Molecular Typing and Epidemiology of Human Listeriosis Cases, Denmark, 2002-2012

Current methodologies available to evaluate the virulence potential among Listeria monocytogenes clonal complexes

Listeria monocytogenes is a foodborne pathogen that causes listeriosis in humans, the severity of which depends on multiple factors, including intrinsic characteristics of the affected individuals and the pathogen itself. Additionally, emerging evidence suggests that epigenetic modifications may also modulate host susceptibility to infection. Therefore, different clinical outcomes can be expected, ranging from self-limiting gastroenteritis to severe central nervous system and maternal-neonatal infections, and bacteremia. Furthermore, L. monocytogenes is a genetically and phenotypically diverse species, resulting in a large variation in virulence potential between strains. Multilocus sequence typing (MLST) has been widely used to categorize the clonal structure of bacterial species and to define clonal complexes (CCs) of genetically related isolates. The combination of MLST and epidemiological data allows to distinguish hypervirulent CCs, which are notably more prevalent in clinical cases and typically associated with severe forms of the disease. Conversely, other CCs, termed hypovirulent, are predominantly isolated from food and food processing environments and are associated with the occurrence of listeriosis in immunosuppressed individuals. Reports of genetic traits associated with this diversity have been described. The Food and Agriculture Organization (FAO) is encouraging the search for virulence biomarkers to rapidly identify the main strains of concern to reduce food waste and economical losses. The aim of this review is to comprehensively collect, describe and discuss the methodologies used to discriminate the virulence potential of L. monocytogenes CCs. From the exploration of in vitro and in vivo models to the study of expression of virulence genes, each approach is critically explored to better understand its applicability and efficiency in distinguishing the virulence potential of the pathogen.

Virulence Potential and Antimicrobial Resistance of Listeria monocytogenes Isolates Obtained from Beef and Beef-Based Products Deciphered Using Whole-Genome Sequencing

Listeria monocytogenes is a ubiquitous bacterial pathogen that threatens the food chain and human health. In this study, whole-genome sequencing (WGS) was used for the genomic characterization of L. monocytogenes (n = 24) from beef and beef-based products. Multilocus Sequence Type (MLST) analysis revealed that ST204 of CC204 was the most common sequence type (ST). Other sequence types detected included ST1 and ST876 of CC1, ST5 of CC5, ST9 of CC9, ST88 of CC88, ST2 and ST1430 of CC2, and ST321 of CC321. Genes encoding for virulence factors included complete LIPI-1 (pfrA-hly-plcA-plcB-mpl-actA) from 54% (13/24) of the isolates of ST204, ST321, ST1430, and ST9 and internalin genes inlABC that were present in all the STs. All the L. monocytogenes STs carried four intrinsic/natural resistance genes, fosX, lin, norB, and mprF, conferring resistance to fosfomycin, lincosamide, quinolones, and cationic peptides, respectively. Plasmids pLGUG1 and J1776 were the most detected (54% each), followed by pLI100 (13%) and pLM5578 (7%). The prophage profile, vB_LmoS_188, was overrepresented amongst the isolates, followed by LP_101, LmoS_293_028989, LP_030_2_021539, A006, and LP_HM00113468. Listeria genomic island 2 (LGI-2) was found to be present in all the isolates, while Listeria genomic island 3 (LGI-3) was present in a subset of isolates (25%). The type VII secretion system was found in 42% of the isolates, and sortase A was present in all L. monocytogenes genomes. Mobile genetic elements and genomic islands did not harbor any virulence, resistance, or environmental adaptation genes that may benefit L. monocytogenes. All the STs did not carry genes that confer resistance to first-line antibiotics used for the treatment of listeriosis. The characterization of L. monocytogenes in our study highlighted the environmental resistance and virulence potential of L. monocytogenes and the risk posed to the public, as this bacterium is frequently found in food and food processing environments.

Antibacterial properties of natural products from marine fungi reported between 2012 and 2023: a review

The oceans are rich in diverse microorganisms, animals, and plants. This vast biological complexity is a major source of unique secondary metabolites. In particular, marine fungi are a promising source of compounds with unique structures and potent antibacterial properties. Over the last decade, substantial progress has been made to identify these valuable antibacterial agents. This review summarizes the chemical structures and antibacterial activities of 223 compounds identified between 2012 and 2023. These compounds, effective against various bacteria including drug-resistant strains such as methicillin-resistant Staphylococcus aureus, exhibit strong potential as antibacterial therapeutics. The review also highlights the relevant challenges in transitioning from drug discovery to product commercialization. Emerging technologies such as metagenomics and synthetic biology are proposed as viable solutions. This paper sets the stage for further research on antibacterial compounds derived from marine fungi and advocates a multidisciplinary approach to combat drug-resistant bacteria.

Comparative Analysis of Growth, Survival, and Virulence Characteristics of Listeria monocytogenes Isolated from Imported Meat

Listeria monocytogenes is an important foodborne pathogen with worldwide prevalence. Understanding the variability in the potential pathogenicity among strains of different subtypes is crucial for risk assessment. In this study, the growth, survival, and virulence characteristics of 16 L. monocytogenes strains isolated from imported meat in China (2018-2020) were investigated. The maximum specific growth rate (μmax) and lag phase (λ) were evaluated using the time-to-detection (TTD) method and the Baranyi model at different temperatures (25, 30, and 37 °C). Survival characteristics were determined by D-values and population reduction after exposure to heat (60, 62.5, and 65 °C) and acid (HCl, pH = 2.5, 3.5, and 4.5). The potential virulence was evaluated via adhesion and invasion to Caco-2 cells, motility, and lethality to Galleria mellonella. The potential pathogenicity was compared among strains of different lineages and subtypes. The results indicate that the lineage I strains exhibited a higher growth rate than the lineage II strains at three growth temperatures, particularly serotype 4b within lineage I. At all temperatures tested, serotypes 1/2a and 1/2b consistently demonstrated higher heat resistance than the other subtypes. No significant differences in the log reduction were observed between the lineage I and lineage II strains at pH 2.5, 3.5, and 4.5. However, the serotype 1/2c strains exhibited significantly low acid resistance at pH 2.5. In terms of virulence, the lineage I strains outperformed the lineage II strains. The invasion rate to Caco-2 cells and lethality to G. mellonella exhibited by the serotype 4b strains were higher than those observed in the other serotypes. This study provides meaningful insights into the growth, survival, and virulence of L. monocytogenes, offering valuable information for understanding the correlation between the pathogenicity and subtypes of L. monocytogenes.

Potential public health hazards related to consumption of poultry contaminated with antibiotic resistant Listeria monocytogenes in Egypt

Listeria monocytogenes is an important foodborne pathogen that incorporated into many serious infections in human especially immunocompromised individuals, pregnant women, the elderly, and newborns. The consumption of food contaminated with such bacteria is considered a source of potential risk for consumers. Therefore, a total of 250 poultry purchased in highly popular poultry stores besides 50 swabs from workers hands in the same stores, in Mansoura City had been tested for the L. monocytogenes prevalence, virulence genes, and antibiotic resistance profile illustrating the health hazards from such poultry. The L. monocytogenes were recovered from 9.6% of poultry samples while not detected from workers hand swabs. The antimicrobial susceptibility of 24 L. monocytogenes strains against 24 antibiotics of seven different classes revealed high susceptibility rates to erythromycin (79.17%), streptomycin (66.67%), gentamycin (66.67%), vancomycin (58.33%), chloramphenicol (58.33%) and cefotaxime (41.67%). The majority (79.2%) of L. monocytogenes were classified as multidrug resistant strains with high resistance to tetracyclines and β-lactams antibiotics while 16.7% of the strains were categorized as extensively resistant ones. The iap virulence-specific determination gene had been detected in all recovered L. monocytogenes isolates while 83.33 and 70.83% of the isolates harbored hylA and actA genes. In addition, the study confirmed the capability of most L. monocytogenes isolates for biofilm formation by moderate to strong production and the quantitative risk assessment illustrated the risk of developing listeriosis as the risk value exceeded 100. The current results illustrate that poultry meat can be a source of pathogenic antibiotic resistant strains that may cause infection with limited or no treatment in immunosuppressed consumers via the food chain.

