Resistance of Listeria monocytogenes to the bacteriocin nisin

The ability of the rumen to absorb the same quantity of VFA with 4 animals previously fed with 2 levels of intake was tested. Animals received maintenance (P1) and half maintenance (P2) energy and nitrogen requirements successively. Absorption was measured with the empty washed rumen technique. Three litres of a solution buffered at pH 6.30 containing VFA (C2:57.1, C3:49.2 and C4:7.4 mM or C2:79.8, C3:23.5 and C4:11.5 mM) and CoEDTA (7.1 mg Co/l) were introduced in the rumen and regularly sampled for 3 h. VFA absorption was linear during the trials. Rates of absorption were expressed as mmol/h or percentage of initial quantity/h for the comparison between VFA. The order of absorption rate (%/h) was C4 > C3 > C2. Water absorption was not significantly different between the periods whereas VFA absorption rates (mmol/h) were significantly reduced after undernutrition. Composition of the solution had no significant effect on VFA absorption rate (%/h).     

Inhibition of Listeria monocytogenes in a pork product by a Lactobacillus sake strain

Fluoxetine has been reported to suppress food intake in animal models of feeding. Fluoxetine increases extracellular serotonin in the brain. 5HT1A autoreceptors regulate synaptic levels of serotonin. A combination of a 5HT1A receptor antagonist and fluoxetine has been previously reported to enhance extracellular levels of serotonin over what is obtained with fluoxetine alone. Thus, a combination of fluoxetine and a 5HT1A antagonist could enhance the ability of fluoxetine to suppress appetite. Fluoxetine was tested in a model of feeding, in which CD-1 mice were trained to drink sweetened condensed milk. Fluoxetine was found to attenuate milk drinking, in a dose-dependent manner, at doses greater than 10 mg/kg, i.p. A 10 mg/kg dose of fluoxetine, which was ineffective by itself, was then combined either with 5-hydroxytryptophan (5HTP), a serotonin precursor, or with S(-) pindolol, a 5HT1A/beta adrenergic receptor antagonist or with LY206130, a more selective 5HT1A receptor antagonist. These treatment paradigms resulted in significant attenuation of the consumption of sweetened condensed milk. Since fluoxetine has been shown to be useful in the treatment of eating disorders and to promote weight loss in obese humans, although at doses greater than those required for the treatment of depression, a combination of fluoxetine with a 5HT1A receptor antagonist could be of clinical utility in the treatment of eating disorders and obesity.     

Inhibition of Listeria monocytogenes by enterocin 4 during the manufacture and ripening of Manchego cheese

Antiviral activity of the acyclic nucleoside phosphonates 9-(2-phosphonylmethoxyethyl)adenine (PMEA) and 9-(3-fluoro-2-phosphonylmethoxypropyl)adenine (FPMPA) against feline immunodeficiency virus (FIV) was investigated in field cats. The study was designed as a placebo-controlled double-blind study enrolling 27 FIV infected cats. Nine cats received PMEA at a dosage of 10 mg/kg body weight, nine cats received FPMPA at a dosage of 25 mg/kg body weight. A variety of parameters were established to evaluate the therapeutic efficacy of the compounds. The improvement was monitored by different aspects: clinical status, index of Karnofsky modified for the cat, laboratory parameters, immunological parameters, surrogate markers, and a virological parameter. Concerning the clinical and immunological parameters cats of both treatment groups disclosed a relevant improvement. Efficacy of antiviral treatment was a little bit higher in the cats treated with PMEA than in the animals injected with FPMPA. However, side effects were also more prominent in the PMEA treated group.     

A tenuous carbon dioxide atmosphere on Jupiter's moon Callisto

An off-limb scan of Callisto was conducted by the Galileo near-infrared mapping spectrometer to search for a carbon dioxide atmosphere. Airglow in the carbon dioxide nu3 band was observed up to 100 kilometers above the surface and indicates the presence of a tenuous carbon dioxide atmosphere with surface pressure of 7.5 x 10(-12) bar and a temperature of about 150 kelvin, close to the surface temperature. A lifetime on the order of 4 years is suggested, based on photoionization and magnetospheric sweeping. Either the atmosphere is transient and was formed recently or some process is currently supplying carbon dioxide to the atmosphere.     

