A revolution in sample collection
30 Oct 2007 by Evoluted New Media
Results of a simple dip dye test. More than 40 years after the pioneering development of single-use laboratory plastics, a major advance in swab technology has resulted in a new generation of swabs with improved sample collection and release. Utilising an innovative ‘flocked’ tip the new swabs are ideal for applications where the sample size is particularly small or where increased sensitivity is required
Results of a simple dip dye test. More than 40 years after the pioneering development of single-use laboratory plastics, a major advance in swab technology has resulted in a new generation of swabs with improved sample collection and release. Utilising an innovative ‘flocked’ tip the new swabs are ideal for applications where the sample size is particularly small or where increased sensitivity is required
SAMPLE collection is a critical step in clinical applications such as the diagnosis of respiratory viral infections, MRSA screening and detection of Chlamydia trachomatis. Certain forensic applications also deal with difficult samples, for example single cells. Problems arise in testing due to the lack of sufficient sample to perform all the required tests and any further necessary confirmatory analysis. The sample also needs to be heterogeneous and representative of the entire sample; otherwise sampling could lead to erroneous results.
The standard method for the collection of cellular samples is the swab. Traditionally compact fibres such as rayon, Dacron or cotton are compressed and shaped to form the swab tip. Due to the structure, once the sample is collected much of it will remain trapped in the compressed fibres rather than released from the swab. With particularly small samples this could mean the entire sample potentially remains within the swab tip, prohibiting subsequent sample analysis and resulting in the loss of both time and results.
The new nylon flocked swabs developed by MicroRheologics and available from Sterilin utilise a spray-on technology to vastly improve both sample collection and release. Short strands of nylon are propelled at high velocity onto the plastic moulded swab tip, with the nylon fibres forming a high density brush-like pile which is perpendicular to the swab. The flocked or brush-effect allows efficient collection of both cellular and liquid samples as capillary action between fibre strands facilitates strong uptake of fluids. The depth of the nylon fibres ensures that the sample is held close to the surface, enabling efficient release when required.
Figure 1. (A) The traditional fibre swab matrix and trapped sample. (B) The nylon flocked swab and collected sample available for release |
Figure 1 shows the structure and the location of the sample for both swab types. With the flocked swab up to 95% of the sample is released compared with 25% from a standard fibre swab. This enables many more tests to be conducted; with a conventional swab it would probably be necessary to take multiple samples. A simple colorimetric test shows that the nylon flocked swab releases significantly more dye when rinsed in water compared to a standard fibre swab (Figure 2).
Several research groups have shown the advantage of the nylon flocked swab for cellular isolation. Daley et al.1 showed that the nylon flocked swab released up to three times more respiratory epithelial cells than the rayon alternative. The use of the nylon flocked swab has also been shown to enhance the sensitivity of commercial kits for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae2.
In house tests have looked at sample collection for molecular analysis by comparing the new nylon flocked swab with the traditional rayon type by analysing the amount of genomic DNA that can be extracted from a buccal cell swab sample. The protocol for DNA extraction using the Wizard SV Genomic DNA purification system (Promega) was first optimised for use with buccal swabs. Nylon and rayon buccal swabs were then taken from 9 individuals and the genomic DNA extracted and measured to determine the efficiency of the flocked compared to the standard rayon swab. Subjects did not ingest food or drink or smoke for 30 minutes prior to sampling. Each subject performed their own swabs and they randomly selected the order of the rayon and nylon flocked swabs. The swab tip was rotated and scraped around the upper gums vestibule three times and immediately placed in cell lysis buffer.
Figure 2. The release of dye from the nylon flocked swab is shown on the left and from a standard fibre swab on the right |
The DNA was extracted using Promega’s Wizard SV genomic DNA purification system, as described in the manufacturer’s instructions. To increase the yield of DNA, the water was heated to 65oC before applying to the spin column. The concentration of the DNA was then measured using a spectrophotometer (Jenway).
The results of the individual samples are shown in Table 1. The rayon swabs yielded between 0.5 and 1.5µg of genomic DNA per swab, whereas the nylon flocked swabs released on average approximately 2.5 times more. Comparison of the two groups using a paired, 2-tailed Student’s t-test gave a p-value of 0.0000012. A p-value of <0.05 is considered significant and <0.001 is considered highly significant. Figure 3 shows the combined data from the 9 individuals and the standard deviation of each group.
The nylon flocked swab offers a significant advantage over the standard rayon by releasing nearly 2.5 times more sample from the fibres. The principle of sample release is applicable for the extraction of molecules such as DNA directly from the sample adhered to the swab or the isolation of cells for culturing and identification. A larger amount of starting material increases the reliability of downstream analysis such as PCR and cell culture. An increased amount of sample could also enable additional analytical techniques to be performed.
Standard and transport swabs are available with different shaped swab tips, including specific swabs for neonatal, pernasal, urethral and endocervical applications. The nylon flocked swabs are certified RNase and DNase-free, making them ideal for molecular analysis.
The e-Swab from Sterilin is a novel transport swab that incorporates the nylon flocked swab with 1ml of liquid amies. The e-Swab differs from conventional gel transport swabs in that the entire sample collected is released into the liquid medium rather than retained on the swab tip, thus generating a homogenous solution of the sample. The sample is then in an ideal format for conducting multiple tests such as centrifugation and subsequent molecular analysis, automated processing as well as microbial culture which is improved due to each plate sub-cultured receiving an equivalent inoculum.
References
1. Daley, P., Castriciano, S., Chernesky, M. and M. Smieja. 2006. Comparison of flocked and rayon swabs for collection of respiratory epithelial cells from uninfected volunteers and symptomatic patients. J. Clin. Microbiol. 44:2265-2267.
2. Chernesky, M., Castriciano, S., Jang, D. and M Smieja. 2006. Use of flocked swabs and a universal transport medium to enhance molecular detection of Chlamydia trachomatis and Neisseria gonorrhoeae. J. Clin. Microbiol. 44: 1084-1086.