Detection of Pathogenic Serogroups and Virulence Genes in Listeria monocytogenes Strains Isolated from Beef and Beef Products Retailed in Gauteng Province, South Africa, Using Phenotypic and Polymerase Chain Reaction (PCR)-Based Methods

South Africa recently (2017-18) experienced the largest outbreak of human listeriosis in the world caused by L. monocytogenes following the consumption of "polony," a ready-to-eat meat product. Most (59%) cases originated from Gauteng province, South Africa. As a follow-up study to the outbreak, we used standard bacteriological and molecular methods to determine the prevalence of pathogenic and virulent serogroups of L. monocytogenes in various beef and beef products retailed in Gauteng province, South Africa. The overall prevalence of Listeria spp. was 28% (112/400), comprising Listeria monocytogenes (9.3%), Listeria innocua (16.3%), and Listeria welshimeri (2.5%) (p < 0.001). It is crucial to have detected that the region (p=0.036), type of product (p=0.032), and temperature at storage (p=0.011) significantly affected the occurrence of L. monocytogenes in beef products. It is alarming that pathogenic serogroups 4b-4d-4e (51.4%) and 1/2a-3a (43.2%) were detected among the isolates of L. monocytogenes. Importantly, they were all carriers of seven virulence-associated genes (hlyA, inlB, plcA, iap, inlA, inlC, and inlJ). Our study also demonstrated that 16.7% of "polony" samples investigated were contaminated with L. monocytogenes. Considering that pathogenic and virulent L. monocytogenes contaminated beef and beef products retailed in South Africa, the food safety risk posed to consumers remains and cannot be ignored. Therefore, it is imperative to reduce the contamination of these products with L. monocytogenes during beef production, processing, and retailing to avoid future outbreaks of human listeriosis in the country.

Listeria innocua infection in an old case of total knee replacement - an unusual case report

Prosthetic implant-associated arthritis due to Listeria is mostly reported for Listeria monocytogenes. Here, we describe a patient who underwent total knee replacement 12 years ago and presented with pain, tenderness, redness and local rise in temperature in the right knee. Purulent fluid was aspirated. Upon microbiological analysis, culture yielded Listeria innocua. L. innocua is rare. Listeria is not reported as a contaminant and routine cultures may be negative. Because of the long interval between surgery and the onset of symptoms, clinical suspicion, radiological investigations and analysing multiple samples are of immense help.

From bytes to bites: Advancing the food industry with three-dimensional food printing

The rapid advancement of three-dimensional (3D) printing (i.e., a type of additive manufacturing) technology has brought about significant advances in various industries, including the food industry. Among its many potential benefits, 3D food printing offers a promising solution to deliver products meeting the unique nutritional needs of diverse populations while also promoting sustainability within the food system. However, this is an emerging field, and there are several aspects to consider when planning for use of 3D food printing for large-scale food production. This comprehensive review explores the importance of food safety when using 3D printing to produce food products, including pathogens of concern, machine hygiene, and cleanability, as well as the role of macronutrients and storage conditions in microbial risks. Furthermore, postprocessing factors such as packaging, transportation, and dispensing of 3D-printed foods are discussed. Finally, this review delves into barriers of implementation of 3D food printers and presents both the limitations and opportunities of 3D food printing technology.

Genomic Characterization of Listeria innocua Isolates Recovered from Cattle Farms, Beef Abattoirs, and Retail Outlets in Gauteng Province, South Africa

