History and epidemiology of listeriosis

Listeria spp., Listeria monocytogenes

Listeriosis is a disease caused by L. monocytogenes, a relevant microorganism as a causative agent of foodborne diseases - FBD. This study aimed to evaluate the distribution of Listeria spp., and L. monocytogenes in different production areas in two small plants (A and B) and two micro-food processing plants (C and D) producing meat derivatives, located in different cities of Colombia. The methodology implemented was i. The analysis of sampling points is based on a harmonised tool. ii. Four samplings in each production plant between 2019 and 2020. iii. Isolation and identification of microorganisms through conventional microbiology, a semi-automated system, molecular serotyping and clonal characterisation by ERIC-PCR. L. monocytogenes frequency in the production plants belonging to the study ranged between 5.9 and 28.6 %; for Listeria spp., plants A and D had isolated, plant A had the highest proportion, while for L. monocytogenes geno-serotypes found were: 1/2a, 1/2c, 4a-4c, 4b, 4d - 4e, with geno-serotype 4b as the most frequent. Furthermore, possible persistent isolates were detected in plant C as the feasible sources of contamination, based on failures in flow management, raw material contaminated with L. monocytogenes, lack of standardised cooking processes and transfer of the microorganism through equipment and surfaces. Finally, in three of the four production plants assayed, L. monocytogenes or Listeria spp. were present in the packaging area in some of the samples taken during the study, which calls for increased and frequent monitoring, as well as constant technical support for the control of L. monocytogenes in micro and small-scale production plants.

Validating the Utility of Multilocus Variable Number Tandem-repeat Analysis (MLVA) as a Subtyping Strategy to Monitor Listeria monocytogenes In-built Food Processing Environments

Listeria monocytogenes is a serious human pathogen and an enduring challenge to control for the ready-to-eat food processing industry. Cost-effective tools that can be deployed by commercial or in-house laboratories to rapidly investigate and resolve contamination events in the built food processing environment are of value to the food industry. Multilocus variable number tandem-repeat analysis (MLVA) is a molecular subtyping method, which along with other same-generation methods such as pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) is being superseded in disease tracking and outbreak investigations by whole-genome sequencing (WGS). In this paper, it is demonstrated that MLVA can continue to play a valuable role as a valid, fast, simple, and cost-effective method to identify and track Listeria monocytogenes subtypes in factory environments, with the method being highly congruent with MLST. Although MLVA does not have the discriminatory power of WGS to identify truly persistent clones, with careful interpretation of results alongside isolate metadata, it remains a powerful tool in situations and locations where WGS may not be readily available to food business operators.

Recent Advances in the Detection of Listeria monocytogenes

Listeria monocytogenes is the third-most severe pathogen causing a yearly outbreak of food poisoning in the world that proliferates widely in the environment. Infants, pregnant mothers, and immuno-compromised people are at high risk. Its ability to grow in both biotic and abiotic environments leads to epidemics that infect 5 out of 10 people annually. Because of the epithelial adhesion (by E-cadherin binding), it can suppress immune cells and thrive in the gastrointestinal tract till the brain through blood flow (E-cadherin). Microbial culture is still used as a gold standard, but takes a long time and often yields false positive results due to incompetence and temperature variations. Therefore, in order to treat it rather than using broad spectrum antibiotics, a standardized time-saving and highly specific technology for early detection is very important. It has been observed that the production of a particular antibody is delaying (so does the detection process) as a result of the inadequate understanding of the pathophysiology of the bacteria. This book chapter provides a brief summary of a pathogen as well as the scientific advances that led to its identification more easily.

Listeria monocytogenes-How This Pathogen Uses Its Virulence Mechanisms to Infect the Hosts

Listeriosis is a serious food-borne illness, especially in susceptible populations, including children, pregnant women, and elderlies. The disease can occur in two forms: non-invasive febrile gastroenteritis and severe invasive listeriosis with septicemia, meningoencephalitis, perinatal infections, and abortion. Expression of each symptom depends on various bacterial virulence factors, immunological status of the infected person, and the number of ingested bacteria. Internalins, mainly InlA and InlB, invasins (invasin A, LAP), and other surface adhesion proteins (InlP1, InlP4) are responsible for epithelial cell binding, whereas internalin C (InlC) and actin assembly-inducing protein (ActA) are involved in cell-to-cell bacterial spread. L. monocytogenes is able to disseminate through the blood and invade diverse host organs. In persons with impaired immunity, the elderly, and pregnant women, the pathogen can also cross the blood-brain and placental barriers, which results in the invasion of the central nervous system and fetus infection, respectively. The aim of this comprehensive review is to summarize the current knowledge on the epidemiology of listeriosis and L. monocytogenes virulence mechanisms that are involved in host infection, with a special focus on their molecular and cellular aspects. We believe that all this information is crucial for a better understanding of the pathogenesis of L. monocytogenes infection.

Selection of Listeria monocytogenes InlA-Binding Peptides Using Phage Display—Novel Compounds for Diagnostic Applications?

Listeria monocytogenes is a pathogenic, gram-positive bacterium causing foodborne infections and listeriosis, an infection responsible for serious medical conditions, especially for pregnant women, newborns, or people with a weak immune system. Even after antibiotic treatment, 30% of clinical infections result in death. L. monocytogenes is able to enter and multiply in mammalian cells. Invasion into epithelial cells in the human intestine is mediated by the interaction of the bacterial surface protein internalin A (InlA) with the host cell receptor E-cadherin (E-cad). We have used phage display to select InlA-specific peptides consisting of 12 amino acids using a randomized, recombinant peptide library. We could demonstrate that the selected peptides bound to recombinant InlA protein as well as to L. monocytogenes cells. In vitro, some of the peptides inhibited the interaction between recombinant InlA and human E-cad. As far as we know, this is the first publication on the development of InlA-specific peptide ligands. In the future, our peptides might be used for the development of innovative diagnostic tools or even therapeutic approaches.

The Saprophytic Lifestyle of Listeria monocytogenes and Entry Into the Food-Processing Environment

Listeria monocytogenes is an environmentally adapted saprophyte that can change into a human and animal bacterial pathogen with zoonotic potential through several regulatory systems. In this review, the focus is on the occurrence of Listeria sensu stricto and sensu lato in different ecological niches, the detection methods, and their analytical limitations. It also highlights the occurrence of L. monocytogenes genotypes in the environment (soil, water, and wildlife), reflects on the molecular determinants of L. monocytogenes for the saprophytic lifestyle and the potential for antibiotic resistance. In particular, the strain-specific properties with which some genotypes circulate in wastewater, surface water, soil, wildlife, and agricultural environments are of particular interest for the continuously updating risk analysis.

