Typing Listeria monocytogenes by random amplified polymorphic DNA (RAPD) fingerprinting

Draft Genome Sequences of Two Listeria monocytogenes Strains Isolated from Raccoon Feces in Japan

Listeria monocytogenes serotype 4b strains RF01 and RF06 were isolated from raccoon feces in Japan. Here, we report the draft genome sequences of the two isolated strains; the genome sizes were 2,918,024 and 2,872,491 bp, with 535× and 510× coverage, for the RF01 and RF06 strains, respectively.

Molecular Tools To Study Preharvest Food Safety Challenges

Preharvest food safety research and activities have advanced over time with the recognition of the importance and complicated nature of the preharvest phase of food production. In developed nations, implementation of preharvest food safety procedures along with strict monitoring and containment at various postharvest stages such as slaughter, processing, storage, and distribution have remarkably reduced the burden of foodborne pathogens in humans. Early detection and adequate surveillance of pathogens at the preharvest stage is of the utmost importance to ensure a safe meat supply. There is an urgent need to develop rapid, cost-effective, and point-of-care diagnostics which could be used at the preharvest stage and would complement postmortem and other quality checks performed at the postharvest stage. With newer methods and technologies, more efforts need to be directed toward developing rapid, sensitive, and specific methods for detection or screening of foodborne pathogens at the preharvest stage. In this review, we will discuss the molecular methods available for detection and molecular typing of bacterial foodborne pathogens at the farm. Such methods include conventional techniques such as endpoint PCR, real-time PCR, DNA microarray, and more advanced techniques such as matrix-assisted layer desorption ionization-time of flight mass spectrometry and whole-genome sequencing.

The incidence and distribution of Listeria monocytogenes in ready-to-eat vegetables in South-Western Nigeria

The study investigated the incidence of Listeria monocytogenes in ready‐to‐eat (RTE) vegetables: (Cucumber, Cucumis sativas; Cabbage, Brassica olerecea; Carrot, Daucus carota; Tomato, Solanum lycopersicum; Lettuce, Lactuca sativa) in six states in South‐Western Nigeria. A total of 555 composite samples were collected from 30 traditional markets within the states and only 244 L. monocytogenes species were isolated by standard methods. The incidence of L. monocytogenes was low and not statistically significant per vegetable type. The percentage distribution of the L. monocytogenes isolates in the RTE vegetables was 28.28, 9.02, 23.36, 19.67, and 19.67 for Cabbage, Carrot, Cucumber, Lettuce, and Tomatoes, respectively. Lagos state had the highest incidence of L. monocytogenes contamination (55%) followed by Ondo (48.89%), Oyo (48.75%), Ogun (44.09%), Osun (34.38%), and Ekiti (33.33%) states, respectively. Although the incidence of L. monocytogenes in the RTE vegetables in South‐Western Nigeria is low, its presence should be a source of concern as it could constitute a public health threat for its consumers.

Prevalence of Listeria monocytogenes in fresh and fermented Italian sausages and ribotyping of contaminating strains

Listeria monocytogenes has been detected in fresh as well as dry and semidry fermented sausages, rendering preparation and consumption of these products as a potential risk to human health. The aims of this study were (1) to evaluate the L. monocytogenes prevalence in 288 fresh and 237 fermented sausages produced in northern Italy; (2) to quantify the average pathogen Most Probable Number (MPN) per g of sausage; (3) to evaluate the sausage strain genetic diversity by automated PvuII ribotyping; and (4) to predict the pathogenicity lineage of these isolates determining their DuPont Identification Library Codes (DUP-IDs) by EcoRI ribotyping. The overall prevalence of L. monocytogenes in the sampled sausages was 28.2%. The percentage of L. monocytogenes positive fresh sausages was significantly higher than that of fermented sausages (i.e. 38.9 vs 15.2%), which had a pathogen load always lower than 10 MPN/g. In contrast, 16.1% of fresh sausages were contaminated by 10 to 100 MPN/g and 20.5% had more than 100 MPN/g. PvuII successfully discriminated sausage isolates with a Simpson's numerical index of discrimination of 0.637. A total of 12 and 9 different PvuII ribogroups were identified among 47 fresh and 24 fermented randomly selected sausage strains, respectively. Six of those ribogroups were shared between strains contaminating both kinds of sausages. According to the evaluation of the strain DUP-IDs, the majority of the isolates investigated in this study were part of the type II L. monocytogenes pathogenicity lineage, but type I lineage strains were identified among fermented sausage isolates. In conclusion, L. monocytogenes prevalence in Italian sausages was estimated to be around 28.2%. However, 84.2% of the samples were contaminated by less than 100 MPN of L. monocytogenes per g and the majority of L. monocytogenes contaminating strains would be classified in the type II pathogenicity lineage, including serotypes 1/2a, 1/2c and 3a.

