C-173. Evaluation of Copan A2B Transport Swabs for Staphylococcus aureus Semi Quantitation in Nasal Samples
Background: There are many swab transport systems for sampling, transport and storage of microbiological specimens. While these systems maintain bacterial viability, their effect on proliferation has not been adequately evaluated. In this study we examined whether the medium in Copan A2B transport tubes supports proliferation of Staphylococcus aureus during 4oC or room temperature storage for up to 96 hours. We also evaluated the Copan A2B transport swab system for semi-quantitating S. aureus in the nares of healthy volunteers. Methods: S. aureus ATCC 29213 was resuspended in 0.9% NaCl, pH 4 or beef heart infusion (BHI) medium (to simulate organic material carry over) and 10 µl of the suspension was used to inoculate tubes containing transport medium. The inoculated tubes were incubated at 4°C or room temperature for 0, 24, 48, 72 and 96 hours. Bacteria were then removed with phosphate-buffered saline - 0.05% Tween 80 and quantitated by plating serial dilutions. For semi-quantitation of nasal samples, both nares of each volunteer were swabbed. Swabs were placed in transport tubes, and streaked within one hour onto Baird Parker agar and tryptic soy agar +5% Sheep Blood using a four-quadrant streak method. Some swabs were held for 24 hours at room temperature and then re-streaked. Plates were incubated at 37ºC for 24 hours and examined for the presence of S. aureus using a 1+ to 4+ scoring method. S. aureus colonies were confirmed by standard methods. Results: Viable organisms were recovered from swabs held under all conditions. Some proliferation of S. aureus was observed at 24 hrs and 48 hrs in the transport medium in the presence of BHI at each temperature, but not in 0.9 % saline at either temperature. Nasal samples from 6 (of 16) volunteers contained S. aureus and were analyzed as described above. All swabs held for 24 hours and then re-streaked had increased in number (ex. from 1+ to 2+). Conclusion: The transport medium does not support proliferation of S. aureus in the absence of organic material. However, with nasal samples, length of storage of the swabs in the transport medium had a significant effect on bacterial growth most likely due to the presence of organic material carried over from the nares.