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Pili and the interaction of Aeromonas species with human peripheral blood polymorphonuclear cells
1Department of Pathology, University of Tasmania Clinical School, Hobart, Australia.
Abstract:
The interaction of differentially piliated Aeromonas strains expressing pili of two broadly different morphologic types (short, rigid (S/R) and/or long, wavy (L/W)) with human peripheral blood mononuclear leukocytes (PMN) was investigated to determine whether host defense cells might exert a selective pressure on pili expression in vivo accounting for the different pili phenotypes of clinical and environmental strains. A majority of Aeromonas veronii biotype sobria strains from water (6/6) and faeces (8/11) readily associated with PMN (> 60% PMN with adherent and/or internalised bacteria), irrespective of their degree, or predominant type, of piliation. Rigid pili of Aeromonas species did not promote interaction with PMN. However, the majority (55%) of strains which interacted well with PMN were adherent to HEp-2 cells. Interaction with PMN is unlikely to be the reason few S/R pili are seen on faecal strains, but it may be a selective pressure on L/W adhesive pili, or other OMP adhesins, resulting in the shedding of strains which have lost critical adhesins.
Insights
Human immune cells, or polymorphonuclear leukocytes (PMN), interact with Aeromonas bacteria. This interaction may influence bacterial pili expression, potentially explaining differences between clinical and environmental strains.
Area of Science:
- Microbiology
- Immunology
- Bacterial Pathogenesis
Background:
- Aeromonas strains exhibit diverse pili types, including short, rigid (S/R) and long, wavy (L/W) forms.
- Pili are crucial for bacterial adhesion and interaction with host cells.
- Differences in pili expression are observed between clinical and environmental Aeromonas isolates.
Purpose of the Study:
- To investigate the interaction between Aeromonas strains with different pili types and human peripheral blood mononuclear leukocytes (PMN).
- To determine if host defense cells (PMN) exert selective pressure on bacterial pili expression in vivo.
- To understand the role of pili in the differential phenotypes of clinical and environmental Aeromonas strains.
Main Methods:
- Culturing Aeromonas strains with varying pili expression.
- Co-incubation of Aeromonas strains with human peripheral blood mononuclear leukocytes (PMN).
- Assessing bacterial association with PMN (adherence and internalization).
- Evaluating bacterial adherence to HEp-2 cells.
Main Results:
- Most Aeromonas veronii biotype sobria strains from water and faeces readily associated with PMN, regardless of pili type or degree.
- Rigid pili (S/R) did not enhance interaction with PMN.
- A majority of strains that interacted well with PMN also adhered to HEp-2 cells (55%).
Conclusions:
- PMN interaction is unlikely to explain the scarcity of S/R pili on faecal strains.
- PMN may exert selective pressure on long, wavy (L/W) adhesive pili or other outer membrane protein (OMP) adhesins.
- This selective pressure could lead to the loss of critical adhesins in certain Aeromonas strains.