A live attenuated DIVA vaccine affords protection against Listeria monocytogenes challenge in sheep

Listeria monocytogenes (Lm) is a deadly foodborne pathogen that comprises 14 serotypes, among which, serotype 4b Lm is the primary cause of listeriosis outbreaks in humans and animals. Here, we evaluated the safety, immunogenicity, and protective efficacy of a serotype 4b vaccine candidate Lm NTSNΔactA/plcB/orfX in sheep. The infection dynamics, clinical features, and pathological observation verified that the triple genes deletion strain has adequate safety for sheep. Moreover, NTSNΔactA/plcB/orfX significantly stimulated humoral immune response and 78% protection against lethal wild-type strain challenge. Notably, the attenuated vaccine could differentiate infected and vaccinated animals (DIVA) via serology determination of the antibody against listeriolysin O (LLO, encoded by hly) and phosphatidylinositol-specific phospholipase C (PI-PLC, encoded by plcB). These data suggest that the serotype 4b vaccine candidate has high efficacy, safety, and DIVA characteristics, and may be used to prevent Lm infection in sheep, which provides a theoretical basis for its future application in livestock and poultry breeding.

Prevalence and Biological Characteristics of Listeria Species Isolated from Livestock and Poultry Meat in Gansu Province, China

Listeria monocytogenes is a widespread foodborne pathogen contaminating foods during their production or processing stages. Fresh meat is susceptible to such contamination if it is not properly preserved. Our study was conducted to reveal the level of contamination and prevalence of Listeria spp. present in livestock and poultry meat from Gansu province. A total of 1,387 samples were collected from five cities in Gansu Province according to standard sampling procedures, of which 174 samples (12.5%) were positive for Listeria species. Among them, 14 isolates of L. monocytogenes (1.0%), 150 isolates of Listeria innocua (10.8%), and ten isolates of Listeria welshimeri (0.7%) were identified by conventional bacteriological and molecular identification methods. All isolates were subjected to serological assays, antimicrobial susceptibility tests, growth curve assays, determination of biofilm-forming capacity, and cluster analysis of the 16S rRNA gene sequences. Four predominant serotypes of L. monocytogenes were identified, including 1/2a (35.7%, 5/14), 1/2b (14.3%, 2/14), 1/2c (42.9%, 6/14), and 4b (7.1%, 1/14). All L. monocytogenes isolates were resistant to tetracycline and cefoxitin. Most L. innocua isolates (63.6%, 14/22) and L. welshimeri (40%, 4/10) were resistant to tetracycline. The high biofilm-forming ability was observed among 1/2c and 1/2a serotype isolates. The cluster analysis of the 16S rRNA gene sequences revealed a close genetic relationship between the three Listeria species. This study fills the gap in the knowledge of livestock and poultry meat that carry Listeria in slaughterhouses and markets in Gansu Province.

Epidemiology and Clinical Features of Listeriosis in Gipuzkoa, Spain, 2010-2020

Background

Listeriosis continues to be one of the most important notifiable foodborne diseases. Nonetheless, in Spain, there are few data on the molecular epidemiology of Listeria monocytogenes infections in recent years.

Aim

To describe clinical features and the molecular epidemiology of human listeriosis over an 11-year period (2010–2020) in Gipuzkoa, Northern Spain.

Methods

A total of 111 isolates, all but one from invasive disease, were studied. Serotyping (agglutination and multiplex polymerase chain reaction [PCR]) and multilocus sequence typing were performed for all isolates. Antibiotic susceptibility was assessed by the broth microdilution method.

Results

The average annual incidence of listeriosis in non-pregnancy-associated cases was 1.55 per 100,000 population, with a 1-month mortality rate of 22.2%. In pregnant women, the average incidence was 0.45 cases per 1,000 pregnancies. Twenty-four sequence types were identified, serotype 4b ST1 (24.3%) being the most frequent followed by 1/2b ST87 (18.9%), which caused two long outbreaks in 2013–2014. A significant association was observed between ST219 and meningitis (p < 0.001). All isolates were susceptible to ampicillin as well as other antibiotics used in listeriosis treatment.

Conclusion

Despite current control measures, listeriosis continues to be an important cause of mortality in the elderly, preterm birth, and miscarriages in pregnant women. Improvements in the control and diagnosis of listeriosis are needed to reduce the impact of this infection on vulnerable populations.

Molecular characterization and in vivo pathogenicity study of Listeria monocytogenes isolated from fresh and frozen local and imported fish in Jordan

Background:

Listeria monocytogenes (L. monocytogenes) is a serious zoonotic and food transmitted human pathogen causing meningitis and abortions. Several outbreaks of listeriosis have been associated with the consumption of ready-to-eat food products; dairy, meat, fish, and contaminated fruits and vegetables worldwide.

Aim:

This study was designed to detect and characterize L. monocytogenes isolated from local and imported fish in Jordan.

Methods:

A total of 170 fish (70 local and 100 imported), of which 140 fresh and 30 frozen samples were used in this study. Listeria monocytogenes was cultured and initially identified using conventional microbiological methods. For confirmation and serotyping of the L. monocytogenes isolates, PCR techniques were used. Using oral and intraperitoneal administration, mice were used to determine the pathogenicity and LD₅₀ of the isolated L. monocytogenes.

Results:

A total of 72 Listeria spp. isolates were cultured from fish. Of those, 24 were positively identified as L. monocytogenes. Other strains of Listeria spp. were L. ivanovii (21), L. innocua (11), and L. grayi (16). Serotyping of the L. monocytogenes indicated that 14 isolates belonged to the 1/2b, 3b serotypes whereas 10 isolates belonged to the 4a and 4c serotypes. All isolates were virulent to mice with an LD₅₀ dose ranging from 3 × 10¹⁰ CFU/ml to 3 × 10^7.5 CFU/ml. All the virulent isolates belonged to the serotype 1/2b. Histopathologically, dead mice showed multiple necrotic lesions in the liver and spleen.

Conclusion:

Results of this study showed the presence of potentially pathogenic L. monocytogenes in fresh and frozen, local, and imported fish in Jordan. Strict monitoring and quality control regulatory measures must be adopted to prevent future outbreaks of food poisoning associated with fish consumption.