Performance of Scoring Systems in Predicting Clinical Outcomes in Patients with Bacteremia of Listeria monocytogenes: A 9-Year Hospital-Based Study

BACKGROUND

Listeria monocytogenes (LM) is a facultative anaerobe, Gram-positive bacillus which is widely distributed in nature, and can be separated from soil, water, and rotten vegetables. Immunocompetent people are less likely to suffer from LM infection or may only show gastrointestinal symptoms. However, immunocompromised elderly people, pregnant women, and newborns may develop life-threatening invasive infections. The mortality rate of LM infection is as high as 25-30%. The aim of this study is to investigate clinical scores of patients with bacteremia of LM confirmed by one or more blood cultures. We analyzed their demographics and laboratory findings in relation to their clinical outcomes.

MATERIALS AND METHODS

This was a hospital-based retrospective study on patients with bacteremia of LM. Data were collected from the electronic clinical database of Taichung Veterans General Hospital between January 2012 and December 2020. Bacteremia of LM was confirmed by at least one blood culture. Demographics, clinical characteristics, and laboratory data were collected for analysis. A variety of clinical scoring systems were used to predict the clinical outcome.

RESULTS

A total of 39 patients had confirmed bacteremia of LM. Among them, 1 neonatal patient was excluded. The remaining 38 patients were studied. They included 16 males (42.1%) and 22 females (57.9%), with a mean age of 59.9 ± 19.6 years. Their hospital stay averaged 23.3 ± 20.9 days. The in-hospital mortality rate was 36.8%. Mortality in Emergency Department Sepsis (MEDS) Score was 6.6 ± 4.0 for survivors and 12.4 ± 4.4 for non-survivors (P < 0.001). The National Early Warning Score (NEWS) was 3.9 ± 2.8 for survivors and 7.8 ± 3.1 for non-survivors (P = 0.001). Regarding the prediction of mortality risk, the AUC of ROC was 0.829 for MEDS and 0.815 for NEWS.

CONCLUSIONS

MEDS and NEWS were both good predictors of the clinical outcome in LM bacteremic patients. In those with higher scores of MEDS (≥10) and NEWS (≥8), we recommended an early goal-directed therapy and appropriate antibiotic treatment as early as possible to reduce mortality. Further large-scale studies are required to gain a deeper understanding of this disease and to ensure patient safety.

Characteristics and Outcomes of Neonates With Blood Stream Infection Due to Listeria monocytogenes

BACKGROUND

Infection due to Listeria monocytogenes (LM) is rare in neonates; thus, its clinical presentation and outcomes are not commonly reported, especially in low- and middle-income countries. In 2017, South Africa had an outbreak due to LM.

OBJECTIVE

To determine demographic characteristics, clinical and laboratory findings and outcomes of all neonates infected with LM during the outbreak period.

METHODS

This is a retrospective analytic study. Clinical and laboratory records of neonates admitted at Chris Hani Baragwanath Academic Hospital from January 2017 to May 2018 with positive blood and cerebrospinal fluid culture with LM were reviewed for demographic characteristics, clinical presentation, ancillary laboratory test results and outcomes at hospital discharge.

RESULTS

There were 42 neonates with positive cultures due to LM. Thirty-four (81%) were born preterm. Mode of delivery was vaginal in 78.6% and 31.0% were HIV exposed. All patients presented within the first 6 days of life as an early-onset disease. Common clinical presentation was respiratory depression (52.4%) and respiratory distress (38.1%) with 69% requiring invasive or noninvasive respiratory support. Common abnormal laboratory findings were high C-reactive protein (77.1%) followed by leukopenia (23.8%). Fourteen patients (40%) had features of meningitis based on blood and cerebrospinal fluid findings (4 culture proven). There were 11 deaths at hospital discharge, giving a mortality rate of 26.2%.

CONCLUSIONS

The majority of neonates infected with LM were born preterm, raising the possibility that LM itself may have been responsible for preterm labor. All presented in the first 6 days of life and most presented with respiratory distress or depression. A high proportion had meningitis, and there was a high-mortality overall.

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.

Non-human Primate Models to Investigate Mechanisms of Infection-Associated Fetal and Pediatric Injury, Teratogenesis and Stillbirth

A wide array of pathogens has the potential to injure the fetus and induce teratogenesis, the process by which mutations in fetal somatic cells lead to congenital malformations. Rubella virus was the first infectious disease to be linked to congenital malformations due to an infection in pregnancy, which can include congenital cataracts, microcephaly, hearing impairment and congenital heart disease. Currently, human cytomegalovirus (HCMV) is the leading infectious cause of congenital malformations globally, affecting 1 in every 200 infants. However, our knowledge of teratogenic viruses and pathogens is far from complete. New emerging infectious diseases may induce teratogenesis, similar to Zika virus (ZIKV) that caused a global pandemic in 2016-2017; thousands of neonates were born with congenital microcephaly due to ZIKV exposure in utero, which also included a spectrum of injuries to the brain, eyes and spinal cord. In addition to congenital anomalies, permanent injury to fetal and neonatal organs, preterm birth, stillbirth and spontaneous abortion are known consequences of a broader group of infectious diseases including group B streptococcus (GBS), Listeria monocytogenes, Influenza A virus (IAV), and Human Immunodeficiency Virus (HIV). Animal models are crucial for determining the mechanism of how these various infectious diseases induce teratogenesis or organ injury, as well as testing novel therapeutics for fetal or neonatal protection. Other mammalian models differ in many respects from human pregnancy including placentation, labor physiology, reproductive tract anatomy, timeline of fetal development and reproductive toxicology. In contrast, non-human primates (NHP) most closely resemble human pregnancy and exhibit key similarities that make them ideal for research to discover the mechanisms of injury and for testing vaccines and therapeutics to prevent teratogenesis, fetal and neonatal injury and adverse pregnancy outcomes (e.g., stillbirth or spontaneous abortion). In this review, we emphasize key contributions of the NHP model pre-clinical research for ZIKV, HCMV, HIV, IAV, L. monocytogenes, Ureaplasma species, and GBS. This work represents the foundation for development and testing of preventative and therapeutic strategies to inhibit infectious injury of human fetuses and neonates.

