Abstract
Purpose :
Swabs are the most widely used sampling devices for ocular surface infections, including infectious corneal ulceration. However, no current standards of care exist to inform optimal swab compositions that maximize pathogen yield from the cornea. We evaluated the performance characteristics of a range of commercially available swabs, with a view to improve the sensitivity of culture-based microbiology and emerging molecular diagnostics for corneal infections.
Methods :
Candidate swabs were chosen according to the American Academy of Ophthalmology Preferred Practice Pattern for Bacterial Keratitis, including mini-tipped flocked (Puritan® PurFlock and HydraFlock, and Copan FLOQSwab®), and traditional spun-fiber swabs (Puritan® polyester, rayon, calcium alginate and cotton). Swab absorption was determined with serial weights before and after immersion in phosphate buffered saline (PBS), and distribution volumes obtained by applying saturated swabs to tryptic soy agar (TSA) using the roll-plate technique per the Clinical Laboratory Standards Institute (CLSI). Recovery efficiencies were determined using a modified CLSI swab-elution protocol. Swabs were contaminated with a standardized inoculum of log-phase Staphylococcus aureus (ATCC 29213), eluted in PBS, and serial dilutions plated in tracks on 0.3% TSA. Viable counts were observed at 18 hours, and recovery efficiency calculated as the ratio of colony forming units (CFU/mL) in swab solutions compared to that of the original liquid culture, corrected for swab absorption.
Results :
Flocked swabs had higher mean absorption values than spun-fiber swabs, both in absolute volume (Fig.1A) and per unit mass (1359–1543% vs. 200–578%, respectively). Agar distribution volumes were also greater among flocked swabs (Fig.1B and C). Mean recovery efficiencies (%) for PurFlock, HydraFlock and FLOQSwab were 78.9±10.1, 84.4±9.0, 84.5±13.9, respectively, compared to 52.7±14.4 for polyester, 91.0±17.7 for rayon, 54.0±15.8 for calcium alginate and 8.1±2.6 for cotton (Fig.2, p<0.001). Bonferroni-adjusted pairwise comparisons revealed significantly lower recovery efficiencies for calcium alginate compared to each flocked swab (all p<0.001).
Conclusions :
New-generation flocked swabs outperformed spun-fiber swabs in terms of absorption, distribution, and recovery efficiency. Their use may translate to greater microbial yield, which could aid in diagnosing low-biomass corneal infections.
This is a 2021 ARVO Annual Meeting abstract.