Viability of Aerobic Microorganisms in Four Swab Systems

Many clinical specimens are collected by a swab transport system. We evaluated and compared the Copan Amies agar swab, Copan Liquid Stuart’s swab, BBL Port-a-cul swab, and Starplex Liquid Stuart’s swab for maintenance of viability of 18 aerobic microorganisms. Swabs were inoculated with 100-ml of a 107 CFU/ml organism suspension, incubated at room temperature for 0, 4, 24, and 48h, and the swabs used to prepare 10-fold serial dilutions in 0.9-ml saline. A 100-ml aliquot of each dilution was inoculated to blood or chocolate agar and incubated for 24-48h in CO2 or aerobically. Colony counts were obtained and the data analyzed as percent recovery compared to the 0h growth results. After 24h and 48h, all microorganisms were recovered from the Copan Amies agar swab and Copan Liquid Stuart’s swab while only 1 N. gonorrhoeae was not recovered in BBL Port-a-cul swab (17/18 recovered). 12/18 (67%) microorganisms were recovered in the Starplex Liquid Stuart’s swab after 24h and 6/18 (33%) after 48h. Apparent growth of the micro-organism after 48h (>10-fold increased recovery from 0h) was observed for 6/8 (33%) in the Copan Amies agar swab, 4/18 (22%) in the Copan Liquid Stuart’s swab, 10/18 (56%) in the BBL Port-a-cul, and 0/18 in the Starplex Liquid Stuart’s swab. The Copan Amies agar swab, the Copan Liquid Stuart’s swab, and the BBL Port-a-cul swab are acceptable transport systems for recovery of aerobic microorganisms. The Starplex Liquid Stuart’s swab is less suitable for transport delays longer than 4 hours based on this data.