An outbreak of febrile gastroenteritis associated with corn contaminated by Listeria monocytogenes

Enhanced surveillance of invasive listeriosis in the Lombardy region, Italy, in the years 2006-2010 reveals major clones and an increase in serotype 1/2a

BACKGROUND

Invasive listeriosis is a rare, life-threatening foodborne disease. Lombardy, an Italian region accounting for 16% of the total population, reported 55% of all listeriosis cases in the years 2006-2010. The aim of our study was to provide a snapshot of listeriosis epidemiology in this region after the implementation of a voluntary laboratory-based surveillance system.

METHODS

We characterized by serotyping, pulsed-field gel electrophoresis, multilocus sequence typing and detection of epidemic clone markers, 134 isolates from 132 listeriosis cases, including 15 pregnancy-related cases, occurring in the years 2006-2010 in Lombardy. Demographic and clinical characteristics of cases have also been described.

RESULTS

The mean age of non pregnancy-associated cases was 64.7 years, with 55.9% of cases being older than 65 years. Cases having no underlying medical conditions accounted for 11.6%. The all-cause fatality rate of 83 cases with a known survival outcome was 25.3%.Serotypes 1/2a and 4b comprised 52.2% and 38.8% of isolates, respectively. Seventy-three AscI pulsotypes and 25 sequence types assigned to 23 clonal complexes were recognized. Moreover, 53 (39.5%) isolates tested positive for the epidemic clone markers. Twelve molecular subtype clusters including at least three isolates were detected, with cluster 11 (1/2a/ST38) including 31 isolates identified during the entire study period. No outbreaks were notified to public health authorities during this period.

CONCLUSIONS

The findings of our study proved that epidemiology of listeriosis in Lombardy is characterized by a high prevalence of major clones and the increasing role of serotype 1/2a. Molecular subtyping is an essential tool in the epidemiology and surveillance of listeriosis. Rapid molecular cluster detection could alert about putative outbreaks, thus increasing the chance of detecting and inactivating routes of transmission.

What is the incubation period for listeriosis?

BACKGROUND

Listeriosis is a foodborne infection with a low incidence but a high case fatality rate. Unlike common foodborne diseases, the incubation period can be long. The first incubation periods were documented during a large listeriosis outbreak published in 1987 by Linnan and al. in the New England Journal of Medicine (range: 3 days to 70 days). Data on the incubation period of listeriosis are scarce. Our study aim was to estimate precisely the incubation period of listeriosis using available data since 1987.

METHODS

We estimated the incubation period of listeriosis using available published data and data from outbreak investigations carried out by the French National Institute for Public Health Surveillance. We selected cases with an incubation period calculated when a patient had a single exposure to a confirmed food source contaminated by Listeria monocytogenes.

RESULTS

We identified 37 cases of invasive listeriosis (10 cases with central nervous system involvement (CNS cases), 15 bacteraemia cases and 12 pregnancy-associated cases) and 9 outbreaks with gastroenteritis. The overall median incubation period of invasive listeriosis was 8 days (range: 1-67 days) and differed significantly by clinical form of the disease (p<0.0001). A longer incubation period was observed for pregnancy-associated cases (median: 27.5 days; range: 17-67 days) than for CNS cases (median: 9 days; range: 1-14 days) and for bacteraemia cases (median: 2 days; range: 1-12 days). For gastroenteritis cases, the median incubation period was 24 hours with variation from 6 to 240 hours.

CONCLUSIONS

This information has implications for the investigation of food borne listeriosis outbreaks as the incubation period is used to determine the time period for which a food history is collected. We believe that, for listeriosis outbreaks, adapting the exposure window for documenting patients' food histories in accordance with the clinical form of infection will facilitate the identification of food products as the source of contamination. We therefore propose to take an exposure window of 14 days before the diagnosis for CNS and bacteraemia cases, and of 6 weeks before the diagnosis, for pregnancy-associated cases.

Recent developments in molecular sub-typing of Listeria monocytogenes

As a vast majority of the human listeriosis cases are caused by serotypes 1/2a, 1/2b and 4b strains, it is imperative that strains from clinical as well as from food and environment are further characterised so that accurate and timely epidemiological determination of sources of the contamination can be established to minimise the disease burden. Recent developments in the field of genomics provide a great opportunity to use these tools towards the development of molecular sub-typing techniques with a greater degree of discrimination spanning the entire length of the genome. This brief review summarises a few of these DNA-based techniques with an emphasis on DNA microarray and other whole genome sequencing-based approaches and their usefulness in Listeria monocytogenes sub-typing and outbreak investigations.

