Survival of anaerobic and aerobic bacteria on cotton swabs in three transport systems

The capacity of aerobic and anaerobic bacteria to survive on cotton swabs placed into a dry gassed-out CO2-filled tube (DGT), dry sterile aerobic tube (DAT), and a tube containing a modified Stuarts' transport medium (MST), was assessed. Pseudomonas aeruginosa increased in numbers by 2 and 3 logs when stored in MST and DAT, respectively. The viability of P. aeruginosa, although retarded when compared to MSA and DAT, was not adversely affected by the CO2 environment in the DGT. The MST maintained relatively constant numbers of Streptococcus pyogenes during the 48-h storage period. The DAT and the DGT were unable to maintain the viability of S. pyogenes. Staphylococcus aureus, when stored in a DGT, DAT, or MST, was maintained in relatively constant numbers throughout the entire storage period. Of the four anaerobic bacteria evaluated (Bacteroides fragilis ssp. thetaiotaomicron, Bacteroides melaninogenicus ssp. asaccharolyticus, Fusobacterium nucleatum, and Peptostreptococcus anaerobius), only B. fragilis ssp. thetaiotamicron survived the 48-h storage period in the DGT. Under these test conditions the DGT did not adequately maintain the viability of the majority of anaerobic bacteria tested (when held on cotton swabs). However, the MST did maintain the viability of all species tested for at least the first 2 h of storage.