Listeria monocytogenes: epidemiology, human disease, and mechanisms of brain invasion

Listeria monocytogenes is a facultative intracellular bacterium that has predilection for causing central nervous systemic infections in humans and domesticated animals. This pathogen can be found worldwide in the food supply and most L. monocytogenes infections are acquired through ingestion of contaminated food. The main clinical syndromes caused by L. monocytogenes include febrile gastroenteritis, perinatal infection, and systemic infections marked by central nervous system infections with or without bacteremia. Experimental infection of mice has been used for over 50 years as a model system to study the pathogenesis of this organism including the mechanisms by which it invades the brain. Data from this model indicate that a specific subset of monocytes, distinguished in part by high expression of the Ly-6C antigen, become parasitized in the bone marrow and have a key role in transporting intracellular bacteria across the blood-brain barriers and into the central nervous system. This Minireview will summarize recent epidemiologic and clinical information regarding L. monocytogenes as a human pathogen and will discuss current in vitro and in vivo data relevant to the role of parasitized monocytes and the pathogenetic mechanisms that underlie its formidable ability to invade the central nervous system.     

Listeric Septicaemia in Sheep Associated with Tick-Borne Fever (Ehrlichiosis Ovis)

Sheep is apparently fairly resistant against infections with Listeria monocytogenes (Lm). Grønstøl (unpublished) found that a high proportion of healthy sheep are carriers of Lm. In such animals Lm may cause clinical disease when resistance is lowered. Tick-borne fever (TBF) is known to reduce the resistance against several infections (Øverås 1972). This report describes listeric septicaemia associated with TBF.     

InlA和InlB介导单核细胞增生李斯特菌入侵宿主细胞分子机制的研究进展

单核细胞增生李斯特菌(Listeria monocytogenes)是一种革兰氏阳性食源性致病菌。在造成宿主食源性感染的过程中, 单核细胞增生李斯特菌能凭借其独特的表面蛋白入侵宿主的非吞噬细胞。内化素蛋白家族(Internalins)是介导单核细胞增生李斯特菌入侵宿主非吞噬细胞的主要因子。本文根据国内外一些最新的研究成果, 结合作者近几年的工作, 综述了在侵染宿主的过程中, 单核细胞增生李斯特菌主要的内化素蛋白InlA和InlB介导细菌入侵宿主细胞的分子机制, 以期为阐明食源性致病菌致病机理、预防和治疗食源性疾病提供理论基础。     

Connatal listeriosis--a case report and the possibilities of microbiological diagnosis

The third most frequent agent of perinatal bacterial meningitis is Listeria monocytogenes, in Hungary, its occurrence is, however, uncommon. This raises the possibility of diagnostical mistakes. A connatal listeriosis case validated microbiologically referred to in this report calls attention to Listeria, as a rare but relevant pathogen of neonatal infections. If clinical background suggests infection, the pathogenic role of L. monocytogenes should be taken into consideration. The etiological significance of the agent has to be verified by a competent clinical microbiology laboratory, since maternal listeriosis should be treated and the serious connatal manifestations should be prevented. Epidemiology of perinatal infection by L. monocytogenes, and its diagnostic tools especially the use of selective media are discussed.     

Antibodies to listeriolysin O reflect the acquired resistance to Listeria monocytogenes in experimentally infected goats

We induced experimental listeriosis in goats by two sequential oral inoculations of Listeria monocytogenes serovar 1/2a at 8 months' interval. Immunoblot analysis with the goat sera demonstrated listeriolysin O (LLO) as the principal protein antigen of L. monocytogenes. Pre-existing antibodies to LLO were, depending on their initial level, associated with either mild clinical symptoms of short duration or the total absence of clinical symptoms. Similarly, the presence and development of such antibodies corresponded with the disappearance pattern of L. monocytogenes from the gastrointestinal tract. These findings suggest that an association exists between antibodies to LLO and acquired resistance to Listeria infections.     

Genetic diversity and molecular typing of Listeria monocytogenes in China

ABSTRACT: 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 isolations. 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 most common 3 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.     

