Comparative genomics analysis of Streptococcus agalactiae reveals that isolates from cultured tilapia in China are closely related to the human strain A909.
BACKGROUND
Streptococcus agalactiae, also referred to as Group B Streptococcus (GBS), is a frequent resident of the rectovaginal tract in humans, and a major cause of neonatal infection. In addition, S. agalactiae is a known fish pathogen, which compromises food safety and represents a zoonotic hazard. The complete genome sequence of the piscine S. agalactiae isolate GD201008-001 was compared with 14 other piscine, human and bovine strains to explore their virulence determinants, evolutionary relationships and the genetic basis of host tropism in S. agalactiae.


RESULTS
The pan-genome of S. agalactiae is open and its size increases with the addition of newly sequenced genomes. The core genes shared by all isolates account for 50 ~ 70% of any single genome. The Chinese piscine isolates GD201008-001 and ZQ0910 are phylogenetically distinct from the Latin American piscine isolates SA20-06 and STIR-CD-17, but are closely related to the human strain A909, in the context of the clustered regularly interspaced short palindromic repeats (CRISPRs), prophage, virulence-associated genes and phylogenetic relationships. We identified a unique 10 kb gene locus in Chinese piscine strains.


CONCLUSIONS
Isolates from cultured tilapia in China have a close genomic relationship with the human strain A909. Our findings provide insight into the pathogenesis and host-associated genome content of piscine S. agalactiae isolated in China.
Guangjin
G
Liu
Wei
W
Zhang
Key Laboratory of Animal Bacteriology, Ministry of Agriculture, Nanjing Agricultural University, Weigang No,1, Nanjing, Jiangsu 210095, China. lucp@njau.edu.cn.
Chengping
C
Lu
D000818:Animals; D002417:Cattle; D002681:China; D005393:Fish Diseases / Q000235:genetics* / Q000382:microbiology; D016680:Genome, Bacterial; D006801:Humans; D010802:Phylogeny; D013290:Streptococcal Infections / Q000235:genetics* / Q000473:pathology; D013292:Streptococcus agalactiae / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D017210:Tilapia / Q000235:genetics / Q000382:microbiology*