Listeriosis Cases and Genetic Diversity of Their L. monocytogenes Isolates in China, 2008-2019

Listeriosis, caused by Listeria monocytogenes, is a severe food-borne infection. The nationwide surveillance in China concerning listeriosis is urgently needed. In the present study, 144 L. monocytogenes isolates were collected from the samples of blood, cerebrospinal fluid (CSF), and fetal membrane/placenta in China for 12 years from 2008 to 2019. We summarized these listeriosis patients’ demographical and clinical features and outcomes. The susceptibility profile for 12 antibiotics was also determined by the broth microdilution method. Multilocus sequence typing (MLST) and serogroups of these listeria isolates were analyzed to designate epidemiological types. We enrolled 144 cases from 29 healthcare centers, including 96 maternal-neonatal infections, 33 cases of bacteremia, 13 cases of neurolisteriosis, and two cutaneous listeriosis. There were 31 (59.6%) fetal loss in 52 pregnant women and four (9.8%) neonatal death in 41 newborns. Among the 48 nonmaternal-neonatal cases, 12.5% (6/48) died, 41.7% (20/48) were female, and 64.6% (31/48) occurred in those with significant comorbidities. By MLST, the strains were distinguished into 23 individual sequence types (STs). The most prevalent ST was ST87 (49 isolates, 34.0%), followed by ST1 (18, 12.5%), ST8 (10, 6.9%), ST619 (9, 6.3%), ST7 (7, 4.9%) and ST3 (7, 4.9%). Furthermore, all L. monocytogenes isolates were uniformly susceptible to penicillin, ampicillin, and meropenem. In summary, our study highlights a high genotypic diversity of L. monocytogenes strains causing clinical listeriosis in China. Furthermore, a high prevalence of ST87 and ST1 in the listeriosis should be noted.

Making Sense of the Biodiversity and Virulence of Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen responsible for listeriosis, an infection that can manifest in humans as bacteremia, meningoencephalitis in immunocompromised patients and the elderly, and fetal-placental infection in pregnant women. Reference strains from this facultative intracellular bacterium have been instrumental in the investigation of basic mechanisms in microbiology, immunology, and cell biology. The integration of bacterial population genomics with environmental, epidemiological, and clinical data allowed the uncovering of new factors involved in the virulence of L. monocytogenes and its adaptation to different environments. This review illustrates how these investigations have led to a better understanding of the bacterium's virulence and the driving forces that shaped it.

Clinical and molecular epidemiology of human listeriosis in Taiwan

OBJECTIVE

To determine serogroups, multilocus sequence typing (MLST) of Listeria monocytogenes isolates and analyze clinical characteristics of these clones focusing on non-perinatal cases.

METHODS

From 2000 to 2015, we analyzed 123 human listeriosis cases at a medical center in northern Taiwan using PCR serogrouping, MLST, and clinical presentations.

RESULTS

The annual incidence of listeriosis increased since 2005 with a peak in 2008 (0.2 per 1000 admission) and decreased thereafter. Of the 115 non-perinatal listeriosis cases, we found a male predominance (60%) with an average age of 63.9 years old (standard deviation: 15.3 years), and almost all patients had underlying conditions including malignancies (61.7%), steroid usage (39.1%), diabetes mellitus (31.3%), renal insufficiency (27.8%), and liver cirrhosis (17.4%). Clinical presentations included bacteremia (74.8%), neurolisteriosis (20.0%), and spontaneous bacterial peritonitis (5.2%). The most frequently identified serogroup-sequence types (ST) were IIB-ST87 (30.9%), followed by IIA-ST378 (16.3%) and IIA-ST155 (14.6%). The 30-day all-cause mortality of non-perinatal listeriosis was 25.2% and was associated with age (Hazard ratio: 1.04, 95% C.I. = 1.01-1.07, p = 0.021), steroid usage (Hazard ratio: 2.54, 95% C.I. = 1.06-6.11, p = 0.038) and respiratory distress at presentation (Hazard ratio: 2.59, 95% C.I. = 1.05-6.39, p = 0.038); while no association was found with serogroups (IIA, IIB, and IVB) or three major ST types by multivariable analysis. All 8 mothers of perinatal listeriosis patients survived and three neonates died (mortality, 37.5%), and IIB-ST87 was the major type (62.5%).

CONCLUSION

Predominant strains in Taiwan could cause significant morbidity and mortality. Further disease monitoring and source surveillance are warranted despite a declining trend of human listeriosis in Taiwan.

Analysis of virulence genes and molecular typing of Listeria monocytogenes isolates from human, food, and livestock from 2008 to 2016 in Iran

The frequency of Listeria monocytogenes isolates collected from a total of 1150 samples including food (n = 300), livestock (n = 50), and human clinical (n = 800) was evaluated during 2008-2016. Antimicrobial resistance patterns, virulence factors, and molecular characteristics of these isolates were analyzed using disk diffusion method, sequencing, serotyping, and pulsed-field gel electrophoresis (PFGE). The analysis of 44 L. monocytogenes isolates showed that 72.7% (32 of 44) of all the isolates belonged to Serotype 1/2c, and 15.9% (7 of 44) belonged to Serotype 3c. All 44 isolates were resistant to one or more antimicrobial agents with the most frequent resistance to penicillin (75%) and tetracycline (47.7%). Of the 44 L. monocytogenes strains, 100, 69.2, and 62.5% of livestock, human, and food strains were resistant to penicillin, respectively. Using pulsed-field gel electrophoresis (PFGE) technique, the isolates' genetic diversity was determined, and 28 PFGE patterns with 8 common (CT) and 20 single types (ST) were identified. This study highlights the high prevalence of Serotype 1/2c in clinical and livestock samples, while different serotypes were observed in food samples. The presence of rare serotypes such as 4c, belonging to the Lineage III, as well as 4e and 1/2c which are infrequent in Iran indicates that paying attention to uncommon serotypes, especially 1/2c, during the listeriosis outbreaks is necessary.

A review of Listeria monocytogenes from meat and meat products: Epidemiology, virulence factors, antimicrobial resistance and diagnosis

Listeria monocytogenes is a zoonotic food-borne pathogen that is associated with serious public health and economic implications. In animals, L. monocytogenes can be associated with clinical listeriosis, which is characterised by symptoms such as abortion, encephalitis and septicaemia. In human beings, listeriosis symptoms include encephalitis, septicaemia and meningitis. In addition, listeriosis may cause gastroenteric symptoms in human beings and still births or spontaneous abortions in pregnant women. In the last few years, a number of reported outbreaks and sporadic cases associated with consumption of contaminated meat and meat products with L. monocytogenes have increased in developing countries. A variety of virulence factors play a role in the pathogenicity of L. monocytogenes. This zoonotic pathogen can be diagnosed using both classical microbiological techniques and molecular-based methods. There is limited information about L. monocytogenes recovered from meat and meat products in African countries. This review strives to: (1) provide information on prevalence and control measures of L. monocytogenes along the meat value chain, (2) describe the epidemiology of L. monocytogenes (3) provide an overview of different methods for detection and typing of L. monocytogenes for epidemiological, regulatory and trading purposes and (4) discuss the pathogenicity, virulence traits and antimicrobial resistance profiles of L. monocytogenes.

Molecular differentiation of cattle Sarcocystis spp. by multiplex PCR targeting 18S and COI genes following identification of Sarcocystis hominis in human stool samples

Sarcocystis spp. are protozoan parasites which can infect a wide range of vertebrates, including humans; the latter can act as definitive hosts for two cattle Sarcocystis spp.: Sarcocystis hominis and Sarcocystis heydorni. Reports of intestinal sarcocystosis are well documented in the literature, but PCR-based methods have been scarcely used to identify Sarcocystis species in human stools, and have been limited to the molecular analysis of 18S ribosomal RNA (18S rRNA) gene sequences. Since the mitochondrial cytochrome c oxidase subunit I (COI) gene is one of the most promising tools for distinguishing between closely related Sarcocystis spp., and taking into account the lack of publicly available S. hominis COI sequences, in the present study we obtained the first partial COI sequence of S. hominis from human stool samples of patient with gastrointestinal symptoms. We designed specific COI primers to develop a multiplex PCR method for the identification of Sarcocystis spp. in cattle. The submission of the COI sequence described herein and the unambiguous identification of S. hominis through the application of the new multiplex PCR is important for determining the prevalence of this zoonotic Sarcocystis spp. in meat and the risk for consumers.