Whole-genome sequencing (WGS) was used for the genomic characterization of one hundred and ten strains of Listeria innocua (L. innocua) isolated from twenty-three cattle farms, eight beef abattoirs, and forty-eight retail outlets in Gauteng province, South Africa. In silico multilocus sequence typing (MLST) was used to identify the isolates' sequence types (STs). BLAST-based analyses were used to identify antimicrobial and virulence genes. The study also linked the detection of the genes to the origin (industries and types of samples) of the L. innocua isolates. The study detected 14 STs, 13 resistance genes, and 23 virulence genes. Of the 14 STs detected, ST637 (26.4%), ST448 (20%), 537 (13.6%), and 1085 (12.7%) were predominant, and the frequency varied significantly (p < 0.05). All 110 isolates of L. innocua were carriers of one or more antimicrobial resistance genes, with resistance genes lin (100%), fosX (100%), and tet(M) (30%) being the most frequently detected (p < 0.05). Of the 23 virulence genes recognized, 13 (clpC, clpE, clpP, hbp1, svpA, hbp2, iap/cwhA, lap, lpeA, lplA1, lspA, oatA, pdgA, and prsA2) were found in all 110 isolates of L. innocua. Overall, diversity and significant differences were detected in the frequencies of STs, resistance, and virulence genes according to the origins (source and sample type) of the L. innocua isolates. This, being the first genomic characterization of L. innocua recovered from the three levels/industries (farm, abattoir, and retail) of the beef production system in South Africa, provides data on the organism's distribution and potential food safety implications.

Deuterium isotope probing (DIP) on Listeria innocua: Optimisation of labelling and impact on viability state

An innovative approach, Raman microspectroscopy coupled with deuterium isotope probing (Raman-DIP), can be used to evaluate the metabolism of deuterated carbon source in bacteria and also to presume different anabolic pathways. This method requires the treatment of cells with heavy water that could affect the bacterial viability state at higher concentration. In this study, we evaluated the effect of heavy water incorporation on the viability state of Listeria innocua cells. We exposed the L. innocua suspensions to different heavy water concentrations (0%, 25%, 50% and 75%) from 30 minutes to 72 h of incubation times at 37°C. The total, viable and viable culturable populations were quantified by qPCR, PMA-qPCR and plate count agar respectively. We analyzed heavy water incorporation by Raman-DIP. The exposure of L. innocua cells to different concentrations of heavy water did not alter their cell viability to 24 h incubation time. In addition, the maximum intensity for C-D band, specific for the incorporation of heavy water, was reached after 2 h of exposure in a media containing 75% v/v D2O but an early detection of the labelling was possible at t = 1 h 30 min. In conclusion, the use of D2O as a metabolic marker was validated and can be developed for the detection of L. innocua cell viability state.

Genome Sequences of Hemolytic and Nonhemolytic Listeria innocua Strains from Human, Food, and Environmental Sources

This report describes genome sequences for nine Listeria innocua strains that varied in hemolytic phenotypes on sheep blood agar. All strains were sequenced using Pacific Biosciences (PacBio) single-molecule real-time (SMRT) chemistry; overall, the average read length of these sequences was 2,869,880 bp, with an average GC content of 37%.

Comparative Genomics of Listeria Species Recovered from Meat and Food Processing Facilities

Listeria species (spp.) are contaminants that can survive in food, on equipment, and on food processing premises if appropriate hygiene measures are not used. Homologous stress tolerance genes, virulence gene clusters such as the prfA cluster, and clusters of internalin genes that contribute to the pathogenic potential of the strains can be carried by both pathogenic and nonpathogenic Listeria spp. To enhance understanding of the genome evolution of virulence and virulence-associated properties, a comparative genome approach was used to analyze 41 genome sequences belonging to L. innocua and L. welshimeri isolated from food and food processing facilities. Genetic determinants responsible for disinfectant and stress tolerance were identified, including the efflux cassette bcrABC and Tn6188_qac_1 disinfectant resistance determinant, and stress survival islets. These disinfectant-resistant genes were more frequently found in L. innocua (12%) than in L. welshimeri (2%). Several isolates representing the presumed nonpathogenic L. innocua still carried virulence-associated genes, including LGI2, LGI3, LIPI-3, and LIPI-4 which were absent in all L. welshimeri isolates. The mobile genetic elements identified were plasmids (pLGUG1 and J1776) and prophages (PHAGE_Lister_vB_LmoS_188, PHAGE_Lister_LP_030_3, PHAGE_Lister_A118, PHAGE_Lister_B054, and PHAGE_Lister_vB_LmoS_293). The results suggest that the presumed nonpathogenic isolates especially L. innocua can carry genes relevant to the strain's virulence and stress tolerance in the food and food processing facilities. IMPORTANCE This study provides genomic insights into the recently expanded genus in order to gain valuable information about the evolution of the virulence and stress tolerance properties of the genus Listeria and the distribution of these genetic elements pertinent to the pathogenic potential across Listeria spp. and clonal lineages in South Africa (SA).

