| The genus Listeria is a group of Gram-positive bacteria with strong environmental adaptability.Listeria monocytogenes and Listeria ivanovii are the only two pathogenic species in the genus Listeria.These two species are phylogenetically similar,and the nucleotide and transcription levels of virulence genes were show a high degree of uniformity.L.monocytogenes can cause various clinical manifestations such as septicemia,diarrhea,meningoencephalitis and diarrhea in human and animals,the mortality rate range from 10%to 30%.L.ivanovii can cause ruminant infection with similar pathological manifestations except meningoencephalitis,which is one of the characters of L.monocytogenes infection in ruminants and humans.Previous studies have shown that Listeria carried by many kinds of animals,soil,and water from different regions,suggesting that Listeria has a strong host adaptability.Listeria can be spread to human beings and animals by contaminated foods,while human beings and animals can continuously infect the ecological environment through fecal-oral route,father affecting human health and ecological safety.The monitoring in Listeria foods,animals and environments can effectively strengthen the control and prevention of listeriosis.Black-headed gull(Larus ridibundus)is a widely distributed migratory wild bird that has been shown to carry several pathogens such as Influenza A virus,Escherichia coli,Salmonella and potentially pathogenic microfungi.In China,black-headed gulls migrate to Kunming by way of Siberia,Mongolia,Neimenggu,Xinjiang,Ningxia,Qinghai,Gansu,Shaanxi and Sichuan every year.Black-headed gulls stayed in Kunming for up to 5 months every year,attracting lots of nearby residents and tourists to contact with them closely,and the gulls also actively forage and defecate in Dianchi lake,which could increase the risk of gulls carried pathogens transmission.In this study,we investigated the prevalence and molecular characteristics of Listeria monocytogenes from black-headed gulls in Dianchi Lake for three consecutive years,and phylogenetic analysis based on core genome SNPs was used to determine the genetic relationship of the strains from Dianchi Lake and other regions.Occurrence of L.monocytogenes in black-headed gull feces in 2016,2017 and 2018 was 1.0%(9/895),1.0%(16/1612)and 0.6%(3/523)respectively and only one isolate from the Dianchi Lake environment had been isolated in 2017(0.7%,1/150).The 29 isolates were subtyped into 5 serotypes by serotyping and 9 sequence types by multilocus sequence typing.The predominant serotype was 4b,while the predominant sequence types were ST 145 and ST201.Based on their prevalence and genomic relationships,ST5 and ST87 were likely to be sourced locally while ST 145 and ST201 were likely to be non-local.L.monocytogenes carried by black-headed gull may travel along the bird migration route and lead to transmission over a large geographical span.Although the prevalence of L.monocytogenes was low,its carriage by the migratory black-headed gulls poses potential public health risks in regions where the migratory birds passage and reside.Listeria ivanovii is also an intracellular bacterium,causing the listeriosis in ruminants and humans.Previous researches had isolated 116 strains of L.ivanovii subsp.ivanovii from wild rodents of different regions in China,and the predominant sequence types were ST1 and ST2.In this study,we first investigated the biological characteristics and virulence of these two clonal strains including motility,metabolism and virulence in cells and mouse model.The results demonstrated the ST1 strains exhibited motility,wide metabolic activity and hypervirulence,whereas the ST2 strains showed non-motility,relative lower metabolic activity and virulence.Considering the transmissible ability from wild rodents and pikas to ecological environment,the L.ivanovii subsp.ivanovii with potential pathogenicity to humans and ruminants should be monitored. |
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