Genetic diversity and molecular typing of Listeria monocytogenes in China

BACKGROUND

Listeria monocytogenes can cause invasive diseases in humans and farm animals and is frequently isolated from dairy products and poultry. Listeriosis is uncommon in China but L. monocytogenes has been isolated from foods and food processing environments in China. However little is known of genetic diversity of Chinese L. monocytogenes isolates and their relationships with global isolates.

RESULTS

Two hundred and twelve isolates of L. monocytogenes from food sources from 12 provinces/cities in China were analysed by serotyping, Pulsed Field Gel Electrophoresis (PFGE) and Multi-locus Sequence Typing (MLST). The predominant serotypes are 1/2a, 1/2b and 1/2c accounting for 90.1% of the isolates. PFGE divided the isolates into 61 pulse types (PTs). Twenty nine PTs were represented by more than one isolates with PT GX6A16.0004 containing the most number of isolates. MLST differentiated the isolates into 36 STs, among which 15 were novel. The 3 most common STs were ST9 (29.1%), ST8 (10.7%) and ST87 (9.2%), accounting for 49.0% of the isolates.

CONCLUSIONS

STs prevalent in other parts of the world are also prevalent in China including 7 STs (ST1-ST3, ST5, ST6, ST8, ST9) which caused maternal fetal infections or outbreaks, suggesting that these STs potentially can also cause severe human infections or outbreaks in China. Surveillance of these STs will provide important information for prevention of listeriosis. This study also enhances our understanding of genetic diversity of L. monocytogenes in China.

Hyperinduction of host beta interferon by a Listeria monocytogenes strain naturally overexpressing the multidrug efflux pump MdrT

Many pathogens regulate or modify their immune-stimulating ligands to avoid detection by their infected hosts. Listeria monocytogenes, a facultative intracellular bacterial pathogen, interacts with multiple components of mammalian innate immunity during its infection cycle. During replication within the cytosol of infected cells, L. monocytogenes utilizes two multidrug efflux pumps, MdrM and MdrT, to secrete the small nucleic acid second messenger cyclic-di-AMP (c-di-AMP). Host recognition of c-di-AMP triggers the production of type I interferons, including beta interferon (IFN-β), which, surprisingly, promote L. monocytogenes virulence. In this study, we have examined the capacity of multiple laboratory and clinical isolates of L. monocytogenes to stimulate host production of IFN-β. We have identified the L. monocytogenes strain LO28 as able to hyperinduce IFN-β production in infected cells ∼30-fold more than the common laboratory clone L. monocytogenes strain 10403S. Genomic analyses determined that LO28 contains a naturally occurring loss-of-function allele of the transcriptional regulator BrtA and correspondingly derepresses expression of MdrT. Surprisingly, while derepression of MdrT resulted in hyperstimulation of IFN-β, it results in significant attenuation in multiple mouse models of infection. While type I interferons may promote L. monocytogenes virulence, this study demonstrates that unregulated expression of the c-di-AMP-secreting efflux pump MdrT significantly restricts virulence in vivo by an unknown mechanism.

Detection of Listeria monocytogenes in ready-to-eat food by Step One real-time polymerase chain reaction

The aim of this study was to follow contamination of ready-to-eat food with Listeria monocytogenes by using the Step One real time polymerase chain reaction (PCR). We used the PrepSEQ Rapid Spin Sample Preparation Kit for isolation of DNA and MicroSEQ® Listeria monocytogenes Detection Kit for the real-time PCR performance. In 30 samples of ready-to-eat milk and meat products without incubation we detected strains of Listeria monocytogenes in five samples (swabs). Internal positive control (IPC) was positive in all samples. Our results indicated that the real-time PCR assay developed in this study could sensitively detect Listeria monocytogenes in ready-to-eat food without incubation.

Complete genome sequence of the animal pathogen Listeria ivanovii, which provides insights into host specificities and evolution of the genus Listeria

We report the complete and annotated genome sequence of the animal pathogen Listeria ivanovii subsp. ivanovii strain PAM 55 (serotype 5), isolated in 1997 in Spain from an outbreak of abortion in sheep. The sequence and its analysis are available at an interactive genome browser at the Institut Pasteur (http://genolist.pasteur.fr/LivaList/).

Listeria monocytogenes-associated joint and bone infections: a study of 43 consecutive cases

BACKGROUND

Little is known about Listeria monocytogenes-associated bone and joint infections. Only case reports of this infection have been published.

METHODS

Retrospective study of culture-proven bone and joint cases reported to the French National Reference Center for Listeria from 1992 to 2010.

