Prevalence, identification by a DNA microarray-based assay of human and food isolates Listeria spp. from Tunisia

A review of the literature of Listeria monocytogenes in Africa highlights breast milk as an overlooked human source

According to the latest WHO estimates (2015) of the global burden of foodborne diseases, Listeria monocytogenes is responsible for one of the most serious foodborne infections and commonly results in severe clinical outcomes. The 2013 French MONALISA prospective cohort identified that women born in Africa has a 3-fold increase in the risk of maternal neonatal listeriosis. One of the largest L. monocytogenes outbreaks occurred in South Africa in 2017-2018 with over 1,000 cases. Moreover, recent findings identified L. monocytogenes in human breast milk in Mali and Senegal with its relative abundance positively correlated with severe acute malnutrition. These observations suggest that the carriage of L. monocytogenes in Africa should be further explored, starting with the existing literature. For that purpose, we searched the peer-reviewed and grey literature published dating back to 1926 to date using six databases. Ultimately, 225 articles were included in this review. We highlighted that L. monocytogenes is detected in various sample types including environmental samples, food samples as well as animal and human samples. These studies were mostly conducted in five east African countries, four west African countries, four north African countries, and two Southern African countries. Moreover, only ≈ 0.2% of the Listeria monocytogenes genomes available on NCBI were obtained from African samples, contracted with its detection. The pangenome resulting from the African Listeria monocytogenes samples revealed three clusters including two from South-African strains as well as one consisting of the strains isolated from breast milk in Mali and Senegal and, a vaginal post-miscarriage sample. This suggests there was a clonal complex circulating in Mali and Senegal. As this clone has not been associated to infections, further studies should be conducted to confirm its circulation in the region and explore its association with foodborne infections. Moreover, it is apparent that more resources should be allocated to the detection of L. monocytogenes as only 15/54 countries have reported its detection in the literature. It seems paramount to map the presence and carriage of L. monocytogenes in all African countries to prevent listeriosis outbreaks and the related miscarriages and confirm its association with severe acute malnutrition.

Listeria monocytogenes in foods-From culture identification to whole-genome characteristics

Listeria monocytogenes is an important foodborne pathogen, which is able to persist in the food production environments. The presence of these bacteria in different niches makes them a potential threat for public health. In the present review, the current information on the classical and alternative methods used for isolation and identification of L. monocytogenes in food have been described. Although these techniques are usually simple, standardized, inexpensive, and are routinely used in many food testing laboratories, several alternative molecular-based approaches for the bacteria detection in food and food production environments have been developed. They are characterized by the high sample throughput, a short time of analysis, and cost-effectiveness. However, these methods are important for the routine testing toward the presence and number of L. monocytogenes, but are not suitable for characteristics and typing of the bacterial isolates, which are crucial in the study of listeriosis infections. For these purposes, novel approaches, with a high discriminatory power to genetically distinguish the strains during epidemiological studies, have been developed, e.g., whole-genome sequence-based techniques such as NGS which provide an opportunity to perform comparison between strains of the same species. In the present review, we have shown a short description of the principles of microbiological, alternative, and modern methods of detection of L. monocytogenes in foods and characterization of the isolates for epidemiological purposes. According to our knowledge, similar comprehensive papers on such subject have not been recently published, and we hope that the current review may be interesting for research communities.

Current State of Salmonella, Campylobacter and Listeria in the Food Chain across the Arab Countries: A Descriptive Review

Foodborne infections caused by bacterial pathogens are a common cause of human illness in the Middle East, with a substantial burden of economic loss and public health consequences. This review aims at elucidating recent literature on the prevalence of Non-Typhoidal Salmonella (NTS), Campylobacter and Listeria monocytogens in the food chain in the Arab countries, and to consolidate available evidence on the public health burden and the status of antimicrobial resistance (AMR) among the concerned three pathogens. The reviewed evidence points to a scarcity of understanding of the magnitude of NTS in the food chain in the Arab countries. Additionally, not much work has been done at the molecular characterization level to address the source-attribution of NTS in the Arab World. Very few surveys have been done on Campylobacter in the food chain in the Gulf Cooperation Council (GCC) countries. There is a gap in quantitative (counts/numbers) surveillance efforts for Campylobacter in the chicken meat supply across all Arab countries, despite the availability of some qualitative (presence/absence) surveillance data. While there are several reports on L. monocytogenes in animal-sourced foods, notably in North African Arab countries, fewer are published on L. monocytogenes in plant-sourced foods. Information on the L. monocytogenes serotypes and strain diversity circulating in the Arab region is widely lacking. Antibiotic resistance in the three pathogens is not fully understood across the Arab region, despite some reports indicating varying trends at the human-food interface. The literature evidence presented in this review stresses that Salmonella, Campylobacter and L. monocytogenes continue to challenge food safety and public health in the Arab countries.

