Serious infection with the bacterium L. monocytogenes mainly manifests as sepsis and/or meningitis. A particular entity is Listeria brain stem encephalitis, which is characterized by progressive brain stem deficits. The condition is fatal unless early treated. The purpose of the present study was to assess the incidence of brain stem encephalitis in a population-based listeriosis material. Medical records from 212 of the 240 patients with serious listeriosis reported in Norway from 1977 to 2000, as well as autopsy material from 8 of these patients, were available. This material was searched for clinical and neuropathological evidence of brain stem infection. Findings indicating brain stem encephalitis were present in 19 of the 172 patients with adult listeriosis (11%) but none of the 40 pregnancy-related listeriosis cases. None of the 19 patients had been diagnosed with Listeria brain stem infection originally. We conclude that brain stem encephalitis is relatively common in this Norwegian listeriosis material.
A 70-year-old woman fell seriously ill overnight with meningitis and was admitted to hospital. Cerebrospinal fluid culture yielded Listeria monocytogenes. One of the first problems in solving a human case of listeriosis suspected to be foodborne is to find the foods likely to have been transmitting L. monocytogenes. Two enrichment procedures and a direct plating procedure were used for isolation of the bacteria from different food items collected from the patient's refrigerator, local retail store and producer. Samples of vacuum-packed products of sliced pork brawn, sliced cooked medwurst and berliner wurst of the same brand harboured L. monocytogenes. Serotyping and restriction enzyme analysis (REA) with pulsed-field gel electrophoresis (PFGE) were used to characterize and compare 41 isolates, including the human strain. At least three clones were present in the foods investigated, and one of these was identical to the human clone. This clone was present in samples of medwurst from the patient's refrigerator and the local retail store. This is, to our knowledge, the first proven foodborne case of listeriosis reported in Sweden.
Microbiological and chemical changes were determined during the smoking and drying of salmon strips processed at 29 to 31 degrees C for 4 days at a facility in Alaska in 1993. During the process, Staphylococcus aureus populations increased to more than 10(5) CFU/g after 2 to 3 days of processing. Subsequent laboratory studies showed that a pellicle (dried skinlike surface) formed rapidly on the strips when there was rapid air circulation in the smokehouse and that bacteria embedded in or under the pellicle were able to grow even when heavy smoke deposition occurred. Under these conditions, an inoculum of 26 CFU/g of S. aureus increased to 10(5) CFU/g after 3 days of processing. Elimination of preprocess drying and reduction in air flow during smoking resulted in smoke deposition before pellicle formation and enabled the product to reach levels of water-phase salt and water activity that inhibit the growth of S. aureus and Listeria monocytogenes. In 1994, these modifications were then applied during processing at an Alaskan facility, and S. aureus could not be detected in the finished product. L. monocytogenes was detected in the raw product area, on the processing tables, and on the raw salmon strips, but it was not detected in the finished product when the smoke was applied before pellicle formation.
Two hundred seventy-nine cases of human listeriosis (92 pregnancy-related cases and 187 non-pregnancy-related cases) caused by a serovar 4b and phagovar 2389:2425:3274:2671:47:108:340 strain were identified in France between March and December 1992. Epidemiological investigations included a case-control study (not described here) and microbiological analyses of foods. Results of the case-control study and characterization of food isolates identified pork tongue in jelly, a ready-to-eat meat product, as the major vehicle of this outbreak, and to a lesser extent, delicatessen products contaminated secondarily during handling in food stores. As far as serotyping, phage typing, DNA macrorestriction pattern analysis (obtained by pulsed-field gel electrophoresis [PFGE]), and ribotyping are concerned, this epidemic strain is phenotypically and genomically closely related to strains responsible for major outbreaks of listeriosis previously observed in Europe and North America. The epidemic strain sensu stricto as defined by PFGE (2/1/3) displayed the same serovar, phagovar, ribovar, and ApaI and NotI PFGE patterns as the epidemic strains from outbreaks in Switzerland, California, and Denmark, but it consistently showed differences in the SmaI PFGE profile. This information greatly contributed to the identification of the major food vehicle (pork tongue in jelly) and further allowed exclusion of other foods (cheese) as possible sources of this major listeriosis epidemic.
