A comparison of Listeria monocytogenes serovar 4b isolates of clinical and food origin in Japan by pulsed-field gel electrophoresis

Implicated Food Products for Listeriosis and Changes in Serovars of Listeria monocytogenes Affecting Humans in Recent Decades

Listeriosis is a foodborne disease with a high fatality rate, and infection is mostly transmitted through ready-to-eat (RTE) foods contaminated with Listeria monocytogenes, such as gravad/smoked fish, soft cheeses, and sliced processed delicatessen (deli) meat. Food products/dishes stored in vacuum or in modified atmospheres and with extended refrigerator shelf lives provide an opportunity for L. monocytogenes to multiply to large numbers toward the end of the shelf life. Elderly, pregnant women, neonates, and immunocompromised individuals are particularly susceptible to L. monocytogenes. Listeriosis in humans manifests primarily as septicemia, meningitis, encephalitis, gastrointestinal infection, and abortion. In the mid 1990s and early 2000s a shift from L. monocytogenes serovar 4b to serovar 1/2a causing human listeriosis occurred, and serovar 1/2a is becoming more frequently linked to outbreaks of listeriosis, particularly in Europe and Northern America. Consumer lifestyle has changed, and less time is available for food preparation. Modern lifestyle has markedly changed eating habits worldwide, with a consequent increased demand for RTE foods; therefore, more RTE and take away foods are consumed. There is a concern that many Listeria outbreaks are reported from hospitals. Therefore, it is vitally important that foods (especially cooked and chilled) delivered to hospitals and residential homes for senior citizens and elderly people are reheated to at least 72°C: cold food, such as turkey deli meat and cold-smoked and gravad salmon should be free from L. monocytogenes. Several countries have zero tolerance for RTE foods that support the growth of Listeria.

Prevalence and characteristics of Listeria monocytogenes in bovine colostrum in Japan

This study was conducted to determine the prevalence and characteristics of Listeria monocytogenes in bovine colostrum in Japan. We collected bovine colostrum samples from 210 dams from 21 dairy farms in Hokkaido prefecture (Japan) between March and June 2009. L. monocytogenes was detected in samples from 6 (28.6%) of the 21 farms. Of the 210 samples, 16 (7.6%) were positive for L. monocytogenes. We recovered 80 L. monocytogenes isolates; 44 (55%) isolates were classified as serotype 1/2b and 36 (45%) were classified as serotype 4b. The isolates were susceptible to penicillin, ampicillin, amoxicillin, gentamicin, kanamycin, streptomycin, erythromycin, vancomycin, tetracycline, chloramphenicol, ciprofloxacin, and trimethoprim-sulfamethoxazole. Pulsed-field gel electrophoresis (PFGE) characterization of the 80 isolates revealed six PFGE types. Two PFGE types corresponded to human listeriosis cases. Most L. monocytogenes isolates possessed virulence-associated genes (actA, hly, iap, inlA, inlC, mpl, plcA, plcB, opuCA, prfA, and clpC). One PFGE type isolate possessed an epidemic clone II marker. Our findings suggest that isolates from bovine colostrum have the potential to cause human and animal listeriosis. This is the first study on the prevalence and characteristics of L. monocytogenes isolated from bovine colostrum obtained from dairy farms. Our results have important implications for improving public health and elucidating the epidemiology of L. monocytogenes in bovine colostrum.

Molecular characterization of Listeria monocytogenes from natural and urban environments