The efficiency of technologies used for epidemiological characterization of Listeria monocytogenes isolates: an update

The characterization of pathogenic bacteria by providing information regarding the identification and source-tracking of the causes of outbreaks is vital for the epidemiological investigations of foodborne diseases. The knowledge of transmission of Listeria monocytogenes (L. monocytogenes) strains from the environment, directly or indirectly (through food processing facilities) to the final food products, due to the complexity of evaluating numerous, affecting parameters is quite limited. The food trade globalization also adds difficulties in tracking the association between the infection occurrence and causative pathogens, aiming to prevent their spread. The occurrence of listeriosis, a notifiable disease throughout the world, can either be sporadic or outbreak-related. Due to the importance of foodborne outbreaks from a public health aspect and its correspondence enormous economic losses, cross-linked surveillance studies regarding the contamination of foods by L. monocytogenes, besides identifying clusters and tracing the sources of infections on an international-scale to prevent and control L. monocytogenes outbreaks sounds very crucial. Contrary to the conventional typing methods, molecular-based techniques, such as whole-genome sequencing, owing to the capacity to discriminate L. monocytogenes strains down to single nucleotide differences, provide an accurate characterization of strains and tracking the causes of outbreaks. However, routinely using molecular-based methods depends on the required improvements in the affordability, proper timing, and preparing reliable, standardized bioinformatics facilities. This work was conducted to critically review the practical potential of diverse typing methods have been used for the characterization of L. monocytogenes and discuss how they might change the future of efforts for control of listeriosis.

Association of Listeria monocytogenes LIPI-1 and LIPI-3 marker llsX with invasiveness

Listeria monocytogenes is an opportunistic pathogen that is widely distributed in the environment. The evolution of its genome has exhibited differences in virulence among strains of the same species. Listeria monocytogenes LIPI-3 (Listeria Pathogenicity Island 3) and LIPI-1 (Listeria Pathogenicity Island 1) are considered responsible for the increased virulence in some strains. The aim of this study was to detect LIPI-1 genes and the llsX gene belonging to LIPI-3 in invasive strains of L. monocytogenes and to establish whether there is a relationship among the invasiveness, presence of the llsX and LIPI-1 genes, and the source of the strains. The results showed that 70% of the strains were invasive, and all these strains except one possessed LIPI-1, which suggests that although there is a correlation between LIPI-1 and invasiveness, the independent mechanisms of LIPI-1 may contribute to invasiveness. In contrast, 35% of the total strains were positive for llsX and were invasive; thus, the results revealed that there is a strong association between llsX and the invasiveness of L. monocytogenes in HEp-2 cells (HeLa contaminant/epithelial in origin). In addition, there is no other association with any other variable in this study. Moreover, the authors found that LIPI-1 and llsX are more frequently found in fresh than in frozen vegetables. Together, the findings provide an approximation for the better understanding of Listeriolysin S (LLS) and its role in the pathogenesis of L. monocytogenes, and a possible relation between virulence factors and food-storage temperature.

Epidemiology of transmissible diseases: Array hybridization and next generation sequencing as universal nucleic acid-mediated typing tools

The magnitude of interest in the epidemiology of transmissible human diseases is reflected in the vast number of tools and methods developed recently with the expressed purpose to characterize and track evolutionary changes that occur in agents of these diseases over time. Within the past decade a new suite of such tools has become available with the emergence of the so-called "omics" technologies. Among these, two are exponents of the ongoing genomic revolution. Firstly, high-density nucleic acid probe arrays have been proposed and developed using various chemical and physical approaches. Via hybridization-mediated detection of entire genes or genetic polymorphisms in such genes and intergenic regions these so called "DNA chips" have been successfully applied for distinguishing very closely related microbial species and strains. Second and even more phenomenal, next generation sequencing (NGS) has facilitated the assessment of the complete nucleotide sequence of entire microbial genomes. This technology currently provides the most detailed level of bacterial genotyping and hence allows for the resolution of microbial spread and short-term evolution in minute detail. We will here review the very recent history of these two technologies, sketch their usefulness in the elucidation of the spread and epidemiology of mostly hospital-acquired infections and discuss future developments.

Serotype to genotype: The changing landscape of listeriosis outbreak investigations

The classical definition of a disease outbreak is the occurrence of cases of disease in excess of what would normally be expected in a community, geographical area or time period. The establishment of an outbreak then starts with the identification of an incidence of cases above the normally expected threshold during a given time period. Subsequently, the cases are examined using a variety of subtyping methods to identify potential linkages. As listeriosis disease has a long incubation period, relating a single source or multiple sources of contaminated food to clinical disease is challenging and time consuming. The vast majority of human listeriosis cases are caused by three serotypes, 1/2a, 1/2b, and 4b. Thus serotyping of isolates from suspected foods and clinical samples, although useful for eliminating some food sources, has a very limited discriminatory power. The advent of faster and more affordable sequencing technology, coupled with increased computational power, has permitted comparisons of whole Listeria genome sequences from isolates recovered from clinical, food, and environmental sources. These analyses made it possible to identify outbreaks and the source much more accurately and faster, thus leading to a reduction in number of illnesses as well as a reduction in economic losses. Initial DNA sequence information also facilitated the development of a simple molecular serotype protocol which allowed for the identification of major disease causing serotypes of L. monocytogenes, including a clade of 4b variant (4bV) strains of L. monocytogenes involved in at least 3 more recent listeriosis outbreaks in the US. Furthermore, data generated using whole genome sequence (WGS) analyses was successfully utilized to develop a pan-genomic DNA microarray as well as a single nucleotide polymorphism (SNP) based analysis. Herein, we present and compare, the two recently developed sub-typing technologies and discuss how these methods are not only important in outbreak investigations, but could also shed light on possible adaptations to different foods and environments.

