Listeria monocytogenes and its role in human infection

Listeria innocua infection in an old case of total knee replacement - an unusual case report

Prosthetic implant-associated arthritis due to Listeria is mostly reported for Listeria monocytogenes. Here, we describe a patient who underwent total knee replacement 12 years ago and presented with pain, tenderness, redness and local rise in temperature in the right knee. Purulent fluid was aspirated. Upon microbiological analysis, culture yielded Listeria innocua. L. innocua is rare. Listeria is not reported as a contaminant and routine cultures may be negative. Because of the long interval between surgery and the onset of symptoms, clinical suspicion, radiological investigations and analysing multiple samples are of immense help.

In vitro protective effect of lactic acid bacteria on Listeria monocytogenes adhesion and invasion of Caco-2 cells

The adhesion of Listeria monocytogenes to intestinal endothelial cells is a crucial step in the infection process, which is not well understood. In this study, we evaluated the potential ability of bacteriocin-producing Enterococcus faecium, Leuconostoc mesenteroides and Lactobacillus sakei strains to prevent the adhesion and invasion of eukaryotic cells by ten different L. monocytogenes isolates. The results showed that E. faecium 130 co-cultured with L. monocytogenes was the most effective in preventing infection of Caco-2 cells, as the vast majority of isolates showed significantly lower adhesion counts and invasion rates below the quantification limit of the method (<30 cfu/plate). L. sakei 1 was the least effective strain in preventing L. monocytogenes infection; only one isolate presented a lower adhesion rate and two isolates reduced the invasion rate of Caco-2 cells. Fluorescence in situ hybridisation (FISH) assay was shown to be an effective tool to illustrate and identify species in co-culture with L. monocytogenes during the adhesion process to Caco-2 cells.

Incidence of Listeria spp. in raw milk in Shahrekord, Iran

Listerosis may be transmitted by direct contact with infected animals or by consumption of contaminated vegetables, meat, or milk products. Raw milk samples obtained from the Milk Industry Foundation, five private dairy companies, and individual dairy farms in Shahrekord, Iran, were tested for the presence of Listeria species. A total of 500 raw milk samples were analyzed by two-stage enrichment techniques. Identification of isolated Listeria was done using the Micro-ID Listeria Kit (Remel, Lenexa, KS). The overall incidence of Listeria species in raw milk was 2.2%. L. monocytogenes was found in 1.6% of the raw milk samples, while L. innocua was found in 0.6% of the samples. Additional studies are needed to assess the public health impact of contaminated milk in Shahrekord.

Bacterial host resistance models in the evaluation of immunotoxicity

To assess potential immunomodulatory effects of a drug, pollutant, or natural product, an analysis of an exposed host's ability to resist challenge with a viable bacteria is one of the best gauges. Many factors govern whether a host exposed to a test agent and then infected becomes ill or dies at rates greater than infected control counterparts. Beyond the status of the host's immunocompetence, a bacterium's route of entry into the host and its inherent virulence are important variables determining how (and rate at which) an infection resolves. A pre-determination of endpoint(s) to be defined is critical during planning of resistance assays. If a study is to determine overall changes in immunocompetence due to exposure (regardless of regimen or dosage of test agent), then assessing shifts in morbidity/mortality at a defined lethal dose [LD(x)] value for the chosen route of infection would suffice. However, if a study is to define extent of immunomodulation in a particular body organ/cavity--or specific alterations in particular aspects of the humoral or cell-mediated immune responses--then careful selection of the pathogen, dose of the inoculum, means of infection of target site, and extent of the post-infection period to be examined, need to be made prior to host exposure to the test toxicant. This review will provide the Reader with background information about bacterial infections and how endpoint selection could be approached when designing resistance assays. An overview of protocols involved in the assays (e.g., bacterial preparation, host infection, post-infection endpoint analyses) and information about three bacteria that are among the most commonly employed in resistance assays is provided as well.