RESULTS

Forty-three patients were studied: 61% were men, and the median age was 72 (range, 16-89); 24 patients exhibited comorbidities (56%). Thirty-six patients (84%) had orthopedic implant devices: prosthetic joints (n = 34) or internal fixation (n = 2); the median time after insertion was 9 years (0.1-22). Subacute infection was more frequent (median, 4 weeks [range, 2-100], 74%) than acute infection (<7 days, 23%), with nonspecific clinical features; 45% of patients had no fever. Blood cultures were positive in 3 of 19 cases. Isolate polymerase chain reaction genogrouping revealed 4 patterns: IVb (21 of 42, 50%), IIa (17 of 42, 40%), IIb (2 of 42, 5%), and IIc (2 of 42, 5%). Five groups of strains with similar pulsotype patterns were identified without an epidemiological link. Antibiotics, primarily amoxicillin (80%) with aminoglycosides (48%), were prescribed for a median duration of 15 weeks (range, 2-88). Eighteen patients (50%) underwent prosthesis replacement; all were successful after median follow-up of 10 months (range, 1-75). Five of 13 patients for whom material was not removed had protracted infection despite prolonged antibiotherapy; 3 of these patients later underwent prosthesis replacement with sustained recovery.

CONCLUSIONS

Osteoarticular listeriosis primarily involves prosthetic joints and occurs in immunocompromised patients. It requires intensive treatment with antibiotherapy and usually requires implant removal or replacement for cure.

Listeria monocytogenes infection of the alimentary tract (enteric listeriosis) of sheep in New Zealand

A retrospective study of the microscopical lesions of nine cases of enteric listeriosis of sheep was conducted. Lesions were present variably in the abomasum and the small and large intestines. The inflammation was multifocal to extensive, mainly neutrophilic and involved the lamina propria, muscularis mucosa and superficial submucosa, with intense focus on the muscularis mucosa. The mesenteric lymph nodes were also affected and, in some sheep, the liver. Large numbers of gram-positive rods were demonstrated within areas of inflammation in the gastrointestinal tract and mesenteric lymph nodes and Listeria spp. were identified immunohistochemically in these lesions. Ultrastructurally, bacteria were found free within the cytoplasm of myofibres of the muscularis mucosa.

Amoxicillin-bearing microparticles: potential in the treatment of Listeria monocytogenes infection in Swiss albino mice

The present study was aimed at evaluating the effectiveness of amoxicillin-bearing HSA (human serum albumin) and PLGA [poly(lactic-co-glycolic acid)] microparticles in combating Listeria monocytogenes infection in Swiss albino mice. Amoxicillin-bearing HSA microspheres were prepared by chemical cross-linking of a drug/albumin mixture with glutaraldehyde, and PLGA microspheres were prepared by the W/O/W (water-in-oil-in-water) emulsion technique. The microspheres were characterized for their size, ζ potential and entrapment efficiency using SEM (scanning electron microscopy) and a Zetasizer. Release kinetics was performed in a phosphate buffer (pH 7.4) at 37°C simulating physiological conditions. Bacterial burden in various vital organs and survival data established enhanced efficacy of PLGA and HSA microspheres as compared with free drug. Among the two delivery systems, PLGA microspheres, when compared with HSA microspheres, imparted better efficacy in terms of reduction in bacterial load as well as increase in survival. The results of the present study clearly demonstrate that microparticles successfully target the infected macrophages and the approach could be well exploited for targeting the intracellular pathogens as well.

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.

Defining causality in emerging agents of acute bacterial diarrheas: a step beyond the Koch’s postulates

Diarrheal illnesses account for significant morbidity and mortality worldwide. Most cases of diarrhea are caused by bacteria, viruses or parasites. Advances in molecular biology and epidemiology have allowed the identification of emerging pathogens that may cause or, at least, may be associated with diarrhea. However, the same advances have also revealed the complexity of the gut microbiome, suggesting that a potential agent of diarrhea may also been found in healthy individuals. In addition, most of the newly identified emerging agents of diarrhea are ubiquitous and have not yet fulfilled Koch’s postulates. Research investigations should address appropriate matched controls and integrate findings from medical microbiology, epidemiology and molecular biology. This integrative approach should provide insights to our knowledge regarding exposition to common source or risk factors. Here, we aim to review some of these emerging bacterial agents of diarrheas and propose guidelines or prescriptions that may help in defining causality.

