Genotype diversity of brucellosis agents isolated from humans and animals in Greece based on whole-genome sequencing

BACKGROUND

Brucellosis is a zoonotic disease whose causative agent, Brucella spp., is endemic in many countries of the Mediterranean basin, including Greece. Although the occurrence of brucellosis must be reported to the authorities, it is believed that the disease is under-reported in Greece, and knowledge about the genomic diversity of brucellae is lacking.

METHODS

Thus, 44 Brucella isolates, primarily B. melitensis, collected between 1999 and 2009 from humans and small ruminants in Greece were subjected to whole genome sequencing using short-read technology. The raw reads and assembled genomes were used for in silico genotyping based on single nucleotide substitutions and alleles. Further, specific genomic regions encoding putative virulence genes were screened for characteristic nucleotide changes, which arose in different genotype lineages.

RESULTS

In silico genotyping revealed that the isolates belonged to three of the known sublineages of the East Mediterranean genotype. In addition, a novel subgenotype was identified that was basal to the other East Mediterranean sublineages, comprising two Greek strains. The majority of the isolates can be assumed to be of endemic origin, as they were clustered with strains from the Western Balkans or Turkey, whereas one strain of human origin could be associated with travel to another endemic region, e.g. Portugal. Further, nucleotide substitutions in the housekeeping gene rpoB and virulence-associated genes were detected, which were characteristic of the different subgenotypes. One of the isolates originating from an aborted bovine foetus was identified as B. abortus vaccine strain RB51.

CONCLUSION

The results demonstrate the existence of several distinct persistent Brucella sp. foci in Greece. To detect these and for tracing infection chains, extensive sampling initiatives are required.

Genotyping of Brucella isolates from animals and humans by Multiple-Locus Variable-number Tandem Repeat Analysis (MLVA)

This study investigates country-wide genotype variations through the genotyping of Brucella strains isolated from domestic ruminants and humans. The Brucella spp. isolated from samples taken from animals and humans were first identified as B. abortus and B. melitensis by real-time PCR, and the MLVA-16 approach was then used for the genotyping of the identified isolates. For the study, 416 Brucella spp. were isolated from aborted fetus samples examined between 2018 and 2021, and 74 Brucella spp. from infected humans. Of the 74 human isolates analyzed, 1.3% were identified as B. abortus and 98.7% (73/74) as B. melitensis. The MLVA-16 typing method revealed 30 clonal groups for B. abortus and 37 clonal groups for B. melitensis from which the dominant genotypes and similarities with human isolates in Türkiye were determined.