Prevalence and antimicrobial resistance of Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 in imported beef cattle in Jordan

This study characterized Listeria monocytogenes, Salmonella enterica, and E. coli O157:H7 by collecting rectoanal mucosal swabs and fecal samples from 518 imported beef cattle at Jordan's major abattoir. A unique 53 L. monocytogenes, 287 S. enterica, and 17 E. coli O157:H7 were isolated from 37, 120 and 9 different animals; respectively. The prevalence of S. enterica, L. monocytogenes and E. coli O157:H7 were 23.2 % (95 % CI, 19.7-27.0 %), 7.1 % (95 % CI, 5.2-9.7 %) and 1.7 % (95 % CI, 0.9-3.3 %); respectively. All L. monocytogenes, all E. coli O157:H7 and 93.0 % of S. enterica isolates resisted at least one antimicrobial class. All L. monocytogenes, 94.1 % of E. coli O157:H7 and 69.7 % of S. enterica isolates exhibited multidrug resistance (resistant to ≥3 antimicrobials classes). Moreover, high percentages of L. monocytogenes (98.1 %), E. coli O157:H7 (64.7 %) and S. enterica (45.3 %) isolates resisted ≥5 antimicrobial classes. More than 90 % of the L. monocytogenes isolates resisted ampicillin, penicillin and erythromycin and more than 75 % resisted vancomycin. S. enterica isolates resisted several treatment-of-choice antimicrobials such as nalidixic acid (85.4 %), ciprofloxacin (26.8 %) and ceftriaxone (19.5 %). Furthermore, greater than 50 % of the E. coli O157:H7 isolates resisted streptomycin, nalidixic acid, tetracycline, ampicillin, sulfamethoxazole-trimethoprim, kanamycin, chloramphenicol and ciprofloxacin. The high prevalence and the high resistance percentages of the studied pathogens toward clinically important antimicrobials is alarming. Thus, applying strict sanitation procedures at the abattoirs in Jordan is crucial to lower the risk of carcasses contamination.

Genetic diversity of Listeria monocytogenes strains in ruminant abortion and rhombencephalitis cases in comparison with the natural environment

BACKGROUND

Listeria monocytogenes is the causative agent of listeriosis, a serious disease affecting both animals and humans. Here, multilocus sequence typing (MLST) was used to characterize the genetic diversity of Listeria monocytogenes strains isolated from the natural environment and animal clinical cases in Europe. The prevalence of clonal complexes (CCs) obtained was compared according to (i) the origin of isolation - clinical cases vs. natural environment - and (ii) the clinical form of animal listeriosis - rhombencephalitis vs. abortion. To this aim, two datasets were constructed. The clinical dataset consisted of 350 animal clinical isolates originating from France and Slovenia and supplemented with isolates from Switzerland and Great Britain. The natural environment dataset consisted of 253 isolates from the natural environment originating from Slovenia and supplemented with isolates from nine other European countries.

RESULTS

For the clinical cases, CC1, CC4-CC217 and CC412 were the most prevalent in rhombencephalitis and CC1, CC37 and CC4-CC217 in abortion. The hypervirulent CC1 and CC4-CC217 prevailed in both datasets. These results indicated that livestock is constantly exposed to hypervirulent CCs. CC1 was significantly associated with a clinical origin, whereas CC9, CC29 and CC14 were associated with the natural environment. CC1 was predominant among rhombencephalitis cases both in cattle and small ruminants, and its prevalence did not differ significantly between these two groups. A novel association of CC37 and CC6 with abortion cases was revealed.

CONCLUSIONS

Here, we show that CC1 and CC4-CC217 are prevalent in isolates of environmental and animal clinical origin, suggesting that ruminants are frequently exposed to hypervirulent CCs. The presence of CC4 in two mastitis cases calls for further attention due to direct threat to the consumer. We showed several associations between CCs and the origin of isolation or clinical form of listeriosis, e.g. CC37 and CC6 with abortion. This study improves our understanding of the population structure of L. monocytogenes isolates from the natural environment and animal clinical cases. Moreover, it provides a basis for future studies aiming to determine the underlying mechanisms of phenotypic traits of interest.

Potential Ad Hoc Markers of Persistence and Virulence in Canadian Listeria monocytogenes Food and Clinical Isolates

The Listeria monocytogenes gene inlA, encoding a surface virulence protein, was examined for the presence of premature stop codon (PMSC) mutations in 82 isolates obtained by the Canadian Food Inspection Agency (CFIA) from foods and food contact surfaces. These mutations were coanalyzed for the presence of stress survival islet 1 (SSI-1) and for the abilities of the isolates to invade Caco-2 intestinal epithelial cells and form biofilms on polystyrene. PMSC mutations were present in one-third of the isolates (predominantly those of serogroup 1/2a), and their presence was correlated with a noninvasive phenotype. The presence of SSI-1 and the ability to form biofilms were also linked to the 1/2a serogroup. Serogroup 4b isolates lacked inlA PMSC mutations and were invasive, but neither formed biofilms nor carried SSI-1. To expand upon these experimental findings, an in silico analysis was performed on L. monocytogenes genomes from Canadian databases of 278 food isolates and 607 clinical isolates. The prevalence of inlA PMSC mutations in genomes of food isolates was significantly higher (P < 0.0001) than that in clinical isolates. Also, a three-codon deletion in inlA associated with a hyperinvasive phenotype was more prevalent in genomes from clinical isolates (primarily of clonal complex 6, serogroup 4b) than in those from food isolates (P < 0.001). In contrast, SSI-1 was significantly overrepresented (P < 0.001) in genomes from food isolates. We propose the hypothesis that SSI-1 and inlA play a role in the evolution of Canadian L. monocytogenes strains into either a virulent (represented by serogroup 4b clinical isolates) or an environmentally persistent (represented by serogroup 1/2a food isolates) phenotype. The combined presence of SSI-1 and inlA PMSC mutations have potential for use as genetic markers for risk assessment when L. monocytogenes is recovered from foods, indicating low potential for pathogenesis.

Listeria Meningitis in Danish Children 2000-2017: A Rare Event Even in a Country With High Rates of Invasive Listeriosis

Listeria monocytogenes meningitis in Danish children 1 month to 17 years from 2000 to 2017 was identified and patient files reviewed. There were 5 cases, equaling an annual incidence of 0.024 per 100,000 children or 0.014 when excluding 2 immunodeficient children. Even in a country with a high general incidence of listeriosis, Listeria meningitis is a rare event in healthy children.