Draft Genome Sequence of Listeria innocua Strain MEZLIS29, Isolated from a Cow in South Africa

Here, we report the draft genome sequence of Listeria innocua strain MEZLIS29, which was isolated from a healthy cow in Flagstaff, Eastern Cape Province, South Africa. The genome was sequenced using the Illumina MiSeq platform and had a length of 2,805,865 bp, with a G+C content of 37.5% and 2,783 coding DNA sequences, 58 tRNAs, 4 noncoding RNAs, and 8 rRNA genes.

Distribution and Characteristics of Listeria spp. in Pigs and Pork Production Chains in Germany

Listeria (L.) monocytogenes is a foodborne pathogen that can cause disease, mainly in elderly, pregnant or immunocompromised persons through consumption of contaminated food, including pork products. It is widespread in the environment and can also be found in asymptomatic carrier animals, for example, in different tissues of pigs. To learn more about their nature, 16 Listeria spp. isolates found in tonsils and intestinal content of pigs and 13 isolates from the slaughterhouse environment were characterized using next-generation sequencing (NGS). A wide distribution of clonal complexes was observed in pigs, as well as in the pork production chain, suggesting multiple sources of entry. Hypervirulent clones were found in pig tonsils, showing the potential risk of pigs as source of isolates causing human disease. The presence of closely related isolates along the production chain suggests a cross-contamination in the slaughterhouse or recontamination from the same source, strengthening the importance of efficient cleaning and disinfection procedures. The phenotypical antimicrobial resistance status of L. monocytogenes isolates was examined via broth microdilution and revealed a low resistance level. Nevertheless, genotypical resistance data suggested multiple resistances in some non-pathogenic L. innocua isolates from pig samples, which might pose a risk of spreading resistances to pathogenic species.

Case Report: Refractory Listeria innocua Meningoencephalitis in a Three-Year-Old Boy

Listeria innocua is widely distributed in the environment and food and is considered a non-pathogenic bacterium for both humans and animals. To our knowledge, only a few cases of L. innocua infection in humans and ruminants have been reported. Moreover, there has been no report on human L. innocua meningoencephalitis. Here, we report a case of severe refractory meningoencephalitis in a three-year-old boy after infection with L. innocua. The child's first symptoms were a runny nose, high fever, and rashes, which quickly progressed to unconsciousness and convulsions. The initial analysis of cerebral spinal fluid revealed remarkably elevated protein levels and increased white blood cells count. The blood culture of the patient in the early stage was positive for L. innocua. In addition, his brain imaging tests were observed dynamically, and the result showed a speedy progression from multiple intracranial abnormal signals to hydrocephalus and interstitial cerebral edema. After receiving antibiotics and symptomatic treatment for nearly 3 months, the patient's condition improved markedly. However, he still had residual complications such as hydrocephalus. Although L. innocua is considered harmless, it can still cause disease in humans, even severe meningoencephalitis, with rapid progression and poor prognosis. Early discovery, diagnosis, and treatment are necessary to elevate the survival rate and life quality of those patients. Antibiotics should be used with sufficient duration and dosage. Cephalosporins are not suitable for the treatment of L. innocua meningoencephalitis and penicillin antibiotics are preferred for children. The presentation of this case will help to expand our knowledge of Listeria infections and provide a potential candidate for pathogens causing severe childhood central nervous system infection.