Characterization of 80 Listeria monocytogenes isolates from urban and natural environments differentiated 7 and 26 EcoRI ribotypes, respectively. Whereas the majority of isolates from the natural environment represented L. monocytogenes lineage II (12 of 13 isolates), urban isolates grouped evenly into lineages I and II (32 and 33 isolates, respectively) and included two lineage III isolates. Multilocus sequence typing of all natural isolates and a randomly selected subset of 30 urban isolates showed a higher overall diversity (Simpson index of discrimination [D] of 0.987 and 0.920, respectively) than did EcoRI ribotyping (D = 0.872 and 0.911, respectively). Combined analysis with ribotype and lineage data for 414 isolates from farm sources, 165 isolates from foods and food-processing environments, and 342 human clinical isolates revealed that lineage I was significantly more common among human (P < 0.0001) isolates, whereas lineage II was more common among isolates from the natural environment, farms, and foods (P < or = 0.05). Among a total of 92 ribotypes, 31 showed significant associations with specific isolate sources. One ribotype (DUP-1039C) was significantly associated with both natural environments and farms. A spatial analysis showed a marginal association between locations in the natural environment positive for L. monocytogenes and a proximity to farms. Our data indicate that (i) L. monocytogenes strains from different sources show a high level of diversity; (ii) L. monocytogenes subtypes differ significantly in their associations with different environments, even though populations overlap; and (iii) a higher proportion of isolates from environmental sources than from human clinical cases can be classified into L. monocytogenes lineage II, which supports the classification of this lineage as an environmentally adapted subgroup.

Analysis of PCR-based methods for characterization of Listeria monocytogenes strains isolated from different sources

Listeria monocytogenes strains, isolated from various sources (food, environment, and animals), were used to test different PCR-based methods to investigate their capability to define the strain origin. RAPD-PCR with three primers and the SAU-PCR method, in which the DNA was first digested with the Sau3A restriction endonuclease and then amplified with a primer designed on the restriction site, were carried out, and the profiles obtained were used to perform cluster analysis. Based on the cluster analysis of Listeria spp. strains, obtained from international collections, the coefficient of similarity was selected. The results obtained showed that the methods tested in the study gave different levels of differentiation between the strains tested. The RAPD protocol using the P1254 primer and the SAU-PCR gave appreciable results only for strains isolated from animals and from a food processing plant in two different periods of the year 2003. Better differentiation was observed using the RAPD-PCR with primer D8635. As a matter of fact, it was able to distinguish L. monocytogenes obtained from different species of animals, different food samples and strains from the same production plant isolated in different periods of the year. Also primer M13 gave positive results, but the coefficient of similarity to use had to be increased to 80%. On the basis of the results observed, RAPD-PCR with primers D8635 and M13 should be considered reliable tools for epidemiological investigations focusing on L. monocytogenes.

Use of PFGE to characterize clonal relationships among Belgian clinical isolates of Listeria monocytogenes

The Belgian Listeria Reference Centre receives between 30 and 50 human clinical strains of Listeria monocytogenes per year. In general, epidemiological data are absent or incomplete, preventing recognition of episodes of listeriosis. However, data on a clonal relationship between strains can indirectly give an idea of the occurrence of episodes. Human isolates of L. monocytogenes from 2001 were serotyped, their arsenic-cadmium resistance profiles were determined, and they were pulsotyped with the application of pulsed-field gel electrophoresis using AscI and ApaI restriction endonucleases. On five occasions, two or more strains presented the same serovar, metal-resistance profile and pulsovar, suggesting a clonal relationship. This is the first report to identify accurately potential listeriosis episodes occurring in Belgium.

Characterization of Listeria monocytogenes recovered from 41 cases of sporadic listeriosis in Austria by serotyping and pulsed-field gel electrophoresis

41 clinical Listeria monocytogenes strains recovered from seven feto-maternal and 34 non-pregnancy associated cases of human listeriosis documented between 1997 and 2000 underwent serotyping and typing by pulsed-field gel electrophoresis (PFGE) applying the enzymes AscI, ApaI and SmaI. The pulsotypes of the clinical strains were compared to the pulsotypes of three L. monocytogenes strains isolated from healthy fecal carriers and nine reference strains isolated from seven outbreaks in Europe and the USA. The 41 clinical strains of Austrian provenance showed 37 pulsotypes. Five sets of two Austrian strains each were indistinguishable by PFGE typing. Epidemiological links were absent between these indistinguishable isolates. One unique pulsotype (AB) was found in three fecal isolates. Five pulsotypes (A, Q, R, AC and AD) were distinguished among the strains associated with outbreaks. Clusters consisting of two, five and six Austrian strains each were indistinguishable from the outbreak-associated pulsotypes A, Q and R, respectively, after PFGE analysis with AscI. Three strains of AscI pulsotype Q and five strains of AscI pulsotype R could be further differentiated by restriction with ApaI and SmaI. One strain each from sporadic cases shared a combined pulsotype with the outbreak strains of pulsotypes A and R, respectively. These PFGE data suggest that a similar genetic background can be found in strains which have been contributing to outbreaks world-wide and in isolates associated with sporadic listeriosis in Austria.

