Epidemiology of human listeriosis

Innovative Strategies in Drug Repurposing to Tackle Intracellular Bacterial Pathogens

Intracellular bacterial pathogens pose significant public health challenges due to their ability to evade immune defenses and conventional antibiotics. Drug repurposing has recently been explored as a strategy to discover new therapeutic uses for established drugs to combat these infections. Utilizing high-throughput screening, bioinformatics, and systems biology, several existing drugs have been identified with potential efficacy against intracellular bacteria. For instance, neuroleptic agents like thioridazine and antipsychotic drugs such as chlorpromazine have shown effectiveness against Staphylococcus aureus and Listeria monocytogenes. Furthermore, anticancer drugs including tamoxifen and imatinib have been repurposed to induce autophagy and inhibit bacterial growth within host cells. Statins and anti-inflammatory drugs have also demonstrated the ability to enhance host immune responses against Mycobacterium tuberculosis. The review highlights the complex mechanisms these pathogens use to resist conventional treatments, showcases successful examples of drug repurposing, and discusses the methodologies used to identify and validate these drugs. Overall, drug repurposing offers a promising approach for developing new treatments for bacterial infections, addressing the urgent need for effective antimicrobial therapies.

Post-infectious hydrocephalus complicating Listeria meningitis in a healthy newborn

Listeria monocytogenes is a relatively uncommon cause of foodborne infection in the general population. Most cases of Listeriosis occur among newborns, pregnant women, the elderly and those with impairment of cellular immunity. Neonatal Listeria meningitis is rare. We present a case of Listeria meningitis at the age of 15 days in a previously healthy neonate who presented with acute onset of fever, poor feeding and lethargy. Sepsis workup revealed L. monocytogenes identified in cerebrospinal fluid PCR and culture. The infant's course was complicated by transient syndrome of inappropriate antidiuretic hormone and subsequent hydrocephalus that required a ventriculoperitoneal shunt placement. Though rare, neonatal infections due to Listeria can present with meningitis leading to serious and devastating complications. Our case emphasises the importance of considering Listeria in cases of neonatal meningitis and the value of close follow-up of such cases through early detection and management of acute and long-term complications.

Foodborne pathogens and their association with well-known enteric infections and emerging non-communicable disorders

Annually, numerous new cases of communicable and non-communicable diseases are diagnosed, and consumption of food/water contaminated with different levels of microbial and chemical agents is responsible for a considerable portion of this burden. Generally, acute foodborne diseases are readily identified, while chronic deleterious effects are often neglected and rarely blamed for health consequences. The present work narrates a journey from consuming foods containing bacteria/bacterial toxins to developing chronic diseases, making humans more susceptible to emerging diseases. We aim to shed light on the chronic effects of foodborne diseases, particularly gastrointestinal disorders (GIDs) and inflammatory bowel diseases (IBDs), which are common chronic symptoms of most foodborne diseases.

An Alternative Rapid Confirmation Method for Identifying Listeria monocytogenes from a Variety of 125 g Food Samples Within Two Days of a PCR Presumptive Positive

Cultural confirmation following detection of a Listeria monocytogenespresumptive positive can take 3-7 days to finalize; this uncertainty is a point of frustration for food producers needing to make time-sensitive disposition decisions. To address the demand for shortened time-to-results, an alternative L. monocytogenes confirmation method consisting of two components, (i) a secondary screen using a different rapid method, and (ii) concurrent cultural isolation followed by next-day colony identification was evaluated. For the study, four food matrices (hot dogs, peanut butter, frozen vegetables, and multicomponent frozen meals) were inoculated with low levels (0.36-1.39 MPN/125 g) of L. monocytogenes per the AOAC guidelines for a matrix study. Analyses were performed on 125 g test portions and started with a PCR primary screen (Bio-Rad iQ-Check Listeria monocytogenes II). Next, all enriched food samples underwent a secondary screen by bioMérieux's GENE-UP LMO2 Real-Time PCR and VIDAS LMX ELFA along with streaking onto RAPID'L.mono Agar. Presumptive positive L. monocytogenes colonies were identified utilizing a high throughput rapid identification method (Hygiena's BAX System L. monocytogenes Real-Time PCR assay, Neogen's ANSR isothermal nucleic acid amplification assay, and Bruker's MALDI Biotyper). Importantly, this study evaluated multiple commercially available options for the secondary screen (n = 2) and rapid identification (n = 3) to allow for easy adoption by testing laboratories. Overall, there was no statistically significant difference (p ≤ 0.05) between the number of L. monocytogenes-positive 125 g samples obtained by the cultural reference method and the alternative confirmation methods (regardless of which method combinations were evaluated). Additionally, this study supports that, when both the primary and secondary screen methods yield a positive result, the sample could be considered a confirmed positive for L. monocytogenes.

Cinnamaldehyde Targets the LytTR DNA-Binding Domain of the Response Regulator AgrA to Attenuate Biofilm Formation of Listeria monocytogenes

The Agr quorum sensing (QS) system is known to contribute to biofilm formation in Listeria monocytogenes. Cinnamaldehyde, a natural food preservative, is considered an inhibitor of Agr-mediated QS in L. monocytogenes. However, the exact mechanism by which cinnamaldehyde acts on Agr remains unclear. In this study, we assessed the effects of cinnamaldehyde on the histidine kinase AgrC and the response regulator AgrA in the Agr system. AgrC kinase activity was not influenced by cinnamaldehyde, and binding between AgrC and cinnamaldehyde was not observed when microscale thermophoresis (MST) was performed, indicating that AgrC was not the target of cinnamaldehyde. AgrA is specifically bound to the agr promoter (P2) to activate the transcription of the Agr system. However, AgrA-P2 binding was prevented by cinnamaldehyde. The interaction between cinnamaldehyde and AgrA was further confirmed with MST. Two conserved amino acids, Asn-178 and Arg-179, located in the LytTR DNA-binding domain of AgrA, were identified as the key sites for cinnamaldehyde-AgrA binding by alanine mutagenesis and MST. Coincidentally, Asn-178 was also involved in the AgrA-P2 interaction. Taken together, these results suggest that cinnamaldehyde acts as a competitive inhibitor of AgrA in AgrA-P2 binding, which leads to suppressed transcription of the Agr system and reduced biofilm formation in L. monocytogenes. IMPORTANCE Listeria monocytogenes can form biofilms on various food contact surfaces, posing a serious threat to food safety. Biofilm formation of L. monocytogenes is positively regulated by the Agr quorum sensing system. Thus, an alternative strategy for controlling L. monocytogenes biofilms is interfering with the Agr system. Cinnamaldehyde is considered an inhibitor of the L. monocytogenes Agr system; however, its exact mechanism of action is still unclear. Here, we found that AgrA (response regulator), rather than AgrC (histidine kinase), was the target of cinnamaldehyde. The conserved Asn-178 in the LytTR DNA-binding domain of AgrA was involved in cinnamaldehyde-AgrA and AgrA-P2 binding. Therefore, the occupation of Asn-178 by cinnamaldehyde suppressed transcription of the Agr system and reduced biofilm formation in L. monocytogenes. Our findings could provide a better understanding of the mechanism by which cinnamaldehyde inhibits L. monocytogenes biofilm formation.