Isolation and characterization of Listeria monocytogenes and other Listeria species in foods of animal origin in Addis Ababa, Ethiopia

Listeriosis is a disease of humans and animals, in which it is one of the important emerging bacterial zoonotic diseases worldwide. Among the different species of the genus Listeria, Listeria monocytogenes (L. monocytogenes) is known to cause listeriosis in humans and animals with low incidence but high case fatality rate. Information on the occurrence and distribution of L. monocytogenes and other Listeria species is very limited both in the veterinary and public health sectors in Ethiopia. The objective of this study was to isolate and characterize L. monocytogenes and other Listeria species from foods of animal origin (cottage cheese, raw beef, raw milk and liquid whole egg) in Addis Ababa, Ethiopia. A total of 391 food samples of animal origin were collected randomly, using a cross-sectional study design from November 2008 to March 2009. L. monocytogenes isolation and characterization were performed according to mainly the United States Food and Drug Administration procedures. Of the samples examined, 102 (26.1%) were found to be positive for Listeria. Listeria species were isolated in 39 (51.3%), 37 (32.2%), 22 (22%) and 4 (4%) of the raw beef, liquid whole egg, raw milk and cottage cheese samples respectively. L. monocytogenes was detected in 5.4% of the samples analyzed. It was isolated mainly from raw milk (13%) and liquid whole egg (4.3%) followed by raw beef (2.6%) and cottage cheese (1%). In addition to L. monocytogenes, other Listeria species were identified as L. innocua (60.8%), L. welshimeri (6.9%), L. seeligeri (3.9%), L. murrayi (2.9%) and L. grayi (2.9%) and L. ivanovii (1.9%). It was shown that L. monocytogenes and other Listeria species are widely spread in occurrence in foods of animal origin in Addis Ababa, Ethiopia.

Listeria monocytogenes infection in the over-60s in England between 2005 and 2008: a retrospective case-control study utilizing market research panel data

A retrospective case-control study of listeriosis in patients in England aged over 60 years is described. The incidence of listeriosis in patients aged ≥60 years in England has doubled since 2001; hence, the investigation of risk factors for infection in this group is important to inform on prevention and control. Standardized epidemiological information has been sought on cases since 2005, but the value of the data accrued is limited without some perception of exposure prevalence in the population at risk of listeriosis. The exposures of listeriosis cases aged ≥60 years reported in England from 2005 to 2008 were compared to those of market research panel members representing the same population (i.e., residents of England aged ≥60 years) and time period. Exposures were grouped to facilitate comparison. Odds ratios and 95% confidence intervals were calculated. Cases were more likely than panel members to report the consumption of cooked meats (beef and ham/pork, but not poultry), cooked fish (specifically smoked salmon) and shellfish (prawns), dairy products (most noticeably milk but also certain cheeses), and mixed salads. They were less likely to report the consumption of other forms of seafood, dairy spread, other forms of dairy, sandwiches, and fresh vegetables. The diversity of high-risk food exposures reflects the ubiquity of the microorganism in the environment and/or the susceptibility of those at risk, and suggests that a wider variety of foods can give rise to listeriosis. Food safety advice on avoiding listeriosis should be adapted accordingly. While not inexpensive, the application of market research data to infectious disease epidemiology can add value to routine surveillance data.

Anti-listerial compounds from Asari Radix

Asari Radix, the roots of Asarum heterotropoides F. Maekawa var. manshuricum F. Maekawa or A. sieboldii F. Maekawa, has traditionally been used for the treatment of various infectious diseases. Since its MeOH extract inhibited the growth of Listeria monocytogenes in a preliminary test, the aim of this study was to isolate and identify the anti-listerial compounds from the plant. Activity-guided fractionation led to the isolation of seven compounds 1-7 from the MeOH extract, and their chemical structures were identified by comparison of the spectroscopic data with those in the literature. Compounds 1-7 exhibited inhibitory activity against all five tested strains of L. monocytogenes with diameter of inhibition zones ranging from 7 to 11 mm in the agar disc diffusion method. Compounds 1-3 and 7 demonstrated potent antimicrobial effects on the L. monocytogenes strains, with MICs between 62.5 and 125 μg/mL. This is the first report that AR possesses inhibitory activity against L. monocytogenes.

Probing the pan-genome of Listeria monocytogenes: new insights into intraspecific niche expansion and genomic diversification

Background

Bacterial pathogens often show significant intraspecific variations in ecological fitness, host preference and pathogenic potential to cause infectious disease. The species of Listeria monocytogenes, a facultative intracellular pathogen and the causative agent of human listeriosis, consists of at least three distinct genetic lineages. Two of these lineages predominantly cause human sporadic and epidemic infections, whereas the third lineage has never been implicated in human disease outbreaks despite its overall conservation of many known virulence factors.