Accurate classification of Listeria species by MALDI-TOF mass spectrometry incorporating denoising autoencoder and machine learning

Listeria monocytogenes belongs to the category of facultative anaerobic bacteria, and is the pathogen of listeriosis, potentially lethal disease for humans. There are many similarities between L. monocytogenes and other non-pathogenic Listeria species, which causes great difficulties for their correct identification. The level of L. monocytogenes contamination in food remains high according to statistics from the Food and Drug Administration. This situation leads to food recall and destruction, which has caused huge economic losses to the food industry. Therefore, the identification of Listeria species is very important for clinical treatment and food safety. This work aims to explore an efficient classification algorithm which could easily and reliably distinguish Listeria species. We attempted to classify Listeria species by incorporating denoising autoencoder (DAE) and machine learning algorithms in matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). In addition, convolutional neural networks were used to map the high dimensional original mass spectrometry data to low dimensional core features. By analyzing MALDI-TOF MS data via incorporating DAE and support vector machine (SVM), the identification accuracy of Listeria species was 100%. The proposed classification algorithm is fast (range of seconds), easy to handle, and, more importantly, this method also allows for extending the identification scope of bacteria. The DAE model used in our research is an effective tool for the extraction of MALDI-TOF mass spectrometry features. Despite the fact that the MALDI-TOF MS dataset examined in our research had high dimensionality, the DAE + SVM algorithm was still able to exploit the hidden information embedded in the original MALDI-TOF mass spectra. The experimental results in our work demonstrated that MALDI-TOF mass spectrum combined with DAE + SVM could easily and reliably distinguish Listeria species.

Distribution and phenotypic and genotypic characterization of Listeria monocytogenes isolated from food, Colombia, 2010-2018

Introduction: Listeria monocytogenes is a food-borne pathogen that may cause infections in humans such as meningitis, meningoencephalitis, and septicemia, as well as abortions. By serological typing 13 serotypes have been identified of which 4b is responsible for most of the outbreaks in the world. Objective: To determine the frequency and distribution of serotypes and molecular subtypes of L. monocytogenes isolated in Colombia from food from 2010 to 2018. Materials and methods: We conducted a retrospective and descriptive study based on the analysis of 2,420 isolates confirmed as L. monocytogenes and other species using biochemical and serological tests, and pulsed-field gel electrophoresis (PFGE) for molecular subtyping. Results: Of the 2,420 isolates received, 2,326 were confirmed as L. monocytogenes. The serotypes found were 4b (52%), 4d-4e (14.5%), 1/2a (11%), 1/2c (9.4%), 1/2b (9%), and 3a, 3b, 3c, 4c, 4d, 4e and 7 (less than 2%). The isolates came from Bogotá (43%), Antioquia (25%), Valle (10%), Nariño (9%), and other departments (7%). The genotypic characterization grouped the isolates in 167 PFGE patterns. The most frequent patterns were identified in various dairy and meat products, and in prepared foods. Conclusion: A 96.1% of the isolates corresponded to L. monocytogenes showing good agreement between isolates and identification. Serotype 4b, highly virulent, was the most frequent. The molecular analysis showed the possible dissemination and permanence over time of several serotypes, which highlights the importance of including this pathogen in epidemiological food surveillance programs.

Virulence Characterization of Listeria monocytogenes, Listeria innocua, and Listeria welshimeri Isolated from Fish and Shrimp Using In Vivo Early Zebrafish Larvae Models and Molecular Study