Development of Optical Label-Free Biosensor Method in Detection of Listeria monocytogenes from Food

The present work describes an alternative method for detecting and identifying Listeria monocytogenes in food samples by developing a nanophotonic biosensor containing bioreceptors and optical transducers. The development of photonic sensors for the detection of pathogens in the food industry involves the implementation of procedures for selecting probes against the antigens of interest and the functionalization of the sensor surfaces on which the said bioreceptors are located. As a previous step to functionalizing the biosensor, an immobilization control of these antibodies on silicon nitride surfaces was carried out to check the effectiveness of in plane immobilization. On the one hand, it was observed that a Listeria monocytogenes-specific polyclonal antibody has a greater binding capacity to the antigen at a wide range of concentrations. A Listeria monocytogenes monoclonal antibody is more specific and has a greater binding capacity only at low concentrations. An assay for evaluating selected antibodies against particular antigens of Listeria monocytogenes bacteria was designed to determine the binding specificity of each probe using the indirect ELISA detection technique. In addition, a validation method was established against the reference method for many replicates belonging to different batches of meat-detectable samples, with a medium and pre-enrichment time that allowed optimal recovery of the target microorganism. Moreover, no cross-reactivity with other nontarget bacteria was observed. Thus, this system is a simple, highly sensitive, and accurate platform for L. monocytogenes detection.

Estimation by flow cytometry of percentages of survival of Listeria monocytogenes cells treated with tetracycline, with or without prior exposure to several biocides

In certain circumstances, disinfectants are used at sublethal concentrations. The aim of this research work was to determine whether contact of Listeria monocytogenes NCTC 11994 with subinhibitory concentrations of three disinfectants widely used in food processing environments and in the health-care system, benzalkonium chloride (BZK), sodium hypochlorite (SHY) and peracetic acid (PAA), can cause the adaptation of the strain to the biocides and increase its resistance to tetracycline (TE). The minimum inhibitory concentrations (MIC; ppm) were 2.0 (BZK), 3500.0 (SHY) and 1050.0 (PAA). On exposure to increasing subinhibitory concentrations of the biocides, the maximum concentrations (ppm) of the compounds that allowed the strain to grow were (ppm) 8.5 (BZK), 3935.5 (SHY) and 1125.0 (PAA). Both the control cells (non-exposed) and the cells that had been in contact with low doses of biocides were treated with different concentrations of TE (0 ppm, 250 ppm, 500 ppm, 750 ppm, 1000 ppm and 1250 ppm) for 24, 48 and 72 h, and the survival percentages determined using flow cytometry, following dying with SYTO 9 and propidium iodide. The cells previously exposed to PAA presented higher survival percentages (P < 0.05) than the rest of the cells for most of the concentrations of TE and treatment times trialled. These results are worrying because TE is sometimes used to treat listeriosis, highlighting the importance of avoiding the use of disinfectant at subinhibitory doses. Furthermore, the findings suggest that flow cytometry is a fast and simple technique to obtain quantitative data on bacterial resistance to antibiotics.

Contrasting Genetic Diversity of Listeria Pathogenicity Islands 3 and 4 Harbored by Nonpathogenic Listeria spp

Listeria monocytogenes causes the severe foodborne disease listeriosis. Several clonal groups of L. monocytogenes possess the pathogenicity islands Listeria pathogenicity island 3 (LIPI-3) and LIPI-4. Here, we investigated the prevalence and genetic diversity of LIPI-3 and LIPI-4 among 63 strains of seven nonpathogenic Listeria spp. from the natural environment, i.e., wildlife (black bears [Ursus americanus]) and surface water. Analysis of the whole-genome sequence data suggested that both islands were horizontally acquired but differed considerably in their incidence and genetic diversity. LIPI-3 was identified among half of the L. innocua strains in the same genomic location as in L. monocytogenes (guaA hot spot) in a truncated form, with only three strains harboring full-length LIPI-3, and a highly divergent partial LIPI-3 was observed in three Listeria seeligeri strains, outside the guaA hot spot. Premature stop codons (PMSCs) and frameshifts were frequently noted in the LIPI-3 gene encoding listeriolysin S. On the other hand, full-length LIPI-4 without any PMSCs was found in all Listeria innocua strains, in the same genomic location as L. monocytogenes and with ~85% similarity to the L. monocytogenes counterpart. Our study provides intriguing examples of genetic changes that pathogenicity islands may undergo in nonpathogenic bacterial species, potentially in response to environmental pressures that promote either maintenance or degeneration of the islands. Investigations of the roles that LIPI-3 and LIPI-4 play in nonpathogenic Listeria spp. are warranted to further understand the differential evolution of genetic elements in pathogenic versus nonpathogenic hosts of the same genus. IMPORTANCE Listeria monocytogenes is a serious foodborne pathogen that can harbor the pathogenicity islands Listeria pathogenicity island 3 (LIPI-3) and LIPI-4. Intriguingly, these have also been reported in nonpathogenic L. innocua from food and farm environments, though limited information is available for strains from the natural environment. Here, we analyzed whole-genome sequence data of nonpathogenic Listeria spp. from wildlife and surface water to further elucidate the genetic diversity and evolution of LIPI-3 and LIPI-4 in Listeria. While the full-length islands were found only in L. innocua, LIPI-3 was uncommon and exhibited frequent truncation and genetic diversification, while LIPI-4 was remarkable in being ubiquitous, albeit diversified from L. monocytogenes. These contrasting features demonstrate that pathogenicity islands in nonpathogenic hosts can evolve along different trajectories, leading to either degeneration or maintenance, and highlight the need to examine their physiological roles in nonpathogenic hosts.