Results

Here we compare the genomes of 26 L. monocytogenes strains representing the three lineages based on both in silico comparative genomic analysis and high-density, pan-genomic DNA array hybridizations. We uncover 86 genes and 8 small regulatory RNAs that likely make L. monocytogenes lineages differ in carbohydrate utilization and stress resistance during their residence in natural habitats and passage through the host gastrointestinal tract. We also identify 2,330 to 2,456 core genes that define this species along with an open pan-genome pool that contains more than 4,052 genes. Phylogenomic reconstructions based on 3,560 homologous groups allowed robust estimation of phylogenetic relatedness among L. monocytogenes strains.

Conclusions

Our pan-genome approach enables accurate co-analysis of DNA sequence and hybridization array data for both core gene estimation and phylogenomics. Application of our method to the pan-genome of L. monocytogenes sheds new insights into the intraspecific niche expansion and evolution of this important foodborne pathogen.

The Opportunistic Pathogen Listeria monocytogenes: Pathogenicity and Interaction with the Mucosal Immune System

Listeria monocytogenes is an opportunistic foodborne pathogen causing listeriosis, an often fatal infection leading to meningitis, sepsis, or infection of the fetus and abortion in susceptible individuals. It was recently found that the bacterium can also cause acute, self-limiting febrile gastroenteritis in healthy individuals. In the intestinal tract, L. monocytogenes penetrates the mucosa directly via enterocytes, or indirectly via invasion of Peyer's patches. Animal models for L. monocytogenes infection have provided many insights into the mechanisms of pathogenesis, and the development of new model systems has allowed the investigation of factors that influence adaptation to the gastrointestinal environment as well as adhesion to and invasion of the intestinal mucosa. The mucosal surfaces of the gastrointestinal tract are permanently exposed to an enormous antigenic load derived from the gastrointestinal microbiota present in the human bowel. The integrity of the important epithelial barrier is maintained by the mucosal immune system and its interaction with the commensal flora via pattern recognition receptors (PRRs). Here, we discuss recent advances in our understanding of the interaction of L. monocytogenes with the host immune system that triggers the antibacterial immune responses on the mucosal surfaces of the human gastrointestinal tract.

Unusual cause of weight loss in a patient with HIV-hepatitis C virus coinfection

Recombinant interferon α (IFN α), alone or in combination, is used extensively in the treatment of hepatitis C infection. IFN therapy is not free of side-effects and autoimmune thyroiditis is one of its rare side-effects. We present here a case of a patient with hepatitis C virus-human immunodeficiency virus coinfection on interferon therapy who presented with significant weight loss. He was found to have IFN-related autoimmune thyrotoxicosis and responded to antithyroid drugs and propanolol. Therefore, this case highlights that IFN-induced thyroiditis is an unusual side-effect and that during treatment, a thyroid-stimulating hormone assay should be performed at regular intervals (every 8-12 weeks).

Multilocus sequence typing of outbreak-associated Listeria monocytogenes isolates to identify epidemic clones

OBJECTIVE

Listeria monocytogenes is a foodborne pathogen found in a wide variety of environments. Subtype characterization of L. monocytogenes isolates from listeriosis outbreaks that have occurred over the last three decades has suggested that a number of outbreaks were caused by a small number of L. monocytogenes epidemic clones (ECs). In this study we compared the prevalence, ecology, and phylogenetic position of outbreak-associated isolates and non-outbreak-associated isolates to probe the evolutionary and ecological characteristics of outbreak-associated L. monocytogenes subtypes, including those representing previously described ECs.

METHODS

Multilocus sequence typing data for isolates from 15 listeriosis outbreaks in Europe and North America were generated and compared, using a phylogenetic framework, with 180 isolates representing a local sampling of diverse sources, including human sporadic cases.

RESULTS

Isolates from 15 listeriosis outbreaks represented eight sequence types (STs). STs corresponding to previously designated ECI (ST1 and ST93) and ECIa (ST29) represented isolates from eight outbreaks. ST17 (corresponding to ECII) was involved in two outbreaks in the United States (1998 and 2002). No other STs were involved in multiple outbreaks. While ST1 was the most common ST among sporadic human cases and non-human listeriosis-related isolates, ST29 was rare among non-human listeriosis-related isolates and was significantly overrepresented among isolates from human listeriosis outbreaks and sporadic cases as compared to isolates from other sources in our local sampling.

CONCLUSIONS

STs associated with outbreaks (and representing previously designated ECs) appear to differ in their ecology. While association of ECI with multiple human listeriosis outbreaks appears to reflect strain abundance across environments, ECIa seems to represent an L. monocytogenes EC that appears to be overrepresented among outbreaks and sporadic cases and thus may have increased transmission potential.