Ruminant rhombencephalitis-associated Listeria monocytogenes alleles linked to a multilocus variable-number tandem-repeat analysis complex

Listeria monocytogenes is among the most important food-borne pathogens and is well adapted to persist in the environment. To gain insight into the genetic relatedness and potential virulence of L. monocytogenes strains causing central nervous system (CNS) infections, we used multilocus variable-number tandem-repeat analysis (MLVA) to subtype 183 L. monocytogenes isolates, most from ruminant rhombencephalitis and some from human patients, food, and the environment. Allelic-profile-based comparisons grouped L. monocytogenes strains mainly into three clonal complexes and linked single-locus variants (SLVs). Clonal complex A essentially consisted of isolates from human and ruminant brain samples. All but one rhombencephalitis isolate from cattle were located in clonal complex A. In contrast, food and environmental isolates mainly clustered into clonal complex C, and none was classified as clonal complex A. Isolates of the two main clonal complexes (A and C) obtained by MLVA were analyzed by PCR for the presence of 11 virulence-associated genes (prfA, actA, inlA, inlB, inlC, inlD, inlE, inlF, inlG, inlJ, and inlC2H). Virulence gene analysis revealed significant differences in the actA, inlF, inlG, and inlJ allelic profiles between clinical isolates (complex A) and nonclinical isolates (complex C). The association of particular alleles of actA, inlF, and newly described alleles of inlJ with isolates from CNS infections (particularly rhombencephalitis) suggests that these virulence genes participate in neurovirulence of L. monocytogenes. The overall absence of inlG in clinical complex A and its presence in complex C isolates suggests that the InlG protein is more relevant for the survival of L. monocytogenes in the environment.     

Antimicrobial resistance of Listeria monocytogenes

Listeria monocytogenes is an opportunistic pathogen that causes rare but frequently fatal infections, termed listerioses. In general, strains of L. monocytogenes are susceptible to a wide range of antibiotics, except for the cephalosporins, fluorochinolones and fosfomycin (Hof, 1991). The current therapy of choice is a combination of ampicillin and aminoglycoside, usually gentamicin (Lorber, 1997). In cases when it is not possible to use a beta-lactam antibiotic, second-choice therapy involves the use of an association of trimethoprim with a sulfonamide, such as in co-trimoxazole, in which the more active in the combination seems trimethoprim, synergized by the sulfa compound. Other second line agents for listeriosis include erythromycin and vancomycin (Temple and Nahata, 2000). The first strains of L. monocytogenes resistant to antibiotics were reported in 1988 (Poyart-Salmeron et al. 1990) The present paper reviews the current state of affairs with regard to the resistance of L. monocytogenes isolated from food products and clinical material to different antibiotics, with particular emphasis on those used in the therapy of listeriosis.     

Suitability of the prfA gene, which encodes a regulator of virulence genes in Listeria monocytogenes, in the identification of pathogenic Listeria spp.

The pathogenesis of listerial infections is complex and involves a number of virulence factors expressed by virulent Listeria species. We have recently described a regulator gene, prfA, that positively regulates the expression of a number of virulence factors in Listeria monocytogenes. When the prfA gene was used as a DNA probe, we found it to be extremely specific for the pathogenic species L. monocytogenes. No reaction was obtained with strains of all other species of this genus. By using this information, an oligonucleotide primer pair was developed that specifically amplifies the prfA gene in L. monocytogenes strains of all known serotypes.     

Suitability of the prfA gene, which encodes a regulator of virulence genes in Listeria monocytogenes, in the identification of pathogenic Listeria spp.

The pathogenesis of listerial infections is complex and involves a number of virulence factors expressed by virulent Listeria species. We have recently described a regulator gene, prfA, that positively regulates the expression of a number of virulence factors in Listeria monocytogenes. When the prfA gene was used as a DNA probe, we found it to be extremely specific for the pathogenic species L. monocytogenes. No reaction was obtained with strains of all other species of this genus. By using this information, an oligonucleotide primer pair was developed that specifically amplifies the prfA gene in L. monocytogenes strains of all known serotypes.     

Staphylococcus saprophyticus ATCC 15305 is internalized into human urinary bladder carcinoma cell line 5637

Invasion of bacteria into nonphagocytic host cells is an important pathogenicity factor for escaping the host defence system. Gram-positive organisms, for example Staphylococcus aureus and Listeria monocytogenes, are invasive in nonphagocytic cells, and this mechanism is discussed as an important part of the infection process. Uropathogenic Escherichia coli and Staphylococcus saprophyticus can cause acute and recurrent urinary tract infections as well as bloodstream infections. Staphylococcus saprophyticus shows strong adhesion to human urinary bladder carcinoma and Hep2 cells and expresses the 'Microbial Surface Components Recognizing Adhesive Matrix molecule' (MSCRAMM)-protein SdrI with collagen-binding activity. MSCRAMMs are responsible for adhesion and collagen binding in S. aureus and are discussed as an important pathogenicity factor for invasion. To investigate internalization in S. aureus, several fluorescence activated cell sorting (FACS) assays have been described recently. We used a previously described FACS assay, with slight modifications, in addition to an antibiotic protection assay and transmission electron microscopy to show that S. saprophyticus ATCC 15305 and the wild-type strain 7108 were internalized into the human urinary bladder carcinoma cell line 5637. The discovery of the internalization of S. saprophyticus may be an important step for understanding the pathogenicity of recurrent infections caused by this organism.     

