Related Experiment Videos
Trojan horse effect: phagocyte-mediated Streptococcus iniae infection of fish
Amir Zlotkin1, Stefan Chilmonczyk, Marina Eyngor
1Department of Clinical Microbiology, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
Abstract:
The salmonid macrophage-like cell line RTS-11 and purified trout pronephros phagocytes were used to analyze in vitro entry and survival of two Streptococcus iniae serotypes. Efficient invasion by S. iniae occurred in both cells, but only the type II strain persisted in pronephros phagocytes for at least 48 h. Ex vivo models of opsonin-dependent phagocytosis by pronephros phagocytes demonstrated increased phagocytosis efficacy. Analysis of phagocytes collected from diseased fish demonstrated that approximately 70% of the bacteria contained in the blood during the septic phase of the disease were located within phagocytes, suggesting an in vivo intracellular lifestyle. In addition to the augmented levels of bacteremia and enhanced survival within phagocytes, S. iniae type II induces considerable apoptosis of phagocytes. These variabilities in intramacrophage lifestyle might explain differences in the outcomes of infections caused by different serotypes. The generalized septic disease associated with serotype II strains is linked not only to the ability to enter and multiply within macrophages but also to the ability to cause considerable death of macrophages via apoptotic processes, leading to a highly virulent infection. We assume that the phenomenon of survival within phagocytes coupled to their apoptosis plays a crucial role in S. iniae infection. In addition, it may provide the pathogen an efficient mechanism of translocation into the central nervous system.
Insights
Certain Streptococcus iniae strains survive and multiply within fish phagocytes, while others cause cell death. This intracellular lifestyle and apoptosis induction explain the varying virulence of S. iniae infections in salmonid fish.
Area of Science:
- Immunology
- Fish Pathology
- Microbiology
Background:
- Streptococcus iniae is a significant pathogen in salmonid aquaculture.
- Understanding bacterial interactions with host immune cells is crucial for disease management.
Purpose of the Study:
- To investigate the in vitro entry and survival mechanisms of different Streptococcus iniae serotypes within fish phagocytes.
- To elucidate the role of phagocyte apoptosis in S. iniae pathogenesis.
Main Methods:
- Utilized the salmonid macrophage-like cell line RTS-11 and primary trout pronephros phagocytes.
- Performed in vitro invasion and survival assays for S. iniae serotypes.
- Analyzed ex vivo opsonin-dependent phagocytosis and phagocyte apoptosis.
Main Results:
- Both S. iniae serotypes efficiently invaded fish phagocytes.
- Only the type II strain demonstrated prolonged survival (≥48 h) within pronephros phagocytes.
- Approximately 70% of blood bacteria in diseased fish were intracellular, indicating an in vivo intracellular lifestyle.
- S. iniae type II induced significant phagocyte apoptosis, correlating with higher virulence.
Conclusions:
- Variations in intracellular lifestyle and apoptosis induction by S. iniae serotypes contribute to differential infection outcomes.
- The ability of S. iniae type II to survive within phagocytes and induce apoptosis is key to its high virulence.
- Intracellular survival and apoptosis may facilitate pathogen translocation to the central nervous system.