Characteristics and distribution of Listeria spp., including Listeria species newly described since 2009

The genus Listeria is currently comprised of 17 species, including 9 Listeria species newly described since 2009. Genomic and phenotypic data clearly define a distinct group of six species (Listeria sensu strictu) that share common phenotypic characteristics (e.g., ability to grow at low temperature, flagellar motility); this group includes the pathogen Listeria monocytogenes. The other 11 species (Listeria sensu lato) represent three distinct monophyletic groups, which may warrant recognition as separate genera. These three proposed genera do not contain pathogens, are non-motile (except for Listeria grayi), are able to reduce nitrate (except for Listeria floridensis), and are negative for the Voges-Proskauer test (except for L. grayi). Unlike all other Listeria species, species in the proposed new genus Mesolisteria are not able to grow below 7 °C. While most new Listeria species have only been identified in a few countries, the availability of molecular tools for rapid characterization of putative Listeria isolates will likely lead to future identification of isolates representing these new species from different sources. Identification of Listeria sensu lato isolates has not only allowed for a better understanding of the evolution of Listeria and virulence characteristics in Listeria but also has practical implications as detection of Listeria species is often used by the food industry as a marker to detect conditions that allow for presence, growth, and persistence of L. monocytogenes. This review will provide a comprehensive critical summary of our current understanding of the characteristics and distribution of the new Listeria species with a focus on Listeria sensu lato.

Locked nucleic acid probe-based real-time PCR for the diagnosis of Listeria monocytogenes in ruminants

Because of its high fatality rate, listeriosis ranks among the most important infectious diseases worldwide. Although ruminants are known as natural reservoirs for Listeria monocytogenes and a possible source of human listeriosis, studies of the prevalence and risk factors associated with ruminant listeriosis are limited to some developed countries. Therefore, this report describes the development of a real-time PCR targeting the hly gene for the absolute quantification of L. monocytogenes based on circular and linear DNA standards. Results show that the PCR that uses circular plasmid as a template gave a 2.6-7.89 greater threshold cycle number than did equimolar linear standards. No cross-amplification was observed when bacteria commonly found in bovine and ovine diseases were tested. The PCR achieved good intra and inter-run reproducibility and a detection limit of 6.1 copies of linear plasmid per reaction. This PCR was then applied to 1134 samples taken from 378 Tunisian ruminants. Based on the test sensitivity (90%) and specificity (100%), the true individual animal prevalence of listeriosis was 5.7% in cattle and 10.2% in sheep. In addition, the true herd-level prevalence was 50.1% in cattle and 26.7% in sheep. A multivariable logistic regression analysis at the animal-population level indicated that for cattle, the variables strata and mastitis were important risk factors, whereas for sheep, the variables strata, age and abortion were found to be associated with listeriosis. At the herd level, risk factors for Listeria test-positivity they were: abortion, herd composition and silage storage for cattle, whereas for sheep were: management system, cleaning frequency, silage storage and floor type. Animal hygiene, food quality and sanitary practices on the farm should be applied as strategies to control this pathogen in ruminant herds.

Fluorescence-based bioassays for the detection and evaluation of food materials

We summarize here the recent progress in fluorescence-based bioassays for the detection and evaluation of food materials by focusing on fluorescent dyes used in bioassays and applications of these assays for food safety, quality and efficacy. Fluorescent dyes have been used in various bioassays, such as biosensing, cell assay, energy transfer-based assay, probing, protein/immunological assay and microarray/biochip assay. Among the arrays used in microarray/biochip assay, fluorescence-based microarrays/biochips, such as antibody/protein microarrays, bead/suspension arrays, capillary/sensor arrays, DNA microarrays/polymerase chain reaction (PCR)-based arrays, glycan/lectin arrays, immunoassay/enzyme-linked immunosorbent assay (ELISA)-based arrays, microfluidic chips and tissue arrays, have been developed and used for the assessment of allergy/poisoning/toxicity, contamination and efficacy/mechanism, and quality control/safety. DNA microarray assays have been used widely for food safety and quality as well as searches for active components. DNA microarray-based gene expression profiling may be useful for such purposes due to its advantages in the evaluation of pathway-based intracellular signaling in response to food materials.