Abstract
BackgroundThe prevalence of human brucellosis in Qinghai Province of China has been increasing rapidly, with confirmed cases distributed across 31 counties. However, the epidemiology of brucellosis transmission has not been fully elucidated. To characterize the infecting strains isolated from humans, multiple-locus variable-number tandem repeats analysis (MLVA) and whole-genome single-nucleotide polymorphism (SNP)-based approaches were employed.MethodsStrains were isolated from two males blood cultures that were confirmed Brucella melitensis positive following biotyping and MLVA. Genomic DNA was extracted from these two strains, and whole-genome sequencing was performed. Next, SNP-based phylogenetic analysis was performed to compare the two strains to 94 B. melitensis strains (complete genome and draft genome) retrieved from online databases.ResultsThe two Brucella isolates were identified as B. melitensis biovar 3 (QH2019001 and QH2019005) following conventional biotyping and were found to have differences in their variable number tandem repeats (VNTRs) using MLVA-16. Phylogenetic examination assigned the 96 strains to five genotype groups, with QH2019001 and QH2019005 assigned to the same group, but different subgroups. Moreover, the QH2019005 strain was assigned to a new subgenotype, IIj, within genotype II. These findings were then combined to determine the geographic origin of the two Brucella strains.ConclusionsUtilizing a whole-genome SNP-based approach enabled differences between the two B. melitensis strains to be more clearly resolved, and facilitated the elucidation of their different evolutionary histories. This approach also revealed that QH2019005 is a member of a new subgenotype (IIj) with an ancient origin in the eastern Mediterranean Sea.
Highlights
The prevalence of human brucellosis in Qinghai Province of China has been increasing rapidly, with confirmed cases distributed across 31 counties
The strains were identified as B. melitensis based on morphology and conventional identification methods according to standard biotyping procedures, including CO2 requirement, inhibition of growth by basic fuchsin and thionin, agglutination with monospecific antisera (A, M) and phage typing (Bk2, Tb)
Identification of Brucella strains The Brucella strains QH2019001 and QH2019001 were identified as B. melitensis biovar 3 using a conventional biotyping method (Table 1)
Summary
The prevalence of human brucellosis in Qinghai Province of China has been increasing rapidly, with confirmed cases distributed across 31 counties. Brucellosis, which is caused by bacteria in the Brucella genus, is one of the most important zoonoses worldwide and is considered a “forgotten, neglected zoonosis” by the World Health Organization [1]. This disease is endemic in regions within Africa, Asia, Latin America and other. In Qinghai Province, the incidence rate has increased from 0.04 per 100 000 people in 2011 to 1.96 per 100 000 people in 2018, with confirmed cases distributed across 31 counties within the entire province. Brucellosis is becoming a major public health problem that impacts human physical and mental health
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