Prevalence, molecular characterization, and antimicrobial resistance profiles of Listeria monocytogenes, Salmonella enterica, and Escherichia coli O157:H7 on dairy cattle farms in Jordan

This study determined the prevalence, pulsed-field gel electrophoresis profiles, and antimicrobial resistance profile of Listeria monocytogenes, Salmonella enterica, and Escherichia coli O157:H7 isolates from dairy cattle farms in Jordan. Samples from bulk tank milk (n = 305), cattle feces (n = 610), and rectoanal mucosal swabs (n = 610) were collected from 61 dairy cattle farms. We confirmed 32 L. monocytogenes, 28 S. enterica, and 24 E. coli O157:H7 isolates from the samples. The farm-level prevalence (at least 1 positive sample per farm) of L. monocytogenes, S. enterica, and E. coli O157:H7 was 27.9, 19.7, and 23.0%, respectively. The prevalence of L. monocytogenes, S. enterica, and E. coli O157:H7 in bulk tank milk was 7.5, 1.6, and 3.3%, respectively. The prevalence of L. monocytogenes and S. enterica in fecal samples was 1.5 and 3.8%, respectively, and the prevalence of E. coli O157:H7 in rectoanal mucosal swabs was 2.3%. Based on disk diffusion testing, all L. monocytogenes, S. enterica, and E. coli O157:H7 isolates exhibited resistance to at least 1 antimicrobial class. Multidrug resistance (resistance to 3 or more classes of antimicrobials) was exhibited by 96.9% of L. monocytogenes, 91.7% of E. coli O157:H7, and 82.1% of S. enterica isolates. Moreover, 93.8, 79.2, and 57.1% of the L. monocytogenes, E. coli O157:H7, and S. enterica isolates, respectively, were resistant to 5 or more antimicrobial classes. More than 50% of L. monocytogenes isolates were resistant to ampicillin, clindamycin, penicillin, erythromycin, quinupristin-dalfopristin, streptomycin, teicoplanin, linezolid, vancomycin, kanamycin, and tetracycline. More than 50% of S. enterica and E. coli O157:H7 isolates were resistant to ampicillin, cephalothin, nalidixic acid, kanamycin, streptomycin, amoxicillin-clavulanic acid, and tetracycline. The prevalence of the studied pathogens this study was comparable to reports from other countries. The isolated pathogens exhibited a high degree of antimicrobial resistance, suggesting that the bacterial flora of dairy cattle in Jordan are under intense antimicrobial selection pressure. Additional research is required to determine the causes and drivers of resistance, and to develop approaches to mitigating antimicrobial resistance.

Isolation and Characterization of Clinical Listeria monocytogenes in Beijing, China, 2014-2016

Listeria monocytogenes is an important foodborne pathogen with a significant impact on public health worldwide. A great number of outbreaks caused by L. monocytogenes has been reported, especially in the United States, and European countries. However, listeriosis has not yet been included in notifiable disease in China, and thus information on this infection has been scarce among the Chinese population. In this study, we described a 3-year surveillance of listeriosis in Beijing, China. Fifty-six L. monocytogenes strains isolated from 49 clinical infectious cases (27 pregnancy-associated infections and 22 non-pregnancy-associated infections) were analyzed by serotyping, pulsed field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and antimicrobial susceptibility testing between 2014 and 2016 in Beijing. The predominant serogroups were 1/2a,3a and 1/2b,3b,7 which accounted for 92% of the overall isolates. Four strains were serogroup 4b,4d,4e, isolated from patients with pregnancy-associated infections. Based on PFGE, these isolates were divided into 32 pulsotypes (PTs) and 3 clusters associated with serogroups. Ten PTs were represented by more than one isolate with PT09 containing the most number of isolates. MLST differentiated the isolates into 18 STs, without new ST designated. The three most common STs were ST8 (18.4%), ST5 (16.3%), and ST87 (12.2%), accounting for 46.9% of the isolates. STs prevalent in other parts of the world were also present in China such as ST1, ST2, ST5, ST8, and ST9 which caused maternal fetal infections or outbreaks. However, the STs and serogroup distribution of clinical L. monocytogenes in Beijing, China was different from those in other countries. Strains of ST1 and ST2 were isolated from patients with pregnancy-associated infection, whereas none of ST155 isolates caused pregnancy-associated cases. Surveillance of molecular characterization will provide important information for prevention of listeriosis. This study also enhances our understanding of genetic diversity of clinical L. monocytogenes in China.

Characterization of Listeria monocytogenes from encephalitis cases of small ruminants from different geographical regions, in Greece

AIMS

The aim of this study was to evaluate the genetic diversity and resistance phenotypes of Listeria monocytogenes strains isolated from clinical encephalitis cases, and compare this population to isolates derived from tank milk of healthy animals.

METHODS AND RESULTS

A total of 57 L. monocytogenes strains isolated from ruminant's listeriosis cases (n = 31) and from tank milk of healthy ruminants (n = 26) were characterized by species PCR, molecular serotyping, PCR detection of virulence genes, pulsed-field gel electrophoresis and antimicrobial susceptibility testing. All strains possessed inlA, inlC, inlJ, plcA, actA, hlyA and iap virulence-associated genes while serotyping analysis revealed that they were mainly assigned into IVb group. Genotyping revealed 50 pulsotypes among the 57 strains assigned into seven clusters while indistinguishable pulsotypes between clinical and milk strains were not identified. Resistance of L. monocytogenes isolates to 14-16 antimicrobial agents tested was observed and 23 antimicrobial resistance profiles (ARPs) were defined while no apparent predominant ARP type was observed among isolates.

CONCLUSIONS

Small ruminants are exposed to a broad range of antimicrobial-resistant as well as genetically diverse strains of L. monocytogenes carrying virulence-associated genes but not all of them associated with the disease. Pulsed-field gel electrophoresis analysis suggests that pulsotypes associated with encephalitis are found in farms only in association with listeriosis.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings are valuable in understanding the ecology of this important food-borne pathogen and creating awareness for the emerging antimicrobial resistance.

Tracing of Listeria monocytogenes Contamination Routes in Fermented Sausage Production Chain by Pulsed-Field Gel Electrophoresis Typing

In this study, the presence of Listeria monocytogenes was assessed along the production process of fermented sausages in a small-scale facility. Following the isolation of the pathogen from the final product (ISO 11290-1), retrospective sampling was performed during the production of a new batch of sausages, including raw materials, casings, additives, sausage mixtures, sausages during fermentation, and environmental samples. L. monocytogenes was recovered from the following sampling points: the defrosting room and the cuttering, mixing, stuffing, and fermentation phases. Ten strains were isolated, molecularly confirmed as L. monocytogenes by means of a molecular detection system, and subjected to pulsed-field gel electrophoresis (PFGE) typing. On the basis of an unweighted pair group method with arithmetic mean (UPGMA) dendrogram from Ascl pulsotypes, the strains were indistinguishable (no band difference). The same pulsotypes of strains present in both batches of sausages, as well as in environmental samples, indicated the persistence of L. monocytogenes in the sausage production unit.

Molecular diversity and antimicrobial susceptibility of Listeria monocytogenes isolates from invasive infections in Poland (1997-2013)

The epidemiology of invasive listeriosis in humans appears to be weakly characterized in Poland, the sixth most populous member state of the European Union. We obtained antimicrobial susceptibility data, PCR-serogroups and genotypic profiles for 344 invasive isolates of Listeria monocytogenes, collected between 1997 and 2013 in Poland. All isolates were susceptible to the 10 tested antimicrobials, except one that was resistant to tetracycline and minocycline and harbored the tet(M), tet(A) and tet(C) genes. Overall, no increasing MIC values were observed during the study period. Four PCR-serogroups were observed: IVb (55.8%), IIa (34.3%), IIb (8.1%) and IIc (1.8%). We identified clonal complexes (CCs) and epidemic clones (ECs) previously involved in outbreaks worldwide, with the most prevalent CCs/ECs being: CC6/ECII (32.6%), CC1/ECI (17.2%), CC8/ECV (6.1%) and CC2/ECIV (5.5%). The present study is the first extensive analysis of Polish L. monocytogenes isolates from invasive infections.

