Comparison of two Swab Transport Systems to Maintain Viability of Clinically Relevant Enteric Pathogenic Bacteria
Background: Studies have indicated that rectal swab specimens can provide accurate test results when used with stool culture and molecular testing of enteric pathogens. The aim of this study was to evaluate two fecal swab systems to transport and maintain clinically relevant enteric pathogenic bacteria: FecalSwab® Transport System (Copan, USA) and Fecal Opti-Swab® (Puritan, USA).
Methods: The following ATCC enteric pathogenic bacteria strains were evaluated for survival after incubation at room temperature (25°C) using the two transport swab systems described above: Escherichia coli ATCC 25922, Shigella flexneri ATCC 12022, Salmonella typhimurium ATCC 14028, Shigella sonnei ATCC 9290 and Yersinia enterocolitica ATCC 9610. A vortex elution protocol proposed by the CLSI standard M40-A2 was performed. This CLSI standard document provides a method of quality control testing, together with acceptance criteria not only for viability but also for overgrowth of bacteria. Briefly, an initial 0.5 MacFarland suspension of each strain was prepared, followed by six 10 fold dilutions (1.5 x 107 to 102 CFU/mL). The last three suspensions with final concentrations of 1.5 x 104 to 102 CFU/mL of each strain were used as working suspensions. Both, FecalSwab and Fecal Opti-Swab systems were inoculated in triplicate with 100µL of each organism working suspensions. Swabs were held at 25°C for 0h, 24h and 48h. Each inoculated swab was cultured and bacterial survival was evaluated after 24h-48h incubation at 35°C.
Results: Cultures from all swabs were averaged and results were compared with the M40-A2 CLSI document acceptance criteria. Bacterial recovery from swabs held at 0h were within the limits accepted by the M40-A2 CLSI document for both, Copan and Puritan fecal transport devices. Additionally, all five strains tested were recovered from all swab systems after 24h and 48h of incubation. Copan FecalSwab was able not only to maintain the organisms viable, but to keep the growth stable for up to 48h of incubation. On the other hand, organisms’ overgrowth were observed after 24h and 48h of incubation in all five species inoculated on the Puritan Fecal Opti-Swab. These overgrowth cultures didn’t remain within the 2 log10 of the initial microorganism concentration, as required by the CLSI M40-A2 document.
Conclusion: Only Copan FecalSwab transport system was able to comply with all criteria for each enteric pathogenic organism’s survival at all time points as described by the CLSI standard M40-A2.