Evaluation of the Copan Liquid Amies Elution Swab (ESwab™) for Maintaining the Viability of Selected Fungi and Mycobacterium spp

ABSTRACT

Background: The use of swabs for obtaining specimens for culture is generally discouraged but remains a common practice. The majority of published studies have focused on the efficiency of swabs for the recovery of bacteria with little or no published data supporting their efficiency for the recovery of fungi or Mycobacterium spp. The ESwab™ consists of a flocked nylon swab for sample collection and liquid Amies transport medium. The objective of this study was to perform a quantitative evaluation of the ESwab™ for maintaining the viability of selected clinically relevant fungi and Mycobacterium spp. For comparative purposes, the BD BBLTM Culture Swab Plus transport system was tested.

Methods: The following organisms were selected for testing: Mycobacterium chelonae, M. fortuitum, Candida albicans, C. krusei, C. parapsilosis, C. glabrata, C. neoformans, Mucor, Fusarium, Exophiala (Wangiella) dermatitidis, and Exophiala jeanselmei. Quantitative viability studies were conducted in triplicate at room temperature. For each swab/organism combination, viable counts were performed at zero (0) time, 24 h, 48 h, and 72 h.

Results: Initial 0-time counts for the organisms tested were ½ to 1 log (base10) higher for the ESwab™ than for the CultureSwab Plus for all organisms except Mucor spp. This trend was also noted for each sampling period (24 h, 48 h, and 72 h) with the percent recovery being higher with the ESwab™. A relatively lower level of release was noted with the respective Mycobacterium representatives but the percent recovery was higher with the ESwab™. A similar fold increase of mold growth was observed with both swabs.

Conclusions: The results indicate that the ESwab™ with liquid Amies transport medium performed better than the CultureSwab Plus with Amies gel agar. The data suggests that the ESwab™ is suitable for preserving the viability of pathogenic yeasts, molds, and Mycobacterium spp.

INTRODUCTION

The ultimate goal of the clinical microbiology laboratory is to generate clinically relevant results. Achieving this goal begins with the appropriate selection, collection, and handling of the specimen. Appropriate specimen management, or the absence of such, affects patient management in many ways. For example, good specimens are essential to accurate laboratory diagnosis that directly impacts on patient outcome, influences therapeutic decisions, affects infection control, and overall plays a major role in laboratory as well as healthcare costs. Although a number of limitations have been associated with the use of swabs (low volume, susceptible to surface and subsurface contamination), their use in the collection of specimens for microbiological culture has been and continues to be popular and widely practiced in the healthcare setting.

The Copan Liquid Amies Elution Swab (ESwab™) Collection and Transport System (Copan Diagnostics Inc., Murieta, CA) consists of a flocked nylon swab for the collection of samples from the nares, throat, vagina, or wounds, and a polypropylene screw-cap containing 1 ml of Modified Liquid Amies transport medium. The specimen is absorbed by capillary action between the fibers and remains close to the surface of the fibers. Following contact with the transport medium, the system is designed for the specimen to elute with minimal entrapment of microorganisms that has been reported as a problem for other swabs (rayon, Dacron) associated with agar-based transport media.

Since the ESwab™ collection and transport system was initially designed to primarily maintain the viability of bacteria in clinical specimens for up to 48 h at both refrigerator and room temperature, the objective of this study was to perform a quantitative evaluation of the ESwab™ for maintaining the viability of selected fungi (yeasts and molds) and Mycobacterium spp at room temperature over a 72 h period.

MATERIALS AND METHODS

A. Transport Systems 

  • Copan Liquid Amies Elution Swab (ESwab™) Collection and Transport System
  • BD, BBLTM CultureSwab Plus Transport System with Amies Gel Medium

B. Media/Supplies

  • Potato Flake Agar without antibiotics
  • Middlebrook 7H10 agar
  • Micropipettes (adjustable)
  • 0.85% Saline

C. Challenge Organisms

1. ATCC strains of Candida albicans (14053), C. krusei (6258), C. parapsilosis (22019), C.
glabrata (66032), Cryptococcus neoformans (14116)

2. The following clinical isolates of molds and Mycobacterium representatives were tested:

  • Mucor spp.
  • Fusarium spp.
  • Exophiala (Wangiella) dermatitidis
  • Exophiala jeanselmei
  • Mycobacterium chelonae
  • M. fortuitum

D. Procedure (Fig. 1)

1. All challenge isolates were cultured on Potato Flake Agar or Middlebrook 7H10 agar prior to
preparing standardized inocula (0.5 McFarland Standard).

2. Conidial suspensions of molds were prepared by flooding Potato Flake agar cultures with
approximately 3 ml of sterile water. The resulting mixture was withdrawn, and the heavy
particles were allowed to settle for 3-5 min. The upper homogenous suspension, containing a
mixture of conidia and hyphal fragments, was removed and vortexed for 15 sec. The turbidity of
the suspension was measured with a MicroScan turbidity meter and adjusted to 0.5 McFarland
Standard with subsequent plate counts being performed.

3. Specific colony counts were determined for each standardized inoculum

4. 100 μl of standardized inoculum was pipetted directly to each swab (3 swabs per time period).
Swabs were returned to the respective transport tube and capped.

5. Swabs representing Time 0 were held at room temperature for 5-10 min before preparing serial
10-fold dilutions in sterile water.

6. 10 μl of each dilution was plated onto Potato Flake agar or Middlebrook 7H10 agar and colonies
were counted following incubation.

7. All testing was performed in triplicate and viability determination was recorded for 0 time.

8. The same procedure was followed for determining colony counts representing 24, 48, and 72 h.