Methods for the isolation and identification of Listeria spp. and Listeria monocytogenes: a review

Listeria monocytogenes is an important food-borne pathogen and is widely tested for in food, environmental and clinical samples. Identification traditionally involved culture methods based on selective enrichment and plating followed by the characterization of Listeria spp. based on colony morphology, sugar fermentation and haemolytic properties. These methods are the gold standard; but they are lengthy and may not be suitable for testing of foods with short shelf lives. As a result more rapid tests were developed based on antibodies (ELISA) or molecular techniques (PCR or DNA hybridization). While these tests possess equal sensitivity, they are rapid and allow testing to be completed within 48 h. More recently, molecular methods were developed that target RNA rather than DNA, such as RT-PCR, real time PCR or nucleic acid based sequence amplification (NASBA). These tests not only provide a measure of cell viability but they can also be used for quantitative analysis. In addition, a variety of tests are available for sub-species characterization, which are particularly useful in epidemiological investigations. Early typing methods differentiated isolates based on phenotypic markers, such as multilocus enzyme electrophoresis, phage typing and serotyping. These phenotypic typing methods are being replaced by molecular tests, which reflect genetic relationships between isolates and are more accurate. These new methods are currently mainly used in research but their considerable potential for routine testing in the future cannot be overlooked.

Multi-virulence-locus sequence typing of Listeria monocytogenes

A multi-virulence-locus sequence typing (MVLST) scheme was developed for subtyping Listeria monocytogenes, and the results obtained using this scheme were compared to those of pulsed-field gel electrophoresis (PFGE) and the published results of other typing methods, including ribotyping (RT) and multilocus sequence typing (MLST). A set of 28 strains (eight different serotypes and three known genetic lineages) of L. monocytogenes was selected from a strain collection (n > 1,000 strains) to represent the genetic diversity of this species. Internal fragments (ca. 418 to 469 bp) of three virulence genes (prfA, inlB, and inlC) and three virulence-associated genes (dal, lisR, and clpP) were sequenced and analyzed. Multiple DNA sequence alignment identified 10 (prfA), 19 (inlB), 13 (dal), 10 (lisR), 17 (inlC), and 16 (clpP) allelic types and a total of 28 unique sequence types. Comparison of MVLST with automated EcoRI-RT and PFGE with ApaI enzymatic digestion showed that MVLST was able to differentiate strains that were indistinguishable by RT (13 ribotypes; discrimination index = 0.921) or PFGE (22 profiles; discrimination index = 0.970). Comparison of MVLST with housekeeping-gene-based MLST analysis showed that MVLST provided higher discriminatory power for serotype 1/2a and 4b strains than MLST. Cluster analysis based on the intragenic sequences of the selected virulence genes indicated a strain phylogeny closely related to serotypes and genetic lineages. In conclusion, MVLST may improve the discriminatory power of MLST and provide a convenient tool for studying the local epidemiology of L. monocytogenes.

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.

Incidence of Listeria monocytogenes in wild animals in Japan

Between 1991 and 1993, the intestinal contents and feces of wild animals in Japan were examined for the presence of Listeria. The wild animals examined included 623 mammals (11 species) and 996 birds (18 species). Listeria species were isolated from 38 (6.1%) of the 623 mammalian samples and 133 (13.4%) of 996 bird samples. The highest incidence of Listeria in the mammals was found in Japanese monkeys (20.0%) and that in birds was found in crows (43.2%). The incidence of Listeria in Japanese monkeys varied from 0 to 40.0% depending on the capture area. L. monocytogenes was isolated from II of these positive samples. Serovars 1/2a and 4b predominated in eight serotyped L. monocytogenes isolates.