The purpose of our study was to review all cases of listeriosis in Iceland during the period 1978-2000 and to analyse the genetic relatedness of their isolates. Case records of all patients in Iceland with listeriosis during the period were reviewed and the isolates compared using serotyping and pulsed-field gel electrophoresis (PFGE) using SmaI, AseI and ApaI restriction enzymes. Forty cases of listeriosis were diagnosed during the period, resulting in a mean annual incidence of 6.9 cases per million and a case fatality rate of 33%. In the first 5 y of the study only serotype 4b was observed; subsequently serotypes 1/2a and 1/2b appeared and serotype 4b declined in prevalence. PFGE yielded 24 different genotypes with 7 clusters of indistinguishable genotypes, each comprising 2-6 cases. During 1992-95 the annual incidence of listeriosis in Iceland rose to 15 cases per million. This was largely due to 2 clusters, 1 of 3 cases and the other of 6. No cases of listeriosis were diagnosed during 1998-2000. Our data show an increased number of cases within clusters in the latter half of the period. At the same time, food processing and distribution has become increasingly centralized in Iceland, suggesting an increased risk of listeriosis outbreaks.
'Gravad' rainbow trout artificially contaminated with Listeria monocytogenes was analyzed by use of a 4 h enrichment period followed by extraction of DNA and PCR amplification. This procedure made it possible to detect 10-100 cfu L. monocytogenes per gram 'gravad' rainbow trout, within 12 h. After a prolonged enrichment period of 24 h, numbers as low as 1-10 cfu L. monocytogenes per gram could be detected. The method described may be a useful tool for screening samples of 'gravad' rainbow trout for the presence of L. monocytogenes, since it is sensitive, rapid and simple.
Five grams of seafood products were inoculated with one to 500 viable or 10(9) heat-killed cells of Listeria monocytogenes. The presence of the pathogen was detected by the polymerase chain reaction (PCR) with primers specific for fragments of the listeriolysin O (hly) gene (two sets) and for the invasion-associated protein (iap) gene (one set). For DNA preparation, boiling, either alone or in combination with lysozyme and proteinase K treatment, was not always sufficient to lyse L. monocytogenes, while treatment with Triton X-100 produced consistently good DNA suitable for amplification. To avoid false-negative and false-positive results, 48 h incubations were necessary and a subculturing step after an initial 24 h incubation greatly improved the results. The primers that amplified regions of the listeriolysin O gene gave clearer and stronger products than primers for the invasion-associated protein gene. Using this method we were able to detect one to five L. monocytogenes cells in 5 g of product in a total of 55 h.
Listeria spp. and Listeria monocytogenes contamination of cold-smoked salmon (n=125) and its processing environment (n=522) were evaluated during surveys conducted in 1997-1998 and 2001 as well as in samples of final products analysed in 2001. The overall frequencies of Listeria spp. and L. monocytogenes in samples from all sources were 15.1% and 11.3%, respectively, but the incidence of L. monocytogenes in cold-smoked salmon final products was only 4%. A total of 201 L. monocytogenes isolates were characterised by Pulsed-Field Gel Electrophoresis (PFGE) in order to trace L. monocytogenes contamination in the processing plants. The combination of AscI and ApaI macrorestriction patterns yielded 24 different pulsotypes in 6 plants. One pulsotype observed by AscI restriction digestion comprised 148 of the 167 typed isolates from two processing plants. Two other pulsotypes predominated in samples from raw material, processing environments and final products. The results indicate that raw material, floors, and drains are potential sources of the L. monocytogenes found on cold-smoked salmon products. This highlights the need to readdress the design and cleaning of processing plants and equipment, and staff behavior. Hindering the introduction into and spread of the organism through the processing environment is necessary to avoid jeopardizing safety of the final product.
The Danish sheep population totals around 144,000 animals, but little is known of the causes and prevalance of diseases. This study focuses on the causes of abortion in Danish sheep. During one breeding season, aborted foetuses and stillbirths with signs of intrauterine death or malformation were submitted for laboratory examination from a population of 3,758 breeding ewes. Samples from 24 incidents of abortion and 21 ewes delivering malformed lambs or lambs with ante partum decomposition were submitted. A specific aetiology was established in 66.7% and 14.3% of the cases, respectively. Bacterial pathogens were the most prevalent cause of abortion. Several of the abortifacients were zoonotic microorganisms, for example Listeria monocytogenes, Campylobacter fetus subsp. fetus, Yersinia pseudotuberculosis and Toxoplasma gondii. The identified microorganisms probably represent the most common causes of abortion in Danish sheep but occurrence in Denmark of other pathogens such as Coxiella burnetii and Chlamydophila abortus cannot be excluded. Due to the high prevalence of zoonotic microorganisms, precautions must be taken in handling abortions or assisting lambing, especially for pregnant women.