Comparison of three methods for the recovery of skin pathogens from impetigo swabs collected in a remote community of Northern Territory, Australia.

BACKGROUND: Impetigo is a common infection in children living in remote areas. Immediate plating of impetigo swabs is the gold standard for bacterial recovery but is rarely feasible in remote regions. Bacterial culture increases our understanding of antibiotic resistance and strain diversity, which guides treatment protocols and epidemiological monitoring.
METHODS: We investigated three practical alternatives for recovering Streptococcus pyogenes and Staphylococcus aureus from transported swabs: dry swabs transported at 4°C with desiccant and plated within 48 h; swabs inoculated into skim milk tryptone glucose glycerol broth (STGGB), transported at 4°C, stored at -70°C and plated within 61 days; and ESwabs inoculated into Amies broth, transported at 4°C and plated within 48 h. Detection of Strep. pyogenes and Staph. aureus from simultaneously collected swabs was compared for the dry vs STGGB (36 sores) and the STGGB vs Amies (39 sores) methods. Swabs were collected from 43 children (75 sores sampled) in a remote community of Northern Territory, Australia in November 2011. The children had impetigo and were participating in the Skin Sore Trial [Australian Clinical Trials Registry ACTRN12609000858291].
RESULTS: Recovery of Strep. pyogenes for dry vs STGGB was 72% (26/36) and 92% (33/36) and for STGGB vs Amies was 92% (36/39) for both methods. Staphylococcus aureus recovery for dry vs STGGB was 69% (25/36) and 72% 26/36) and for STGGB vs Amies was 74% (29/39) and 85% (33/39).
CONCLUSION: STGGB and Amies media provided higher recovery of Strep. pyogenes than dry swabs. These results and the opportunity to batch and store specimens for molecular studies support the use of STGGB transport media for future impetigo research.