Differentiation of Listeria monocytogenes and Listeria innocua by 16S rRNA genes and intraspecies discrimination of Listeria monocytogenes strains by random amplified polymorphic DNA polymorphisms

Differences in the 16S rRNA genes (16S rDNA) which can be used to discriminate Listeria monocytogenes from Listeria innocua have been detected. The 16S rDNA were amplified by polymerase chain reaction with a set of oligonucleotide primers which flank a 1.5-kb fragment. Sequence differences were observed in the V2 region of the 16S rDNA both between L. monocytogenes Scott A and L. innocua and between different L. monocytogenes serotypes. Although L. monocytogenes SLCC2371 had the same V2 region sequence as L. innocua, the two species were different within the V9 region at nucleotides 1259 and 1292, in agreement with previous studies (R.-F. Wang, W.-W. Cao, and M.G. Johnson, Appl. Environ. Microbiol. 57:3666-3670, 1991). Intraspecies discrimination of L. monocytogenes strains was achieved by using the patterns generated by random amplified polymorphic DNA primers. Although some distinction can be made within the L. monocytogenes species by their 16S rDNA sequence, a far greater discrimination within species could be made by generating random amplified polymorphic DNA patterns from chromosomal DNA. By using a number of 10-bp primers, unique patterns for each isolate which in all cases examined differentiate between various L. monocytogenes serotypes, even though they may have the same 16S rRNA sequences, could be generated.     

荧光定量PCR检测单核细胞增生性李斯特氏菌

[目的]建立一种快速检测单核细胞增生性李斯特氏菌的实时荧光定量PER方法.[方法]针对单核细胞增生性李斯特氏菌的特异基因hlyA,结合锁定寡核苷酸(LNA),设计引物和探针,利用阳性质粒和模拟标本建立单核细胞增生性李斯特氏菌实时定量荧光PCR检测方法.[结果]以单核细胞增生性李斯特氏菌为模板克隆了hlyA基因,得到阳性质粒,并进一步建立了荧光定量PCR方法,得到标准曲线Y=-3.273 X+37.640,相关系数R<'2>=1.000;该方法的灵敏度可以达到1.2×10 CFU/ml;人工污染猪肉检出限可以达到3.2×10<'2>CFU/ml.[结论]建立了快速检测单核细胞增生性李斯特氏菌的实时荧光定量PCR方法,为实现食品中单核细胞增生性李斯特氏菌的快速检测构建了一个技术平台.     

Regulation of hly expression in Listeria monocytogenes by carbon sources and pH occurs through separate mechanisms mediated by PrfA

Expression of the PrfA-controlled virulence gene hly (encoding the pore-forming cytolysin listeriolysin) is under negative regulation by readily metabolized carbon sources in Listeria monocytogenes. However, the hyperhemolytic strain NCTC 7973 exhibits deregulated hly expression in the presence of repressing sugars, raising the possibility that a defect in carbon source regulation is responsible for its anomalous behavior. We show here that the activity of a second glucose-repressed enzyme, alpha-glucosidase, is 10-fold higher in NCTC 7973 than in 10403S. Using hly-gus fusions, we show that the prfA allele from NCTC 7973 causes deregulated hly-gus expression in the presence of sugars in either the wild-type or the NCTC 7973 background, while the 10403S prfA allele restores carbon source regulation. However, the prfA genotype does not affect the regulation of alpha-glucosidase activity by repressing sugars. Of the two mutational differences in PrfA, only a Gly145Ser change is important for regulation of hly-gus. Therefore, NCTC 7973 and 10403S have genetic differences in at least two loci: one in prfA that affects carbon source regulation of virulence genes and another in an unidentified gene(s) that up-regulates alpha-glucosidase activity. We also show that the decrease in pH associated with utilization of sugars negatively regulates hly-gus expression, although sugars can affect hly-gus expression by another mechanism that is independent of pH.     

Macrophages activated by Listeria monocytogenes induce organ-specific autoimmunity