Typing of Listeria monocytogenes isolates originating from the food processing industry with automated ribotyping and pulsed-field gel electrophoresis

A total of 486 Listeria monocytogenes isolates originating from 17 Finnish food processing plants (representing meat, poultry, fish, and dairy production) were collected and typed by automated ribotyping using EcoRI as the restriction enzyme. The isolates were divided into 16 different ribotypes (RTs). Some of these isolates (121), representing all EcoRI types and 16 food plants, were subjected to ribotyping with the PvuII enzyme, to pulsed-field gel electrophoresis (PFGE) typing with AscI and SmaI restriction enzymes, and to serotyping with O-antigen antisera. Nineteen ribotypes were generated with PvuII, 42 macrorestriction patterns were generated with AscI and 24 with SmaI, and three serotypes were generated with antisera. When the results were combined, the overall number of RTs was 23, and that of the PFGE types was 46. Thus, the overall discrimination power of PFGE was higher (discrimination index [DI] 0.966) than that of ribotyping (DI 0.906). The most common serotype (90.1% of the isolates) was 1/2, and isolates of serotype 4 (3.3%) were rare. There was no connection between food sectors and RTs or PFGE types, but PFGE indicated the single plants (78.3% of the types) better than ribotyping (56.5%). On the basis of its automation and on the availability of identification databases, automated ribotyping had some advantages over PFGE. Overall, automated ribotyping can be considered a practical and rapid tool when Listeria contamination is suspected and when screening a large number of isolates is necessary, e.g., when tracing contamination sources. However, in cases of outbreaks, the identical patterns must be confirmed by PFGE, which is a more discriminatory method.

Listeriosis in Iceland, 1978-2000: a description of cases and molecular epidemiology

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.

Control of Listeria monocytogenes in the food-processing environment

The purpose of this paper is to provide guidance to food processors in controlling Listeria monocytogenes in food-processing environments. Of particular concern are outbreaks of a few to several hundred scattered cases involving an unusually virulent strain that has become established in the food-processing environment and contaminates multiple lots of food over days or months of production. The risk is highest when growth occurs in a food before it is eaten by a susceptible population. The information presented in this paper provides the basis for the establishment of an environmental sampling program, the organization and interpretation of the data generated by this program, and the response to Listeria-positive results. Results from such a program, including examples of niches, are provided. Technologies and regulatory policies that can further enhance the safety of ready-to-eat foods are discussed.

RAPD- and actA gene-typing of Listeria monocytogenes isolates of human listeriosis, the intestinal contents of cows and beef

Seventy-five L. monocytogenes isolates of human listeriosis, the intestinal contents of cows and beef were divided into 5 major clusters, 17 sub-clusters and 28 minor clusters by typing using random amplification of polymorphic DNA (RAPD). According to their major RAPD category, L. monocytogenes isolates serotyped as 1/2b and 4b were distinguished from L. monocytogenes isolates of serovars 1/2a and 1/2c. Moreover serovar 4b was distinguished from serovar 1/2b by a difference in the RAPD sub-cluster category. All L. monocytogenes were found to possess either actA gene Type I or II, and only one actA gene type was detected in each RAPD minor cluster. actA gene Type II was observed in 32.0%, 38.5% and 18.9% of isolates from humans, cows and beef, respectively, and was detected more frequently in serovar 4b (46.9%) than in serovars 1/2a (22.2%), 1/2b (7.7%) and 1/2c (0.0%). Twenty (80%) of 25 human isolates fell within three minor RAPD types (II-d (16%), V-p-1 (36%), V-p-2 (28%)). Two isolates from humans and beef were found to have the same RAPD type (Type IV-k-1), actA gene type (Type I) and serovar (1/2b). Our results suggest that only a few genotypes of L. monocytogenes are predominant in human listeriosis in Japan, although the human isolates were collected over a broad span of time and a wide geographical range. Our results also suggest that RAPD-, actA gene- and sero-typing can be useful for epidemiological analysis.