Evaluation of ESwab™ a New Multipurpose Liquid Swab Transport System for Aerobic and Anaerobic Bacteriology

REVISED ABSTRACT

We receive a multiplicity of swab types including Liquid Stuart for aerobic culture and direct assays and Amies Agar Gel for aerobic and anaerobic culture. No single transport serves all our needs and we would like a more versatile multipurpose swab. We evaluated new ESwab™ (Copan Diagnostics) as a single replacement for all swab transports. ESwab™ (ES) was tested for its ability to maintain aerobes in comparison with Becton Dickinson CultureSwab (BDS) and Starplex StarSwab (STS) Liquid Stuarts and for anaerobes in comparison with Becton Dickinson CultureSwab Plus (BDA) and Starplex StarSwab (STA) Amies Gel. We also compared ES, BDS and STS using spiked cultures of S. pyogenes (SP) to evaluate suitability of using ES with Biostar Strep A OIA Max (BIOSTR) direct assay. Viability test were performed using Roll-Plate Method (CLSI M40-A) on swabs held at room temp (20 – 25°C) for 0, 24 & 48h time points. Test strains included N. gonorrhoeae (NG) ATCC 43069, H. influenzae (HI) ATCC 10211, SP ATCC 19615, P. anaerobius (PA) ATCC 27337 and P. melaninogenica (PM) ATCC 25845. Swabs from each device were inoculated with 100ul of dilutions (neat to 10-4) made from 0.5 McFarland suspension of each organism. Swabs were inoculated in triplicate. Colony counts were compiled for each dilution & incubation time point and compared to 0hr counts to determine percent recovery. For the BIOSTR study ES, BDS & STS were inoculated with 107, 106 & 105 cfu of 4 strains of SP. ES maintained viability of all 5 ATCC strains at 24h with higher percent recovery than the other systems. At 24h NG recovery was 3.8% with ES, 3.7% BDS, 0.1% STS; HI 56.7% ES, 32.5% BDS, 0% STS; SP 115% ES, 85.5% BDS, 75.1% STS; PA 4.4% ES, 2.8% BDA, 0.0% STA; PM 23.4% ES, 6.6% BDA and 0% STA. At 48h recovery for HI was 35.2% with ES, 7.6% BDS, 0% STS; SP 124% ES, 65.8% BDS, 63% STS; PA 0.0% with ES & STA and 0.1% with BDA; PM 2.2% ES and 0% with BDA & STA. In BIOSTR study all 4 strains of SP were positive at 106 cfu conc. with ES and 2/4 positive with BDS & STS. ES is able to maintain aerobes and anaerobes for at least 24h and demonstrated a greater level of sensitivity in BIOSTR to other swabs. Further evaluation of ES with antigen and molecular assays is needed.

INTRODUCTION:

The Network of The Chester County Hospital (CCH) is like many small community hospitals in this country; the core of CCH comprises a 238 bed hospital with satellite locations in West Chester, Downingtown, Exton, Kennett Square, and Lionville, Pennsylvania that include various out-patient labs and drawing stations that collect throat cultures and urine samples. In addition to this we service and collect samples from various physicians’ offices. We receive a multiplicity of swab transport systems including Liquid Stuart for aerobic culture and rapid direct Strep A assays and Amies Agar Gel for routine aerobic and anaerobic culture. No single swab serves all our needs. Liquid Stuart is not suitable for maintaining anaerobic bacteria and Amies Agar Gel which works well for anaerobes but is not validated for use with many rapid strep antigen tests or other assays because of potential interference from the agar gel component. We decided to evaluate ESwab™ a new liquid based transport system from Copan Diagnostics Inc. (Corona, California) which supports aerobic and anaerobic bacteria. ESwab™ is unique and comprises a patented flocked nylon swab and 1ml of Liquid Amies Medium. The flocked swab consists of 50,000 – 60,000 short strands of nylon which are glued in an organized perpendicular fashion onto the surface of a molded applicator stick. The perpendicular strands of fiber provide an open structure that efficiently absorbs and elutes the patient’s specimen by capillary hydraulics. As soon as the swab is placed into the liquid medium the entire patient sample is automatically eluted. With traditional swab transports the laboratory processes the swab applicator for culture or rapid assay but in the case of ESwab™ one or more aliquots of the liquid medium suspension can be removed for various microbiology analyses. We were attracted to evaluate this new swab because it has the potential for multipurpose use for aerobic and anaerobic culture and because it is liquid based it could allow us to perform our rapid Strep assays. Consequently ESwab™ might allow The Chester County Hospital network to standardize on one swab for all our current and future bacteriology needs.

We tested ESwab™ (ES) ability to maintain the viability of aerobic bacteria in comparison with Becton Dickinson Liquid Stuart CultureSwab (BDS) and Starplex StarSwab (STS) Liquid Stuarts and for viability of anaerobes in comparison with Becton Dickinson Amies Agar Gel CultureSwab Plus (BDA) and Starplex StarSwab (STA) Amies Gel. Viability tests were performed using the Roll-Plate Method (CLSI M40-A) on swabs held at room temp (20 – 25°C) for 0, 24 & 48h time points. We also compared ES, BDS and STS liquid transports using dilutions of cultures of S. pyogenes (SP) to evaluate suitability of using ES with Inverness (formally Biostar) Strep A OIA Max (BIOSTR) direct assay.

METHODS:

Comparative Viability Study

1. Materials:

Commercial Transport Swabs

  • ES Liquid Amies ESwab™
  • BDS Liquid Stuart CultureSwab
  • STS Liquid Stuart StarSwab
  • BDA Amies Agar Gel without Charcoal CultureSwab Plus
  • STA Amies Agar Gel without Charcoal StarSwab

2. Test Protocol (CLSI Roll-Plate Method)

The protocol used for viability studies was based upon the Roll-Plate Method as described in CLSI (formerly NCCLS) standard Quality Control of Microbiology Transport Systems. M40-A Vol 23 No. 34, 2003. Initial inoculum used for each investigation was prepared by making a direct suspension in 0.85% physiological saline (pH 6.8 to 7.2) of isolated colonies selected from an 18 to 24 hrs agar plate, fastidious and anaerobic bacteria required up to 48 hrs of incubation. The initial bacterial suspension was prepared to a concentration of approximately 1.5 x 108 CFU (equivalent to 0.5 McFarland Standard).

Preparation of dilutions:
Seven dilutions (10-1, 10-1.5, 10-2, 10-2.5, 10-3, 10-3.5 and 10-4) were prepared.