Growth and inactivation of Listeria monocytogenes in sterile extracts of fruits and vegetables: Impact of the intrinsic factors pH, sugar and organic acid content

Intrinsic characteristics of fresh produce, such as pH, water activity, acid content and nutrient availability are critical factors in determining the survival and growth of Listeria monocytogenes (Lm). In this study, sterile fresh produce juice was used to analyze Lm growth potential among 14 different commodities and to identify physicochemical characteristics in those juices that affect Lm growth. Significant growth of Lm was observed in juices with pH ≥5.6 and low acidity (0.04-0.07 % titratable acidity (TA)) (cantaloupe, carrot, celery, green pepper, parsley, and romaine lettuce), slight reduction of Lm was observed in juices with pH 4.1 (tomato) and pH 3.9 (mango), and no Lm counts were recovered from juices with pH ≤3.8 and high acidity (0.28-1.17 % TA) (apple, blueberry, grape, peach, and pineapple). Although these acidic fruit juices possessed a high sugar content, the pH and acidity of produce juice seemed to be the primary determinants for Lm growth. The neutralization of acidic juices (i.e., Fuji and Gala apple, blueberry, grape, mango, pineapple, peach, and tomato) enabled Lm growth at 37 °C in all juices except for Gala apple and peach. Strong decline in Lm populations in Gala apple, grape and peach juices might be linked to sensitivity to organic acids, such as malic acid. Furthermore, Lm populations significantly decreased in pH-neutral (7.6) cauliflower juice, suggesting that potential antilisterial substances may play a role in Lm decline in cauliflower juice.

Synthetic Analogs of Antimicrobial Peptides from Limulus Inhibit the Growth of Listeria monocytogenes by Increasing Cell Membrane Permeability and Suppressing Virulence Genes

Listeria monocytogenes is a foodborne pathogen that can cause listeriosis in humans and animals. It is of significant concern to the food industry as it can grow at low temperatures. Aggravatingly, only some of the commonly used food preservatives can effectively inhibit the growth of LM. In this study, the effectiveness of synthetic analogs of antimicrobial peptides from Limulus in inhibiting the growth of LM was studied. As determined by the Kirby–Bauer disc diffusion method, the diameters of the inhibition zones produced by the synthetic antimicrobial peptides ranged from 8.24 mm to 8.86 mm, and the minimum inhibitory concentrations (MICs) of the peptides ranged from 40 μg/mL to 160 μg/mL. At their MICs, initially, the synthetic antimicrobial peptides exhibited bacteriostatic effects on LM. They permeabilized the cell membrane of the bacterium and suppressed virulence genes (the inlA, prfA, and hly genes) in the bacterium. However, the bacteriostatic effects were effective only for 1 h, after which the bacterium slowly became resistant to them. After 6 h, the bacterium resumed its growth. Although cells in treatment groups resumed their growth after 6 h, the growth of the cells was inhibited compared to the growth of cells in the control group. Further studies are necessary to reduce the resistance of LM to the antibacterial effects of the synthetic antimicrobial peptides.

Asymptomatic Carriage of Listeria monocytogenes by Animals and Humans and Its Impact on the Food Chain

Humans and animals can become asymptomatic carriers of Listeria monocytogenes and introduce the pathogen into their environment with their feces. In turn, this environmental contamination can become the source of food- and feed-borne illnesses in humans and animals, with the food production chain representing a continuum between the farm environment and human populations that are susceptible to listeriosis. Here, we update a review from 2012 and summarize the current knowledge on the asymptomatic carrier statuses in humans and animals. The data on fecal shedding by species with an impact on the food chain are summarized, and the ways by which asymptomatic carriers contribute to the risk of listeriosis in humans and animals are reviewed.

Growth Inhibition of Listeria monocytogenes in Fresh White Cheese by Mustard Oil Microemulsion

ABSTRACT

Although essential oils exhibit antimicrobial properties, their application is limited, owing to their strong volatility and poor water solubility. Emulsification is a valid strategy for improving chemical stability. In this study, we prepared a mustard oil (MO) emulsion with egg yolk lecithin and evaluated its antimicrobial activity against Listeria monocytogenes in vitro and in cheese curd. The particle size of the MO emulsion was approximately 0.19 μm and remained stable for 30 days of storage. The MO emulsion showed strong antimicrobial activity against L. monocytogenes in vitro. Moreover, 40 ppm of MO was sufficient to inhibit the growth of L. monocytogenes in culture, and the addition of 160 ppm of MO decreased the population of L. monocytogenes. When 50 ppm of emulsified MO was added to milk during cheese curd production and it was stored at 10°C for 10 days, the growth of L. monocytogenes was suppressed. When the cheese curd with MO emulsion was stored at 4°C, the bacterial count was significantly decreased (P < 0.05), and no bacterial growth was observed after 14 days of storage. Furthermore, the sensory characteristics of cheese curd with the MO emulsion were acceptable. These results indicate MO emulsions may be useful in controlling the growth of L. monocytogenes in fresh cheese.

HIGHLIGHTS

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.

Listeria toxin promotes phosphorylation of the inflammasome adaptor ASC through Lyn and Syk to exacerbate pathogen expansion

Inflammasome activation exacerbates infectious disease caused by pathogens such as Listeria monocytogenes, Staphylococcus aureus, and severe acute respiratory syndrome coronavirus 2. Although these pathogens activate host inflammasomes to regulate pathogen expansion, the mechanisms by which pathogen toxins contribute to inflammasome activation remain poorly understood. Here we show that activation of inflammasomes by Listeria infection is promoted by amino acid residue T223 of listeriolysin O (LLO) independently of its pore-forming activity. LLO T223 is critical for phosphorylation of the inflammasome adaptor ASC at amino acid residue Y144 through Lyn-Syk signaling, which is essential for ASC oligomerization. Notably, a Listeria mutant expressing LLO T223A is impaired in inducing ASC phosphorylation and inflammasome activation. Furthermore, the virulence of LLO T223A mutant is markedly attenuated in vivo due to impaired ability to activate the inflammasome. Our results reveal a function of a pathogen toxin that exacerbates infection by promoting phosphorylation of ASC.