Prevalence, Characterization, and Antimicrobial Susceptibility of Listeria monocytogenes from Raw Beef and Slaughterhouse Environments in Korea

The prevalence of Listeria monocytogenes in raw beef and in slaughterhouse environments was investigated from April 2019 to February 2020. Three hundred raw beef samples were purchased from 50 retailers and 10 restaurants (5 samples per source). One hundred and thirty-four samples from slaughterhouse environments were collected by swabbing (10 × 10 cm) the surfaces, gloves, splitting saw, and drains. L. monocytogenes was detected and identified according to the method described in ISO 11290-1, and confirmed by 16S rRNA sequencing. L. monocytogenes was detected in raw beef (2/300, 0.7%), gloves used in carcass splitting (6/21, 28.6%), the splitting saw (1/18, 5.6%), and the drain zone (1/15, 6.7%). All isolates were serotype 1/2a or 1/2c, based on screening using multiplex PCR-based serogrouping assay and serotyping kit for O-H antigens. Pulsed-field gel electrophoresis (PFGE) following ApaI digestion of eight PFGE pulsotypes and four PFGE groups were identified. Biofilm formation analysis using Crystal Violet staining revealed the highest biofilm formation in strain LM-16, followed by D190613. Although L. monocytogenes isolates were susceptible to most antimicrobials, some resistance to penicillin (8/15, 53.3%) and tetracycline (2/15, 13.3%) was observed. Through PFGE, G190426, G190829, and G200210 isolated from the same location in this study were genetically homologous similar to the LM-16 strain, previously isolated from beef carcass in 2006. These results suggest that LM-16 has been continuously present in biofilms in the slaughterhouse environments since 2006. Our study indicates that L. monocytogenes contamination in raw beef could consistently occur during beef processing in slaughterhouse environments through contact with gloves, splitting saws, and drains.

High Prevalence of Listeria monocytogenes in Smoked Duck: Antibiotic and Heat Resistance, Virulence, and Genetics of the Isolates

This study aimed at determining the genetic and virulence characteristics of the Listeria monocytogenes from smoked ducks. L. monocytogenes was isolated by plating, and the isolated colonies were identified by PCR. All the obtained seven L. monocytogenes isolates possessed the virulence genes (inlA, inlB, plcB, and hlyA) and a 385 bp actA amplicon. The L. monocytogenes isolates (SMFM2018 SD 1-1, SMFM 2018 SD 4-1, SMFM 2018 SD 4-2, SMFM 2018 SD 5-2, SMFM 2018 SD 5-3, SMFM 2018 SD 6-2, and SMFM 2018 SD 7-1) were inoculated in tryptic soy broth (TSB) containing 0.6% yeast extract at 60°C, followed by cell counting on tryptic soy agar (TSA) containing 0.6% yeast extract at 0, 2, 5, 8, and 10 min. We identified five heat resistant isolates compared to the standard strain (L. monocytogenes ATCC13932), among which three exhibited the serotype 1/2b and D-values of 5.41, 6.48, and 6.71, respectively at 60°C. The optical densities of the cultures were regulated to a 0.5 McFarland standard to assess resistance against nine antibiotics after an incubation at 30°C for 24 h. All isolates were penicillin G resistant, possessing the virulence genes (inlA, inlB, plcB, and hlyA) and the 385-bp actA amplicon, moreover, three isolates showed clindamycin resistance. In conclusion, this study allowed us to characterize L. monocytogenes isolates from smoked ducks, exhibiting clindamycin and penicillin G resistance, along with the 385-bp actA amplicon, representing higher invasion efficiency than the 268-bp actA, and the higher heat resistance serotype 1/2b.

Prevalence, characterization and antimicrobial resistance of Listeria monocytogenes isolated from beef meat in Meknes city, Morocco

Introduction

Listeria monocytogenes is one of the most pathogenic bacteria related to the consumption of contaminated food. This study aims to determine the prevalence of L. monocytogenes in raw beef meat in Meknes city of Morocco, to evaluate its pathogenicity and resistance to antimicrobials.

Methods

During four seasons, a total of 140 samples were collected from supermarkets, butcheries and Souk (weekly traditional market). The PCR method was used to examine the presence of specific and virulence genes in the isolated strains, and also to identify their serotypes. The antimicrobial resistance was determined.

Results

The results show a prevalence of 7.14% which depends on retail sites and also on the season's variation. The majority of the strains were detected in butcheries (6 strains), and supermarkets (4 strains). Moreover, the majority of strains were detected during summer (50%). Concerning virulence genes, the seven researched genes were detected in 100% of isolated strains. The majority of strains were of the (1/2a, 1/2c, 3a and 3c) serogroup (70%), while two of them were of the (1/2b, 3b, 4b and 4d) serogroup (20%). All isolates were resistant to at least one antimicrobial, while three strains were resistant to nine tested antimicrobials. However, they were highly susceptible to amikacin, imipenem, gentamicin, sulfamethoxazole and chloramphenicol.

Conclusions

According to results, isolated L. monocytogenes from analyzed beef meat shows a high level of pathogenicity and resistance to the most used antimicrobials in listeriosis therapy, which calls for the severe application of quality systems at the slaughterhouses and retail sites level.

Occurrence and Characteristics of Listeria monocytogenes in Ready-to-Eat Meat Products in Poland

ABSTRACT

Listeria monocytogenes is a potential hazard for food safety and therefore for public health. The aim of the present study was to determine the prevalence and characteristics of L. monocytogenes in Polish ready-to-eat (RTE) meat products for retail sale. Among the 184,439 food samples collected within the framework of a national official control and monitoring program, only 0.3% were positive for L. monocytogenes. A significant group of products that did not meet the criteria were RTE meat products. This group accounted for 40% of all noncompliant samples. Seventy L. monocytogenes isolates from these RTE meat products (meat, sausages, and delicatessen products with meat) were examined. The majority of the tested isolates (51%) belonged to serogroup 1/2a-3a followed by 1/2c-3c (21%), 1/2b-3b-7 (14%), and 4ab-4b-4d-4e (13%). Serogroup 4a-4c was not present among the tested isolates. All L. monocytogenes isolates harbored the virulence-associated genes inlA, inlC, inlJ, and lmo2672. The llsX marker was detected in 12 (17%) of the 70 isolates. Ampicillin resistance was the most common resistance phenotype and was identified in 83% of the L. monocytogenes isolates. A low incidence of resistance to amoxicillin-clavulanic acid (6% of isolates) was also detected. All L. monocytogenes isolates were susceptible to chloramphenicol, gentamicin, ciprofloxacin, meropenem, sulfamethoxazole-trimethoprim, tetracycline, and erythromycin. This work provides useful information regarding contamination of RTE meat products with L. monocytogenes, which may have implications for food safety risks.