A comparison of selected methods for measuring the virulence properties of Listeria spp

The comparative ability of different methods to assess virulence of Listeria species was investigated in ten Listeria strains. All strains were initially subjected to pulsed-field gel electrophoresis analysis to determine their relatedness. Virulence characteristics were subsequently tested for by (i) determining the presence of six virulence genes by polymerase chain reaction; (ii) testing for the production of listeriolysin O, phosphatidylcholine phospholipase C, and phosphatidylinositol-specific phospholipase C; (iii) investigating the hydrophobicity of the strains; (iv) determining the strains ability to attach to, enter, and replicate within the Caco-2 cells. Variations in most of the virulence characteristics were obvious across the strains for the range of tests performed. A wide range of anomalous results among methods were apparent. In particular, the presence of virulence genes was found to be unrelated to the production of virulence-associated proteins in vitro, while virulence protein production and hydrophobicity in Listeria monocytogenes were found to be unrelated or marginally related, respectively, to the ability to invade the Caco-2 cell line. It was concluded that the methods investigated were unable to consistently and unequivocally measure the differences in the virulence properties of the strains.

Pathogenicity and production of virulence factors by Listeria monocytogenes isolates from channel catfish

Pathogenicity of four channel catfish Listeria monocytogenes isolates (CCF1, CCF4, HCC7, and HCC23) was examined in a comparative manner with virulent type strains L. monocytogenes ATCC 19115 and EGD and avirulent type strain ATCC 15313 in BDF and A/J mice. Isolates HCC7 and CCF1 (both serovar 1) caused similar percent mortalities and 50% lethal concentration values when compared with virulent type strains and were therefore considered pathogenic. The presence of the virulence factors listeriolysin (LLO), phosphotidylcholine-phospholipase (PC-PLC), and phosphotidylinositol-phospholipase (PI-PLC) was determined using specific activity tests. The virulent catfish isolates were positive for production of LLO, PC-PLC, and PI-PLC. However, catfish isolate HCC23 was not virulent in mice despite being hemolytic, suggesting that not every hemolytic L. monocytogenes strain is virulent. With the exception of HCC7, all virulent strains displayed enhanced LLO production in a special stress medium, whereas almost undetectable LLO activity was present when catfish isolates and virulent type strain L. monocytogenes were grown in a rich medium such as brain heart infusion. Avirulent strains were found to lack or have decreased expression of LLO, PC-PLC, or PI-PLC.

Production of monoclonal antibodies to Listeria monocytogenes and their application to determine the virulence of isolates from channel catfish

We produced monoclonal antibodies (MAbs) to the extracellular proteins of Listeria monocytogenes EGD grown in Chelex-treated improved minimal medium. Ten of the positive hybridomas generated were chosen for further characterization. Seven of the MAbs reacted with a protein having a molecular mass of 60 kDa. These MAbs inhibited listeriolysin (LLO)-mediated hemolysis, and two of them were specific for LLO and none of the other thiol-activated toxins tested. In an enzyme-linked immunosorbent assay and Western blot analysis, five of the anti-LLO MAbs reacted with ivanolysin from Listeria ivanovii. Three of the 10 MAbs reacted with a 29-kDa protein on Western blots and neutralized the phosphatidylcholine-specific phospholipase C (PC-PLC) activity of L. monocytogenes. These three anti-PC-PLC MAbs did not react with phospholipases from five different gram-positive bacteria. However, the anti-PC-PLC MAbs recognized a 27-kDa extracellular protein from L. ivanovii and neutralized sphingomyelinase activity in a hemolysis test that demonstrates the antigenic relatedness of listerial phospholipases. These data indicate that listerial thiol-activated toxins possess species-specific epitopes and share group-specific epitopes. This is the first description of MAbs that neutralize listerial PC-PLC, and the data suggest that there is antigenic similarity between L. monocytogenes PC-PLC and L. ivanovii sphingomyelinase. The reactions of the MAbs with catfish isolates of L. monocytogenes suggested that some of the isolates examined lack the LLO and/or PC-PLC required for pathogenicity. The MAbs described here differentiated some catfish isolates from previously described type strain-pathogenic isolates and could be useful for detecting and determining the virulence of L. monocytogenes in food and clinical samples and for detecting L. ivanovii in veterinary clinical samples.

Listeria monocytogenes-associated acute hepatitis in a liver transplant recipient

We report a case of Listeria monocytogenes bacteriemia with liver involvement mimicking acute viral hepatitis in a liver transplant recipient. The patient presented with fever, jaundice and alanine aminotransferase levels ten times the upper limit of normal. Liver biopsy showed signs of acute hepatitis and occasional granulomas. Both blood and liver biopsy cultures were positive for Listeria monocytogenes. The patient received a 3 week course of ampicillin and gentamicin with clinical and biochemical recovery. Liver involvement during Listeria infections is unusual, and most cases occur in patients with underlying hepatic disease and impaired cell-mediated immunity. To our knowledge only one such case has previously been reported in a liver transplant patient. Furthermore, in the present case we isolated the causal agent from the liver biopsy specimen.