Listeria monocytogenes at the interface between ruminants and humans: A comparative pathology and pathogenesis review

The bacterium Listeria monocytogenes (Lm) is widely distributed in the environment as a saprophyte, but may turn into a lethal intracellular pathogen upon ingestion. Invasive infections occur in numerous species worldwide, but most commonly in humans and farmed ruminants, and manifest as distinct forms. Of those, neuroinfection is remarkably threatening due to its high mortality. Lm is widely studied not only as a pathogen but also as an essential model for intracellular infections and host-pathogen interactions. Many aspects of its ecology and pathogenesis, however, remain unclear and are rarely addressed in its natural hosts. This review highlights the heterogeneity and adaptability of Lm by summarizing its association with the environment, farm animals, and disease. It also provides current knowledge on key features of the pathology and (molecular) pathogenesis of various listeriosis forms in naturally susceptible species with a special focus on ruminants and on the neuroinvasive form of the disease. Moreover, knowledge gaps on pathomechanisms of listerial infections and relevant unexplored topics in Lm pathogenesis research are highlighted.

Listeria monocytogenes faecal carriage is common and depends on the gut microbiota

Listeria genus comprises two pathogenic species, L. monocytogenes (Lm) and L. ivanovii, and non-pathogenic species. All can thrive as saprophytes, whereas only pathogenic species cause systemic infections. Identifying Listeria species' respective biotopes is critical to understand the ecological contribution of Listeria virulence. In order to investigate the prevalence and abundance of Listeria species in various sources, we retrieved and analyzed 16S rRNA datasets from MG-RAST metagenomic database. 26% of datasets contain Listeria sensu stricto sequences, and Lm is the most prevalent species, most abundant in soil and host-associated environments, including 5% of human stools. Lm is also detected in 10% of human stool samples from an independent cohort of 900 healthy asymptomatic donors. A specific microbiota signature is associated with Lm faecal carriage, both in humans and experimentally inoculated mice, in which it precedes Lm faecal carriage. These results indicate that Lm faecal carriage is common and depends on the gut microbiota, and suggest that Lm faecal carriage is a crucial yet overlooked consequence of its virulence.

Modelling the potential role of media campaigns on the control of Listeriosis

Human Listeria infection is a food-borne disease caused by the consumption of contaminated food products by the bacterial pathogen, Listeria. In this paper, we propose a mathematical model to analyze the impact of media campaigns on the spread and control of Listeriosis. The model exhibited three equilibria namely; disease-free, Listeria-free and endemic equilibria. The food contamination threshold is determined and the local stability analyses of the model is discussed. Sensitivity analysis is done to determine the model parameters that most affect the severity of the disease. Numerical simulations were carried out to assess the role of media campaigns on the Listeriosis spread. The results show that; an increase in the intensity of the media awareness campaigns, the removal rate of contaminated food products, a decrease in the contact rate of Listeria by humans results in fewer humans getting infected, thus leading to the disease eradication. An increase in the depletion of media awareness campaigns results in more humans being infected with Listeriosis. These findings may significantly impact policy and decision-making in the control of Listeriosis disease.

Listeria Bacteremia Presenting With Cerebral Abscess and Endocarditis in an Elderly Patient With Chronic Immune Thrombocytopenia

Central nervous system involvement by Listeria monocytogenes usually presents as meningitis, meningoencephalitis or, less frequently, rhombencephalitis. Listerial brain abscesses are rare. Moreover, only 5-8% of listerial bacteremia is complicated by infective endocarditis (IE). A 70-year-old man with chronic immune thrombocytopenia (ITP) presented to our emergency department with acute onset of altered mental status and right-sided weakness. He was afebrile, with no heart murmurs or peripheral IE stigmata. Neurologic examination showed disorientation, expressive aphasia, and right-sided hemiparesis. Laboratory findings were unremarkable except for leukocytosis and hyponatremia. Brain MRI showed an irregular rim-enhancing lesion in the left frontal lobe, suspicious for a high-grade glial neoplasm. The lesion was excised, and he was started empirically on vancomycin, ceftriaxone, and metronidazole. After blood cultures grew Listeria monocytogenes, antibiotics were de-escalated to ampicillin and gentamicin. Echocardiography showed mitral valve vegetation. By Day 6, his mental status had improved. On Day 9, he was discharged to our inpatient rehabilitation center to complete six weeks on IV ampicillin and IV gentamicin. Pathology of the brain mass was subsequently reported as a listerial brain abscess. Chronic treatment with high-dose oral glucocorticoids and pre-existing ITP have been independently implicated as predisposing factors in listerial brain abscess. There is a propensity to misdiagnose listerial brain abscess as an intracranial neoplasm due to similar clinical/imaging findings. In addition, Listeria monocytogenes is an atypical cause of IE. Therefore, a high index of suspicion is necessary for early recognition and successful treatment of listerial brain abscess and listerial endocarditis in high-risk patients.

Neonatal listeriosis presentation and outcome: a prospective study of 189 cases

CONTEXT

Listeriosis is caused by the foodborne pathogen Listeria monocytogenes. It can present as a maternal-neonatal infection. We implemented the nationwide prospective cohort MONALISA and analyzed the features of neonatal listeriosis.

METHODS

We studied all neonates born alive from mothers with microbiologically-proven maternal-neonatal listeriosis enrolled from November 2009 to December 2017. We analyzed presentation, neonatal outcome at discharge and predictors of severe presentation and outcome. The study is registered at clinicaltrials.gov (NCT01520597).

RESULTS

We studied 189 infants. 133/189 (70%) had abnormal clinical status at birth, including acute respiratory distress in 106/189 (56%). 132/189 (70%) infants developed early-onset listeriosis and 12/189 (6%) late onset listeriosis who all presented with acute meningitis. 17/189 (9%) had major adverse outcomes: 3% death (5/189), 6% (12/189) severe brain injury, 2% (3/189) severe bronchopulmonary dysplasia, 15/17 in infants born < 34 weeks of gestation (p < 0.0001 versus infants born ≥ 34 weeks of gestation). Maternal antimicrobial treatment ≥ 1 day before delivery was associated with a significant decrease of infants' severity (resulting in significantly less inotropic drugs, fluid resuscitation, or mechanical ventilation requirement), OR 0.23 [95% confidence interval CI 0.09-0.51], p < 0.0001).