HIGHLIGHTS

Danger-associated metabolic modifications during bacterial infection of macrophages

In this review, we propose that certain modifications in cellular metabolism might function as danger signals triggering inflammasome-mediated immune responses. We propose to call them danger-associated metabolic modifications (DAMMs). As intracellular bacteria can actively modulate macrophage metabolism for their benefit, infected host cells might sense bacteria-induced metabolic alterations and activate immune reactions. Here we report the known metabolic interactions that occur during infection of macrophages by intracellular bacteria and discuss the possible emergence of DAMMs upon bacteria-induced alterations of cellular metabolism.

A Batf3/Nlrp3/IL-18 Axis Promotes Natural Killer Cell IL-10 Production during Listeria monocytogenes Infection

The bacterial pathogen Listeria monocytogenes (Lm) capitalizes on natural killer (NK) cell production of regulatory interleukin (IL)-10 to establish severe systemic infections. Here, we identify regulators of this IL-10 secretion. We show that IL-18 signals to NK cells license their ability to produce IL-10. IL-18 acts independent of IL-12 and STAT4, which co-stimulate IFNγ secretion. Dendritic cell (DC) expression of Nlrp3 is required for IL-18 release in response to the Lm p60 virulence protein. Therefore, mice lacking Nlrp3, Il18, or Il18R fail to accumulate serum IL-10 and are highly resistant to systemic Lm infection. We further show that cells expressing or dependent on Batf3 are required for IL-18-inducing IL-10 production observed in infected mice. These findings explain how Il18 and Batf3 promote susceptibility to bacterial infection and demonstrate the ability of Lm to exploit NLRP3 for the promotion of regulatory NK cell activity.

Antibacterial Effect of a Mixed Natural Preservative against Listeria monocytogenes on Lettuce and Raw Pork Loin

A mixed natural preservative, including grapefruit seed extract (GSE), cinnamaldehyde (CA), and nisin, was investigated for the reduction of Listeria monocytogenes growth on lettuce and raw pork loin. The MIC of each natural preservative was investigated for L. monocytogenes strains tested. Following central composite design, lettuce and pork loin were inoculated with a cocktail of three strains of L. monocytogenes (ATCC 15313, H7962, and NADC 2045 [Scott A]) and treated with the mixed natural preservative that included GSE (0.64 to 7.36 ppm), CA (1.6 to 18.4 ppm), and nisin (0.48 to 5.5 ppm). The MIC of GSE was 31.25 ppm in tested L. monocytogenes strains, and of CA was 500 and 1,000 ppm in L. monocytogenes ATCC 15313 and the other L. monocytogenes strains, respectively. The MIC of nisin was 250 ppm. The R2 value of this model was more than 0.9, and the lack of fit was not significant. The mixed natural preservative showed a synergistic antimicrobial effect and reduced the growth of L. monocytogenes by 4 to 5 log CFU/g on lettuce. In addition, the reduction of L. monocytogenes on pork loin was 3 log CFU/g. The mixed natural preservative, which consisted of GSE (6 to 8 ppm), CA (15 to 20 ppm), and nisin (5 to 6 ppm), increased the antibacterial effect against L. monocytogenes. These results suggest that the use of the mixed natural preservative could reduce the economic cost of food preparation, and response surface methodology is considered effective when measuring synergy among antimicrobials.

Sequelae of Fetal Infection in a Non-human Primate Model of Listeriosis

Listeria monocytogenes (Lm) is a common environmental bacterium that thrives on vegetation and soil matter, but can infect humans if contaminated food products are ingested, resulting in severe disease in immunosuppressed populations, including pregnant women and newborns. To better understand how the unique immunological milieu of pregnancy increases susceptibility to infection, we study listeriosis in cynomolgus macaques, a non-human primate that closely resembles humans in placentation and in the physiology, and immunology of pregnancy. Non-human primates are naturally susceptible to Lm infection, and spontaneous abortions due to listeriosis are known to occur in outdoor macaque colonies, making them ideal models to understand the disease pathogenesis and host-pathogen relationship of listeriosis. We have previously shown that Lm infection in the first trimester has a high rate of miscarriage. This study expands on our previous findings by assessing how the quantity of Lm as well as stage of pregnancy at the time of exposure may influence disease susceptibility. In the current study we inoculated a cohort of macaques with a lower dose of Lm than our previous study and although this did not result in fetal demise, there was evidence of in utero inflammation and fetal distress. Animals that were reinfected with an equivalent or higher dose of the same strain of Lm resulted in approximately half of cases continuing to term and half ending in fetal demise. These cases had inconsistent bacterial colonization of the fetal compartment, suggesting that Lm does not need to directly infect the placenta to cause adverse pregnancy outcomes. Timed surgical collection of tissues following inoculation demonstrated that transmission from mother to fetus can occur as soon as 5 days post-inoculation. Lastly, third trimester inoculation resulted in pregnancy loss in 3 out of 4 macaques, accompanied by characteristic pathology and Lm colonization. Collectively, our studies demonstrate that common laboratory culture tests may not always recover Lm despite known maternal ingestion. Notably, we also find it is possible for maternal infection to resolve in some cases with no discernible adverse outcome; however, such cases had evidence of a sterile intrauterine inflammatory response, with unknown consequences for fetal development.

Listeria monocytogenes in Brazilian foods: occurrence, risks to human health and their prevention

Listeria monocytogenes is a foodborne pathogen which occurs mainly in ready-to-eat food products, especially in artisanal products manufactured from raw milk such as some types of cheese, meat products and leafy vegetables. L. monocytogenes requires special attention in the food industry because of its ability to survive under adverse conditions and form biofilms on different surfaces in food processing environments. The potential for product contamination by L. monocytogenes strains in the industrial environment emphasizes the importance of preventive measures in the food industry. This review presents an overview on the main characteristics, pathogenicity and occurrence data of L. monocytogenes in Brazilian foods. The main prevention measures to avoid contamination by L. monocytogenes in foods are also highlighted, especially the adoption of quality assurance programs by the food industry.