A simple colony-blot method for identification of Listeria in food samples

A method for identification of Listeria in food samples was developed. It consisted of cultivating of suspected specimen on standard agar medium, direct absorption of grown colonies onto nitrocellulose membrane and processing of the latter with rabbit serum raised against purified cell wall protein Lm79/39 of L. monocytogenes. Analysis using anti-rabbit peroxidase conjugate and 4-chloro-1-naphthol and H2O2 solutions allowed direct detection of Listeria colonies which remained readily available for subsequent isolation.

Anti-DNA.RNA antibodies: an efficient tool for non-isotopic detection of Listeria species through a liquid-phase hybridization assay

This study was undertaken to evaluate the potential of a new approach using anti-DNA.RNA monoclonal antibodies to detect Listeria in both pure culture and inoculated meat and meat products. A sensitive liquid-phase assay was first developed, based on the formation in solution of a hybrid between a 784-bp DNA probe, specific for the genus Listeria, and target rRNA. Monoclonal antibody and antisera raised against hybrid nucleic acids were then used in various immunoenzymatic assays to detect specific hybrids formed in solution. System 2, using a double sandwich enzyme-linked immunosorbent assay, and system 1, using a biotinylated probe, proved to be very effective. The method using biotin-streptavidin complex, however, resulted in a higher background signal. System 2 described here, using unlabeled probe, was more effective. This strategy allowed the detection of as little as 2.5 pg target RNA from pure culture and 500 cells from inoculated meat homogenate, even in the presence of other contaminating bacteria. The assay was more sensitive and could be completed within 3 h, as opposed to several days when conventional culture methods were used.

Listeria septicemia complicating bone marrow transplantation for Diamond-Blackfan syndrome

Infection with Listeria monocytogenes is uncommon in patients receiving cytotoxic chemotherapy, and is even rarer among recipients of bone marrow transplantation. Hemosiderosis, either idiopathic or caused by transfusion, appears to be another risk factor. We report a 3-year-old Chinese girl with transfusion-dependent Diamond-Blackfan syndrome who had L. monocytogenes septicemia when she received an allogeneic bone marrow transplantation. She was treated successfully with intravenous ampicillin. Our case adds to the clinical evidence that patients with iron overload are susceptible to listeriosis, particularly when they are immunocompromised and do not receive iron-chelation treatment.

The occurrence and seasonal changes in the isolation of Listeria spp. in shop bought food stuffs, human faeces, sewage and soil from urban sources

Eight hundred and twenty-two shop-bought food specimens, 136 soil and 692 faecal specimens were cultured for Listeria spp. in a regular, year round survey. 19.7% (162/822) of the foods, 93.9% (108/115) of the sewage, 14.7% (20/136) soils and 1% (7/692) of faeces yielded Listeria spp. with 10.5% foods, 60.0% sewage, 0.7% soils and 0.6% faeces containing L. monocytogenes. No seasonal variation was noted in isolates from either sewage or foods, with L. monocytogenes and L. innocua being the commonest species in both L. ivanovii when isolated from foods was strongly associated with mutton. Poultry was most likely to contain L. monocytogenes (65.6%, 21/32) and in the greatest numbers. A high percentage of beef (34.6%, 9/26), lamb (40%, 8/20), pork (28.1%, 9/32) and sausages (34.7%, 8/23) also contained L. monocytogenes. L. monocytogenes was rarely isolated from paté (1/40) or soft cheeses (1/251), both of which have been involved with foodborne listeriosis outbreak in the UK. Listeria spp. were commonest in faeces and soils in July to September but the predominant species isolated were different with L. monocytogenes and L. innocua the commonest from faeces and L. ivanovii and L. seeligeri the most common from soil.

