Uptake and replication in Acanthamoeba castellanii of a virulent (pVAPA-positive) strain of Rhodococcus equi and its isogenic, plasmid-cured strain.

This study examines the role of a specific plasmid, referred to as pVAPA, in the bacterium Rhodococcus equi’s ability to survive and replicate within a type of amoeba called Acanthamoeba castellanii. The results indicate that the presence of pVAPA reduces the amoebae’s ability to consume the bacteria, and enhances the bacteria’s ability to multiply within them.

Introduction to the Study

• The bacterium Rhodococcus equi is a critical player in this study. It is a type of bacterium that lives in the soil and can also act as an intracellular pathogen, causing lung disease in young horses.
• This bacterium’s virulence in horses is connected to a specific plasmid it carries, known as pVAPA. This plasmid produces a protein known as virulence-associated protein A (VapA), which aids the bacterium’s ability to replicate within animal cells.
• The researchers decided to test whether this plasmid might also help R. equi survive against environmental predators, like amoebae. The amoebae species they investigated is called Acanthamoeba castellanii.

Experiment Design

• The researchers created isogenic strains of R. equi, meaning strains that are genetically identical except for one specific factor. In this case, one strain possessed the pVAPA plasmid (pVAPA-positive) and the other did not (pVAPA-negative).
• They then compared how well these strains were consumed by (phagocytosed) and survived within A. castellanii.

Research Findings

• The results showed that the amoebae consumed significantly more of the pVAPA-negative strain than the pVAPA-positive strain.
• Additionally, the pVAPA-positive strain displayed significantly greater replication within the amoebae over both a 48-hour period and a 9-day period.
• These outcomes suggest that the VapA plasmid reduces the rate at which R. equi is consumed by A. castellanii, and it also enhances replication.