CONCLUSION

Antenatal maternal antimicrobial treatment is associated with reduced neonatal listeriosis severity, justifying the prescription of preemptive maternal antimicrobial therapy when maternal-fetal listeriosis is suspected. Neonatal outcome is better than reported earlier, and its major determinant is gestational age at birth.

A fluorescence immunoassay for a rapid detection of Listeria monocytogenes on working surfaces

Listeria monocytogenes is a foodborne pathogen responsible for human listeriosis. The increasing incidence of listeriosis induced governments and food manufacturing enterprises to act to diminish the problem. Several methods for the detection of Listeria monocytogenes in food industries were developed. However, they are time-consuming and require the use of specialized equipment. To reduce the detection time of Listeria monocytogenes in food, in this work we developed a fluorescence sandwich immunoassay based on the use of an innovative chitosan-cellulose nanocrystal (CNC) membrane that improves the antigen capture during bacterial growth. The combined use of CNC film for the capture of p60 protein-specific antigen together with the use of fluorescence detection reduced the time of analysis from 24 to 12 h with a limit of detection (LOD) of the assay of 10² CFU/mL (2 Log). In addition, the use of monoclonal anti-PepD covalently immobilized to a CNC membrane assured a high specificity of the assay. Interestingly, the obtained results show no cross-reactivity with the five most diffused pathogen bacteria strains tested.

Myeloid Cell CK2 Regulates Inflammation and Resistance to Bacterial Infection

Kinase activity plays an essential role in the regulation of immune cell defenses against pathogens. The protein kinase CK2 (formerly casein kinase II) is an evolutionarily conserved kinase with hundreds of identified substrates. CK2 is ubiquitously expressed in somatic and immune cells, but the roles of CK2 in regulation of immune cell function remain largely elusive. This reflects the essential role of CK2 in organismal development and limited prior work with conditional CK2 mutant murine models. Here, we generated mice with a conditional (floxed) allele of Csnk2a, which encodes the catalytic CK2α subunit of CK2. When crossed to Lyz2-cre mice, excision of Csnk2a sequence impaired CK2α expression in myeloid cells but failed to detectably alter myeloid cell development. By contrast, deficiency for CK2α increased inflammatory myeloid cell recruitment, activation, and resistance following systemic Listeria monocytogenes (Lm) infection. Results from mixed chimera experiments indicated that CK2α deficiency in only a subset of myeloid cells was not sufficient to reduce bacterial burdens. Nor did cell-intrinsic deficiency for CK2α suffice to alter accumulation or activation of monocytes and neutrophils in infected tissues. These data suggest that CK2α expression by Lyz2-expressing cells promotes inflammatory and anti-bacterial responses through effects in trans. Our results highlight previously undescribed suppressive effects of CK2 activity on inflammatory myeloid cell responses and illustrate that cell-extrinsic effects of CK2 can shape inflammatory and protective innate immune responses.

Survival and Virulence of Listeria monocytogenes during Storage on Chocolate Liquor, Corn Flakes, and Dry-Roasted Shelled Pistachios at 4 and 23°C

ABSTRACT

The survival and virulence of Listeria monocytogenes was assessed during storage on three low-moisture foods (LMFs): chocolate liquor, corn flakes, and shelled, dry-roasted pistachios (water activity [aw] of 0.18, 0.27, and 0.20, respectively). The LMFs were inoculated with a four-strain cocktail of L. monocytogenes at 8 log CFU/g, dried, held until the aw stabilized, and then stored at 4°C and 25 to 81% relative humidity (RH) and at 23°C and 30 to 35% RH for at least 336 days. At 4°C, L. monocytogenes remained stable on the LMFs for at least 336 days. At 23°C, L. monocytogenes levels declined on the chocolate liquor, corn flakes, and pistachios at initial rates of 0.84, 0.88, and 0.32 log CFU/g/month, respectively. After 8 months at 23°C, L. monocytogenes levels on the chocolate liquor and corn flakes decreased to below the limit of detection (i.e., 0.48 log CFU/g). Relative populations of each strain were assessed before storage (i.e., day 0) and after 6 and 12 months of storage at 23 and 4°C, respectively. Generally, a decline in the relative level of the serotype 1/2a strain was observed during storage, coupled with the relative increase in other strains, depending on the LMF and storage temperature. The total viable populations of L. monocytogenes determined by the PMAxx quantitative PCR method after >12 months of storage at 4°C were significantly (1.8- to 3.7-log) higher than those obtained by plating on tryptic soy agar with yeast extract. Decreases in the culturable population of L. monocytogenes during storage on the LMFs were the result of both cellular inactivation and transition to a viable-but-nonculturable state. The surviving cells, specifically after long-term storage at 4°C on the chocolate liquor and pistachios, remained infectious and capable of intracellular replication in Caco-2 enterocytes. These results are relevant for predictive modeling used in microbial health risk assessments and support the addition of LMFs to food safety questionnaires conducted during listeriosis outbreaks.

HIGHLIGHTS

Serotyping and antibiotic resistance of Listeria monocytogenes isolated from raw water buffalo milk and milk products

This study was aimed to investigate the presence of Listeria monocytogenes in raw water buffalo milk and milk products, besides determining its serotype and the extent of its resistance against various antibiotics. A total of 188 samples of raw water buffalo milk and milk products were collected from Samsun Province, Turkey between November 2012 and May 2013. The classical culture technique was used to isolate and identify L. monocytogenes, as described in EN ISO 11290-1. The isolates were confirmed as L. monocytogenes by using PCR with (hylA) primers specific for the hemolysin gene. The antimicrobial susceptibility test was achieved by using the VITEK 2 compact system and VITEK 2 AST-P640 card. L. monocytogenes was found in 7 (3.7%) of the 188 samples. Four of them were obtained from cheese and three from milk samples. Whereas, L. monocytogenes was not detected in any of the clotted cream samples. A total of 13 isolates were confirmed by PCR as L. monocytogenes. Among these isolates, one was 1/2c (or 3c) (7.6%), three were 4b (or 4d, 4e) (23%), four were 1/2b (or 3b) (30.7%), and the other five isolates were serotype 1/2a (or 3a) (38.4%). The highest antimicrobial resistance was recorded against fosfomycine (100%) followed by oxacillin (92%), penicillin (84%), and erythromycin (69%). However, no resistance was determined against ciprofloxacin, gentamicin, and tigecycline. PRACTICAL APPLICATION: This study showed that some samples of raw buffalo milk and the milk products were contaminated with Listeria monocytogenes. The serotype with the highest prevalence was determined as L. monocytogenes 1/2a. This study also demonstrated that most of the L. monocytogenes isolates had developed multiresistance to many frequently used medical antimicrobial agents.