Perinatal listeriosis in a Dutch woman returning from holiday in France

A case is reported of perinatal infection and fetal death due to Listeria monocytogenes serotype 4B in a 28-weeks pregnant woman, who had spent her holiday in an area in France where an epidemic outbreak of listeriosis had occurred. Sero- and phage-typing combined with sensitive DNA-typing demonstrated that the Listeria was identical to the strain responsible for the outbreak in France. Although listeriosis appears to be an uncommon cause of perinatal infection, practicing obstetricians should be aware of the possibility.

Diagnostic ultrastructure of Listeria monocytogenes in human central nervous tissue

The pathogenesis of Listeria monocytogenes infection of the human central nervous system is poorly understood and ultrastructural aspects are not documented. A case of fatal human L. monocytogenes meningoencephalitis is described, in which diagnosis was confirmed by blood culture and in which special staining (Brown's) showed slender gram-positive bacilli in inflamed areas of the brainstem at autopsy. Electron microscopy of blocks rescued from formalin revealed rods, up to 2.5 microns long x 0.4 microns in diameter, with gram-positive type cell walls and distinctive conic ends, the latter being apparent in axial section only. The organism was either free within the cytoplasm or within endosomes or phagosomes of macrophages, smooth muscle cells, and endothelial cells. In one instance, one was seen adhering to the luminal aspect of the vascular endothelium. Central nervous system parenchymal cell infection was suspected but not confirmed. Intra-cytoplasmic bacteria were surrounded by an electron-transparent halo and, beyond that, a cloud of host-derived microfilaments, as previously described by others in vitro and in animals. The morphology of L. monocytogenes is compared with that of other intracellular pathogens and is found to be distinctive, suggesting the value of ultrastructural study in diagnosis. Such work could also help to solve outstanding pathogenetic questions of central nervous system invasion and spread.

Sodium chloride, potassium chloride, and virulence in Listeria monocytogenes

Virulence, as determined in a mouse model, and the virulence factor activities of catalase, superoxide dismutase, and listeriolysin O were examined in a parental strain (10403S) and in a nonhemolytic mutant strain (DP-L224) of Listeria monocytogenes. The cells were propagated in media containing various concentrations of sodium chloride or potassium chloride. Strains 10403S and DP-L224 exhibited significant increases in catalase activity and listeriolysin O activity when grown in medium containing either salt at 428 mM. The superoxide dismutase activities for both strains increased when they were grown in medium containing either salt. The superoxide dismutase activity was significantly increased only when cells were propagated in medium containing no salt compared with that when they were propagated in medium containing either salt at 1,112 mM. In addition, the listeriolysin O activity was highest for cells propagated in medium containing KCl at 428 mM, while the activity was significantly less for cells propagated in medium containing NaCl at an equal concentration. Virulence was examined in mouse livers and spleens after intravenous infection, and approximate 50% lethal doses were determined after intragastric and intraperitoneal infection. Each method of infection indicated that listeriolysin O is required for virulence, while growth in salt-containing medium or the production of higher levels of catalase, superoxide dismutase, and listeriolysin O do not appear to enhance the virulence of L. monocytogenes.

Listeria monocytogenes hepatitis in a liver transplant recipient: a case report and review of the literature

Listeria is an uncommon cause of hepatitis in adults. We report the case of a liver transplant recipient who presented with a clinical picture of acute hepatitis, 8 months after grafting. Blood cultures yielded Listeria monocytogenes. The patient made a full clinical recovery after adequate antimicrobial therapy (ampicillin and gentamicin intravenously for 4 weeks). Hepatitis was attributed to the Listeria infection. We believe this is the first reported case of Listeria hepatitis in an organ transplant recipient.

Development of a 16S rRNA-based oligomer probe specific for Listeria monocytogenes

Crude rRNA was isolated from Listeria monocytogenes, L. innocua, and L. ivanovii and sequenced by a reverse transcriptase method. Only two sequence regions were found to differ for L. monocytogenes versus L. innocua or L. ivanovii. Two oligonucleotide probes (RL-1 and RL-2) complementary to these two regions of rRNA of L. monocytogenes were synthesized. The RL-1 probe had one base while the RL-2 probe had two bases which differed for L. monocytogenes versus L. innocua and L. ivanovii. Use of a dried gel hybridization in place of Northern (RNA) hybridization or dot blot hybridization indicated that the RL-2 probe hybridized with all 36 strains of L. monocytogenes tested but not with 6 other Listeria species and 11 other bacteria tested. The RL-2 probe is specific for L. monocytogenes, while the RL-1 probe showed some cross-reactions with other Listeria species. An alkaline phosphatase-labeled RL-2 probe could be used in a dot blot hybridization test and gave good results, but a 32P-labeled RL-2 probe was more sensitive than the nonradioactive probe and the 32P-labeled probe was useable for up to 2 months, even though the 32P was highly degenerated.

