Turkey Embryo Lethality Assay of Streptococcus gallolyticus Field Isolates from Poultry

Area of Science:

• Veterinary Microbiology
• Poultry Disease Research
• Bacterial Pathogenesis

Background:

• Emergence of *Streptococcus gallolyticus* as a leading cause of fatal bacterial sepsis in commercial turkey poults since 2020.
• Limited understanding of the specific virulence factors contributing to *S. gallolyticus* pathogenicity in poultry.

Purpose of the Study:

• To evaluate the virulence potential of different *Streptococcus gallolyticus* strains, including subspecies *pasteurianus* and *gallolyticus*, using a turkey embryo lethality assay.
• To investigate the role of potential virulence factors, such as Acb protein and L-arabinose metabolism, in *S. gallolyticus* infection.

Main Methods:

• Isolation and identification of eight *S. gallolyticus* strains from turkey poult outbreaks using API systems.
• Whole-genome sequencing to identify genetic distinctness and potential virulence factors.
• Inoculation of turkey embryos with varying doses of *S. gallolyticus* strains to determine embryo mortality and assess virulence.

Main Results:

• Highest cumulative embryo mortality was observed with a neurological *S. gallolyticus* subsp. *pasteurianus* strain and another *S. gallolyticus* subsp. *pasteurianus* strain at high doses.
• Bacterial sepsis, characterized by hemorrhages and organ congestion, was consistent with observed embryo mortality.
• Only one of three strains with Acb-like protein showed increased mortality, suggesting Acb alone is not the sole determinant of enhanced virulence.

Conclusions:

• Virulence of *S. gallolyticus* in turkey embryos is strain-dependent, with neurological isolates showing higher pathogenicity.
• The Acb protein may not be solely responsible for enhanced virulence; other factors like L-arabinose metabolism could play a significant role.
• Further research into novel virulence factors is warranted to understand and combat *S. gallolyticus* infections in poultry.