重症单核细胞增多性李斯特菌脑膜脑炎1例

李斯特菌脑膜脑炎是单核细胞增多性李斯特菌(LM)引起的细菌性脑膜脑炎,通常发生于免疫功能低下者.LM是人畜共患致病菌,通过污染的食物传播.欧美国家报道较多,国内报道较少.李斯特菌脑膜脑炎病死率高,临床表现与其他细菌性脑膜炎类似.脑脊液检查与结核性脑膜炎亦难鉴别,确诊依赖于脑脊液涂片及培养.本文报道1例重症李斯特菌脑膜脑...     

T cell reactivity to Listeria monocytogenes amongst us

In the last two decades, listeriosis, caused by the intracellular pathogen Listeria monocytogenes, became one of the most concerning food-born infections. Although it had been known before as an infectious disease of limited importance, listeriosis was brought into attention of scientists due to the frequent outbreaks recently reported. Despite the major progress made towards understanding the mechanisms of virulence of L. monocytogenes, our current knowledge into the process of Listeria-associated pathogenesis and virulence is still partial and fragmentary. In this study we demonstrate that T lymphocytes with reactivity to L. monocytogenes are frequently present in healthy individuals (73%), most probably as a consequence of subclinical infections. Host resistance to infection by L. monocytogenes involves a series of interactions between cells of the immune system, of which the antigen presenting cell/T lymphocyte partnership is essential. The ability of memory T cells to respond when exposed to their target antigen is traditionally assessed by measuring uptake of [3H] - thymidine. Our study has been carried out by means of an alternative methodology based on flow-cytometry, an approach which has several advantages on [3H] - thymidine incorporation technique: allows targeted analysis of particular cell types, simultaneous assessment of various cellular markers, and circumvents handling of radioisotopes.     

Listeria monocytogenes: comparative interpretation of mouse virulence assay

Being an opportunistic bacterial pathogen, Listeria monocytogenes demonstrates significant strain variations in virulence and pathogenicity. The availability of laboratory procedures to ascertain the pathogenic potential of L. monocytogenes bacteria would greatly enhance the control and prevention of listerial infections. As a method that measures all virulent determinants, mouse virulence assay has been frequently used for assessing L. monocytogenes virulence. The pathogenic potential of a given L. monocytogenes strain as determined by mouse virulence assay is often calculated from mouse mortality data in combination with colony forming units (CFUs) derived from plate counts, and expressed by medium lethal dose (LD(50)). In this report, we describe an alternative method [i.e., relative virulence (%)] that does not involve CFU estimation, and is comparable to LD(50) for interpretation of mouse virulence assay for L. monocytogenes. The relative virulence (%) is obtained by dividing the number of dead mice with the total number of mice tested for a particular strain using a known virulent strain (e.g., L. monocytogenes EGD) as reference. Besides providing a more direct interpretation in comparison with LD(50) values for mouse virulence assay, this method requires fewer dosage groups per L. monocytogenes strain, and eliminates CFU estimation that is step subject to variations between runs and also between laboratories.     

Macrophage intracellular signaling induced by Listeria monocytogenes

Macrophages are critical for control of Listeria monocytogenes infections; accordingly, the interactions of L. monocytogenes with these cells have been intensively studied. It has become apparent that this facultative intracellular pathogen interacts with macrophages both prior to entry and during the intracellular phase. This review covers recent work on signaling induced in macrophages by L. monocytogenes, especially intracellular signals induced by secreted proteins including listeriolysin O and two distinct phospholipases C.     