Listeria monocytogenes, a food-borne pathogen

The gram-positive bacterium Listeria monocytogenes is an ubiquitous, intracellular pathogen which has been implicated within the past decade as the causative organism in several outbreaks of foodborne disease. Listeriosis, with a mortality rate of about 24%, is found mainly among pregnant women, their fetuses, and immunocompromised persons, with symptoms of abortion, neonatal death, septicemia, and meningitis. Epidemiological investigations can make use of strain-typing procedures such as DNA restriction enzyme analysis or electrophoretic enzyme typing. The organism has a multifactorial virulence system, with the thiol-activated hemolysin, listeriolysin O, being identified as playing a crucial role in the organism's ability to multiply within host phagocytic cells and to spread from cell to cell. The organism occurs widely in food, with the highest incidences being found in meat, poultry, and seafood products. Improved methods for detecting and enumerating the organism in foodstuffs are now available, including those based on the use of monoclonal antibodies, DNA probes, or the polymerase chain reaction. As knowledge of the molecular and applied biology of L. monocytogenes increases, progress can be made in the prevention and control of human infection.

Enteral feeding and infection in the immunocompromised patient

Evidence is accumulating that immunocompromised individuals are at an increased risk of infection from foodborne pathogens including Campylobacter jejuni, Listeria monocytogenes, Salmonella spp. Normal bacterial flora and contaminants of foods and enteral feeds can also result in nosocomial infection in susceptible individuals. Safe food handling, low-microbial diets, and measures to reduce bacterial contamination of enteral foods can reduce exposure to potential pathogens in the food supply.

Listeria faecal carriage by renal transplant recipients, haemodialysis patients and patients in general practice: its relation to season, drug therapy, foreign travel, animal exposure and diet

About 2.3% (16/700) of faecal specimens from renal transplant recipients and patients having home haemodialysis as well as patients attending their general practitioners with symptoms of gastroenteritis yielded Listeria species 40% of positive faeces contained more than one Listeria species or serovar. The proportion of positive specimens was similar in all three patient groups. Listeria were isolated from 5.6% (10/177) of renal transplant recipients on one or more occasions over the period of a year. The commonest species was L. monocytogenes and type 4b the commonest serovar. Carriage was more common in July and August than other times of year, and less than 28 weeks in duration. In renal transplant recipients carriage was positively related to treatment with ranitidine, consumption of more than three types of cheese in the previous 20 months, and consumption of English cheddar cheese more than once per week.

Maternal listeriosis in pregnancy without fetal or neonatal infection

Maternal infection with Listeria monocytogenes without fetal or neonatal involvement is relatively rare. Eleven cases arising in England and Wales between 1967 and 1988 are presented.

Cloning of the listeriolysin O gene and development of specific gene probes for Listeria monocytogenes

A clone containing 3.1 kb of Listeria DNA was selected from a gene library of Listeria monocytogenes Scott A strain. The Escherichia coli clone produced hemolysin on sheep blood agar and in sonicated extracts but very little in the culture supernatant. This 3.1-kb DNA fragment and a 650-bp HindIII fragment located within the listeriolysin gene were used as probes in a colony hybridization assay. Both probes were specific for L. monocytogenes and did not hybridize with any other Listeria strains at high stringency. Two synthetic probes, one from the 650-bp HindIII fragment and one from the carboxy-terminal region of the protein, were also specific for L. monocytogenes.