Listeriosis is one of the most notable foodborne diseases and is characterized by high rates of mortality. L. monocytogenes is the main cause of human listeriosis outbreaks, however, there are isolated cases of disease caused by other species of the genus Listeria. The aim of this study was to evaluate strains of L. monocytogenes (n = 7), L. innocua (n = 6), and L. welshimeri (n = 2) isolated from fish and shrimps for their virulence based on the presence of virulence genes and the in vivo Danio rerio (zebrafish) larvae models. A total of 15 strains were analyzed. The zebrafish larvae model showed that the larvae injected with L. monocytogenes strains were characterized by the lowest survival rate (46.5%), followed by L. innocua strains (64.2%) and L. welshimeri (83.0%) strains. Multiplex PCRs were used for detection of selected virulence genes (luxS, actA2, prfA, inlB, rrn, iap, sigB, plcB, actA, hlyA), the majority of which were present in L. monocytogenes. Only a few virulence-related genes were found in L. welshimeri, however, no correlation between the occurrence of these genes and larval survival was confirmed. This research highlights the importance of the potential impact that Listeria spp. strains isolated from fish and shrimps may have on consumers.

Contamination Pathways can Be Traced along the Poultry Processing Chain by Whole Genome Sequencing of Listeria innocua

Foodborne infection with Listeria causes potentially life-threatening disease listeriosis. Listeria monocytogenes is widely recognized as the only species of public health concern, and the closely related species Listeria innocua is commonly used by the food industry as an indicator to identify environmental conditions that allow for presence, growth, and persistence of Listeria spp. in general. In our study, we analyze the occurrence of Listeria spp. in a farm-to-fork approach in a poultry production chain in Egypt and identify bacterial entry gates and transmission systems. Prevalence of Listeria innocua at the three production stages (farm, slaughterhouse, food products) ranged from 11% to 28%. The pathogenic species Listeria monocytogenes was not detected, and Listeria innocua strains under study did not show genetic virulence determinants. However, the close genetic relatedness of Listeria innocua isolates (maximum 63 SNP differences) indicated cross-contamination between all stages from farm to final food product. Based on these results, chicken can be seen as a natural source of Listeria. Last but not least, sanitary measures during production should be reassessed to prevent bacterial contamination from entering the food chain and to consequently prevent human listeriosis infections. For this purpose, surveillance must not be restricted to pathogenic species.

Occurrence, Diversity of Listeria spp. Isolates from Food and Food-Contact Surfaces and the Presence of Virulence Genes

This study evaluates the hazards posed by foodborne bacteria of the Listeria genus by analyzing the occurrence, diversity and virulence of Listeria spp.in food and food-manufacturing plants. Seventy-five isolates obtained from the routine analysis of 653 samples taken by three diagnostic laboratories in Northern Italy were genotypically differentiated by Repetitive Extragenic Palindrome (rep) PCR, with the GTG5 primer identified by sequencing the 16S rRNA gene and examined by specific PCR tests for the presence of L. monocytogenes virulence determinants occasionally found to occur in other species of the genus. Within this sample, 76% (n = 57) isolates were identified as L. innocua, 16% (n = 12) as L. monocytogenes, 6.6% (n = 5) as L. welshimeri and 1.3% (n = 1) as L. seeligeri. All L. monocytogenes isolates belonged to the serotype 1/2a and were predicted to be virulent for the presence of the inlJ internalin gene. Potentially virulent strains of L. innocua, L. seeligeri and L. welshimeri, carrying the L. monocytogenesinlA gene and/or hly gene, were identified, and most isolates were found to possess the toxin–antitoxin system mazEF for efficient adaptation to heat shock. Results indicated the need to reinforce food-contamination-prevention measures against all Listeria species by defining efficiently their environmental distribution.

Occurrence and antibiogram of Listeria species in raw pork, beef, and chicken meats marketed in Enugu State, Southeast Nigeria

AIM

This study was undertaken to isolate Listeria (L.) species from raw meats sold in markets in Enugu State, Southeast Nigeria, and to determine the antibacterial resistance profile.

MATERIALS AND METHODS

Twenty-five grams of beef (n=144), chicken meat (n=144), and pork (n=144) were collected randomly from supermarkets and general markets in Enugu State. Isolation of Listeria was done using half and full Fraser broths, and polymyxin acriflavine lithium chloride ceftazidime aesculin mannitol agar. Identification of isolates was done using an analytical profile index kit specific for Listeria. Confirmation of the genus Listeria was done by a polymerase chain reaction. The resistance of the isolates was determined using the disk diffusion method.