Pregnancy-related listeriosis

About one in seven cases of listeriosis occurs in pregnant women, and, although listeriosis is rare, it is the third leading cause of death from food-borne infections. Pregnancy-related listeriosis increases the risk for fetal and neonatal mortality by approximately 21%. During pregnancy, infections are more likely to occur in the third trimester (66%) than the first trimester (3%). However, fetal and neonatal adverse effects are less common as gestational age increases or with older gestational age at birth. Pregnant women seem highly susceptible in some listeriosis outbreaks making up a large percentage of cases, whereas others contain very few. Whether this results from differences in strains of L. monocytogenes, exposures, or other factors remains to be determined. Food and Agriculture Organization of United Nations/World Health Organization (FAO/WHO) estimates the human lethal dose for 50% (LD₅₀ ) for fetal/neonatal loss is 1.9 × 10⁶ colony forming units (CFUs) L. monocytogenes. Animal models have been developed for pregnancy-related listeriosis showing similar susceptibility and clinical outcomes as in humans. Nonhuman primate and guinea pig animal models have similar (LD₅₀ ) values to the estimated human LD₅₀ . Additional animal studies are needed to understand the pathways leading to fetal and neonatal listeriosis in humans. More information is needed to understand dose response, to model risk for listeriosis at lower concentrations, and to determine why some pregnant women may be more susceptible than others. To better treat listeriosis during pregnancy, biomarkers for early diagnosis of listeriosis are also needed. Last, pregnant women need to be educated about avoiding high-risk foods, like Mexican-style cheese and ready-to-eat meats. Birth Defects Research 109:324-335, 2017.© 2017 Wiley Periodicals, Inc.

Targeting calpains: A novel immunomodulatory approach for microbial infections

Calpains are a family of Ca²⁺ dependent cytosolic non-lysosomal proteases with well conserved cysteine-rich domains for enzymatic activity. Due to their functional dependency on Ca²⁺ concentrations, they are involved in various cellular processes that are regulated by intracellular ca²⁺ concentration (i.e. embryo development, cell development and migration, maintenance of cellular architecture and structure etc.). Calpains are widely studied proteases in mammalian (i.e. mouse and human) physiology and pathophysiology due to their ubiquitous presence. For example, these proteases have been found to be involved in various inflammatory disorders such as neurodegeneration, cancer, brain and myocardial ischemia and infarction, cataract and muscular dystrophies etc. Besides their role in these sterile inflammatory conditions, calpains have also been shown to regulate a wide range of infectious diseases (i.e. sepsis, tuberculosis, gonorrhoea and bacillary dysentery etc.). One of these regulatory mechanisms mediated by calpains (i.e. calpain 1 and 2) during microbial infections involves the regulation of innate immune response, inflammation and cell death. Thus, the major emphasis of this review is to highlight the importance of calpains in the pathogenesis of various microbial (i.e. bacterial, fungal and viral) diseases and the use of calpain modulators as potential immunomodulators in microbial infections.

Prevalence and Persistence of Listeria monocytogenes in Ready-to-Eat Tilapia Sashimi Processing Plants

A 2-year study was performed at two ready-to-eat tilapia sashimi processing plants (A and B) to identify possible routes of contamination with Listeria monocytogenes during processing. Samples were collected from the aquaculture environments, transportation tanks, processing plants, and final products. Seventy-nine L. monocytogenes isolates were found in the processing environments and final products; 3.96% (50 of 1,264 samples) and 3.86% (29 of 752 samples) of the samples from plants A and B, respectively, were positive for L. monocytogenes . No L. monocytogenes was detected in the aquaculture environments or transportation tanks. The predominant L. monocytogenes serotypes were 1/2b (55.70%) and 4b (37.97%); serotypes 3b and 4e were detected at much lower percentages. At both plants, most processing sections were contaminated with L. monocytogenes before the start of processing, which indicated that the cleaning and sanitizing methods did not achieve adequate pathogen removal. Eleven seropulsotypes were revealed by pulsed-field gel electrophoresis and serotyping. Analysis of seropulsotype distribution revealed that the contamination was disseminated by the processing work; the same seropulsotypes were repeatedly found along the work flow line and in the final products. Specific seropulsotypes were persistently found during different sampling periods, which suggests that the sanitation procedures or equipment used at these plants were inadequate. Plant staff should improve the sanitation procedures and equipment to reduce the risk of L. monocytogenes cross-contamination and ensure the safety of ready-to-eat tilapia products.

Strategies Used by Bacteria to Grow in Macrophages

Intracellular bacteria are often clinically relevant pathogens that infect virtually every cell type found in host organisms. However, myeloid cells, especially macrophages, constitute the primary cells targeted by most species of intracellular bacteria. Paradoxically, macrophages possess an extensive antimicrobial arsenal and are efficient at killing microbes. In addition to their ability to detect and signal the presence of pathogens, macrophages sequester and digest microorganisms using the phagolysosomal and autophagy pathways or, ultimately, eliminate themselves through the induction of programmed cell death. Consequently, intracellular bacteria influence numerous host processes and deploy sophisticated strategies to replicate within these host cells. Although most intracellular bacteria have a unique intracellular life cycle, these pathogens are broadly categorized into intravacuolar and cytosolic bacteria. Following phagocytosis, intravacuolar bacteria reside in the host endomembrane system and, to some extent, are protected from the host cytosolic innate immune defenses. However, the intravacuolar lifestyle requires the generation and maintenance of unique specialized bacteria-containing vacuoles and involves a complex network of host-pathogen interactions. Conversely, cytosolic bacteria escape the phagolysosomal pathway and thrive in the nutrient-rich cytosol despite the presence of host cell-autonomous defenses. The understanding of host-pathogen interactions involved in the pathogenesis of intracellular bacteria will continue to provide mechanistic insights into basic cellular processes and may lead to the discovery of novel therapeutics targeting infectious and inflammatory diseases.

Lmo0171, a novel internalin-like protein, determines cell morphology of Listeria monocytogenes and its ability to invade human cell lines

Internalins comprise a class of Listeria monocytogenes proteins responsible for activation of signalling pathways leading to phagocytic uptake of the bacterium by the host cell. In this paper, a possible role of Lmo0171-a new member of the internalin family was investigated. Disruption of the lmo0171 gene resulted in important cell morphology alterations along with a decrease in the ability to invade three eukaryotic cell lines, that is Int407, Hep-2 and HeLa and diminished adhesion efficiency to int407, thereby suggesting bifunctionality of the newly characterised Lmo0171 internalin.