DNA probes for unambiguous identification of Listeria monocytogenes epidemic clone II strains

Listeria monocytogenes epidemic clone II (ECII) strains have been responsible for two major multistate outbreaks of food-borne listeriosis in the United States, but their prevalence and ecology remain poorly understood. In this study, we describe DNA probes that unambiguously identify this clonal group. These probes were able to differentiate ECII strains of outbreak, sporadic, or environmental origin from other L. monocytogenes strains of the same serotype (4b).

Occurrence of Listeria monocytogenes in salami manufactured in the Marche Region (Central Italy)

The aim of the present study was to investigate the occurrence of Listeria monocytogenes in salami samples collected from production plants of the Marche Region, and to assess the end-product acceptability based on the former Italian regulations and European Commission (EC) Regulation No 2073/2005. Based on the limits specified in the former Italian regulations, the percentage of non-acceptable samples was 34.3%, whereas based on the limits specified in EC Regulation N degrees 2073/2005, a lower percentage (17.1%) was seen. A similar trend was seen also when only the Ciauscolo salami were considered, with 45.2 and 27.4% of non-acceptable samples, respectively. No correlations were identified between occurrence of L. monocytogenes and the main parameters or the manufacturing processes.

Chicken salad as the source of a case of Listeria monocytogenes infection in Connecticut

Listeriosis is a severe infection with high morbidity and mortality. We report a fatal case of listeriosis in a patient with a history of Crohn's disease who consumed chicken salad purchased from a retail food establishment before developing listeriosis. As part of the regulatory testing programs, the U.S. Department of Agriculture Food Safety and Inspection Service and the Florida Department of Agriculture and Consumer Affairs found that chicken products from a single food-production establishment were contaminated with Listeria monocytogenes, resulting in a product recall. The case patient's Listeria isolate was subtyped by pulsed-field gel electrophoresis (PFGE) and matched the Listeria isolates from the recalled chicken products. Identification of the source of Listeria involved collaboration among two state public health laboratories and epidemiologists and state and federal regulatory agencies. PFGE typing can be used to reveal correlations between clusters of human illness and contaminated food products and to rapidly identify sources of Listeria infection to allow implementation of corrective actions at both the state and national levels.

Surveillance for Listeria monocytogenes and listeriosis, 1995-2004

Canadian cases and outbreaks of illness caused by Listeria monocytogenes between 1995 and 2004 were assessed. Isolates (722 total) were characterized by serotyping, and pulsed-field gel electrophoresis (PFGE) was performed to provide a means of detecting case clusters. Rates of listeriosis remained fairly consistent during the period of study, and patient characteristics were similar to those seen in studies of other populations. Most isolates were obtained from blood and cerebrospinal fluid, although during some outbreak investigations isolates were also obtained from stools. Serotype 1/2a predominated in isolates from patients in Canada, followed by serotypes 4b and 1/2b. Outbreaks caused by L. monocytogenes that occurred during the period of study were caused by isolates with serotypes 1/2a and 4b. A retrospective analysis of PFGE data uncovered several clusters that might have represented undetected outbreaks, suggesting that comprehensive prospective PFGE analysis coupled with prompt epidemiological investigations might lead to improved outbreak detection and control.

Safety-based shelf life model for frankfurters based on time to detect Listeria monocytogenes with initial inoculum below detection limit

The growth of Listeria monocytogenes inoculated on frankfurters at four inoculum levels (0.1, 0.04, 0.01, and 0.007 CFU/g) was examined at 4, 8, and 12 degrees C until the time L. monocytogenes populations reached a detectable limit of at least 2 CFU/g. A scaled-down assumption was made to simulate a 25-g sample from a 100-lb batch size in a factory setting by using a 0.55-g sample from a 1,000-g batch size in a laboratory. Samples of 0.55 g were enriched in PDX-LIB selective medium, and presumptive results were confirmed on modified Oxford agar. Based on the time to detect (TTD) from each inoculum level and at each temperature, a shelf life model was constructed to predict the detection or risk levels reached by L. monocytogenes on frankfurters. The TTD increased with reductions in inoculum size and storage temperature. At 4 degrees C the TTDs (+/- standard error) observed were 42.0 +/- 1.0, 43.5 +/- 0.5, 50.7 +/- 1.5, and 55.0 +/- 3.0 days when the inoculum sizes were 0.1, 0.04, 0.01, and 0.007 CFU/g, respectively. From the same corresponding inoculum sizes, the TTDs at 8 degrees C were 4.5 +/- 0.5, 6.5 +/- 0.5, 7.0 +/- 1.0, and 8.5 +/- 0.5 days. Significant differences (P < 0.05) between TTDs were observed only when the inoculum sizes differed by at least 2 log. On a shelf life plot of 1n (TTD) versus temperature, the Q10 (increase in TTD for a 10 degrees C increase in temperature) values ranged from 24.5 to 44.7 and with no significant influence from the inoculum densities. When the observed TTDs were compared with the expected detection times based on the data obtained from a study with an inoculum size of 10 to 20 CFU/g, significant deviations were noted at lower inoculum levels. These results can be valuable in designing a safety-based shelf life model for frankfurters and in performing quantitative risk assessment of listeriosis at low and practical contamination levels.