RESULTS

Listeria was isolated from 39/144 (27.1%) chicken meat, 19/144 (13.2%) pork, and 66/144 (45.8%) beef samples cultured. Listeria innocua was the predominant species in chicken meat (52.6%) and beef (81.8%) samples. Listeria grayi, Listeria welshimeri, and Listeria ivanovii were also isolated from the beef and chicken meat samples. More than 65% of the isolates were resistant to penicillin, rifampicin, ciprofloxacin, sulfamethoxazole-trimethoprim, and cephalothin. All the isolates from beef and pork samples and 23 (92%) from chicken meat samples, were resistant to ≥3 classes of antibacterial agents. Mean multiple antibiotic resistance index (MARI) was 0.77 (range=0.42-1.00), 0.58 (range=0.25-0.83), and 0.79 (range=0.58-0.92) for the isolates from beef, chicken meat, and pork samples, respectively. All the isolates had MARI >0.2.

CONCLUSION

Multidrug-resistant Listeria strains contaminate raw beef, pork, and chicken meats marketed in Enugu State, Southeast Nigeria.

Genome Sequence of Listeria innocua Strain MEZLIS26, Isolated from a Goat in South Africa

Here, we report the draft genome sequence of Listeria innocua strain MEZLIS26, isolated from a healthy goat in Flagstaff, Eastern Cape Province, South Africa. The genome was sequenced using the Illumina MiSeq platform and had a length of 2,800,777 bp, with a G+C content of 37.4%, 2,755 coding DNA sequences (CDSs), 49 transfer RNAs (tRNAs), and 4 noncoding RNAs (ncRNAs).

Here, we report the draft genome sequence of Listeria innocua strain MEZLIS26, isolated from a healthy goat in Flagstaff, Eastern Cape Province, South Africa. The genome was sequenced using the Illumina MiSeq platform and had a length of 2,800,777 bp, with a G+C content of 37.4%, 2,755 coding DNA sequences (CDSs), 49 transfer RNAs (tRNAs), and 4 noncoding RNAs (ncRNAs).

Coresistance to Benzalkonium Chloride Disinfectant and Heavy Metal Ions in Listeria monocytogenes and Listeria innocua Swine Isolates from China

The development of coresistance to disinfectants and heavy metals contributes to the fitness of Listeria spp. in foods or food processing environments, where life-threatening Listeria monocytogenes coexist and coevolve with other Listeria spp. Despite extensive research on L. monocytogenes, coresistance to disinfectants and heavy metals is less documented for other Listeria spp. In this study, we screened 30 L. monocytogenes and 27 Listeria innocua isolates recovered from 273 swine samples for resistance to quaternary ammonium compound benzalkonium chloride (BC) and to heavy metals cadmium (Cd) and arsenic (As). Moreover, we evaluated the potential mechanisms of resistance by detecting the efflux pump activity in BC resistance and the presence of resistance determinants. The average minimum inhibitory concentrations of BC in L. innocua (10.7 ± 2.0) were significantly higher than that in L. monocytogenes (6.9 ± 3.7) (p < 0.05). Resistance to BC and heavy metals was correlated, where all BC-resistant L. innocua and As-resistant L. monocytogenes isolates were coresistant to BC and Cd. Twenty percent and 66.7% of BC resistance in L. monocytogenes and L. innocua were related to reserpine-associated efflux pumps, whereas all cases of BC resistance were related to carbonyl cyanide 3-chlorophenylhydrazone-associated efflux pumps. The cadA1 and cadA2 genes were present in Cd-resistant isolates but not in Cd-sensitive isolates, and cadA3 was undetectable in all isolates examined. cadA4 conferring lower level of Cd resistance was copresent with arsA1 and arsA2 in the Cd-resistant and As-susceptible L. monocytogenes isolate LM3. Our findings suggest that swine serves as a reservoir for developing resistance to disinfectant and heavy metals in L. monocytogenes and L. innocua, which share common resistance mechanisms such as efflux pumps and resistance genes. This work provides new insight into the coresistance events of other Listeria as a potential contributor of the resistance in L. monocytogenes.