Pregnancy-related listeriosis in France, 1984 to 2011, with a focus on 606 cases from 1999 to 2011

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Stress response and adaptation of Listeria monocytogenes 08-5923 exposed to a sublethal dose of carnocyclin A

Carnocyclin A (CCLA) is an antimicrobial peptide produced by Carnobacterium maltaromaticum ATCC PTA-5313, which can be used to control the growth of Listeria monocytogenes in ready-to-eat meat products. The aim of this research was to elucidate the cellular responses of L. monocytogenes 08-5923 exposed to a sublethal dose of CCLA. Microarray, quantitative reverse transcription-PCR, tandem mass spectrometry, and electron microscopy were used to investigate the alteration in gene expression, protein production, and morphological changes in cells of Listeria following treatment with CCLA. The genes involved in metabolism (baiE, trn, and pykA), cell wall synthesis (murZ and dacB2), and cell division (clpE and divIVA) were upregulated following a 15-min exposure to CCLA as a result of stress responses. Genes involved in cell division, cell wall synthesis, flagellar synthesis, and metabolism were downregulated after 4 h as a result of adaptation. Analysis of total soluble proteins confirmed the downregulation of pykA and gnd after 4 h of exposure to CCLA. The absence of flagella was observed in L. monocytogenes following 30 h of exposure to CCLA. A sublethal dose of CCLA induced adaptation in L. monocytogenes 08-5923 by inhibition of expression of genes and proteins critical for synthesis of cell wall structures and maintaining metabolic functions. Both the mannose- and cellobiose-specific phosphotransferase systems could be targets for CCLA.

Pregnancy-associated listeriosis in England and Wales

Listeriosis is a rare but severe foodborne disease with low morbidity and high case-fatality rates. Pregnant women, unborn and newborn babies are among the high-risk groups for listeriosis. We examined listeriosis cases reported to the enhanced surveillance system in England and Wales from 1990 to 2010 to identify risk factors influencing outcome. Cases were defined as pregnancy-associated if Listeria monocytogenes was isolated from a pregnant woman or newborn infants aged <28 days. Of the 3088 cases reported, pregnancy-associated listeriosis accounted for 462 (15%) cases and 315 cases resulted in a live birth. Several factors were identified as affecting the severity and outcome of listeriosis in pregnancy in both mother and child including: presence or absence of maternal symptoms, gestational age at onset of symptoms, and clinical presentation in the infant (meningitis or septicaemia). Deprivation, ethnicity and molecular serotype had no effect on outcome.

Acute oral safety study of sodium caseinate glycosylated via maillard reaction with galactose in rats

In order to potentially use sodium caseinate (SC) glycated with galactose (Gal) in the food industry as a new functional ingredient with proved technological and biological properties, an evaluation of oral acute toxicity has been carried out. An acute safety study with SC-Gal glycoconjugates in the Wistar rat with a single oral gavage dose of 2,000 mg/kg of body weight was conducted. The SC-Gal glycoconjugates were well tolerated; no adverse effects or mortality was observed during the 2-week observation period. No abnormal signs, behavioral changes, body weight changes, or alterations in food and water consumption occurred. After this period, no changes in hematological and serum chemistry parameters, organ weights, or gross pathology or histopathology were detected. It was concluded that SC-Gal glycoconjugates obtained via the Maillard reaction were well tolerated in rats at an acute oral dose of 2,000 mg/kg of body weight. The SC-Gal glycoconjugates have a low order of acute toxicity, and the oral 50 % lethal dose for male and female rats is in excess of 2,000 mg/kg of body weight.

Behavioral risk factors associated with listeriosis in the home: a review of consumer food safety studies

Listeria monocytogenes causes human listeriosis, which is associated with the highest hospitalization and mortality rates of all foodborne illnesses. In recent years, the incidence of listeriosis has doubled in Europe, almost exclusively among older adults (≥ 60 years of age). Food safety factors associated with increased risk of listeriosis include lack of adherence to "use by" dates and ineffective refrigerated storage of foods. Consequently, older adult consumers' implementation of safe food practices should be evaluated. This article is a review of consumer food safety cognitive and behavioral data relating to risk factors associated with listeriosis in the home as reported in 165 consumer food safety studies. Overall, only 41% of studies included assessment of consumer cognitive or behavioral data associated with listeriosis; of these studies 59% included data on safe refrigeration, 54% included data on storage time for opened ready-to-eat foods, and 49% included data on adherence to use-by dates. In most (83%) of the studies, survey-based data collection methods (questionnaires/interviews) were used; thus, the majority of findings were based on self-report (74%) and knowledge (44%). Observation (31%) and focus groups (12%) were less commonly used, resulting in a lack of actual behaviors and attitudinal data relating to listeriosis risk factors. Only 7% of studies included food safety data for older adults. Although older adults may fail to implement recommended practices, this review reveals a need for in-depth research to determine food safety attitudes and actual behaviors of older adults in conjunction with knowledge and selfreport of practices linked to increased risks of listeriosis. Such data combined with review findings would inform targeted food safety education to reduce risks associated with listeriosis in the home.

An internalin a probe-based genosensor for Listeria monocytogenes detection and differentiation

Internalin A (InlA), a protein required for Listeria monocytogenes virulence, is encoded by the inlA gene, which is only found in pathogenic strains of this genus. One of the best ways to detect and confirm the pathogenicity of the strain is the detection of one of the virulence factors produced by the microorganism. This paper focuses on the design of an electrochemical genosensor used to detect the inlA gene in Listeria strains without labelling the target DNA. The electrochemical sensor was obtained by immobilising an inlA gene probe (single-stranded oligonucleotide) on the surfaces of screen-printed gold electrodes (Au-SPEs) by means of a mercaptan-activated self-assembled monolayer (SAM). The hybridisation reaction occurring on the electrode surface was electrochemically transduced by differential pulse voltammetry (DPV) using methylene blue (MB) as an indicator. The covalently immobilised single-stranded DNA was able to selectively hybridise to its complementary DNA sequences in solution to form double-stranded DNA on the gold surface. A significant decrease of the peak current of the voltammogram (DPV) upon hybridisation of immobilised ssDNA was recorded. Whole DNA samples of L. monocytogenes strains could be discriminated from other nonpathogenic Listeria species DNA with the inlA gene DNA probe genosensor.