Susceptibility to Intracellular Infections: Contributions of TNF to Immune Defense

An interesting puzzle is the fact that an infection of a tumor necrosis factor α (TNF)-deficient host with pathogens such as bacteria or parasites that reside intracellularly inevitably ends fatally. Is this due to one specific role of TNF in the immune defense or are different functions responsible for this outcome? In this review we provide an update of the functions of TNF in the defense against the intracellular pathogens Listeria monocytogenes, Mycobacterium tuberculosis, and Leishmania major. Furthermore, we discuss the role of TNF in the generation of proinflammatory macrophages in mouse models of infection and summarize briefly the potential consequences of anti-TNF treatment for infectious diseases.

Listeria Endophthalmitis Cured With Linezolid in an Immunocompetent Farmer Woman: Hazard of a Sweep of a Cow's Tail

We report the first case of an unexpected exogenous Listeria monocytogenes endophthalmitis in a previously healthy woman after a cow’s tail’s sweep, successfully treated with surgery and linezolid. It is the first case carried out with linezolid to treat Listeria endophthalmitis. Therefore, it may challenge the requirement for intravenous antibiotics for long-term treatment.

Draft Genome Sequence of a Listeria monocytogenes Isolate of Core Genome Multilocus Sequence Typing Complex Type 2521 from Ready-to-Eat Meat Sausage Related to an Outbreak (Sigma1) in Germany

We report here the draft genome sequence of a Listeria monocytogenes strain, core genome multilocus sequence typing (cgMLST) complex type 2521 (CT2521), isolated from ready-to-eat meat sausage related to a protracted and supraregional listeriosis outbreak (Sigma1) in Germany from 2014 to 2019.

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.

Outbreak of Listeriosis in South Africa Associated with Processed Meat

BACKGROUND

An outbreak of listeriosis was identified in South Africa in 2017. The source was unknown.

METHODS

We conducted epidemiologic, trace-back, and environmental investigations and used whole-genome sequencing to type Listeria monocytogenes isolates. A case was defined as laboratory-confirmed L. monocytogenes infection during the period from June 11, 2017, to April 7, 2018.

RESULTS

A total of 937 cases were identified, of which 465 (50%) were associated with pregnancy; 406 of the pregnancy-associated cases (87%) occurred in neonates. Of the 937 cases, 229 (24%) occurred in patients 15 to 49 years of age (excluding those who were pregnant). Among the patients in whom human immunodeficiency virus (HIV) status was known, 38% of those with pregnancy-associated cases (77 of 204) and 46% of the remaining patients (97 of 211) were infected with HIV. Among 728 patients with a known outcome, 193 (27%) died. Clinical isolates from 609 patients were sequenced, and 567 (93%) were identified as sequence type 6 (ST6). In a case-control analysis, patients with ST6 infections were more likely to have eaten polony (a ready-to-eat processed meat) than those with non-ST6 infections (odds ratio, 8.55; 95% confidence interval, 1.66 to 43.35). Polony and environmental samples also yielded ST6 isolates, which, together with the isolates from the patients, belonged to the same core-genome multilocus sequence typing cluster with no more than 4 allelic differences; these findings showed that polony produced at a single facility was the outbreak source. A recall of ready-to-eat processed meat products from this facility was associated with a rapid decline in the incidence of L. monocytogenes ST6 infections.

CONCLUSIONS

This investigation showed that in a middle-income country with a high prevalence of HIV infection, L. monocytogenes caused disproportionate illness among pregnant girls and women and HIV-infected persons. Whole-genome sequencing facilitated the detection of the outbreak and guided the trace-back investigations that led to the identification of the source.

Listeriosis Outbreak in South Africa: A Comparative Analysis with Previously Reported Cases Worldwide

Listeria species are Gram-positive, rod-shaped, facultative anaerobic bacteria, which do not produce endospores. The genus, Listeria, currently comprises 17 characterised species of which only two (L. monocytogenes and L. ivanovii) are known to be pathogenic to humans. Food products and related processing environments are commonly contaminated with pathogenic species. Outbreaks and sporadic cases of human infections resulted in considerable economic loss. South Africa witnessed the world's largest listeriosis outbreak, characterised by a progressive increase in cases of the disease from January 2017 to July 2018. Of the 1060 laboratory-confirmed cases of listeriosis reported by the National Institute of Communicable Diseases (NICD), 216 deaths were recorded. Epidemiological investigations indicated that ready-to-eat processed meat products from a food production facility contaminated with L. monocytogenes was responsible for the outbreak. Multilocus sequence typing (MLST) revealed that a large proportion (91%) of the isolates from patients were sequence type 6 (ST6). Recent studies revealed a recurrent occurrence of small outbreaks of listeriosis with more severe side-effects in humans. This review provides a comparative analysis of a recently reported and most severe outbreak of listeriosis in South Africa, with those previously encountered in other countries worldwide. The review focuses on the transmission of the pathogen, clinical symptoms of the disease and its pathogenicity. The review also focuses on the major outbreaks of listeriosis reported in different parts of the world, sources of contamination, morbidity, and mortality rates as well as cost implications. Based on data generated during the outbreak of the disease in South Africa, listeriosis was added to the South African list of mandatory notifiable medical conditions. Surveillance systems were strengthened in the South African food chain in order to assist in preventing and facilitating early detection of both sporadic cases and outbreaks of infections caused by these pathogens in humans.