Atypical Hemolytic Listeria innocua Isolates Are Virulent, albeit Less than Listeria monocytogenes

Listeria innocua is considered a nonpathogenic Listeria species. Natural atypical hemolytic L. innocua isolates have been reported but have not been characterized in detail. Here, we report the genomic and functional characterization of representative isolates from the two known natural hemolytic L. innocua clades. Whole-genome sequencing confirmed the presence of Listeria pathogenicity islands (LIPI) characteristic of Listeria monocytogenes species. Functional assays showed that LIPI-1 and inlA genes are transcribed, and the corresponding gene products are expressed and functional. Using in vitro and in vivo assays, we show that atypical hemolytic L. innocua is virulent, can actively cross the intestinal epithelium, and spreads systemically to the liver and spleen, albeit to a lesser degree than the reference L. monocytogenes EGDe strain. Although human exposure to hemolytic L. innocua is likely rare, these findings are important for food safety and public health. The presence of virulence traits in some L. innocua clades supports the existence of a common virulent ancestor of L. monocytogenes and L. innocua.

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 Listeria monocytogenes prevalence in foods, animals and human origin from Iran: a systematic review and meta-analysis

Background

Listeria monocytogenes as the main causative agent of human listeriosis is an intracellular bacterium that has the capability to infect a wide range of cell types. Human listeriosis is a sporadic foodborne disease, which is epidemiologically linked with consumption of contaminated food products. Listeriosis may range from mild and self-limiting diseases in healthy people to severe systemic infections in susceptible populations. This study aimed to investigate the prevalence of L. monocytogenes in food resources and human samples from Iran.

Methods

A systematic search was performed by using electronic databases from papers that were published by Iranian authors Since January of 2000 to the end of April 2017. Then, 47 publications which met our inclusion criteria were selected for data extraction and analysis by Comprehensive Meta-Analysis Software.

Results

The pooled prevalence of L. monocytogenes in human origin was 10% (95% CI: 7–12%) ranging from 0 to 28%. The prevalence of L. monocytogenes in animals was estimated at 7% (95% CI: 4–10%) ranging from 1 to 18%. Moreover, the pooled prevalence of L. monocytogenes in Iranian food samples was estimated at 4% (95% CI: 3–5%) ranging from 0 to 50%. From those 12 studies which reported the distribution of L. monocytogenes serotypes, it was concluded that 4b, 1/2a, and 1/2b were the most prevalent serotypes.

Conclusions

The prevalence of L. monocytogenes and prevalent serotypes in Iran are comparable with other parts of the world. Although the overall prevalence of human cross-contamination origin was low, awareness about the source of contamination is very important because of the higher incidence of infections in susceptible groups.

Electronic supplementary material

The online version of this article (10.1186/s12889-018-5966-8) contains supplementary material, which is available to authorized users.

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.

Analysis of Listeria using exogenous volatile organic compound metabolites and their detection by static headspace-multi-capillary column-gas chromatography-ion mobility spectrometry (SHS-MCC-GC-IMS)

Listeria monocytogenes is a Gram-positive bacterium and an opportunistic food-borne pathogen which poses significant risk to the immune-compromised and pregnant due to the increased likelihood of acquiring infection and potential transmission of infection to the unborn child. Conventional methods of analysis suffer from either long turn-around times or lack the ability to discriminate between Listeria spp. reliably. This paper investigates an alternative method of detecting Listeria spp. using two novel enzyme substrates that liberate exogenous volatile organic compounds in the presence of α-mannosidase and d-alanyl aminopeptidase. The discriminating capabilities of this approach for identifying L. monocytogenes from other species of Listeria are investigated. The liberated volatile organic compounds (VOCs) are detected using an automated analytical technique based on static headspace–multi-capillary column–gas chromatography–ion mobility spectrometry (SHS–MCC–GC–IMS). The results obtained by SHS–MCC–GC–IMS are compared with those obtained by the more conventional analytical technique of headspace–solid phase microextraction–gas chromatography–mass spectrometry (HS–SPME–GC–MS). The results found that it was possible to differentiate between L. monocytogenes and L. ivanovii, based on their VOC response from α-mannosidase activity.

