Shigella sonnei utilises colicins during inter-bacterial competition

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Gut Microbiome

Background:

• The mammalian colon harbors dense commensal bacteria, necessitating competition for enteric pathogens like Shigella.
• Shigella species cause millions of infections annually, with Shigella sonnei being a major cause.
• Previous studies suggested Shigella sonnei utilizes a Type VI Secretion System (T6SS) for competitive advantage.

Purpose of the Study:

• To investigate the roles of T6SS and colicins in the anti-bacterial activity of Shigella sonnei.
• To determine which mechanism contributes to Shigella sonnei's competitive fitness in the gut environment.

Main Methods:

• Analysis of T6SS gene integrity in Shigella sonnei strains.
• Construction of strains with inducible T6SS operons.
• In vitro assays to assess anti-bacterial activity against various bacterial species.
• Testing activity against colicin-resistant strains and assessing the impact of colicin plasmid removal.

Main Results:

• The T6SS operon in Shigella sonnei shows evidence of functional degradation.
• Synthetically induced T6SS did not exhibit anti-bacterial activity in vitro.
• Anti-bacterial activity was attributed to colicin production.
• Loss of colicin plasmid or presence of colicin resistance abrogated Shigella sonnei's killing activity.

Conclusions:

• Colicins, not T6SS, are responsible for the observed anti-bacterial activity in Shigella sonnei.
• Colicin activity is sufficient for Shigella sonnei's niche competition within the gastrointestinal tract.