Disease presentation in relation to infection foci for non-pregnancy-associated human listeriosis in England and Wales, 2001 to 2007

Listeriosis is a rare but severe food-borne disease, affecting unborn or newly delivered infants, the elderly, and the immunocompromised. The epidemiology of listeriosis in England and Wales changed between 2001 and 2007, with more patients > or = 60 years old presenting with bacteremia (but without central nervous system [CNS] involvement). In order to explain this increase and understand the altered disease presentation, clinical, microbiological, and seasonal data on bacteremic cases of Listeria monocytogenes infection identified through national surveillance were compared with those for patients with CNS infections. Logistic regression analysis was applied while controlling for age. Bacteremic patients, who presented more frequently with gastrointestinal symptoms, were more likely to have underlying medical conditions than CNS patients. This was most marked in patients with malignancies, particularly digestive organ malignancies. Treatment to reduce stomach acid secretion modified the effect of nonmalignant underlying conditions on outcome, i.e., patients with an underlying condition who were not taking acid-suppressing medication were equally likely to have a bacteremic or a CNS infection. However, this type of therapy did not modify the effect of malignancies on the likelihood of having a bacteremic or a CNS infection. The increase in the incidence of human listeriosis among patients > or = 60 years old in England and Wales between 2001 and 2007 appears to have occurred in those with cancer or other conditions whose treatment included acid-suppressing medication. Therefore, this vulnerable patient group needs specific dietary advice on avoiding risk factors for listeriosis.

Bioconverted products of essential fatty acids as potential antimicrobial agents

This review deals with the recent findings on the microbial conversion of essential fatty acids (EFAs) through Pseudomonas aeruginosa PR3 NRRL-B-18602, and the antimicrobial properties of bioconverted EFAs, with particular emphasis on n-3 or n-6 fatty acids. The first section deals with the most recent and some background literature on which have been the latest developments with respect to bioconverted EFAs as potential antibacterial agents, in particular the inhibition of severe foodborne and food spoilage bacteria causing deleterious effects in food and human beings. The second section of the review deals with the inhibition of certain important plant pathogenic fungi through the bioconverted EFAs which cause drastic losses to food and agriculture industries. Also we have given emphasis through the literature on the importance of microbial bioconversion of EFAs along with their possible applications in various beneficial fields.

Quantification of Listeria monocytogenes in minimally processed leafy vegetables using a combined method based on enrichment and 16S rRNA real-time PCR

Modern lifestyle markedly changed eating habits worldwide, with an increasing demand for ready-to-eat foods, such as minimally processed fruits and leafy greens. Packaging and storage conditions of those products may favor the growth of psychrotrophic bacteria, including the pathogen Listeria monocytogenes. In this work, minimally processed leafy vegetables samples (n = 162) from retail market from Ribeirão Preto, São Paulo, Brazil, were tested for the presence or absence of Listeria spp. by the immunoassay Listeria Rapid Test, Oxoid. Two L. monocytogenes positive and six artificially contaminated samples of minimally processed leafy vegetables were evaluated by the Most Probable Number (MPN) with detection by classical culture method and also culture method combined with real-time PCR (RTi-PCR) for 16S rRNA genes of L. monocytogenes. Positive MPN enrichment tubes were analyzed by RTi-PCR with primers specific for L. monocytogenes using the commercial preparation ABSOLUTE QPCR SYBR Green Mix (ABgene, UK). Real-time PCR assay presented good exclusivity and inclusivity results and no statistical significant difference was found in comparison with the conventional culture method (p < 0.05). Moreover, RTi-PCR was fast and easy to perform, with MPN results obtained in ca. 48 h for RTi-PCR in comparison to 7 days for conventional method.

Listeriolysin O affects barrier function and induces chloride secretion in HT-29/B6 colon epithelial cells

Listeria monocytogenes is a food-borne pathogen, which is able to induce diarrhea when residing in the intestine. We studied the effect of listeriolysin O (LLO), an extracellular virulence factor of L. monocytogenes, on intestinal transport and barrier function in monolayers of HT-29/B6 human colon cells using the Ussing technique to understand the pathomechanisms involved. Mucosal addition of LLO, but not a LLO mutant, induced a dose- and pH-dependent increase in short-circuit current (I(SC)). Sodium and chloride tracer flux and DIDS sensitivity studies revealed that I(SC) was mainly due to electrogenic chloride secretion. Barrier function was impaired by LLO, as assessed by transepithelial resistance (R(t)) and mannitol flux measurements. Intracellular signal transduction occurred through Ca(2+) release from intracellular stores and PKC activation. In conclusion, listeriolysin induces chloride secretion and perturbs epithelial barrier function, thus potentially contributing to Listeria-induced diarrhea.

