Abstract
The monophasic variant of Salmonella Typhimurium has emerged and increased rapidly worldwide during the past two decades. The loss of genes encoding the second-phase flagella and the acquirement of the multi-drug resistance cassette are the main genomic characteristics of the S. Typhimurium monophasic variant. In this study, two Salmonella strains were isolated from the knee effusion and feces of a 4-year-old girl who presented with a case of septic arthritis and fever, respectively. Primary serovar identification did not detect the second-phase flagellar antigens of the strains using the classical slide agglutination test. Whole-genome sequencing analysis was performed to reveal that the replacement of the fljAB operon by a 4.8-kb cassette from E. coli caused the non-expression of phase-2 flagellar antigens of the strains, which were confirmed to be a novel S. Virchow monophasic variant (Salmonella 6,7,14:r:-) by core-genome multi-locus sequence typing (cgMLST). Compared to the 16 published S. Virchow genomes, the two strains shared a unique CRISPR type of VCT12, and showed a close genetic relationship to S. Virchow BCW_2814 and BCW_2815 strains, isolated from Denmark and China, respectively, based on cgMLST and CRISPR typing. Additionally, the acquisition of Salmonella genomic island 2 (SGI2) with an antimicrobial resistance gene cassette enabled the strains to be multidrug-resistant to chloramphenicol, tetracycline, trimethoprim, and sulfamethoxazole. The emergence of the multidrug-resistant S. Virchow monophasic variant revealed that whole-genome sequencing and CRISPR typing could be applied to identify the serovaraints of Salmonella enterica strains in the national Salmonella surveillance system.
Highlights
Salmonella enterica includes more than 2500 serovars and represents a major foodborne pathogen, which mainly causes gastroenteritis
Meningitis is diagnosed in less than 1% of clinical salmonellosis; Salmonella infections account for 0.8% of osteomyelitis cases
Genome sequencing analysis revealed that the presence of cmlA9, sul1, drfA1, tetA(G), and gyrA(S83F) in both isolates was involved in the antimicrobial resistance phenotype
Summary
Salmonella enterica includes more than 2500 serovars and represents a major foodborne pathogen, which mainly causes gastroenteritis. Fever and back pain were reported as the main symptoms for vertebral osteomyelitis caused by Salmonella infection [5]. Ohio caused septic arthritis and a bone abscess in a 44-year-old immunocompetent man in Japan, and the S. Ohio strain was isolated from his bone abscess and from joint tissue of his swollen left knee [6]. S. Newport was reported to cause left knee pain in a 36-year-old man with a fever of 38 ◦C and new-onset diabetes, whereas the bacteria were isolated from his blood, pus, knee aspirate, and tibia tissue [7]. Montevideo was another rare Salmonella serovar, identified to induce septic arthritis of the knee in a 59-year-old woman who presented with a painful and swollen right knee associated with a fever of 38.8 ◦C [8]. The antimicrobial resistance genotype and phenotype were determined in order to reveal the evolution of the monophasic variant strains
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