Pathogenicity of Human ST23 Streptococcus agalactiae to Fish and Genomic Comparison of Pathogenic and Non-pathogenic Isolates

Abstract

Streptococcus agalactiae, or Group B Streptococcus (GBS), is a major pathogen causing neonatal sepsis and meningitis, bovine mastitis, and fish meningoencephalitis. CC23, including its namesake ST23, is not only the predominant GBS strain derived from human and cattle, but also can infect a variety of homeothermic and poikilothermic species. However, it has never been characterized in fish. This study aimed to determine the pathogenicity of ST23 GBS to fish and explore the mechanisms causing the difference in the pathogenicity of ST23 GBS based on the genome analysis. Infection of tilapia with 10 human-derived ST23 GBS isolates caused tissue damage and the distribution of pathogens within tissues. The mortality rate of infection was ranged from 76 to 100%, and it was shown that the mortality rate caused by only three human isolates had statistically significant difference compared with fish-derived ST7 strain (P < 0.05), whereas the mortality caused by other seven human isolates did not show significant difference compared with fish-derived ST7 strain. The genome comparison and prophage analysis showed that the major genome difference between virulent and non-virulent ST23 GBS was attributed to the different prophage sequences. The prophage in the P1 region contained about 43% GC and encoded 28–39 proteins, which can mediate the acquisition of YafQ/DinJ structure for GBS by phage recombination. YafQ/DinJ belongs to one of the bacterial toxin–antitoxin (TA) systems and allows cells to cope with stress. The ST23 GBS strains carrying this prophage were not pathogenic to tilapia, but the strains without the prophage or carrying the pophage that had gene mutation or deletion, especially the deletion of YafQ/DinJ structure, were highly pathogenic to tilapia. In conclusion, human ST23 GBS is highly pathogenic to fish, which may be related to the phage recombination.

12/111phiA Prophage Domestication Is Associated with Autoaggregation and Increased Ability to Produce Biofilm in Streptococcus agalactiae

“…Using BlastN tools, a search for prophages similar to 12/111phiA identified 10 Javan-like prophages from the genome of Streptococci [ 50 ], and 12/111phiA-like features in the genomes of 13 GBS strains ( Table S5 ; Figure 2 ) and 10 non-GBS Streptococci , including S. urinalis , S. constellatus , S. canis , and S. equi . In particular, prophage MR1-Z1-201_Phi carried by a ST23 GBS, isolated in the U.K. from a seal, shared 93% identity (78% cover) with 12/111phiA ( Figure 2 ) and yielded three genes identical to the three ORFs endonuclease , yafQ , and relB carried by 12/111phiA (100% identity; 100% cover) [ 51 ].…”

An Unusual Cause of Tenosynovitis by Group B Streptococcus in the Immunocompromised Patient: A Case Report

“…ST23 has been identified as a dominant strain commonly associated with invasive GBS infections (Chang et al, 2014;Ezhumalai et al, 2020). Another study found that human ST23 GBS can be pathogenic to fish, possibly due to phage recombination (Wang et al, 2017). In conclusion, detailed history and clinical suspicion are the critical factors to diagnose GBS infections in tenosynovitis.…”

Neuroimaging in Zoonotic Outbreaks Affecting the Central Nervous System: Are We Fighting the Last War?

“…The invasive serotype III sequence type 283 (ST283) Streptococcus agalactiae was identified as the causative organism, with the same strain identified among farmed freshwater fish used for food preparation. [60][61][62] The outbreak stopped after affected fish imports into Singapore were banned and stricter rules were established governing raw fish dishes. 60 However, there have been other, smaller outbreaks of human meningitis in Hong Kong and Southeast Asia involving the ST283 strain, suggesting a potential public health threat of this foodborne zoonosis in Asia.…”