Carriage and potential long distance transmission of Listeria monocytogenes by migratory black-headed gulls in Dianchi Lake, Kunming

Listeria monocytogenes is a high risk pathogen which can cause invasive diseases in humans. We previously reported that black-headed gulls from Dianchi Lake of Kunming carrying L. monocytogenes, while the characteristics of these isolates and the relationship with habitats of migratory gulls have not been explored. In this study, we investigated the prevalence and molecular characteristics of Listeria monocytogenes from black-headed gulls in Dianchi Lake, and phylogenetic analysis based on core genome SNPs was used to determine the genetic relationship of the strains from Dianchi Lake and other regions. Occurrence of L. monocytogenes in black-headed gull feces in 2016, 2017 and 2018 was 1.0%, 1.0% and 0.6% respectively. The predominant serotype of 28 isolates was 4b, while the predominant sequence types were ST145 and ST201. Based on their prevalence and genomic relationships, ST5 and ST87 were likely to be sourced locally while ST145 and ST201 were likely to be non-local. L. monocytogenes may travel along the bird migration route leading to transmission over a large geographical span carried by black-headed gull. Although the prevalence of L. monocytogenes was low, its carriage by the migratory black-headed gulls poses potential public health risks in regions where the migratory birds passage and reside.

Oncologic Emergencies: The Fever With Too Few Neutrophils

BACKGROUND

Cancer is associated with a variety of complications, including neutropenic fever, which can result in severe morbidity and mortality. This oncologic emergency requires ED management.

OBJECTIVE

This narrative review provides focused updates for emergency clinicians regarding neutropenic fever.

DISCUSSION

Neutropenic fever is defined by fever with oral temperature >38.3°C or temperature >38.0°C for 1 hour with an absolute neutrophil count (ANC) < 1000 cells/microL. Patients who have received chemotherapy within 6 weeks of presentation are at high risk for neutropenia. While most patients with neutropenic fever do not have an identifiable bacterial source of fever, clinicians should treat patients for bacterial infection. Rapid assessment and management are vital to improving outcomes in patients with suspected or confirmed neutropenic fever. History and examination should focus on the most common sites of infection: the gastrointestinal tract, blood, skin, lung, and urinary tract. However, physical examination and laboratory or imaging assessment may not display classic signs of infection. Blood cultures should be obtained, and broad-spectrum antibiotics are recommended. Oncology consultation is an integral component in the care of these patients. Several risk scores can assist in stratifying patients who may be appropriate for discharge home and follow-up.

CONCLUSIONS

Neutropenic fever is an oncologic emergency. Rapid diagnosis and care of patients with neutropenic fever can improve outcomes, along with oncology consultation.

Whole-Genome Sequence of a Serotype 1/2b Listeria monocytogenes Strain Isolated from Raw Seafood in Japan

Listeria monocytogenes is a pathogen typically acquired through the ingestion of foods. It has been specifically reported that the pathogen is widely distributed in raw seafood in Japan.

Listeria monocytogenes is a pathogen typically acquired through the ingestion of foods. It has been specifically reported that the pathogen is widely distributed in raw seafood in Japan. Here, we report the whole-genome sequence and sequence type (ST) of a Listeria monocytogenes strain isolated from salmon roe sold in the Japanese retail market.

Lactobacillus casei expressing Internalins A and B reduces Listeria monocytogenes interaction with Caco-2 cells in vitro

Listeria monocytogenes has been implicated in a number of outbreaks including the recent largest outbreak in South Africa. Current methods for prevention of foodborne L. monocytogenes infection are inadequate, thus raising a need for an alternative strategy. Probiotic bioengineering is considered a prevailing approach to enhance the efficacy of probiotics for targeted control of pathogens. Here, the ability of Lactobacillus casei expressing the L. monocytogenes invasion proteins Internalins A and B (inlAB) to prevent infection was investigated. The inlAB operon was cloned and surface‐expressed on L. casei resulting in a recombinant strain, Lbc^InlAB, and subsequently, its ability to inhibit adhesion, invasion and translocation of L. monocytogenes through enterocyte‐like Caco‐2 cells was examined. Cell surface expression of InlAB on the Lbc^InlAB was confirmed by Western blotting and immunofluorescence staining. The Lbc^InlAB strain showed significantly higher (P < 0.0001) adherence, invasion and translocation of Caco‐2 cells than the wild‐type L. casei strain (Lbc^WT), as well as reduced L. monocytogenes adhesion, invasion and transcellular passage through the cell monolayer than Lbc^WT. Furthermore, pre‐exposure of Caco‐2 cells to Lbc^InlAB significantly reduced L. monocytogenes‐induced cell cytotoxicity and epithelial barrier dysfunction. These results suggest that InlAB‐expressing L. casei could be a potential practical approach for prevention of listeriosis.

In vitro antibacterial and early stage biofilm inhibitory potential of an edible chitosan and its phenolic conjugates against Pseudomonas aeruginosa and Listeria monocytogenes

In the present study, the antibacterial potential of chitosan grafted with phenolics (CPCs) such as caffeic acid (CCA), ferulic (CFA), and sinapic acid (CSA) were evaluated against foodborne pathogens like Pseudomonas aeruginosa (PA) and Listeria monocytogenes (LM). The geometric means of minimum inhibitory concentration (MIC range 0.05-0.33 mg/ml), bactericidal concentration (MBC range 0.30-0.45 mg/ml), biofilm inhibitory concentration (BIC range 0.42-0.83 mg/ml), and biofilm eradication concentration (BEC range 1.71-3.70 mg/ml) of CPCs were found to be lower than the MIC (0.12-1.08 mg/ml), MBC (0.17-1.84 mg/ml), BIC (4.0-4.50 mg/ml), and BEC (17.4-23.0 mg/ml) of unmodified chitosan against PA and LM. CPCs attenuated the biofilms of PA and LM by increasing the membrane permeability of bacteria embedded within the biofilms. Further, sub MIC of CPCs (0.5 × MIC) significantly reduced the biofilm adhesion (p < 0.001) by representative strains of LM (CCA: 72.2 ± 3.5, CFA: 79.3 ± 0.9, and CSA: 74.9 ± 1.5%) and PA (CCA: 64 ± 1.1, CFA: 67.8 ± 0.8, and CSA: 65.7 ± 4.9%). These results suggested the antibacterial and anti-biofilm potential of CPCs that can be exploited to control foodborne pathogenic infections.

Infectious Disease Emergencies in Oncology Patients

Oncology patients are a unique patient population in the emergency department (ED). Malignancy and associated surgical, chemotherapeutic, or radiation therapies put them at an increased risk for infection. The most ominous development is neutropenic fever, which happens often and may not present with signs or symptoms other than fever. A broad differential diagnosis is essential when considering infectious disease pathology in both neutropenic and non-neutropenic oncology patients in the ED.

