Release of bacteria in absolute numbers (volume-restricted setting).

<p>Viable counts of bacterial suspension after release by 5 different swab types were determined by serial dilutions and plate counting as described in the methods section. CFU = colony forming units. Results from statistical analysis are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102215#pone.0102215.s005" target="_blank">table S5</a>.</p

Relative bacterial release compared to initial uptake (volume-unrestricted setting).

<p>Ratios were determined by comparison of viable counts of absorbed and released bacteria. Results from statistical analysis are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102215#pone.0102215.s003" target="_blank">table S3</a>.</p

Volume uptake and release (volume-unrestricted setting).

<p>Volumes were determined by measuring weight [mg] of round-bottom tubes before and after uptake or deposition of fluids by 5 different swab types. Results from statistical analysis are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102215#pone.0102215.s001" target="_blank">table S1</a>.</p

Release of bacteria in absolute numbers (volume-unrestricted setting).

<p>Viable counts of bacterial suspension after release by 5 different swab types were determined by serial dilutions and plate counting as described in the methods section. CFU = colony forming units. Results from statistical analysis are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102215#pone.0102215.s002" target="_blank">table S2</a>.</p

Relative bacterial release compared to initial uptake (volume-restricted setting).

<p>Ratios were determined by comparison of viable counts of absorbed and released bacteria. Results from statistical analysis are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102215#pone.0102215.s006" target="_blank">table S6</a>.</p

Some Are More Equal - A Comparative Study on Swab Uptake and Release of Bacterial Suspensions

<div><p>Objectives</p><p>Swabs are widely used to collect samples for microbiological analyses from various clinical settings. They vary by material, size, and structure of the tip. This study investigates the uptake and release capacities for liquid and bacteria.</p><p>Methods</p><p>Five swabs were analyzed for their uptake and release capacities of S<i>taphylococcus aureus</i> and <i>Staphylococcus epidermidis</i> suspensions. Two approaches were investigated providing volume-restricted and unrestricted amounts of bacterial suspensions to mimic various clinical situations. Volume and bacterial uptake and release were measured in milligrams and by counting colony forming units (CFU), respectively.</p><p>Results</p><p>Volume uptake and release in the unrestricted setting varied highly significant between 239.6 mg and 88.7 mg (p<0.001) and between 65.2 mg and 2.2 mg (p<0.001), respectively. In the volume-restricted setting the complete volume was absorbed by all swabs, volume release could only be detected for flocked swabs (2.7 mg; p<0.001). Highest amount of CFU release was detected for the MWE Dryswab in the unrestricted setting for both <i>S. aureus</i> and <i>S. epidermidis</i> with 1544 CFU and 553 CFU, respectively, lowest release for the Sarstedt neutral swab with 32 CFU and 17 CFU, respectively (p<0.001). In the volume-restricted setting MWE Σ-Swab released the highest bacterial amount with 135 CFU <i>S. aureus</i> and 55 CFU <i>S. epidermidis</i>, respectively, the lowest amount was released by Mast Mastaswab with 2 CFU <i>S. aureus</i> and 1 CFU <i>S. epidermidis</i>, respectively (p<0.001). Within the range of the utilized bacterial concentrations, uptake/release ratios were identical for the particular swab types and independent of the bacterial species.</p><p>Conclusions</p><p>The influence of the swab type on subsequent diagnostic results is often underestimated. Uptake and release of the investigated bacteria vary significantly between different swab types and sampling conditions. For best diagnostic outcome swabs should be chosen according to the examined situation and the swab performance profile.</p></div

Bacterial release into Amies medium (volume-restricted setting).

<p>Viable counts of bacterial suspension after release by flocked swabs were determined by serial dilutions and plate counting as described in the methods section. CFU = colony forming units. Results from statistical analysis are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102215#pone.0102215.s007" target="_blank">table S7</a>.</p

Relative bacterial release into Amies medium compared to initial uptake (volume-restricted setting).

<p>Ratios were determined by comparison of viable counts of absorbed and released bacteria. Results from statistical analysis are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102215#pone.0102215.s008" target="_blank">table S8</a>.</p

Volume uptake and release (volume-restricted setting).

<p>Volumes were determined by measuring weight [mg] of round-bottom tubes before and after uptake or deposition of fluids by 5 different swab types. Results from statistical analysis are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102215#pone.0102215.s004" target="_blank">table S4</a>.</p

Nasal Screening for MRSA: Different Swabs – Different Results!

<div><p>Objectives</p><p>Swab-based nasal screening is commonly used to identify asymptomatic carriage of <i>Staphylococcus aureus</i> in patients. Bacterial detection depends on the uptake and release capacities of the swabs and on the swabbing technique itself. This study investigates the performance of different swab-types in nasal MRSA-screening by utilizing a unique artificial nose model to provide realistic and standardized screening conditions.</p><p>Methods</p><p>An anatomically correct artificial nose model was inoculated with a numerically defined mixture of MRSA and <i>Staphylococcus epidermidis</i> bacteria at quantities of 4×10² and 8×10² colony forming units (CFU), respectively. Five swab-types were tested following a strict protocol. Bacterial recovery was measured for direct plating and after elution into Amies medium by standard viable count techniques.</p><p>Results</p><p>Mean recovered bacteria quantities varied between 209 and 0 CFU for MRSA, and 365 and 0 CFU for <i>S. epidermidis</i>, resulting swab-type-dependent MRSA-screening-sensitivities ranged between 0 and 100%. Swabs with nylon flocked tips or cellular foam tips performed significantly better compared to conventional rayon swabs referring to the recovered bacterial yield (p<0.001). Best results were obtained by using a flocked swab in combination with Amies preservation medium. Within the range of the utilized bacterial concentrations, recovery ratios for the particular swab-types were independent of the bacterial species.</p><p>Conclusions</p><p>This study combines a realistic model of a human nose with standardized laboratory conditions to analyze swab-performance in MRSA-screening situations. Therefore, influences by inter-individual anatomical differences as well as diverse colonization densities in patients could be excluded. Recovery rates vary significantly between different swab-types. The choice of the swab has a great impact on the laboratory result. In fact, the swab-type contributes significantly to true positive or false negative detection of nasal MRSA carriage. These findings should be considered when screening a patient.</p></div