Growth and filamentation of cold-adapted, log-phase Listeria monocytogenes exposed to salt, acid, or alkali stress at 3°C

In Canada, there is a zero tolerance for Listeria in a 125-g sample of product in which growth of Listeria monocytogenes can occur, and a limit of ≤100 CFU/g in ready-to-eat (RTE) food products that support limited growth during the stated shelf life and/or RTE refrigerated foods with a shelf life of ≤5 days. L. monocytogenes can form filaments in response to pH and osmotic, atmospheric, and temperature stress, which can result in an underestimation of the risk of RTE foods as filaments form single colonies on plate count agars but can divide into individual cells once the stress is removed. The objective was to investigate the filamentation characteristics of three strains of L. monocytogenes exposed to saline, acidic, basic, and simultaneous acidic and saline environments at 3°C. After 4 days at 3°C, log-phase cells grown in tryptic soy broth (TSB) were longer than cells grown at 15°C, and 68% of cells were below the reference value of the 90th percentile of control cultures. When cultures growing at 3°C were exposed to additional stresses, increases in the proportion and length of filaments in the population were observed, while increases in log CFU per milliliter were reduced. After 4 days of incubation at 3°C, the log CFU per milliliter of L. monocytogenes increased by 1.1 U in TSB and 0.4 to 0.5 U in TSB with 4% NaCl, TSB with a pH of 6.0 with 4% NaCl, and TSB with a pH of 5.5. Moreover, the longest 10% of cells were 6.4 to 8.5 times longer than control cells, and only 20 to 30% of cells were below the reference value. Cultures grown in TSB at pH 6.0 with 4% NaCl experienced more sustained filamentation than cultures grown in TSB with 4% NaCl, but less than cultures grown in TSB at pH 6.0. The mechanism involved in filamentation could be different for cells exposed to NaCl than exposed to acid, and additional stress might not necessarily result in more extensive filament formation. These findings contribute to a better understanding of the widespread potential of filament formation and the potential implications for food safety.

Control of Listeria monocytogenes and spoilage bacteria on smoked salmon during storage at 5 °C after X-ray irradiation

In this study, smoked salmon fillets were artificially inoculated with Listeria monocytogenes (3.7 ± 0.2 log CFU g(-1)) and treated with X-ray irradiation generated by a RS 2400 X-ray machine (Rad Source Technologies Inc.) using doses of 0.0, 0.1, 0.5, 1.0, and 2.0 kGy. Unirradiated and irradiated samples were then stored at 5 °C for 35 days and tested for L. monocytogenes count after 0, 5, 10, 15, 20, 25, 30, and 35 days. Also, uninoculated-untreated and uninoculated-treated samples with the lowest and highest X-ray doses (0.1 and 2.0 kGy) were stored at 5 °C and examined for psychrotrophs and mesophiles counts after 0, 5, 10, 15, 20, 25, 30, and 35 days. The initial L. monocytogenes population (3.7 log CFU g(-1) ) was significantly (p < 0.05) reduced to an undetectable level (<1.0 log CFU g(-1)) by treatment with 1.0 kGy X-ray. Treatment with 0.1 kGy X-ray significantly reduced the initial psychrotrophs and mesophiles counts from 5.3 and 3.0 to 3.3 and 2.3, respectively. However, L. monocytogenes, psychrotrophs and mesophiles counts were gradually increased during storage. Treatment with 2.0 kGy X-ray kept the L. monocytogenes population under detectable level until 35 days. Treatment with 2.0 kGy X-ray kept the mesophiles and psychrotrophs counts within the acceptable level until 35 days. These results revealed that treatment with X-ray irradiation can significantly reduce the risk of listeriosis and extend the shelf life of smoked salmon during storage at 5 °C.

Listeria monocytogenes strains selected on ciprofloxacin or the disinfectant benzalkonium chloride exhibit reduced susceptibility to ciprofloxacin, gentamicin, benzalkonium chloride, and other toxic compounds

Listeria monocytogenes is a leading agent for severe food-borne illness and death in the United States and other nations. Even though drug resistance has not yet threatened therapeutic interventions for listeriosis, selective pressure associated with exposure to antibiotics and disinfectants may result in reduced susceptibility to these agents. In this study, selection of several L. monocytogenes strains on either ciprofloxacin (2 μg/ml) or the quaternary ammonium disinfectant benzalkonium chloride (BC; 10 μg/ml) led to derivatives with increased MICs not only to these agents but also to several other toxic compounds, including gentamicin, the dye ethidium bromide, and the chemotherapeutic drug tetraphenylphosphonium chloride. The spectrum of compounds to which these derivatives exhibited reduced susceptibility was the same regardless of whether they were selected on ciprofloxacin or on BC. Inclusion of strains harboring the large plasmid pLM80 revealed that MICs to ciprofloxacin and gentamicin did not differ between the parental and plasmid-cured strains. However, ciprofloxacin-selected derivatives of pLM80-harboring strains had higher MICs than those derived from the plasmid-cured strains. Susceptibility to the antimicrobials was partially restored in the presence of the potent efflux inhibitor reserpine. Taken together, these data suggest that mutations in efflux systems are responsible for the multidrug resistance phenotype of strains selected on ciprofloxacin or BC.

Inhibition of growth of pathogenic bacteria in raw milk by legume protein esters

Protein isolates from soybean and chickpea, as well as their methylated esters, were tested for their inhibitory action against the propagation of pathogenic bacteria in raw milk during its storage either at room temperature or under refrigeration. Raw milk was inoculated with a mixed culture of Listeria monocytogenes Scott A and Salmonella enterica serovar Enteritidis strain PT4 at ca. 2 log CFU ml⁻¹. Aerobic plate count, coliform count, and presumptive E. coli in raw milk treated with esterified legume proteins were inhibited by 2 to 3 log relative to a control after 6 to 8 days of storage at 4°C. At room temperature, bacterial populations (aerobic plate count, coliform count, and presumptive E. coli) in raw milk treated with esterified legume proteins were inhibited by ca. 1.5 to 1.6 log relative to the control after 12 h. Supplementation of raw milk with esterified soybean protein could significantly inhibit the counts of the two inoculated pathogens (L. monocytogenes Scott A and Salmonella Enteritidis PT4), which were initially inoculated at ca. 2 log CFU ml⁻¹, by ca. 2.4 log and 1.6 log CFU ml⁻¹, respectively, on day 8 of storage under cold conditions. Corresponding reductions amounting to 2.7 and 1.8 log CFU ml⁻¹ were observed after 12 h of storage at room temperature. Supplementation of raw milk with esterified soybean protein (0.5%) reduced the maximum level of titratable acidity to 0.21 and maintained the pH level at 6.4 after 8 days of storage under cold conditions as compared with 4 days for untreated raw milk. Similar results were observed when raw milk was stored at room temperature for 10 h.