Characterization by DNA restriction endonuclease analysis of Listeria monocytogenes strains related to the Swiss epidemic of listeriosis

Listeria monocytogenes strains responsible for outbreaks of listeriosis were studied by using serotyping and phage typing. An additional approach based on restriction endonuclease analysis (REA) of the chromosomal DNA was used to characterize L. monocytogenes strains collected from various sources during and after a Swiss outbreak of listeriosis (1983 to 1987). Among the 169 wild-type strains of Listeria spp. that were examined, 161 (95%) belonged to the species L. monocytogenes, of which 109 were of human origin. Ten different REA profiles were obtained from the 120 L. monocytogenes serotype 4b strains tested. All 57 serotype 4b strains that were identified as Swiss epidemic strains by phage typing clustered in two closely related REA profiles. In particular, 10 L. monocytogenes 4b strains isolated from the brand of soft cheese responsible for the outbreak and from its direct environment were indistinguishable from isolates from 40 patients by both phage typing and REA analysis. However, 5 of the 17 non-phage-typeable L. monocytogenes strains and 18 L. monocytogenes strains with a phage type different from those of the Swiss epidemic types showed the same profile. REA enabled the characterization of non-phage-typeable strains and, thus, seems a promising tool for L. monocytogenes typing, especially during epidemiological investigations.

A comparative study of clinical and food isolates of Listeria monocytogenes and related species

Ninety-six isolates of presumptive or confirmed Listeria monocytogenes were obtained from local clinical (30 isolates) or food laboratories (66 isolates). Minimal biochemical analysis identified only 80% of these isolates as L. monocytogenes the remaining included L. seeligeri, 1%, or the non-haemolytic L. innocua, 19%. The 27 clinical and 50 food isolates, mainly from meat products, frozen confectionaries, and cheeses, confirmed as L. monocytogenes were compared biochemically and serologically. Twenty-one isolates, including some strains of L. innocua and L. seeligeri, were examined for pathogenicity in immunocompromized mice and 44 typed using bacterial restriction endonuclease DNA analysis (BRENDA). Only isolates of L. monocytogenes were found to be pathogenic. Biovar-typing of the isolates was unreliable and provided poor discrimination. Serogroups 1/2 and 4 predominated among clinical and food isolates and BRENDA provided better discrimination among isolates. Ten stable and reproducible restriction patterns were observed among the Listeria sp. isolates studied. Overall, a combination of techniques gave the best discrimination and indicated their potential for use as epidemiological tools.

Catalase, superoxide dismutase, and hemolysin activities and heat susceptibility of Listeria monocytogenes after growth in media containing sodium chloride

The activities of catalase, superoxide dismutase, and a thiol-activated hemolysin produced by four strains of Listeria monocytogenes propagated in media containing various concentrations of sodium chloride were examined. L. monocytogenes 7644 showed an increase in catalase, superoxide dismutase, and thiol-activated hemolysin activities when grown in a medium containing 2.5% (wt/vol) NaCl followed by a decrease in activities when propagated in media containing salt concentrations higher than 2.5%. L. monocytogenes LCDC 81-861 demonstrated enhanced catalase activity when grown in media containing NaCl ranging from 1.5 to 4.6% and increased superoxide dismutase activity when propagated in media containing 1.5 to 3.5% NaCl. L. monocytogenes LCDC 81-861 did not exhibit any detectable hemolysin activity under the conditions tested. After growth in various NaCl-containing media, both strains were subjected to sublethal heat injury for 30 min at 55 degrees C. L. monocytogenes LCDC 81-861 showed increased sensitivity to the heat treatment when grown in media containing 4.6 and 6.5% NaCl, whereas L. monocytogenes 7644 did not exhibit enhanced heat lability.

Evaluation of the Mast ID and API 50CH systems for identification of Listeria spp

A multipoint inoculation technique (Mast ID) for the identification and species determination of Listeria monocytogenes (sensu strictu) and six other species of the genus Listeria was evaluated. This was compared with the commercially available API 50CH system. Both methods successfully identified all 123 strains tested. The Mast ID system is inexpensive and utilizing a multipoint inoculation technique permits the screening of up to 21 isolates per 9-cm petri dish. The API 50CH system was more expensive and time consuming and is therefore suitable only for the examination of smaller numbers of strains.

Recurrent Listeria monocytogenes bacteraemia in a liver transplant patient

We report a case of a recurrent Listeria monocytogenes bacteraemia in a 46 year-old liver transplant patient. Serotyping revealed that the two episodes of bacteraemia were caused by different strains. The possibility of a recrudescence of a persisting infection was rejected. We concluded that the recurrent bacteraemia in this predisposed patient was due to re-infection, and that antibiotic treatment (amoxicillin plus an aminoglycoside) resulted in a complete eradication of the infective microorganism. Therefore long-term suppressive antibiotic treatment was not indicated. The source of these L. monocytogenes infections was not found.

