Multi-Virulence-Locus Sequence Typing of 4bListeria monocytogenesIsolates Obtained from Different Sources in India over a 10-Year Period

Ecology of Listeria monocytogenes and Listeria species in India: the occurrence, resistance to biocides, genomic landscape and biocontrol

Listeria monocytogenes, the causative agent of listeriosis, has been implicated in increasing foodborne outbreaks worldwide. The disease is manifested in various forms ranging from severe sepsis in immune-compromised individuals, febrile gastroenteritis, still birth, abortions and meningoencephalitis. In India, data from studies on the detection and molecular epidemiological analysis of L. monocytogenes are only recently emerging. The presence of Listeria in different ecological niches has been recorded from India, including foods, soil, vegetables, mangrove swamps, seafood, freshwater fishes, clinical cases, and also insects. The organism has also been isolated from women with spontaneous abortions, miscarriage or recurrent obstetric history, aborted foetuses, animal clinical cases and wildlife samples. A novel species of Listeria has also been characterized. Listeria monocytogenes strains isolated from clinical, environmental, and foods showed biofilm-forming abilities. Listeria monocytogenes serotype 4b isolates of ST328, a predominant and unique ST observed in India, was repeatedly isolated from different sources, times, and geographical locations. Here, we reviewed the occurrence of Listeria in different sources in India, its resistance to biocides, and provide epidemiological analysis on its genomic landscape.

Listeria contamination in chevon and mutton from retail meat shops and slaughter house environment of Punjab, India

Listeria monocytogenes is recognized as an emerging pathogen, with limited information or statistics on this pathogen. Moreover, poor hygienic practices in the unorganized meat sector favor its growth and survival. Therefore, the present study was carried out in Punjab, India to assess the prevalence of Listeria spp. in chevon and mutton samples, followed by its characterization. The prevalence of Listeria in chevon, mutton and swab samples collected from butchers' shops and slaughter houses was 1.82%, 3.21% and 6.66%, respectively. The 18 (2.67%) L. monocytogenes strains isolated from 786 samples carried one or more virulence-associated gene. Based on virulence genes, 6/18 isolates were potentially pathogenic. Serovar 4b (44.4%) was predominant, followed by serovars 1/2a (22.2%), 1/2b (22.2%) and 1/2c (11.1%). Detection of L. monocytogenes in meat and environment samples indicated poor hygiene, potential cross-contamination and risk of listeriosis to consumers and occupational workers. The findings of the study were also relevant to the fact that most of the slaughtering in Punjab, India is carried out in unorganized way, and this meat is not stored propery. Moreover, in the absence of a systematic foodborne disease surveillance and monitoring program, a database on foodborne diseases is absent, and needs to be established.

Diversity of Listeria monocytogenes within a U.S. dairy herd, 2004-2010

Listeria monocytogenes, the causative agent of listeriosis, is frequently isolated from the environment. Dairy cows and dairy farm environments are reservoirs of this pathogen, where fecal shedding contributes to its environmental dispersal and contamination of milk, dairy products, and meat. The molecular diversity of 40 L. monocytogenes isolates representing 3 serogroups (1/2a, 1/2b, and 4b) collected between 2004 and 2010 from the feces of dairy cattle on a single dairy farm was assessed using a multivirulence locus sequence typing (MVLST) assay. The dairy farm L. monocytogenes MVLST patterns were compared to those from 138 strains isolated globally from clinical cases, foods, and the environment. Results of the study demonstrated that several distantly related L. monocytogenes strains persisted among members of the herd over the course of the study while other strains were transient. Furthermore, some strains isolated during this study appear to be distantly related to previously isolated L. monocytogenes while others are closely related to Epidemic Clones associated with human illness. This work demonstrates that dairy cows can be reservoirs of a diverse population of potentially human pathogenic L. monocytogenes that represents a risk to consumers of milk, dairy products, and meat.

Phylogenomic grouping of Listeria monocytogenes

The precise delineation of lineages and clonal groups are a prerequisite to examine within-species genetic variations, particularly with respect to pathogenic potential. A whole-genome-based approach was used to subtype and subgroup isolates of Listeria monocytogenes. Core-genome typing was performed, employing 3 different approaches: total core genes (CG), high-scoring segment pairs (HSPs), and average nucleotide identity (ANI). Examination of 113 L. monocytogenes genomes available in-house and in public domains revealed 33 phylogenomic groups (PGs). Each PG could be differentiated into a number of genomic types (GTs), depending on the approach used: HSPs (n = 57 GTs), CG (n = 71 GTs), and ANI (n = 83 GTs). Demarcation of the PGs was concordant with the 4 known lineages and led to the identification of sublineages in the lineage groups I, II, and III. In addition, PG assignments had discriminatory power similar to multi-virulence-locus sequence typing types and clonal complexes of multilocus sequence typing. Clustering of genomically highly similar isolates from different countries, sources, and isolation dates using whole-genome-based PG suggested that dispersion of phylogenomic clones of L. monocytogenes preceded their subsequent evolution. Classification according to PG may act as a guideline for future epidemiological studies.