Occurrence, Antibiotic Resistance, and Population Diversity of Listeria monocytogenes Isolated From Fresh Aquatic Products in China

Listeria monocytogenes is an important Gram-positive foodborne pathogen. However, limited information is available on the comprehensive investigation and potential risk of L. monocytogenes in fresh aquatic products, which are popular to consumers in China. This study aimed to determine the occurrence, virulence profiles, and population diversity of L. monocytogenes isolated from aquatic products in China. In total, 846 aquatic product samples were collected between July 2011 and April 2016 from 43 cities in China. Approximately 7.92% (67/846) aquatic product samples were positive for L. monocytogenes, 86.57% positive samples ranged from 0.3 to 10 MPN/g, whereas 5.97% showed over 110 MPN/g by the Most Probable Number method, which included two samples of products intended to be eaten raw. Serogroups I.1 (serotype 1/2a), I.2 (serotype 1/2b), and III (serotype 4c) were the predominant serogroups isolated, whereas serogroup II.1 (serotype 4b) was detected at much lower frequencies. Examination of antibacterial resistance showed that nine antibacterial resistance profiles were exhibited in 72 isolates, a high level susceptibility of 16 tested antibiotics against L. monocytogenes were observed, indicating these common antibacterial agents are still effective for treating L. monocytogenes infection. Multilocus sequence typing revealed that ST299, ST87, and ST8 are predominant in aquatic products, indicating that the rare ST299 (serotype 4c) may have a special ecological niche in aquatic products and associated environments. Except llsX and ptsA, the 72 isolates harbor nine virulence genes (prfA, actA, hly, plcA, plcB, iap, mpl, inlA, and inlB), premature stop codons (PMSCs) in inlA were found in four isolates, three of which belonged to ST9. A novel PMSC was found in 2929-1LM with a nonsense mutation at position 1605 (TGG→TGA). All ST87 isolates harbored the ptsA gene, whereas 8 isolates (11.11%) carried the llsX gene, and mainly belonged to ST1, ST3, ST308, ST323, ST330, and ST619. Taken together, these results first reported potential virulent L. monocytogenes isolates (ST8 and ST87) were predominant in aquatic products which may have implications for public health in China. It is thus necessary to perform continuous surveillance for L. monocytogenes in aquatic products in China.

Listeria monocytogenes Isolated from Illegally Imported Food Products into the European Union Harbor Different Virulence Factor Variants

Unregulated international flow of foods poses a danger to human health, as it may be contaminated with pathogens. Recent studies have investigated neglected routes of pathogen transmission and reported the occurrence of Listeria monocytogenes in food illegally imported into the European Union (EU), either confiscated at four international airports or sold illegally on the Romanian black market. In this study we investigated the genotype diversity and the amino acid sequence variability of three main virulence factors of 57 L. monocytogenes isolates. These isolates were derived from 1474 food samples illegally imported into the EU and originated from 17 different countries. Multilocus sequence typing revealed 16 different sequence types (STs) indicating moderate genotype diversity. The most prevalent STs were ST2, ST9, and ST121. The pulsed-field gel electrophoresis (PFGE) analysis resulted in 34 unique pulsotypes. PFGE types assigned to the most prevalent STs (ST2, ST9, and ST121) were highly related in their genetic fingerprint. Internalin A (InlA) was present in 20 variants, including six truncated InlA variants, all harbored by isolates of ST9 and ST121. We detected eight ST-specific listeriolysin O (LLO) variants, and among them, one truncated form. The actin-assembly-inducing protein ActA was present in 15 different ST-specific variants, including four ActA variants with an internal truncation. In conclusion, this study shows that L. monocytogenes, isolated from illegally imported food, have moderate genotype diversity, but diverse virulence factors variants, mainly of InlA.

An outbreak of listeriosis linked to turkey meat products in the Czech Republic, 2012-2016

Since 2012-2016 an increased number of listeriosis cases, especially from one region of the Czech Republic, were observed. Most of them were caused by strains of serotype 1/2a, clonal complex 8, indistinguishable by pulsed-field gel electrophoresis. Twenty-six human cases were reported, including two neonatal cases in twins. Three cases were fatal. The typing of Listeria monocytogenes isolates from food enabled to confirm a turkey meat delicatessen as the vehicle of infection for this local outbreak in the Moravian-Silesian Region. The food strains belonging to identical pulsotype were isolated from ready-to-eat turkey meat products packaged by the same producer between 2012 and 2016. This fact confirms that the described L. monocytogenes outbreak strain probably persisted in the environment of the aforementioned food-processing plant over several years. Whole-genome sequencing confirmed a very close relationship (zero to seven different alleles) between isolates from humans, foods and swabs from the environment of the food-processing plant under investigation.

Increasing Incidence of Listeriosis and Infection-associated Clinical Outcomes

BACKGROUND

Listeriosis caused by Listeria monocytogenes has a high case-fatality rate (CFR) of approximately 20% to 30%. An increasing incidence of listeriosis has been reported in many countries recently. We investigated the annual incidence, clinical characteristics, and outcomes of listeriosis at three different hospitals in Korea and evaluated the effects of appropriate empiric antimicrobial treatments on patient outcomes.

METHODS

We retrospectively collected the data of all culture-positive cases of human listeriosis from three hospitals of different sizes in Korea during 2006-2016 and calculated the annual number of cases and incidence per 100,000 admissions.

RESULTS

A total of 58 patients with L. monocytogenes were included in this study. The incidence of listeriosis was significantly higher in 2013-2016 than in 2006-2012 (RR 3.1; 95% CI 1.79-5.36; P<0.001), mainly because of an increase in patients over 60 years of age (RR 3.69; 95% CI 1.70-8.02; P<0.001). Multivariate analysis showed that healthcare-associated infection (adjusted OR, 12.15; 95% CI, 2.56-86.01; P=0.004) and empirical treatment with first-line antimicrobial agents (adjusted OR, 0.08; 95% CI, 0.00-0.63; P=0.044) were associated with CFR.

CONCLUSIONS

Healthcare-associated infections caused by L. monocytogenes are associated with high CFR. Adequate initial empirical treatments could reduce CFR, suggesting that careful consideration of an empirical antimicrobial regimen is warranted for elderly or immunocompromised patients admitted to the hospital.

Implicated Food Products for Listeriosis and Changes in Serovars of Listeria monocytogenes Affecting Humans in Recent Decades

Listeriosis is a foodborne disease with a high fatality rate, and infection is mostly transmitted through ready-to-eat (RTE) foods contaminated with Listeria monocytogenes, such as gravad/smoked fish, soft cheeses, and sliced processed delicatessen (deli) meat. Food products/dishes stored in vacuum or in modified atmospheres and with extended refrigerator shelf lives provide an opportunity for L. monocytogenes to multiply to large numbers toward the end of the shelf life. Elderly, pregnant women, neonates, and immunocompromised individuals are particularly susceptible to L. monocytogenes. Listeriosis in humans manifests primarily as septicemia, meningitis, encephalitis, gastrointestinal infection, and abortion. In the mid 1990s and early 2000s a shift from L. monocytogenes serovar 4b to serovar 1/2a causing human listeriosis occurred, and serovar 1/2a is becoming more frequently linked to outbreaks of listeriosis, particularly in Europe and Northern America. Consumer lifestyle has changed, and less time is available for food preparation. Modern lifestyle has markedly changed eating habits worldwide, with a consequent increased demand for RTE foods; therefore, more RTE and take away foods are consumed. There is a concern that many Listeria outbreaks are reported from hospitals. Therefore, it is vitally important that foods (especially cooked and chilled) delivered to hospitals and residential homes for senior citizens and elderly people are reheated to at least 72°C: cold food, such as turkey deli meat and cold-smoked and gravad salmon should be free from L. monocytogenes. Several countries have zero tolerance for RTE foods that support the growth of Listeria.