LISTERIA MONOCYTOGENES: OCORRÊNCIA EM PRODUTOS LÁCTEOS E SUAS IMPLICAÇÕES EM SAÚDE PÚBLICA

RESUMO Listeria monocytogenes é o agente causador da listeriose, uma grave doença de origem alimentar que causa severas infecções em humanos com altas taxas de mortalidade. O leite e seus derivados estão entre os produtos alimentícios mais frequentemente envolvidos na transmissão de L. monocytogenes. A listeriose acomete, sobretudo, indivíduos imunodeprimidos, grávidas, recém-nascidos e idosos, o que ressalta o caráter oportunista deste micro-organismo e sua importância para a saúde pública. No presente trabalho, faz-se uma revisão narrativa crítica sobre o risco à saúde humana decorrente da ingestão de leite e derivados contaminados por L. monocytogenes, bem como se discutem os fatores que determinam a contaminação por L. monocytogenes na cadeia de produção e distribuição de leite e derivados. São apresentados e avaliados os dados de ocorrência de L. monocytogenes em leite cru e em produtos lácteos no Brasil, tendo em vista seu potencial de envolvimento em casos de listeriose humana. Adicionalmente, são indicadas as principais áreas de pesquisa e atuação para prevenir a contaminação de L. monocytogenes em produtos lácteos.

Incidence and persistence of Listeria monocytogenes in the catfish processing environment and fresh fillets

Incidence of Listeria spp. in whole raw catfish, catfish fillets, and processing environments from two catfish processing facilities was determined in August 2008 and August 2009. Thirty-nine (18.4%) of 212 samples collected in August 2008 were positive for Listeria monocytogenes. Prevalences of Listeria species L. innocua and L. seeligeri-L. welshimeri-L. ivanovii were 11.3 and 23.6%, respectively. Of 209 samples collected in August 2009, 12.4% were positive for L. monocytogenes, 11% for L. innocua, and 19.6% for L. seeligeri-L. welshimeri-L. ivanovii. No Listeria grayi was detected in any of the samples. L. monocytogenes was not found in catfish skins and intestines, but was detected in catfish fillets, on food contact surfaces, and on non-food contact surfaces with frequencies of 45.0, 12.0, and 11.1%, respectively. In August 2008 isolates, serotypes 1/2b (62.2%) and 3b (15.6%) were frequently isolated, whereas the majority of the August 2009 isolates (92.3%) were serotype 1/2b. Genotyping analyses revealed that some genotypes of L. monocytogenes isolates were detected in one facility even after a year, but no persistence of L. monocytogenes was observed in the other facility. In addition, some L. monocytogenes isolates from fresh fillets showed genotypes that were either identical, or more than 90% similar, to those of L. monocytogenes isolates from food contact surfaces in the processing lines. The results of this study suggest that processing environment rather than whole raw catfish is an important source of L. monocytogenes contamination in the catfish fillets. These results should assist the catfish industry to develop better control and prevention strategies for L. monocytogenes.

Pregnancy-associated listeriosis

Infection by Listeria monocytogenes in pregnant women may result in fetal loss or invasive disease in the newborn. We examined listeriosis cases reported through the U.S. Listeria Initiative during 2004-2007. Cases were classified as pregnancy-associated if illness occurred in a pregnant woman or an infant aged <28 days. Of 758 reported Listeria cases, 128 (16.9%) were pregnancy-associated. Maternal infection resulted in four neonatal deaths and 26 (20.3%) fetal losses. Invasive illnesses in newborns (n=85) were meningitis (32.9%) and sepsis (36.5%). Pregnant women with Listeria were more likely to report Hispanic ethnicity (52.8% vs. 25.6%, respectively; OR 3.3 95% CI 2.2-4.8) than mothers giving live birth in the USA during 2005 and were more likely to report consumption of Mexican-style cheese (OR 2.6, 95% CI 1.6-4.2) than were non-pregnant patients with Listeria infection. Pregnant woman comprised a considerable proportion of reported listeriosis cases. Further declines in pregnancy-associated listeriosis will require education about avoiding high-risk foods, and continued regulatory and industry efforts to decrease Listeria in foods.

Interference of raw milk autochthonous microbiota on the performance of conventional methodologies for Listeria monocytogenes and Salmonella spp. detection

Pathogen detection in foods by reliable methodologies is very important to guarantee microbiological safety. However, peculiar characteristics of certain foods, such as autochthonous microbiota, can directly influence pathogen development and detection. With the objective of verifying the performance of the official analytical methodologies for the isolation of Listeria monocytogenes and Salmonella in milk, different concentrations of these pathogens were inoculated in raw milk treatments with different levels of mesophilic aerobes, and then submitted to the traditional isolation procedures for the inoculated pathogens. Listeria monocytogenes was inoculated at the range of 0.2-5.2 log CFU/mL in treatments with 1.8-8.2 log CFU/mL. Salmonella Enteritidis was inoculated at 0.9-3.9 log CFU/mL in treatments with 3.0-8.2logCFU/mL. The results indicated that recovery was not possible or was more difficult in the treatments with high counts of mesophilic aerobes and low levels of the pathogens, indicating interference of raw milk autochthonous microbiota. This interference was more evident for L. monocytogenes, once the pathogen recovery was not possible in treatments with mesophilic aerobes up to 4.0 log CFU/mL and inoculum under 2.0 log CFU/mL. For S. Enteritidis the interference appeared to be more non-specific.

Listeriosis in Norway 1977–2003

In Europe, the incidence of invasive listeriosis has increased substantially during the last decades. We here present data from 289 listeriosis cases reported in Norway during the period 1977-2003, of which 12 cases were associated with 2 outbreaks and 39 cases were pregnancy-related. Medical records were obtained from 209 cases with listeriosis reported in 1977-2000. While the incidence of pregnancy-related listeriosis has remained stable at an average rate of 34 per million pregnant women per y during the period, the incidence of sporadic, non-pregnancy-related cases has increased from 1.1 to 3.7 per million per y. The present Norwegian incidence of reported cases is lower than in Denmark, but the case fatality rate is higher, indicating a possible under-reporting of mild listeriosis cases in Norway. We discuss how preventive measures, case identification and surveillance may have influenced listeriosis incidence in Norway.