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R-plasmid RP1 increases sensitivity of Proteus mirabilis to normal body defences
1Department of Pharmaceutical Sciences, Aston University, Birmingham.
Abstract:
The bactericidal action of non-immune whole blood on Proteus mirabilis was increased when the bacteria contained the R-plasmid RP1. This effect was due mainly to increased phagocytosis. Iron-depleted stationary-phase cells were more sensitive than carbon-depleted cells. The contribution of serum was usually negligible but was increased during a minor non-specific infection. Most plasmid-containing phenotypes were more sensitive than were those without plasmids but there were considerable differences between stationary and exponentially-growing cells. The R-plasmid-mediated increase in sensitivity to phagocytosis may be due in part to the presence of additional glycosylated proteins in the outer membrane.
Insights
The R-plasmid RP1 enhances bacterial killing by non-immune whole blood, primarily through increased phagocytosis. This plasmid-mediated sensitivity is influenced by nutrient depletion and bacterial growth phase.
Area of Science:
- Microbiology and Immunology
- Bacterial Pathogenesis
- Host-Pathogen Interactions
Background:
- Non-immune whole blood possesses bactericidal activity against various pathogens.
- Bacterial plasmids can influence interactions with the host immune system.
- Nutritional status and growth phase affect bacterial susceptibility.
Purpose of the Study:
- To investigate the effect of the R-plasmid RP1 on the bactericidal activity of non-immune whole blood against Proteus mirabilis.
- To determine the mechanisms underlying plasmid-mediated changes in bacterial sensitivity.
- To assess the influence of environmental factors like nutrient depletion and growth phase.
Main Methods:
- Assays measuring the bactericidal activity of non-immune whole blood against Proteus mirabilis strains with and without the R-plasmid RP1.
- Phagocytosis assays to quantify bacterial uptake by immune cells.
- Comparison of bacterial sensitivity under different nutrient-depleted conditions (iron vs. carbon) and growth phases (stationary vs. exponential).
Main Results:
- The R-plasmid RP1 significantly increased the bactericidal action of non-immune whole blood on Proteus mirabilis.
- Increased phagocytosis was identified as the primary mechanism for this enhanced killing.
- Iron-depleted stationary-phase cells exhibited greater sensitivity compared to carbon-depleted cells, and plasmid-containing cells were generally more sensitive.
Conclusions:
- The R-plasmid RP1 confers increased sensitivity to non-immune whole blood killing in Proteus mirabilis, mainly via enhanced phagocytosis.
- Bacterial nutrient status and growth phase modulate this plasmid-mediated immune evasion or susceptibility.
- Outer membrane alterations, potentially involving glycosylated proteins, may contribute to the R-plasmid-mediated increase in phagocytosis sensitivity.