Listeria Monocytogenes Serovars Research Articles

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.

Biopreservation of fresh-cut pear using Lactobacillus rhamnosus GG and effect on quality and volatile compounds

In recent years, the consumption of minimally processed fruit has increased. However, unfortunately, these products could be an appropriate vehicle for the transmission of foodborne pathogens. In this study, the antagonistic capacity of the probiotic strain Lactobacillus rhamnosus GG against a cocktail of 5 serovars of Salmonella and 5 serovars of Listeria monocytogenes on fresh-cut pear at conditions simulating commercial application was assessed. Moreover, its effect on fruit quality, particularly on the volatile profile, was determined, during 9 days of storage at 5 °C. L. monocytogenes population was reduced by approximately 1.8 log-units when co-inoculated with L. rhamnosus GG. However, no effect was observed in Salmonella. Fruit quality (soluble solids content and titratable acidity) did not change when the probiotic was present. A total of 48 volatile compounds were identified using gas chromatography. Twelve of the compounds allowed to discriminate L. rhamnosus GG-treated and untreated pears. Considering their odour descriptors, their increases could be positive in the flavour perception of L. rhamnosus GG-treated pear. The probiotic was able to control L. monocytogenes population on fresh-cut pear, which could be a vehicle of probiotic microorganisms as quality of fruit was not affected when the probiotic was present.

Complete Genome Sequences of Two Listeria monocytogenes Serovars, 1/2a and 4b, Isolated from Dairy Products in Brazil.

Listeria monocytogenes is the foodborne pathogen responsible for a bacterial infection called listeriosis. Here, we present the whole-genome sequences of two L. monocytogenes serovars, 1/2a and 4b, which are considered the most prevalent in food processing plants and listeriosis outbreaks, respectively.

Presence and molecular characterization of the major serovars of Listeria monocytogenes in ten Sardinian fermented sausage processing plants

The aim of the present study was to investigate the occurrence of Listeria monocytogenes in ten Sardinian fermented sausage processing plants. A total of 230 samples were collected and 40 L. monocytogenes isolates were obtained and subjected to serotyping and investigated for the presence of ten virulence-associated genes using multiplex PCR assays. The isolates were further subjected to PFGE and investigated for their adhesion abilities in polystyrene microtiter plates. L. monocytogenes was found in 6% of food contact surfaces, in sausages at the end of acidification (3%) and ripening (8%). Serotyping revealed the presence of four serovars: 1/2c (37.5%), 1/2b (27.5%), 4b (22.5%) and 1/2a (12.5%). All virulence-associated genes were detected in 67.5% of the isolates. Isolates from processing environment, semi-processed and finished products showed high pulsotype diversity and the majority of isolates presented weak adhesion capability. The detection of the pathogen in fermented sausages confirms the ability of L. monocytogenes to overcome the hurdles of the manufacturing process.

Characterization of the novel Listeria monocytogenes PCR serogrouping profile IVb-v1

The World Health Organization Collaborating Centre for Listeria (WHOCCL) has developed in 2004 a multiplex PCR assay that separates the 4 major Listeria monocytogenes serovars (1/2a, 1/2b, 1/2c, and 4b) into distinct PCR serogroups. A new PCR profile has been recently identified, constituted of amplified DNA fragments of prs, ORF2819, ORF2110 and lmo0737. Here we characterize 22 L. monocytogenes isolates of the WHOCCL collection with this PCR IVb variant 1 (IVb-v1) profile. The 22 isolates belong to the clinically predominant serovar 4b, exhibit 6 distinct pulsed-field gel electrophoresis ApaI/AscI combined profiles, and belong to 2 unrelated multilocus sequence types, indicating that the novel profile does not correspond to a recent clonal emergence. We have updated the WHOCCL serogroup-related PCR typing scheme to include this new profile.

Incidence and Contamination Level of Listeria monocytogenes and Other Listeria spp. in Ready-to-Eat Meat Products in Jordan

The objective of the present study was to investigate the incidence and contamination levels of different Listeria monocytogenes serovars in ready-to-eat meat products (RTE-MP) collected from different outlets and processing plants in Jordan in order (i) to provide information to Jordanian health authorities on the incidence of L. monocytogenes in RTE-MP sold and consumed in Jordan and (ii) to ascertain the risks of these products for consumers. Two hundred forty RTE-MP samples, 120 beef and 120 poultry, were analyzed. European International Organization for Standardization (EN ISO) 11290-1 and -2 standard protocols were used for detection and enumeration of L. monocytogenes. The identity of suspected L. monocytogenes was confirmed using PCR. Three Listeria spp., L. monocytogenes, L. innocua, and L. welshimeri, were isolated. L. innocua and L. welshimeri were the most and least frequently isolated with 56 and 36 samples, respectively. L. monocytogenes was isolated from 41 samples (17.1%): 23 from beef and 18 from poultry samples. The contamination levels of L. monocytogenes were <or=100 CFU/g in 97.5% (40 samples) of the positive samples. Only one beef sample with a count of >100 CFU/g was found. The L. monocytogenes strains isolated fell into two serotypes (1 and 4) and four different serovars (1/2a, 1/2b, 1/2c, and 4b).