We have previously reported an experimental autoimmune model induced by the local infection of Listeria monocytogenes. The unilateral inoculation of virulent Listeria into a testis of a normal mouse induced a delayed-type hypersensitivity response against testicular antigen and caused autoimmune orchitis in the contralateral testis. The orchitis was transferred to naive mice by T cells from the intratesticularly infected mice. In this paper, we demonstrated that avirulent Listeria, which lacks the expression of listeriolysin O, failed to induce any anti-testicular responses or contralateral orchitis even when it was inoculated at a high dose into the testis. Furthermore, the intraperitoneal inoculation of virulent Listeria with testicular antigen induced the anti-testicular responses and orchitis although intraperitoneal inoculation of testicular antigen with avirulent Listeria failed to induce them. The difference between virulent and avirulent Listeria in the induction of anti-testicular responses was supposed to be dependent on the difference in macrophage activation by the two bacterial strains because, first, the anti-testicular responses were elicited in normal mice when macrophages from virulent Listeria-infected mice were intraperitoneally transferred with testicular antigen although no viable bacteria were detected from the macrophages, and secondly, in contrast, the intraperitoneal co-inoculation of macrophages from avirulent Listeria-infected mice and testicular antigen failed to elicit any anti-testicular responses. Finally, we found that the virulent Listeria-induced macrophages expressed a higher level of CD80 (B7-1) and CD86 (B7-2) molecules than did the avirulent Listeria-induced macrophages and naive peritoneal macrophages. These results thus suggest that virulent Listeria activates macrophages to induce autoreactive T cells while avirulent Listeria does not. The up-regulation of B7 molecules by virulent Listeria infection is a candidate of the mechanism for the activation of autoreactive T cells.     

High-pressure destruction kinetics of Listeria monocytogenes on pork

OBJECTIVE: To define the incidence of complications of endotracheal intubation and the factors associated with these complications. STUDY DESIGN: During a 22-month period, 227 intubated infants weighing <1,501 g were followed prospectively in a neonatal intensive care unit. Detailed records of events associated with airway management were kept after every intubation, in addition to clinical data. RESULTS: Eleven infants (4.8%) developed respiratory stridor after extubation which was treated with either systemic corticosteroids, racemic epinephrine and/or reintubation for respiratory failure. Four infants were submitted for bronchoscopy, mild subglottic stenosis with tracheal edema was found in 1 patient, granulation tissue and airway edema were noted in 3 infants. Traumatic intubation, prolonged ventilation, multiple intubations and bacterial colonization of the endotracheal tube were the factors associated with postextubation stridor. CONCLUSIONS: Subglottic stenosis is an infrequent complication of endotracheal intubation with current airway management of very-low-birth-weight infants. Less severe complications are still common, but they are usually amenable to clinical treatment. Bronchoscopy should be performed selectively only in infants with clinical evidence of airway obstruction after extubation.     

Listeria monocytogenes arthritis of several joints

A patient with rheumatoid arthritis (RA) developed an infection caused by Listeria monocytogenes in her left knee and both shoulder joints. The clinical presentation of the disease was rather indolent with relatively moderate joint symptoms. Moreover, the synovial fluid sample was only slightly turbid with a white blood cell count of 23.5 x 10(9)/1. As compared to the earlier reported cases of L. monocytogenes septic arthritis, our patient is unique because she had infection in several joints. The polyarticular joint involvement combined with the clinical symptoms resembling the activation of RA posed us diagnostic difficulties.     

The molecular mechanisms of actin-based intracellular motility by Listeria monocytogenes

A rapid, sensitive method was developed for the quantification of the R- and S-enantiomers of ketoprofen and their acyl glucuronide conjugates in the plasma and dialysate of hemodialysis-dependent anephric patients. Unconjugated R- and S-ketoprofen plasma concentrations were determined directly by liquid chromatography using a S,S-Whelk-O1 chiral stationary phase. R- and S-Ketoprofen glucuronide for use as standard were resolved using a C18 reversed-phase HPLC column with a mobile phase containing the ion-pair reagent tetrabutylammonium hydrogen sulfate. Plasma glucuronides, however, could not be directly quantified due to matrix interference. Therefore, the glucuronides were isolated using reversed-phase HPLC and quantified after alkaline hydrolysis using the S,S-Whelk-O1 chiral stationary phase column.     

Expression of listeriolysin O and ActA by intracellular and extracellular Listeria monocytogenes

A gene encoding a chitin synthase with a myosin motor-like domain (csm1) was isolated from Pyricularia oryzae using a PCR fragment amplified from a fungal chitin synthase conserved region. The deduced amino acid sequence of csm1 is homologous to that of CsmA of Aspergillus nidulans (65% identity). The putative gene product of csm1 is consisted of the myosin motor-like domain and a chitin synthase domain as in A. nidulans csmA. The chitin synthase domain of its C-terminus was also homologous to Aspergillus fumigatus ChsE (61.4% identity) and Ustilago maydis Chs6 (48.6% identity) that encode class V chitin synthases. Northern analysis demonstrated that the csm1 was expressed throughout the mycelial growth of P. oryzae. This is the first report on the isolation of the gene encoding a class V chitin synthase with the myosin motor-like domain from P. oryzae.     

