New Direct Quantitative Method for Comparative Evaluation of Swab Collection and Transport Systems
Comparative evaluations of swab collection/transport systems have been based on qualitative 4 quadrant streak methods or on more complex quantitative elution/dilution methods. We evaluated the BBL CultureSwab Plus (BBL) and the Starplex Starswab II (STAR) by a new, direct roll-plate quantitative method and compared results to a standard quantitative elution/dilution method. A total of 10 organisms were tested by both swab systems using both quantitative methods. For the roll-plate method, 100 ul of a 105 and of a 106 CFU/ml suspension of each organism was added to the swabs. Duplicate swabs of each type were cultured after incubation at room temperature of 0, 4, 8, 24, and 48 h to appropriate media by rolling approximately 120o of the swab over the surface of the agar plate. This inoculation was performed twice more by rotating the plate 60o and rotating the swab 120o to ensure contact of the entire swab to the entire agar surface. For the elution/dilution method, 100 ul of a 105 or 106 CFU/ml organism suspension was added to BBL and STAR swabs. After incubation at room temperature for 0, 4, 8, 24, and 48 h, swabs were placed into 0.9 ml sterile saline and mixed well to elute the organism from the swab. Two further 1:10 dilutions in sterile saline were prepared and 100 ul of each of the 3 dilutions were plated to appropriate media. All media were incubated at 35oC for up to 48 h. Colony counts were obtained for each incubation period and compared to the 0 h colony count to determine % recovery of each organism by each test method. The % recovery was considered to be in agreement (± one-log10 in % recovery) for 39 of the 40 (97.5%) STAR comparative determinations and for 38 of the 40 (95%) BBL determinations. The 3 discrepancies included H. influenzae recovered at 0.2 % with the BBL elution/dilution method and at 5% with the roll-plate method after 24 h, and at 48 h, the S. pneumoniae in STAR recovered at 0.03% and the H. influenzae in BBL recovered at 0.2% while the organisms were not recovered by the corresponding elution/dilution methods. The new roll-plate method is an accurate and easy-to-perform method for comparing swab collection/transport systems.