Survey of Listeria monocytogenes and Other Listeria sp. Contamination in Different Common Ready-to-Eat Food Products in Jordan

Incidence and contamination levels of different Listeria monocytogenes serovars and different Listeria sp. in 360 samples of common ready-to-eat food products in Jordan were investigated. The presence of L. monocytogenes was determined using EN ISO protocol and confirmed using PCR technique. Five Listeria sp.: L. monocytogenes, L. innocua, L. ivanovvi, L. welshimeri and L. seeligeri were isolated. L. monocytogenes was isolated from 19 samples (5.3%), from 6 RTE dairy samples; 6 RTE vegetables samples and 4 traditional dishes samples and 3 miscellaneous samples. L. innocua and L. ivanovvi were the most and least frequently isolated species, 24 and 3 samples, respectively. L. welshimeri was isolated from 8 samples and L. seeligeri from 7 samples. The contamination levels of L. monocytogenes were found to be < or = 100 CFU g(-1) in 84.2% (16 samples) of the positive samples. Only 15.8% (3 samples; 1 vegetable, 1 traditional dish and 1 miscellaneous samples) of the positive samples were found with counts >100 CFU g(-1). L. monocytogenes strains isolated fell into 2 serotype, 1 and 4 and to 5 different serovars, 1/2a, 1/2b, 1/2c, 4a, 4c.

The origin of Listeria monocytogenes 4b isolates is signified by subproteomic profiling

Among the 13 known serovars of Listeria monocytogenes, strains exhibiting the serovar 4b are the most prevalently involved in epidemics of human listeriosis. The molecular reasons for the major involvement of serovar 4b strains in all major foodborne outbreaks in contrast to the lower prevalence of this serovar among food isolates remain indefinite. In order to provide further insight in the protein expression of L. monocytogenes 4b strains, the cytoplasmic and extracellular proteomes of L. monocytogenes 4b strains from different origins, i.e. environmental, clinical and asymptomatical carriage, were investigated by two-dimensional gel electrophoresis. Statistical hierarchical clustering analysis on subproteomic profiles clearly discriminated the strains according to their origin. Protein spots differentiating the subproteome patterns were identified using MALDI-TOF MS through their peptide mass fingerprint.

Antibacterial Activities of the Extracts of Some Herbs Used in Turkish Herby Cheese Against Listeria Monocytogenes Serovars

In this study, antimicrobial activities of the four different extracts (in methanol, ethanol, n‐hexane and water) of some herbs including Allium vineale, Chaerophyllum macropodum , and Prangos ferulacea were investigated against Listeria monocytogenes serovars 1/2b, 4b, and 4ab. For many centuries, these herbs were used in food production in Turkey. While water extracts of all the plants did not show any antibacterial activity, the other extracts of these plants showed variable degrees of antibacterial activity against L. monocytogenes serovars tested. The extracts of Allium vineale showed higher antibacterial activity than the other plants. The methanol extracts of all the plants exhibited higher activity than the ethanol and n-hexane extracts. L. monocytogenes 4ab was the most sensitive serovar to extracts of these plants. The results indicated that the methanol and ethanol extracts of these plants displayed remarkable activity against L. monocytogenes serovars and therefore, they could be used as natural anti-Listeria monocytogenes additives in herby cheese.

Sorovares de Listeria monocytogenes e espécies relacionadas, isoladas de material clínico humano

Using phenotype techniques, characterization was realized of species and serovars of 255 strains of Listeria isolated from human material: 220-86.3% were from patients with possible invasive disease, while 35-13.7% were from colonized healthy individuals. The strains were collected in several regions of Brazil from 1969-2000. In individuals aged 0-10 or 41-60 years old Listeria monocytogenes was isolated more often in cerebral spinal fluid than in blood cultures, including samples from renal transplant recipients. All Listeria monocytogenes serovars were detected in blood culture strains. The predominant serovars characterized were 4b (154-60.3%) and 1/2a (74-29%). In this study, Listeria monocytogenes causing invasive diseases, such as meningitis or septicemia, or colonizing individuals, were identified. Consequently further studies focusing on clinical and pathological as well as epidemiological issues, including risk factors associated with foodborne transmission should be pursued.

