Toxin production by meticillin-resistant Staphylococcus aureus strains is related to differences in cytokine levels by peripheral blood mononuclear cells

Abstract number: P759

Kolonitsiou F., Spiliopoulou A., Chini V., Krevata M., Anastassiou E.D., Spiliopoulou I.

Objectives: To investigate the immune system response in terms of secreted cytokines, to the existence of staphylococcal virulence factors among meticillin-resistant Staphylococcus aureus (MRSA) isolates.

Methods: Twenty-two, 18 clinical and four reference MRSA strains were characterised on the basis of toxin gene profile by PCRs (PVL, tst, enterotoxins of the egc operon, eta, etb). Clones were defined by agr typing and MLST, while tst expression was calculated by quantitative reverse-transcription PCR (RT-PCR). Peripheral blood mononuclear cells from healthy donors were isolated by standard procedures and were co-cultured in 24-well flat bottom tissue culture plates with live MRSA cells at a ratio of 25:1. Cytokine measurements, using the Luminex® xMAPTM technology, were performed in cell-free supernatants collected at 6 and 12 hours. The 8-plex assay kit was used for simultaneous quantitative determination of the following cytokines: TNFa, IL-1b, IL-6, IL-8, IL-10, IL-12p40, IL-13 and GM-CSF.

Results: MRSA elicited production of detectable amounts of all eight cytokines. A negative correlation was detected between PVL genes carriage and production of GM-CSF at six hours, and TNFa, IL-6, IL-10, IL-13 and GM-CSF at 12h. The presence of tst gene was correlated with release of greater amounts of TNFa, IL-6, IL-8, IL-10, IL-13 and GM-CSF at 6 and 12h. The presence of tst gene correlated with lower levels of IL-12p40 at 12h. Expression level of tst and presence of the remaining superantigens were not related to cytokines' levels. Analysis of agr types and cytokine profile showed that MRSA of agr1 (including tst-positives) induced production of greater amounts of TNFa, IL-6, IL-8, IL-10, IL-13, GM-CSF and IL-12p40 at 12h than agr2 (including egc-positives) and agr3 (including PVL and egc-positives) MRSA. All differences were statistically significant (p < 0.05).

Conclusions: Our data reinforce the knowledge that toxic shock syndrome toxin-1 has strong proinflammatory and immunoregulatory properties, perhaps in association with other factors, as it directs immune system to TH2 response by promoting the release of IL-10 and IL-13 and down-regulating the production of IL-12p40. PVL has a diminished potential towards triggering immune responses, as strains possessing PVL genes elicited production of lower amounts of pro-inflammatory cytokines and cytokines of adaptive immune response.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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