An outbreak of febrile gastroenteritis associated with jellied pork contaminated with Listeria monocytogenes

In September 2008, the Austrian Agency for Health and Food Safety (AGES) learned of an outbreak of diarrheal illness that included a 71-year-old patient hospitalized for gastroenteritis with a blood culture positive for Listeria monocytogenes. Three stool specimens provided by seven of 19 persons attending a day trip to a foreign city, including a final break at an Austrian tavern, yielded L. monocytogenes. All isolates were of serovar 4b and had fingerprints indistinguishable from each other. A cohort study revealed that the outbreak of gastroenteritis occurred among 16 persons who had eaten dinner at the wine tavern on September 6. Of the 15 persons who ate from platters of mixed cold-cuts, 12 (80%) developed symptoms of febrile gastroenteritis within 24-48 h. The median age of those who became ill was 62 years. A 72-year-old patient recovered from gastroenteritis but was hospitalized with bacterial meningitis on day 19 after the dinner. The epidemiological investigation identified the consumption of mixed cold-cuts (including jellied pork) at the wine tavern as the most likely vehicle of the foodborne outbreak (P = 0.0015). This hypothesis was confirmed by microbiological investigation of jellied pork produced by the tavern owner on September 3. L. monocytogenes was isolated from leftover food in numbers of 3 x 10(3)-3 x 10(4) colony forming units/g and was indistinguishable from the clinical outbreak isolates. Symptoms reported by the 12 patients included unspecified fever (12x), diarrhea (9x), headache (5x), vomiting (4x), body aches (2x) and sore throat (1x). Active case finding identified one case of rhombencephalitis (female, age 48) among another group of four guests, among whom only the patient and her asymptomatic husband had eaten jellied pork on September 6. This is the first outbreak of L. monocytogenes-associated gastroenteritis reported in Austria. The occurrence of a secondary case of meningitis (diagnosed on day 19 after consumption of jellied pork) indicates a significant risk of systemic listeriosis among elderly patients with febrile gastroenteritis caused by L. monocytogenes; antibiotic therapy should therefore be considered in such cases of documented listerial gastroenteritis.

Expression of internalin A and biofilm formation among Listeria monocytogenes clinical isolates

Internalin A (InlA), a cell wall-bound protein of Listeria monocytogenes, is among the major components involved in the adhesion to and invasion of host cells expressing specific forms of E-cadherin. Some L. monocytogenes strains secrete truncated non-functional forms of InlA. The purpose of this study is to compare the biofilm-forming abilities of L. monocytogenes strains from clinical sources expressing InlA proteins in the different forms. A total of 70 L. monocytogenes strains were examined using SDS-PAGE, Western blot, DNA sequencing, and microtitre plate biofilm formation assays. We found that 8 of the 70 strains expressed truncated InlA, and that this group of strains exhibited significantly enhanced biofilm-forming ability compared to the group expressing full-length InlA. Further experiments showed that: (i) L. monocytogenes biofilms were detached by treatment with protease K; (ii) protein fragments resulting from proteolysis, rather than intact proteins, are responsible for biofilm enhancement, because biofilm formation was impaired by the protease inhibitor alpha2-macroglobulin; (iii) truncated and/or proteolytically cleaved InlA are likely involved in the biofilm enhancement, based on the effects that anti-InlA monoclonal antibodies produced on the biofilm formation of L. monocytogenes strains expressing either truncated or full-length InlA. These data provide a basis for further investigation of the molecular structure and composition of L. monocytogenes biofilms.

Emerging infections of the gastrointestinal tract

Infections account for significant GI morbidity and mortality worldwide. New organisms are being identified, associated with diarrhoeal illness and some with other gastrointestinal illness as well. Among GI viruses, Sapovirus is now recognised to cause diarrhoea, especially in children. A hypervirulent strain of Clostridium difficile has caused epidemics in many countries. Newly identified bacterial species that may cause diarrhoea include Campylobacter concisus, Arcobacteria, Edwardsiella tarda, Aeromonas, Plesiomonas and Laribacter. Helicobacteria are reviewed, as well as the role of gastric acid suppression in predisposing to enteric infections.