Bactericidal and antibiofilm activity of bactenecin-derivative peptides against the food-pathogen Listeria monocytogenes: New perspectives for food processing industry

Antimicrobial peptides have received great attention for their potential benefits to extend the shelf-life of food-products. Innate defense regulator peptide-1018 (IDR-1018) represents a promising candidate for such applications, due to its broad-spectrum antimicrobial activity, although food-isolated pathogens have been poorly investigated. Herein, we describe the design and the structural-functional characterization of a new 1018-derivative peptide named 1018-K6, in which the alanine in position 6 was replaced with a lysine. Spectroscopic analysis revealed a noticeable switch from β-sheet to helical conformations of 1018-K6 respect to IDR-1018, with a faster folding kinetic and increased structural stability. Moreover, 1018-K6 evidenced a significant antibiofilm/bactericidal efficiency specifically against Listeria monocytogenes isolates from food-products and food-processing environments, belonging to serotype 4b involved in the majority of human-listeriosis cases, with EC₅₀ values two- five-fold lower than those measured for IDR-1018. Therefore, a single amino-acid substitution in IDR-1018 sequence produced severe changes in peptide conformation and antimicrobial performances.

Genomic and phenotypic diversity of Listeria monocytogenes clonal complexes associated with human listeriosis

Listeria monocytogenes is a pathogen of significant concern in many ready to eat foods due to its ability to survive and multiply even under significant environmental stresses. Listeriosis in humans is a concern, especially to high-risk populations such as those who are immunocompromised or pregnant, due to the high rates of morbidity and mortality. Whole genome sequencing has become a routine part of assessing L. monocytogenes isolated from patients, and the frequency of different genetic subtypes associated with listeriosis is now being reported. The recent abundance of genome sequences for L. monocytogenes has provided a wealth of information regarding the variation in core and accessory genomic elements. Newly described accessory genomic regions have been linked to greater virulence capabilities as well as greater resistance to environmental stressors such as sanitizers commonly used in food processing facilities. This review will provide a summary of our current understanding of stress response and virulence phenotypes of L. monocytogenes, within the context of the genetic diversity of the pathogen.

Prevalence and molecular characteristics of Listeria monocytogenes in cooked products and its comparison with isolates from listeriosis cases

This study aimed to investigate the prevalence and molecular characteristics of Listeria monocytogenes in cooked products in Zigong City, China. The overall occurrence of the L. monocytogenes in the ready-to-eat (RTE) shops and mutton restaurants surveyed was 16.2% (141/873). An occurrence of 13.5% was observed in RTE pork, 6.5% in RTE vegetables, and more than 24.0% in either cooked mutton or cooked haggis. Serotype 1/2b (45.4%), 1/2a (33.3%), and 1/2c (14.2%) were the predominant types. By comparing the clonal complexes (CCs) based on multilocus sequence typing (MLST) of the L. monocytogenes from cooked foods in Zigong City and 33 listeriosis cases from different districts of China, CC87, CC9, CC8, and CC3 were showed to be prevalent in cooked products and CC87 and CC3 were the first two frequent types in the 33 clinic-source strains. All CC87 stains harbored the newly reported Listeria pathogenicity island 4 (LIPI-4) gene fragment ptsA, and all CC3 strains possessed the Listeria pathogenicity island 3 (LIPI-3) gene fragment llsX. These may increase the occurrence of the strains belonging to CC87 and CC3 in listeriosis cases in China and also underline the risk of infection owing to the consumption of the cooked products from Zigong. ST619 (serotype 1/2b) harbored both llsX and ptsA, indicating a potential hypervirulent sequence type in Zigong.

Surveillance of listeriosis in the Tel Aviv District, Israel, 2010-2015

This study analyses the epidemiologic, clinical and molecular findings of all culture-confirmed cases of listeriosis notified from 2010 to 2015 in the Tel Aviv District, which is known to have high rates of listeriosis. All clinical isolates of Listeria monocytogenes were subtyped using two-enzyme pulsed-field gel electrophoresis. During the studied period, 102 cases of listeriosis were notified, including 23 pregnancy-associated cases (23%). Among 79 non-pregnancy-associated cases, 18 had neuro-invasive disease (21%). There were 26 deaths associated with the disease. Using molecular identification, we found a number of clusters of identical bacterial clones, which pointed to possible sources of infection. The high rates of morbidity and mortality resulting from listeriosis, as well as the diverse ways of infection demonstrated in this study, accentuate the need to boost public health actions, in order to raise awareness and better control high-risk contamination routes.

Will the emergence of core genome MLST end the role of in silico MLST?

The technological advancement of molecular epidemiological analysis using next-generation sequencing (NGS) for foodborne pathogens has a groundbreaking impact over the past three years. In particular, the emergence of cg (core genome) multilocus sequence typing(MLST) has a significant impact. This is because this technology made it possible for many researchers to carry out molecular epidemiological analysis on foodborne pathogens in a common language, using common definitions. The resolution of core genome MLST (cgMLST) far surpasses that of MLST, which only uses seven (usually, in some cases five) housekeeping genes. Therefore, cgMLST would in no doubt terminate the role of conventional MLST as the molecular epidemiological tool. However, the role of MLST would probably not end all together. Rather, the sequence type (ST) of the conventional MLST is expected to be used as in silico MLST by a wider range of researchers than ever in the next 10 years. This is because, with the arrival of the NGS era, we have come to be able to obtain ST of conventional MLST by simply entering the NGS text file into one's own PC. In other words, acquisition of ST data is no longer limited to researchers aiming to conduct MLST for the first place. The impact of such a change is large. In silico MLST will continue to be used as a tool for understanding the broad characteristics of bacterial strains. This review aimed to summarize the main information on STs that have been accumulated for representative foodborne pathogens, in particular for potential NGS users in this new era who have been not familiar with MLST until now.

Listeria monocytogenes in Food-Processing Facilities, Food Contamination, and Human Listeriosis: The Brazilian Scenario

Listeria monocytogenes is a foodborne pathogen that contaminates food-processing environments and persists within biofilms on equipment, utensils, floors, and drains, ultimately reaching final products by cross-contamination. This pathogen grows even under high salt conditions or refrigeration temperatures, remaining viable in various food products until the end of their shelf life. While the estimated incidence of listeriosis is lower than other enteric illnesses, infections caused by L. monocytogenes are more likely to lead to hospitalizations and fatalities. Despite the description of L. monocytogenes occurrence in Brazilian food-processing facilities and foods, there is a lack of consistent data regarding listeriosis cases and outbreaks directly associated with food consumption. Listeriosis requires rapid treatment with antibiotics and most drugs suitable for Gram-positive bacteria are effective against L. monocytogenes. Only a minority of clinical antibiotic-resistant L. monocytogenes strains have been described so far; whereas many strains recovered from food-processing facilities and foods exhibited resistance to antimicrobials not suitable against listeriosis. L. monocytogenes control in food industries is a challenge, demanding proper cleaning and application of sanitization procedures to eliminate this foodborne pathogen from the food-processing environment and ensure food safety. This review focuses on presenting the L. monocytogenes distribution in food-processing environment, food contamination, and control in the food industry, as well as the consequences of listeriosis to human health, providing a comparison of the current Brazilian situation with the international scenario.

Comparative genomics of human and non-human Listeria monocytogenes sequence type 121 strains

The food-borne pathogen Listeria (L.) monocytogenes is able to survive for months and even years in food production environments. Strains belonging to sequence type (ST)121 are particularly found to be abundant and to persist in food and food production environments. To elucidate genetic determinants characteristic for L. monocytogenes ST121, we sequenced the genomes of 14 ST121 strains and compared them with currently available L. monocytogenes ST121 genomes. In total, we analyzed 70 ST121 genomes deriving from 16 different countries, different years of isolation, and different origins—including food, animal and human ST121 isolates. All ST121 genomes show a high degree of conservation sharing at least 99.7% average nucleotide identity. The main differences between the strains were found in prophage content and prophage conservation. We also detected distinct highly conserved subtypes of prophages inserted at the same genomic locus. While some of the prophages showed more than 99.9% similarity between strains from different sources and years, other prophages showed a higher level of diversity. 81.4% of the strains harbored virtually identical plasmids. 97.1% of the ST121 strains contain a truncated internalin A (inlA) gene. Only one of the seven human ST121 isolates encodes a full-length inlA gene, illustrating the need of better understanding their survival and virulence mechanisms.