Characterization of Listeria monocytogenes isolates from food animal clinical cases: PFGE pattern similarity to strains from human listeriosis cases

Twenty-one isolates of Listeria monocytogenes from food animal clinical cases that involved meningitis or meningoencephalitis, encephalitis, mastitis and abortion were characterized by serotyping and pulsed-field gel electrophoresis (PFGE) in order to improve our understanding of the genetic links between individual strains and strains recovered from human listeriosis cases. Results showed that five of the isolates were serotype 1/2a, six were 1/2b, nine were 4b, and one was untypeable. A caprine, two bovine and an ovine brain isolate shared identical PFGE patterns indicating that strains of L. monocytogenes are not host specific. Other isolates exhibited distinct patterns that were not shared, indicating a genetic diversity. Dendrogram analysis revealed that PFGE patterns of the isolates clustered primarily according to serotype. We compared the PFGE types obtained for these isolates with PFGE types for human clinical isolates present in the CDC national PulseNet database. Six (29%) of the twenty-one strains had patterns that were indistinguishable from pathogenic human isolates in the database. Our observations offer preliminary evidence that food animals could be significant reservoirs of L. monocytogenes that lead to human infections and support the inclusion of PFGE patterns of veterinary clinical isolates in the national PulseNet database for increased surveillance.     

新生儿及产妇感染单核细胞增生李斯特菌分离株的血清型、耐药性及分子特征研究

为探讨广西南宁地区新生儿及产妇感染的单核细胞增生李斯特菌(Listeria monocytogenes, Lm)的血清型、药物敏感性及其分子流行病学特征,本研究回顾性收集2015-2017年广西壮族自治区妇幼保健院新生儿科及产科送检标本中分离的Lm,对其进行体外药物敏感性检测、血清学分型以及多位点序列分型(multilocus sequence typing, MLST)分析菌株间的同源性;同时分析患儿及其母亲的临床特征及危险因素。结果显示,广西南宁地区新生儿感染Lm发病率较低,2015-2017年发病率为0.091‰;所有分离的Lm分属4b(83.3%)和1/2a(16.7%)2个血清型;药物敏感性试验结果显示,Lm对青霉素、氨苄西林、复方新诺明及美罗培南均100%敏感,暂未发现耐药菌株;MLST分型共获得2个序列型(sequence types,ST),以ST­1型(83.3%)为主。其中分离自同一新生儿患者(Case 2)外周血(Lm2)、耳拭子(Lm3)及其母亲羊水(Lm4)、宫颈分泌物(Lm5)的4株菌具有相同的血清型、药物敏感性表型以及MLST分型。感染Lm的患儿主要表现为发热、肺炎、发绀、败血症及脑膜炎;而产妇感染则具有非特异性的临床特征。结果提示,广西南宁地区存在的Lm菌株为致病性较强的4b、1/2a血清型菌株;Lm可通过母婴垂直传播引起新生儿感染。因此,临床医师应重视孕产妇及新生儿Lm病原学检查、早期诊断和及时合理地使用抗生素预防、治疗,从而减少Lm引起的母婴感染。     

Ly6G+ neutrophils are dispensable for defense against systemic Listeria monocytogenes infection

Listeria monocytogenes is a facultative intracellular bacterium that causes systemic infections in immunocompromised hosts. Early recruitment of myeloid cells, including inflammatory monocytes and neutrophils, to sites of L. monocytogenes infection is essential for the control of infection and host survival. Because previous experimental studies used depleting or blocking Abs that affected both inflammatory monocytes and neutrophils, the relative contributions of these cell populations to defense against L. monocytogenes infection remain incompletely defined. In this article, we used highly selective depletion strategies to either deplete inflammatory monocytes or neutrophils from L. monocytogenes-infected mice and demonstrate that neutrophils are dispensable for early and late control of infection. In contrast, inflammatory monocytes are essential for bacterial clearance during the innate and adaptive phases of the immune response to L. monocytogenes infection.     

Identification of an essential gene of Listeria monocytogenes involved in teichoic acid biogenesis

Listeria monocytogenes is a facultative intracellular gram-positive bacterium responsible for severe opportunistic infections in humans and animals. We had previously identified a gene encoding a putative UDP-N-acetylglucosamine 2-epimerase, a precursor of the teichoic acid linkage unit, in the genome of L monocytogenes strain EGD-e. This gene, now designated lmo2537, encodes a protein that shares 62% identity with the cognate epimerase MnaA of Bacillus subtilis and 55% identity with Cap5P of Staphylococcus aureus. Here, we addressed the role of lmo2537 in L. monocytogenes pathogenesis by constructing a conditional knockout mutant. The data presented here demonstrate that lmo2537 is an essential gene of L. monocytogenes that is involved in teichoic acid biogenesis. In vivo, the conditional mutant is very rapidly eliminated from the target organs of infected mice and thus is totally avirulent.