Inactivation of Listeria monocytogenes in milk by pulsed electric field

Pasteurized whole, 2%, and skim milk were inoculated with Listeria monocytogenes Scott A and treated with high-voltage pulsed electric field (PEF). The effects of milk composition (fat content) and PEF parameters (electric field strength, treatment time, and treatment temperature) on the inactivation of the bacterium were studied. No significant differences were observed in the inactivation of L. monocytogenes Scott A in three types of milk by PEF treatment. With treatment at 25 degrees C, 1- to 3-log reductions of L. monocytogenes were observed. PEF lethal effect was a function of field strength and treatment time. Higher field strength or longer treatment time resulted in a greater reduction of viable cells. A 4-log reduction of the bacterium was obtained by increasing the treatment temperature to 50 degrees C. Results indicate that the use of a high-voltage PEF is a promising technology for inactivation of foodborne pathogens.     

Bacterial endocarditis produced by Listeria monocytogenes. Case presentation and review of literature

A patient with endocarditis produced by Listeria monocytogenes is presented, the twelfth such case reported. A review of the available literature shows that the infection has involved only the left side of the heart, has not been associated with debilitating diseases, and carries a significant mortality rate. Otherwise, clinical and laboratory features have been the same as those of usual forms of bacterial endocarditis. It is pointed out that the Listeria organism is commonly mistaken for Erysipelothrix and diphtheroids and that a battery of tests should be employed before one disregards these microorganisms as "contaminants".     

Phosphatidylinositol-specific phospholipase C from Listeria monocytogenes contributes to intracellular survival and growth of Listeria innocua

Listeria monocytogenes is a facultative intracellular organism that is capable of replicating within macrophage and macrophage-like cells. The species secretes a phosphatidylinositol-specific phospholipase C (PI-PLC) encoded by the plcA gene. A plcA gene from L. monocytogenes was cloned downstream of a gram-positive promoter in the plasmid pWS2-2. To determine what effect plcA would have on intracellular survival when introduced into Listeria innocua, a species that does not growth intracellularly or contain plcA, transformation with the recombinant pWS2-2 plasmid was performed. Phospholipase C activity in Listeria innocua/pWS2-2 was confirmed on a brain heart infusion-phosphatidylinositol agar plate, whereas wild-type L. innocua did not produce PI-PLC activity. Intracellular growth of L. innocua/pWS2-2 was subsequently measured in the macrophage-like cell line J774 by Giemsa staining and viable count determinations at specific time points following infection. The J774 cells infected with wild-type L. innocua showed a falling viable count through 8 h postinfection. Although J774 cells infected with L. innocua/pWS2-2 also initially displayed reduced viable counts, the viable count rose after 6 h postinfection and increased further at 8 h postinfection before a subsequent decline again at 16 h postinfection. Giemsa staining revealed fewer than 6 bacteria in individual macrophage cells at 2 h postinfection, and yet approximately 15% of the J774 cells had 6 to 12 bacteria localized to one area of the macrophage cell after 6 h; moreover, electron micrographs showed that the L. innocua/pWS2-2 cells were replicating inside the phagosome of the host cell. Furthermore, Thoria Sol labeling demonstrated that lysosomes had fused with these phagosomes, and acridine orange staining revealed that the compartments were acidified. These results demonstrate that L. innocua cells transformed with the plasmid-borne plcA gene, and expressing functional PI-PLC, are able to grow intracellularly in what appear to be phagolysosomes, although between 3 and 6 h is needed for this to manifest itself. Intracellular growth specifically in L. innocua may be a secondary function associated with the plcA gene product. The addition of this one gene, plcA, to a species of Listeria that in the wild-type state does not replicate intracellularly apparently can now allow some of the bacteria to transiently multiply inside the phagosomes of host macrophage cells.     

Detection of Listeria monocytogenes in humans, animals and foods

The Listeria monocytogenes-carrying rates were 100% for listeriosis patients and 1.3% for healthy humans. The L. monocytogenes contamination rates for retail sliced beef (34.2%) and pork (36.4%) were significantly higher (p < 0.05) than those for cattle (2.0%) and pigs (0.8%) and for cattle (4.9%) and swine (7.4%) carcasses. The percentages of serotypes 1/2a, 1/2b and 4b which are most dominant in human patients were high in isolates from fresh (90.0%) and processed (100%) fish and shellfish and imported natural cheese (96.7%).