Genetic typing, virulence genes and drug resistance analysis of Campylobacter fetus subsp. testudinum / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To analyze the molecular epidemiological characteristics of Campylobacter fetus subsp. testudinum ( Cft). Methods:Fifteen strains of Cft collected in our laboratory from 2010 to 2022 were subjected to whole-genome sequencing. Their epidemiological characteristics were analyzed based on the global genome data of Cft on GenBank database. MLST-GrapeTree software was used to obtain the genetic structure of Cft strains. A phylogenetic tree was constructed using core-genome single nucleotide polymorphism (cgSNP) analysis, and the sequence clusters were identified using rhierBAPS. Virulence genes and drug resistance genes of Cft strains were annotated using CARD, ResFinder and VFDB database. Their susceptibility to antibiotics was tested using E-test method and the results were analyzed using the CLSI-M45 sensitivity standard for Campylobacter jejuni/ Campylobacter coli. Results:Based on average nucleotide identity (ANI) analysis, the genome data of 41 Cft strains including 24 isolated from human, 13 from animals and four of unknown sources were collected from GenBank database. Among the 24 human-derived strains, 20 were linked to Asian descent and only one was linked to Caucasian descent (spouse of Asian descent), showing statistically significant differences in human ethnicity. All of the 13 animal-derived strains were originated from reptilian sources, including six from turtles, four from snakes and three from lizards. MLST revealed that ST46 was the predominant ST in China, while ST15 was the major sequence type in the United States. Grapetree analysis also demonstrated that the genetic diversity in China was greater than that in the United States. The phylogenetic tree constructed based on cgSNP and BAPS identified six distinct sequence clusters. The Chinese isolates were scattered in diverse sequence clusters and closely related to animal-derived strains, while the American isolates mainly belonged to ST15. The genes encoding virulence factors such as flagella, glycosylation systems and adhesins were carried by all of the 41 Cft strains (100.00%). The invasion-related virulence genes, such as the genes encoding the IV type secretion system ( virB4, virB9, virD4) and the resistance-related tetO efflux pump gene were specifically identified in the emerging ST74 clones. In vitro drug susceptibility testing of 15 Chinese isolates revealed 46.67% of the Cft strains were resistant to ciprofloxacin and 100.00% were sensitive to erythromycin. Conclusions:The global sequence clusters of Cft isolates showed a great genetic diversity. Most of the people with Cft infection had basic immune diseases and might have eaten or had contact with reptiles. Notably, the Chinese domestic infection of ST46 and the emerging ST74 should arouse our more attention.