Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) remains an important cause of nosocomial and community-associated infections due to its ability to produce toxins and evade host’s immune responses. The aim of the present study was to investigate the association of monocytes immune response in terms of cytokines produced after inoculation with different MRSA clones. Thirty-one clinical MRSA strains were selected on the basis of clonal types, accessory gene regulator (agr) groups and toxin genes carriage. Isolates were identified as S. aureus by Gram stain, catalase, coagulase production and PCR for nuc gene. The presence of mecA, lukS/lukF-PV (Panton-Valentine Leukocidin) and tst (Toxic Shock Syndrome Toxin-1) genes, as well as, the determination of agr groups was performed by PCR. Clonality was investigated by means of multi-locus sequence typing (MLST). Peripheral blood mononuclear cells were stimulated with live bacterial cells for 45 min at a ratio of 1:10. Cells were incubated for 10 h and supernatants were collected. The levels of Tumor Necrosis Factor alpha (TNFa), IL-1b, IL-8, IL-6, IL-12p40, IL-10, interferon-gamma (IFN-γ) and IL-2, were measured by Human Cytokine Multiplex Immunoassay kit. Thirteen strains were tst and 12 lukS/lukF-PV-positive. Seven strains belonged to ST80 and ST225, five to ST30 and ST239, while the remaining seven isolates were grouped together as “other.” Strains belonging to ST80 induced statistically lower levels of TNFa, IL-1b, IL-8, IL-6, IL-10, IFN-γ, and IL-2. PVL-positive strains classified into ST80 clone induced statistically lower concentrations of most cytokines as compared to PVL-positive strains belonging to other clones, tst-positive strains and toxin-negative ones. Strains of agr3 group belonging to ST80 induced statistically lower concentrations of most tested cytokines as compared to agr3 strains not-belonging to ST80, agr2 or agr1. This low induction of immune response by MRSA ST80 cannot be attributed to the presence of neither lukS/lukF-PV nor agr3.
Highlights
Staphylococcus aureus remains an important cause of infections, especially in skin and soft tissue, but can provoke severe ones such as necrotizing pneumonia, bacteraemia and endocarditis
Thirty-one clinical MRSA strains recovered from inpatients and outpatients with skin and soft tissue infections (SSTIs) or bloodstream infections (BSIs) at the University General Hospital of Patras during 2011–2014 were selected to be studied, representing the main clones identified in Greece, classified into different agr groups and carrying the genes of the superantigen Toxic Shock Syndrome Toxin-1 (TSST-1; tst) and the Panton-Valentine Leukocidin (PVL) (Table 1)
Strains were classified into agr1 (11), agr2 and agr3 (10 strains each); no MRSA belonged to agr4 group
Summary
Staphylococcus aureus remains an important cause of infections, especially in skin and soft tissue, but can provoke severe ones such as necrotizing pneumonia, bacteraemia and endocarditis (van Belkum et al, 2009). In Greece, S. aureus accounts for 9% of bacteraemias, while 40% of them are caused by MRSA (Kolonitsiou et al, 2017). MRSA was initially isolated from healthcare-associated infections causing outbreaks and gradually becoming endemic in the hospital setting with ST225 and ST239 being the most prominent clones (Drougka et al, 2014; Monecke et al, 2018). In the Mediterranean area and especially in Greece such infections are mainly due to ST80 clone which during the last decade invaded the healthcare setting causing a large proportion of healthcareassociated infections (Witte, 2009; Drougka et al, 2014)
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