Comparative efficiency of swab types for recovery of Escherichia coli and HF183 from household surfaces

AIMS: Swabs are used in environmental microbiology studies to assess contamination on surfaces, providing critical information for the water, sanitation, and hygiene (WASH) sector in particular. However, the effects of different swab types and drying times on detection is underexplored. We evaluated the effects of these variables on efficiency of recovery and recapture (absolute recovery) of microbial targets. METHODS AND RESULTS: We tested the performance of polyester, foam, and nylon-flocked swabs for recovery of the sewage-associated Bacteroides marker gene HF183 and the Escherichia coli marker EC23S857 using qPCR, and culture methods to quantify viable E. coli. Surfaces were swabbed while wet, immediately after drying, and 24 hours post-drying. Polyester swabs recaptured significantly more HF183 and E. coli DNA than foam swabs and were on par with nylon-flocked swabs for recapturing culturable E. coli. A significant decrease in the recapture of culturable E. coli was observed from wet to dry conditions, including no detection in 24-hour dry treatments. DNA (HF183 and EC23S857) was much more efficiently recovered than culturable E. coli, e.g. nylon-flocked swabs recovered ∼55% of DNA from wet surfaces, compared to 2.4% recovery for culturable E. coli. Foam swabs generally produced the least precise results among the swab types. CONCLUSIONS: Polyester swabs were the most effective for DNA recapture and recovery of culturable E. coli was most strongly affected by drying time.