An unusual presentation of Listeria monocytogenes rhombencephalitis

We describe a case of 52-year-old woman with a medical history of Crohn's disease presented abrupt fever, asymmetrical multiple cranial nerve palsies and focal neurological symptoms localized to the brainstem. The patient was initially diagnosed with ischaemic stroke, because of acute clinical course and results of neuroimaging. Cerebrospinal fluid analysis revealed mild infection with negative Gram staining and culture. Final diagnosis of Listeria monocytogenes brainstem infection (rhombencephalitis) was set up on the basis of further clinical course and positive blood cultures. Listerial rhombencephalitis should be kept in mind in immunocompromised adult patients who develop fever, asymmetrical multiple cranial nerve palsies and focal neurological symptoms localized to the brainstem even without typical neuroimaging, cerebrospinal fluid findings and negative cultures. Early diagnosis and adequate antibiotic treatment is of crucial importance.

Listeria monocytogenes Circulating in Rabbit Meat Products and Slaughterhouses in Italy: Prevalence Data and Comparison Among Typing Results

Rabbit meat has outstanding dietetic and nutritional properties. However, few data on microbiological hazards associated with rabbit productions are available. In this study, the presence of Listeria monocytogenes was determined in 430 rabbit carcasses, 256 rabbit meat cuts and products, and 599 environmental sponges collected from four Italian rabbit slaughterhouses over a period of 1 year. Prevalence of L. monocytogenes among the 1285 rabbit meat and environmental samples was 11%, with statistically significant differences between slaughterhouses. The highest prevalence (33.6%) was observed in rabbit meat cuts and products; the majority of positive environmental samples were collected from conveyor belts. Overall, 27.9% and 14.3% of rabbit cuts and carcasses, respectively, had L. monocytogenes counts higher than 1 colony-forming unit (CFU)/10 g. A selection of 123 isolates from positive samples was genotyped and serotyped to determine genetic profiles and diversity among L. monocytogenes isolates contaminating different slaughterhouses and classes of products investigated. Discriminatory power and concordance among the results obtained using multilocus variable-number tandem-repeat analysis (MLVA), multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE), automated EcoRI ribotyping, and serotyping were assessed. The isolates selected for typing were classified into serotypes 1/2a (52.8%), 1/2c (32.5%), and 1/2b (14.6%). The majority of the isolates were classified as ST14 (34.1%), ST9 (35.5%), ST121 (17.9%), and ST224 (14.6%). The greatest discriminatory power was observed with the MLVA typing, followed by MLST, PFGE, and ribotyping. The best bidirectional concordance was achieved between PFGE and MLST. There was 100% correlation between both MLST and MLVA with serotype. Moreover, a high unidirectional correspondence was observed between MLVA and both MLST and PFGE, as well as between PFGE and both MLST and serotyping. The results of this study show for the first time in Italy prevalence and genetic profiles of L. monocytogenes isolated in rabbit products and slaughterhouses.

Biomarker Tools to Design Clinical Vaccines Determined from a Study of Annual Listeriosis Incidence in Northern Spain

Two regions of northern Spain, Gipuzkoa, and Cantabria present high annual incidence of listeriosis (1.86 and 1.71 cases per 100,000 inhabitants, respectively). We report that the high annual incidences are a consequence of infection with highly virulent Listeria monocytogenes isolates linked to fatal outcomes in elderly patients with cancer. In addition, listeriosis patients with cancer present low IL-17A/IL-6 ratios and significantly reduced levels of anti-GAPDH_1–22 antibodies, identified as two novel biomarkers of poor prognosis. Analysis of these biomarkers may aid in reducing the incidence of listeriosis. Moreover, GAPDH_1–22-activated monocyte-derived dendritic cells of listeriosis patients with cancer seem useful tools to prepare clinical vaccines as they produce mainly Th1 cytokines.

Salmonella Dublin patients in Denmark and their distance to cattle farms

BACKGROUND

The Salmonella serotype Dublin is specifically adapted to cattle but may infect humans leading to severe disease. We described human S. Dublin cases and investigated a potential spatial relation between their addresses and cattle farms in Denmark.

METHODS

We extracted S. Dublin patient surveillance data, 2000-2014, and performed descriptive analyses. We geocoded residential and cattle farm addresses and mapped their incidence by region, province and municipality. We used linear correlation and spatial autocorrelation analysis at the municipality level and calculated the direct network distance from the nearest farm to the residential address of cases and 20,000 randomly selected citizens representing the background population.

RESULTS

We identified 484 S. Dublin cases, 57% were male, median age 65 years. Seven patients (1%) acquired their infection abroad. The 30 days all-cause mortality was 13%. Overall, cumulative incidence was 8.0 per 100,000 inhabitants. Cattle farms were located predominantly in the western part of the country. Neither visual inspection nor correlation analysis indicated a relationship between municipalities with high incidences of human cases and cattle farms. Global Moran's Index analysis showed municipalities with high incidence of cases to be randomly distributed. We found equal direct network distances between cattle farms and both addresses of S. Dublin cases and the background population.

CONCLUSIONS

We found S. Dublin infections in Denmark to affect the elderly, be serious and acquired domestically. Our findings indicate that the risk of infection with S. Dublin in Denmark is independent of living in the proximity to cattle farms.

Diversity of Listeria monocytogenes Strains of Clinical and Food Chain Origins in Belgium between 1985 and 2014

Listeriosis is a rare but severe disease, mainly caused by Listeria monocytogenes. This study shows the results of the laboratory-based surveillance of Listeriosis in Belgium over the period 1985-2014. Besides the incidence and some demographic data we present also more detailed microbiological and molecular characteristics of human strains isolated since 2000. The strains from the latter period were compared to food and animal strains from the same period. Our study shows that different food matrices were commonly contaminated with L. monocytogenes presenting the same PFGE profile as in patient's isolates. Since 1985, we observed a significant decrease in incidence of the Materno-Neonatal cases (from 0.15 to 0.04 cases /100,000 inhabitants-year), which is probably to be attributed to active prevention campaigns targeting pregnant women. Despite the strengthening of different control measures by the food industry, the incidence of non-Materno-Neonatal listeriosis increased in Belgium (from 0.3 to 0.7 cases /100,000 inhabitants-year), probably due to the rise of highly susceptible patients in an aging population. This significant increase found in non-Materno-Neonatal cases (slope coefficient 7.42%/year, P<0.0001) can be attributed to significant increase in incidence of isolates belonging to serovars 1/2a (n = 393, slope coefficient 6.62%/year, P<0.0001). Although resistance to antimicrobials is rare among L. monocytogenes isolates, a trend to increasing MIC values is evident with chloramphenicol, amoxicillin, tetracycline and ciprofloxacin. We show that fluoroquinolone resistance is not linked to chromosomal mutations, but caused by a variety of efflux pumps. Our study also shows that huge majority of known underlying pathologies (426 out of 785 cases) were cancers (185/426, 43.1%) and haematological malignancies (75/185, 40.5%). Moreover the risk population is susceptible to low levels of contamination in food stressing the need of prevention campaigns specifically targeting these persons.