Evaluation of Fastidious Bacterial Survival in Two Swab Transport Systems

Abstract

Swabs are frequently used to collect and transport specimens to clinical laboratory. However they are often considered to be a less desirable specimen collection device. In the last years new swab systems were designed to improve the absorbance of the sample and at the same time, optimize release of microorganisms into the liquid transport medium, ensuring optimum sensitivity for subsequent test procedures. The aim of this study was to evaluate two of these new swab systems to transport and maintain fastidious bacteria: ESwab™ Transport System (Copan, USA) and Sigma Transwab System (MW&E, UK), both with liquid Amies medium. Methods: The following isolates were evaluated for survival after incubation at room (25ºC) and refrigerator (4ºC) temperatures: Streptococcus pyogenes: ATCC 19615, N. gonorrhoeae: ATCC 43069, H. influenza: ATCC 10211, S. pneumonia: ATCC 6305, P. anaerobius: ATCC 27337 and F. nucleatum: ATCC 25586. A vortex elution method (CLSI M40-A) was performed using a 0.5 McFarland suspension of each strain and a 1:10 dilution was prepared. Swabs were inoculated in triplicate with 100μL of each microorganism suspension and held at 25ºC and 4ºC for 0h, 24h and 48h. Bacterial survival was evaluated after 48h incubation at 35ºC. Results: Cultures from all swabs dilutions were averaged. Bacterial recovery from swabs held for 0h was similar for both systems. However, after 24h and 48h incubation, bacterial recovery rates from Sigma Swab were lower compared to the ones from the ESwab™. Both swab systems maintain bacterial viability up to 48h when stored at 4ºC, and for both species of Streptococcus when stored at 25ºC. None of the swabs maintained viability for N. gonorrhoeae, P. anaerobius and F. nucleatum after 48h at 25ºC and only Copan ESwab™ was able to maintain viability of these species for 24h at 25ºC. H. influenzae survived for up to 48h at 25ºC in the ESwab™ and up to 24h at 25ºC in the Sigma Swab. Conclusion: Bacteria tested showed greater survival in the Copan ESwab™ system compared to Sigma Swab. In summary, it was possible to conclude that Copan ESwab™ performed better than Sigma Swab for transport and storage of fastidious bacteria at room temperature.

Introduction

In the last years new swab systems were designed to improve the absorbance of the sample and at the same time, optimize release of microorganisms into the liquid transport medium, ensuring optimum sensitivity for subsequent test procedures. Two of these new swab systems are: ESwab™ Transport System (Copan, USA) and Sigma Transwab System (MW&E, UK), both with liquid Amies medium.

The ESwab™ (Elution Swab) Transport System is a new liquid based transport system for bacteriology swab samples. Unlike traditional fiber wound swabs Copan’s nylon flocked swabs provide superior sample absorption and release characteristics. The entire patient’s sample is instantly eluted on contact with the ESwab™ transport medium; there is no need for the operator to rim, ring or vortex the swab.

Sigma Transwab System (Σ-Swab^®) is a new specimen collection device that incorporates a screw cap tube and Liquid Transport Medium. The specimen is collected using Σ-Swab^®, an open celled, polyurethane foam-tipped swab which allows complete flow through of reagents and microorganisms. After the specimen is placed into the tube of liquid medium, the microorganisms in the specimen are dispersed through the medium, producing a uniform suspension ready for use.

Objectives

To evaluate 2 new swab systems to transport and maintain fastidious bacteria:

• ESwab™ Transport System (Copan, USA)
• Σ-Swab^® (Sigma) Transwab System (MW&E, UK)