Virulence Gene Sequencing Highlights Similarities and Differences in Sequences in Listeria monocytogenes Serotype 1/2a and 4b Strains of Clinical and Food Origin From 3 Different Geographic Locations

The prfA-virulence gene cluster (pVGC) is the main pathogenicity island in Listeria monocytogenes, comprising the prfA, plcA, hly, mpl, actA, and plcB genes. In this study, the pVGC of 36 L. monocytogenes isolates with respect to different serotypes (1/2a or 4b), geographical origin (Australia, Greece or Ireland) and isolation source (food-associated or clinical) was characterized. The most conserved genes were prfA and hly, with the lowest nucleotide diversity (π) among all genes (P < 0.05), and the lowest number of alleles, substitutions and non-synonymous substitutions for prfA. Conversely, the most diverse gene was actA, which presented the highest number of alleles (n = 20) and showed the highest nucleotide diversity. Grouping by serotype had a significantly lower π value (P < 0.0001) compared to isolation source or geographical origin, suggesting a distinct and well-defined unit compared to other groupings. Among all tested genes, only hly and mpl were those with lower nucleotide diversity in 1/2a serotype than 4b serotype, reflecting a high within-1/2a serotype divergence compared to 4b serotype. Geographical divergence was noted with respect to the hly gene, where serotype 4b Irish strains were distinct from Greek and Australian strains. Australian strains showed less diversity in plcB and mpl relative to Irish or Greek strains. Notable differences regarding sequence mutations were identified between food-associated and clinical isolates in prfA, actA, and plcB sequences. Overall, these results indicate that virulence genes follow different evolutionary pathways, which are affected by a strain's origin and serotype and may influence virulence and/or epidemiological dominance of certain subgroups.

Molecular Tracing to Find Source of Protracted Invasive Listeriosis Outbreak, Southern Germany, 2012-2016

We investigated 543 Listeria monocytogenes isolates from food having a temporal and spatial distribution compatible with that of the invasive listeriosis outbreak occurring 2012–2016 in southern Germany. Using forensic microbiology, we identified several products from 1 manufacturer contaminated with the outbreak genotype. Continuous molecular surveillance of food isolates could prevent such outbreaks.

Phenotypic and Genotypic Analysis of Antimicrobial Resistance among Listeria monocytogenes Isolated from Australian Food Production Chains

The current global crisis of antimicrobial resistance (AMR) among important human bacterial pathogens has been amplified by an increased resistance prevalence. In recent years, a number of studies have reported higher resistance levels among Listeria monocytogenes isolates, which may have implications for treatment of listeriosis infection where resistance to key treatment antimicrobials is noted. This study examined the genotypic and phenotypic AMR patterns of 100 L. monocytogenes isolates originating from food production supplies in Australia and examined this in the context of global population trends. Low levels of resistance were noted to ciprofloxacin (2%) and erythromycin (1%); however, no resistance was observed to penicillin G or tetracycline. Resistance to ciprofloxacin was associated with a mutation in the fepR gene in one isolate; however, no genetic basis for resistance in the other isolate was identified. Resistance to erythromycin was correlated with the presence of the ermB resistance gene. Both resistant isolates belonged to clonal complex 1 (CC1), and analysis of these in the context of global CC1 isolates suggested that they were more similar to isolates from India rather than the other CC1 isolates included in this study. This study provides baseline AMR data for L. monocytogenes isolated in Australia, identifies key genetic markers underlying this resistance, and highlights the need for global molecular surveillance of resistance patterns to maintain control over the potential dissemination of AMR isolates.

Detection of Listeria Spp. and Listeria Monocytogenes in Biological Samples by SYBR Green I and TaqMan Probe-based Real-time PCRs

INTRODUCTION

The aim of the study was the application and comparison of real-time PCR methods based on the fluorescence of SYBR Green I intercalating dye and TaqMan probes for the detection of the 23S rDNA gene of Listeria spp. and the hlyA gene of Listeria monocytogenes in biological samples of the liver, brain, and blood.

MATERIAL AND METHODS

Five strains of L. monocytogenes and single strains of each species L. ivanovii, L. innocua,L. grayi, L. welshimeri, and L. seeligeri were used for the experiments. Additionally, five strains of other species of bacteria were used for evaluation of the specificity of tests. In the first stage of the study SYBR Green I real-time PCRs, one allowing detection of the 23S rDNA gene and two based on the amplification the hlyA gene, were performed. In the next part, three TaqMan probe-based real-time PCRs allowing confirmation of belonging to Listeria spp. and L. monocytogenes were conducted.

RESULTS

The observation of amplification curves in real-time PCRs enabled the detection of both genes. A high regression coefficient of 0.99 was found for all reactions. Specific amplification products were obtained for the 23S rDNA and hlyA genes which confirm their belonging to Listeria spp. and L. monocytogenes, respectively. Other microbial species did not reveal real-time PCR products.

CONCLUSION

Both real-time PCR methods for the detection of Listeria spp. and L. monocytogenes in biological samples demonstrated a significant sensitivity and high specificity.

Loop-mediated isothermal amplification (LAMP): A novel rapid detection platform for pathogens

Foodborne bacterial infections and diseases have been considered to be a major threat for public health in the worldwide. Increased incidence of human diseases caused by foodborne pathogens have been correlated with growing world population and mobility. Loop-mediated isothermal amplification (LAMP) has been regarded as an innovative gene amplification technology and emerged as an alternative to PCR-based methodologies in both clinical laboratory and food safety testing. Nowadays, LAMP has been applied to detection and identification on pathogens from microbial diseases, as it showed significant advantage in high sensitivity, specificity and rapidity. The high sensitivity of LAMP enables detection of the pathogens in sample materials even without time consuming sample preparation. An overview of LAMP mainly containing the development history, reaction principle and its application to four kind of foodborne pathogens detection are presented in this paper. As concluded, with the advantages of rapidity, simplicity, sensitivity, specificity and robustness, LAMP is capable of applications for clinical diagnosis as well as surveillance of infection diseases. Moreover, the main purpose of this paper is to provide theoretical basis for the clinical application of LAMP technology.