The influence of mixed staphylococcal populations on the activity of phagocytes
Abstract number: 1134_04_185
Sadowska B., Wieckowska-Szakiel M., Rudnicka W., Rozalska B.
Staphylococcus aureus invades the hosts from the skin or mucosa, which are always colonized with commensal microorganisms including S. epidermidis. Thus at an early stage of S. aureus invasion polymicrobial rather than monomicrobial infection occurs. If so, the phagocytes, which are a key component of innate immunity, interact with the mixed bacterial populations. We hypothesised that the interaction of the phagocytes with a mixture of staphylococci may differ from their interaction with homogeneous populations of these bacteria.
A clinical S. aureus B1 strain, a parental S. aureus 8325-4, alpha-toxin negative mutant S. aureus DU 1090 and S. epidermidis RP12 were used for the study. The mouse granulocytes and macrophages were infected with the bacteria of each strain separately or with the mixture of two bacterial strains. FITC-labelled staphylococci were prepared to determine their adherence to the phagocytes. To estimate the ingestion and intracellular killing of these bacteria a colony forming units-assay was used. The production of IL-12 and TNF-alpha by phagocytes infected with different cultures of staphylococci was measured with DuoSet ELISA.
For all strains of S. aureus, irrespective of the tested pair of bacteria and type of phagocytes, their adhesive properties were stronger in mixed populations than in unispecies. On the other hand, the adherence of S. epidermidis to the phagocytes in the presence of each S. aureus strain was reduced. In the phagocytic cells infected with any mixed population of staphylococci the bacterial uptake and intracellular killing were diminished as compared with the cells infected with homogeneous population of these bacteria. The production of IL-12 was below detection limit, even after 2 hours incubation of bacteria with phagocytes. The level of TNF-alpha depended on the time of incubation of the cells with bacteria, but the stimulatory effect of homo- and heterogeneous cultures of staphylococci was similar.
Our data suggest that phagocytes can discriminate between various strains of staphylococci. The differences in the process of phagocytosis of congeneric and mixed staphylococcal populations could also result from the intercellular bacterial communication. Collectively, our data contribute to a better understanding of the role of commensal bacteria in the interaction of the phagocytes with bacterial pathogens. Supported by Grant No. 3PO4C08124 (KBN).
|Session name:||XXIst ISTH Congress|
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