and TNF-α were elevated in blood at 6 h and 24 h. Histopathology showed increased meningeal infiltration, vascular inflammation of meningeal vessels, hemorrhages, and ventriculitis. In the treatment model, brain levels of IL-6 and IL-17A and blood levels of IL-6 and IFN-γ were elevated. Compared to ST6, infection with ST1 led initially to higher levels of IL-1β and TNF-α in blood and more profound neuropathological damage. At 16 h post inoculation, IL-1β, IL-10, and TNF-α in blood and IL-6, IL17A, TNF-α, and IFN-γ levels in brain were higher in ST1 compared to ST6 without differences in CFUs between STs. At 24 h, neuropathology score was higher in ST1 compared to ST6 (p = 0.002) infected mice.ConclusionsWe developed and validated a murine model of listerial meningitis. ST1-infected mice had a more severe inflammatory response and brain damage as compared to ST6-infected mice.

Whole-Genome Sequences of Listeria monocytogenes Sequence Type 6 Isolates Associated with a Large Foodborne Outbreak in South Africa, 2017 to 2018.

ABSTRACTWe report whole-genome sequences for 10 Listeria monocytogenes sequence type 6 isolates associated with a large listeriosis outbreak in South Africa, which occurred over the period of 2017 to 2018. The possibility of listeriosis spreading beyond South Africa’s borders as a result of exported contaminated food products prompted us to make the genome sequences publicly available.

Listeria monocytogenes Sequence Types 121 and 14 Repeatedly Isolated Within One Year of Sampling in a Rabbit Meat Processing Plant: Persistence and Ecophysiology.

Listeria monocytogenes is a foodborne pathogen adapted to survive and persist in multiple environments. Following two previous studies on prevalence and virulence of L. monocytogenes ST121 and ST14 repeatedly collected in a the same rabbit-meat processing plant, the research questions of the present study were to: (1) assess persistence of L. monocytogenes isolates from the rabbit-plant; (2) select genes associated to physiological adaptation to the food-processing environment; (3) compare presence/absence/truncation of these genes in newly sequenced and publicly available ST121 and ST14 genomes. A total of 273 draft genomes including ST121 and ST14 newly sequenced and publicly available draft genomes were analyzed. Whole-genome Single Nucleotide Polymorfism (wgSNP) analysis was performed separately on the assemblies of ST121 and ST14 draft genomes. SNPs alignments were used to infer phylogeny. A dataset of L. monocytogenes ecophysiology genes was built based on a comprehensive literature review. The 94 selected genes were screened on the assemblies of all ST121 and ST14 draft genomes. Significant gene enrichments were evaluated by statistical analyses. A persistent ST14 clone, including 23 out of 27 newly sequenced genomes, was circulating in the rabbit-meat plant along with two not persistent clones. A significant enrichment was observed in ST121 genomes concerning stress survival islet 2 (SSI-2) (alkaline and oxidative stress), qacH gene (resistance to benzalkonium chloride), cadA1C gene cassette (resistance to 70 mg/l of cadmium chloride) and a truncated version of actA gene (biofilm formation). Conversely, ST14 draft genomes were enriched with a full-length version of actA gene along with the Listeria Genomic Island 2 (LGI 2) including the ars operon (arsenic resistance) and the cadA4C gene cassette (resistance to 35 mg/l of cadmium chloride). Phenotypic tests confirmed ST121 as a weak biofilm producer in comparison to ST14. In conclusion, ST121 carried the qacH gene and was phenotypically resistant to quaternary ammonium compounds. This property might contribute to the high prevalence of ST121 in food processing plants. ST14 showed greater ability to form biofilms, which might contribute to the occasional colonization and persistence on harborage sites where sanitizing procedures are difficult to display.