Direct molecular versus culture-based assessment of Gram-positive cocci in biopsies of patients with major abscesses and diabetic foot infections.

Major abscesses and diabetic foot infections (DFIs) are predominant subtypes of complicated skin and skin structure infections (cSSSIs), and are mainly caused by Staphylococcus aureus and ß-hemolytic streptococci. This study evaluates the potential benefit of direct pathogen-specific real-time polymerase chain reaction (PCR) assays in the identification of causative organisms of cSSSIs. One-hundred and fifty major abscess and 128 DFI biopsy samples were collected and microbial DNA was extracted by using the Universal Microbe Detection kit for tissue samples. Pathogen-specific PCRs were developed for S. aureus and its virulence factor Panton-Valentine leukocidin (PVL), Streptococcus pyogenes, S. agalactiae, S. dysgalactiae, and the S. anginosus group. Identification by pathogen-specific PCRs was compared to routine culture and both methods were considered as the gold standard for determination of the sensitivity and specificity of each assay. Direct real-time PCR assays of biopsy samples resulted in a 34 % higher detection of S. aureus, 37 % higher detection of S. pyogenes, 18 % higher detection of S. agalactiae, 4 % higher detection of S. dysgalactiae subspecies equisimilis, and 7 % higher detection of the S. anginosus group, compared to routine bacterial culture. The presence of PVL was mainly confined to S. aureus isolated from major abscess but not DFI biopsy samples. In conclusion, our pathogen-specific real-time PCR assays had a higher yield than culture methods and could be an additional method for the detection of relevant causative pathogens in biopsies.

Polymorphisms in cytokine genes IL6, TNF, IL10, IL17A and IFNG influence susceptibility to complicated skin and skin structure infections.

Complicated skin and skin structure infections (cSSSIs) are caused by Gram-positive and Gram-negative, aerobic and anaerobic pathogens, with a polymicrobial aetiology being frequent. Recognition of invading pathogens by the immune system results in the production of pro- and anti-inflammatory cytokines, which are extremely important for intercellular communication and control of infection. This study assessed whether genetic variation in genes encoding cytokines influences the susceptibility to cSSSIs. For the association study, 318 patients with cSSSI and 328 healthy controls were genotyped for single nucleotide polymorphisms (SNPs) in cytokine genes IL1A, IL1B, IL1RN, TNF, IL10, IL17A, IL17F and IFNG. For immunological validation, peripheral blood mononuclear cells (PBMCs) from 74 healthy individuals, genotyped for SNPs of interest, were stimulated with Staphylococcus aureus or Escherichia coli and corresponding cytokine levels were determined by enzyme-linked immunosorbent assay (ELISA). Polymorphisms IL6 rs1800797, TNF rs1800629, IL10 rs1800871, IL17A rs8193036 and IFNG rs2069705 influenced susceptibility to cSSSIs. No differences in cytokine responses, stratified for genotype, were detected after PBMC stimulation. No association with cSSSIs was observed for polymorphisms IL1A rs17561 and rs1800587, IL1B rs16944 and rs1143627, IL1RN rs4251961, TNF rs361525, IL10 rs1800896, IL17A rs2275913 and IL17F rs763780. In conclusion, polymorphisms in IL6, TNF, IL10, IL17A and IFNG are associated with susceptibility to cSSSIs.