Rhombencephalitis caused by Listeria monocytogenes in a pastured bull

A pastured 2-y-old cross-breed bull developed brainstem encephalitis (rhombencephalitis); Listeria monocytogenes was isolated from the brain. In the brainstem, there was perivascular cuffing, multiple microabscesses, and positive immunostaining for L. monocytogenes. Samples of bovine feces, water, feedstuffs, milking parlor soil, and bulk tank milk were collected from the dairy farm. Seven isolates of the genus Listeria were obtained, 6 of L. innocua and 1 of L. monocytogenes, which was found in the pasture where the bull grazed. Both isolates belonged to serotype 4b and were positive for internalins A, C, and J. According to the DNA fragment patterns of pulsed-field gel electrophoresis, the isolates were closely related. The source of infection was the pasture, implying that listeriosis should not be discounted in cases with compatible clinical signs but the absence of silage feeding.

Matrix-assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) Can Precisely Discriminate the Lineages of Listeria monocytogenes and Species of Listeria

The genetic lineages of Listeria monocytogenes and other species of the genus Listeria are correlated with pathogenesis in humans. Although matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has become a prevailing tool for rapid and reliable microbial identification, the precise discrimination of Listeria species and lineages remains a crucial issue in clinical settings and for food safety. In this study, we constructed an accurate and reliable MS database to discriminate the lineages of L. monocytogenes and the species of Listeria (L. monocytogenes, L. innocua, L. welshimeri, L. seeligeri, L. ivanovii, L. grayi, and L. rocourtiae) based on the S10-spc-alpha operon gene encoded ribosomal protein mass spectrum (S10-GERMS) proteotyping method, which relies on both genetic information (genomics) and observed MS peaks in MALDI-TOF MS (proteomics). The specific set of eight biomarkers (ribosomal proteins L24, L6, L18, L15, S11, S9, L31 type B, and S16) yielded characteristic MS patterns for the lineages of L. monocytogenes and the different species of Listeria, and led to the construction of a MS database that was successful in discriminating between these organisms in MALDI-TOF MS fingerprinting analysis followed by advanced proteotyping software Strain Solution analysis. We also confirmed the constructed database on the proteotyping software Strain Solution by using 23 Listeria strains collected from natural sources.

Strain-level bacterial identification by CeO2-catalyzed MALDI-TOF MS fatty acid analysis and comparison to commercial protein-based methods

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has emerged as a rapid approach for clinical bacterial identification. However, current protein-based commercial bacterial ID methods fall short when differentiating closely related species/strains. To address this shortcoming, we employed CeO2-catalyzed fragmentation of lipids to produce fatty acids using the energy inherent to the MALDI laser as a novel alternative to protein profiling. Fatty acid profiles collected from Enterobacteriaceae, Acinetobacter, and Listeria using CeO2-catalyzed metal oxide laser ionization (MOLI MS), processed by principal component analysis, and validated by leave-one-out cross-validation (CV), showed 100% correct classification at the species level and 98% at the strain level. In comparison, protein profile data from the same bacteria yielded 32%, 54% and 67% mean species-level accuracy using two MALDI-TOF MS platforms, respectively. In addition, several pathogens were misidentified by protein profiling as non-pathogens and vice versa. These results suggest novel CeO2-catalyzed lipid fragmentation readily produced (i) taxonomically tractable fatty acid profiles by MOLI MS, (ii) highly accurate bacterial classification and (iii) consistent strain-level ID for bacteria that were routinely misidentified by protein-based methods.