A RE-PCR method to distinguish Listeria monocytogenes serovars

Strains (107) of L. monocytogenes were tested with a PCR-restriction enzyme analysis with two new original primers. A segment of 1395 bp containing the entire iap gene in L. monocytogenes was amplified by the PCR technique. The PCR product was cleaved with the restriction enzymes HindIII and RsaI, and the fragments generated were separated by gel electrophoresis. Two groups of serovars were obtained: one group contained serovars 1/2a and 1/2c, the other group contained serovars 1/2b, 3b and 4b. The PCR-restriction enzyme analysis method described in this paper could be a useful tool for the unambiguous division of L. monocytogenes into two serovar groups, and it could be used to study the evolution of different serotypes and groups of serotypes in foods produced in the same processing plant and processed during the same month. The RE-PCR method used can give a rapid confirm at the subgroup level in the laboratory of an epidemiological association between human disease and suspected sources of contaminated food.

Virulence of Listeria monocytogenes Serovars and Listeria spp. in Experimental Infection of Mice

Wild strains of Listeria monocytogenes, Listeria ivanovii, Listeria seeligeri, Listeria innocua, and Listeria welshimeri were isolated from infected animals and foodstuffs. Their virulence was tested in Swiss mice after intraperitoneal injection of a fixed number of organisms. The presence of hemolysin was determined using the CAMP test. Bacteria were enumerated in peritoneal lavage fluid, liver, and spleen. Spleen weights were measured, and the presence of L. monocytogenes in the brain was also investigated. L. innocua, L. seeligeri, and L. welshimeri were not found to be pathogenic for mice. L. ivanovii was detected in liver, spleen, and peritoneal lavage fluid but at lower levels than L. monocytogenes (p<0.001). The pathogenic capabilities of four different serovars of L. monocytogenes (4b, 1/2a, 1/2b, 1/2c) were compared. Serovars l/2b and l/2c, which are frequently isolated from foodstuffs, were found to colonize the liver and spleen to a lesser extent than serovar 4b (p<0.01 and <0.001 respectively). The behavior of serovar l/2a, the most commonly isolated from foodstuffs, was strain dependent. Two out of the four strains tested were strongly hemolytic and were as virulent as strains of serovar 4b, while the other two were weakly hemolytic, and avirulent like L. innocua. These results could account for the relatively small number of human Listeria infections due to L. monocytogenes serogroup 1/2, despite the very frequent occurrence of this serovar in foodstuffs.

Distribution of serovars ofListeria monocytogenes isolated from different categories of patients with listeriosis

An analysis was made of the distribution of serovars of Listeria monocytogenes isolated from 1363 patients with listeriosis. Overall, serovar 4b was found in 64% of cases, serovar 1/2a in 15%, serovar 1/2b in 10%, and serovar 1/2c in 4%. The patients were categorised as pregnancy associated cases, non-pregnant previously healthy cases, and non-pregnant cases with severe underlying illness. The serovars were unequally distributed between these three groups of patients. Serovar 1/2b occurred most often in the non-pregnant cases with severe underlying illness, and serovar 1/2c occurred least frequently in the pregnancy associated cases. Serovar 4b occurred more often in the pregnancy associated cases than in previously healthy non-pregnant cases, and more often in the latter than in those with underlying illness. Similar distributions of the serovars between the categories of patients occurred over different time periods. These results may be interpreted as indicating an association between virulence and serological type of Listeria monocytogenes.

Amino Acid Requirement of Six Strains of Listeria monocytogenes

Different serovars of Listeria monocytogenes grew well in a chemically defined medium. Sixteen amino acids were tested for the growth of L. monocytogenes. Most strains required cystine, valine, isoleucine, and leucine. Phenylalanine was a stimulatory growth factor for all six strains of Listeria. Whilst tryptophan was essentially required by NCTC 7973, LM and C-286 and stimulatory for 4155 and C-294, none of the strains did exhibit requirements of asparagine, glutamine, proline, histidine and tyrosine as essential/stimulatory growth factor.

Vitamin and nitrogen base requirements for listeria monocytogenes and haemolysin production

A complete chemically defined medium is described for the growth of different serovars of Listeria monocytogenes. The medium supported rapid, luxuriant and transferable growth. At the same time haemolysin production was induced to the same extent as in tryptose phosphate broth. Riboflavin and calcium-pantothenate were essential for the growth of all six strains tested. Biotin, pyridoxal-hydrochloride and p-aminobenzoic acid were either essential or stimulatory to all strains. Most strains did not require folic acid, thiamin, nicotinic acid and inositol, but they were stimulatory for some strains. Adenine was essential for two strains (NCTC 7973, 5214 m) while cytosine exhibited an inhibitory effect on the growth of all the strains.