Evaluation of the Biological Sampling Kit (BiSKit) for large-area surface sampling

Abstract

Current surface sampling methods for microbial contaminants are designed to sample small areas and utilize culture analysis. The total number of microbes recovered is low because a small area is sampled, making detection of a potential pathogen more difficult. Furthermore, sampling of small areas requires a greater number of samples to be collected, which delays the reporting of results, taxes laboratory resources and staffing, and increases analysis costs. A new biological surface sampling method, the Biological Sampling Kit (BiSKit), designed to sample large areas and to be compatible with testing with a variety of technologies, including PCR and immunoassay, was evaluated and compared to other surface sampling strategies. In experimental room trials, wood laminate and metal surfaces were contaminated by aerosolization of Bacillus atrophaeus spores, a simulant for Bacillus anthracis, into the room, followed by settling of the spores onto the test surfaces. The surfaces were sampled with the BiSKit, a cotton-based swab, and a foam-based swab. Samples were analyzed by culturing, quantitative PCR, and immunological assays. The results showed that the large surface area (1 m2) sampled with the BiSKit resulted in concentrations of B. atrophaeus in samples that were up to 10-fold higher than the concentrations obtained with the other methods tested. A comparison of wet and dry sampling with the BiSKit indicated that dry sampling was more efficient (efficiency, 18.4%) than wet sampling (efficiency, 11.3%). The sensitivities of detection of B. atrophaeus on metal surfaces were 42 +/- 5.8 CFU/m2 for wet sampling and 100.5 +/- 10.2 CFU/m2 for dry sampling. These results demonstrate that the use of a sampling device capable of sampling larger areas results in higher sensitivity than that obtained with currently available methods and has the advantage of sampling larger areas, thus requiring collection of fewer samples per site.

FIG. 1.

BiSKit. The components include a BiSKit sampling unit, a 30-ml sample collection bottle with buffer, a dropper attachment, and a rubber cap.

FIG. 2.

Comparison of sampling methods for experimental room trials. Wood laminate or metal surfaces were contaminated by aerosolization of B. atrophaeus spores into the room. Duplicate samples were collected by each sampling method and were analyzed by culturing and QPCR. The bar heights indicate the means for eight samples (wood laminate) or four samples (metal), and the error bars indicate standard errors. The sample areas were as follows: BiSKit, 1 m²; SSP kit, 317 cm²; cotton swab, 100 cm².

FIG. 3.

Comparison of wet and dry sampling with the BiSKit in the experimental room. Metal surfaces (1 m²) were contaminated with 10⁵ B. atrophaeus spores in a liquid suspension and allowed to dry. Samples were collected and were analyzed by culturing. Following initial processing, a sample was processed a second time by removing the foam collection material and hand mixing in buffer for 1 min. The bar heights indicate the means for eight samples (dry) or four samples (wet), and the error bars indicate standard errors.

FIG. 4.

Comparison of wet and dry sampling with the BiSKit in the experimental room. Metal and wood laminate surfaces (1 m²) were contaminated by aerosolization and deposition of dry B. atrophaeus spores in the room. Samples were collected and were analyzed by culturing and PCR. The bar heights indicate the means for four samples, and the error bars indicate standard errors.