Abstract: 【Objective】 This study was conducted to investigate the reasons why Listeria monocytogenes Lm873 exhibited attenuated virulence despite harboring virulence island 4 (LIPI-4),and assess the potential public health risk of strain Lm873 triggering human listeriosis outbreaks based on genomics. 【Method】 Taking the Listeria monocytogenes attenuated strain Lm873 as the research object,the differences in growth curve between it and the hypervirulent strain Lm928 under different temperatures,pH,NaCl concentration conditions,the differences in motility under different temperatures and the oxidative stress resistance under different concentrations of oxidants were compared.The whole genome of strain Lm873 was sequenced,and its genome characteristics,virulence genes,genome evolution,and functional annotation were analyzed. 【Result】 No significant differences in growth profiles were observed between the two strains at different temperatures and pH of 3.0,7.0 and 9.0 (P＞0.05).However,a significant reduction in the growth rate of strain Lm873 was detected at 12 h in a medium with pH 5.0 compared with strain Lm928 (P＜0.05).The growth patterns in 4.5% and 7.0% NaCl solutions were comparable for both strains (P＞0.05),yet strain Lm873 exhibited significantly lower growth in 0.5% NaCl solution at 8 h and in 10.0% NaCl solution at 12 h compared with Lm928 (P＜0.05).In the motility test,the average diameter of the motility halo of strain Lm873 was significantly lower than that of strain Lm928 when cultured at 28 and 37 ℃ (P＜0.05).Strain Lm928 grew on the medium containing CdCl₂,but Lm873 did not.There was no significant difference in the growth ability of strains Lm873 and Lm928 on the medium containing 0.25,0.5 and 1 mmol/L CuCl₂.On low concentration H₂O₂ medium,strain Lm928 grew,while Lm873 did not,whereas neither strain Lm928 nor Lm873 grew on high concentration H₂O₂ medium.Genomic analysis revealed that the genome of strain Lm873 was approximately 2 972 618 bp in length with GC content of approximately 37.88%,exhibiting distinct genetic features.Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain Lm873 shared the highest similarity with HPB2262,suggesting close evolutionary relationships among them.Furthermore single nucleotide polymorphism (SNP) analysis positioned it closely alongsided Chinese clinical isolate SHL012 and the U.S.-based listeriosis-causing strain FSLJ1-194,demonstrating substantial genetic similarity.Comparative genomic analysis revealed that strain Lm873 lacked genes associated with cadmium ion transport and cation-transporting ATPases compared to Lm928.KEGG pathway analysis further demonstrated that Lm873 harbored fewer annotated genes involved in flagellar assembly.Additionally,Lm873 carried multiple antibiotic resistance genes conferring multidrug resistance phenotypes. 【Conclusion】 The presence of LIPI-4 in Lm873,yet its reduced virulence,was attributed to its diminished transmission capacity,infectivity,and environmental resilience.Phylogenetic analysis suggested that Lm873 could possess the potential to trigger outbreaks of human listeriosis.

Key words: Listeria monocytogenes; growth curve; oxidative stress; motility; whole genome analysis