Efficacy of a variety of disinfectants against Listeria spp

The efficacy of 14 disinfectants against Listeria innocua and two strains of Listeria monocytogenes in the presence of organic matter was studied. Quantitative efficacy tests were used. Many of the disinfectants tested were not as effective on Listeria spp. when the test organisms were dried onto the surface of steel disks (carrier tests) as they were when the organisms were placed in suspension (suspension test). The presence of whole serum and milk (2% fat) further reduced the disinfectant capacities of most of the formulations studied. Only three disinfectants (povidone-iodine, chlorhexidine gluconate, and glutaraldehyde) were effective in the carrier test in the presence of serum; however, all three were ineffective when challenged with milk (2% fat). Only one solution, sodium dichloroisocyanurate, was effective in the presence of milk. All but four formulations (chloramine-T, phosphoric acid, an iodophor, and formaldehyde) were effective in the suspension tests, regardless of the organic load. L. monocytogenes was observed to be slightly more resistant to disinfection than L. innocua was. There was no difference in disinfectant susceptibility between the two strains of L. monocytogenes. These findings emphasize the need for caution in selecting an appropriate disinfectant for use on contaminated surfaces, particularly in the presence of organic material.

Listeria monocytogenes meningitis in the acquired immune deficiency syndrome--limitations of conventional typing methods in tracing a foodborne source

Listeria monocytogenes is an unusual pathogen in the acquired immune deficiency syndrome (AIDS). We report a case of meningitis caused by L. monocytogenes in a patient with AIDS dementia who had eaten cheese from which a similar organism was isolated.

Identification and enumeration of virulent Listeria strains

Recent outbreaks and a continuous increase in cases of listeriosis underscore the need for rapid, sensitive and reliable techniques to detect Listeria. Of the species of Listeria, only L. monocytogenes has been found to be associated with human infections. One factor which definitely contributes to its pathogenicity is the presence of hemolysins, although L. ivanovii and L. seeligeri also elaborate hemolysins. Based upon cloned hemolysin genes, we have developed DNA probes specifically for detecting L. monocytogenes. The technique combines growth of bacterial colonies on selective agar plates and DNA hybridization of these colonies on a solid matrix. This technique permits identification and enumeration, and the entire procedure can be completed in 3-4 days. Our method was found to be suitable for identifying and enumerating this organism in various foods, the main vehicle of human infection. Advantages and disadvantages of this technique are discussed and compared with other existing techniques.

Evaluation of API 20 STREP system for identifying Listeria species

The API 20 STREP system was used to identify 146 known strains from seven species of the genus Listeria, including both pathogenic and environmental strains. The gallery was easy to use and tests, with the exception of leucine arylamidase (LAP) and starch fermentation (AMD), were simple to interpret. Identification to genus level was satisfactory but differentiation between species was poor. Using the API 20 STREP the haemolytic species L monocytogenes, seeligeri, and ivanovii could easily be differentiated from the non-haemolytic species L welshimeri, innocua, grayii and murrayi. Of the haemolytic species, L monocytogenes could not be distinguished from L seeligeri but L ivanovii could be separated from the two other haemolytic species because it fermented ribose. Non-haemolytic L welshimeri could not be differentiated from non-haemolytic L innocua, but mannitol and ribose fermenting non-haemolytic L grayi and L murrayi were easily differentiated from the other two non-haemolytic species. The API 20 STREP identified Listeria in four hours and therefore might be used for rapid identification of strains causing infection in man. It would, however, not be useful to identify environmental isolates when speciation is important.

Listeria monocytogenes meningitis in previously healthy adults

A retrospective study of four sporadic cases of Listeria monocytogenes meningitis is reported. Contrary to the conventional epidemiology these patients were adults who were not immuno-compromised. Although all four cases produced positive cerebrospinal fluid cultures, in three, listeria was not microscopically identified. Protein and glucose contents of cerebrospinal fluids were variable and all samples showed lymphocytic pleocytosis. All four had neutrophil leucocytosis in peripheral blood. The unwary may dismiss lymphocytic meningitis as being of 'viral' origin, thereby making an important diagnostic misjudgement of vital therapeutic importance. Intravenous ampicillin is the drug of first choice for treatment of listeria meningitis; third generation cephalosporins are ineffective.