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Updated: Aug 13, 2026
Aseptic Laboratory Techniques: Plating Methods
Published on: May 11, 2012
Comparison of bacteria growth in single and pooled platelet concentrates after deliberate inoculation and storage
S J Wagner1, G Moroff, A J Katz
1Jerome H. Holland Laboratory for the Biomedical Sciences, American Red Cross Blood Services, Rockville, Maryland, USA.
Background:
The ability to store pools of platelet concentrates (PCs) for extended periods would provide logistical flexibility. However, reports of severe adverse reactions due to the transfusion of contaminated PCs led to an examination of whether the total bacteria levels after storage of pools containing a deliberately inoculated platelet unit would be significantly different than the levels in paired unpooled concentrates.
Study Design And Methods:
A single PC was deliberately inoculated on Day 0 with one of three bacterial species (0.1-8.0 colony-forming units/mL). On Day 1, the deliberately inoculated PC was divided into three equal parts and either 1) pooled with 5 half-volume, ABO- and Rh-identical PCs; 2) similarly pooled and white cell reduced; or 3) kept as a control. Sterile connections were used during pooling; modified storage containers were used to ensure the correct surface-to-volume ratio of the single unit.
Results:
Between Day 2 and Day 5 of storage, in 26 of 36 paired samples, nonfiltered pools containing Escherichia coli had greater total numbers of bacteria than did the paired single PCs. Day 2 pools had total bacteria levels approximately five times higher (colony-forming units/mL x container volume) than those in single units (p < 0.05). There was rapid growth of Staphylococcus aureus by Day 2 in pooled and unpooled PCs; by Day 3, total bacteria levels were approximately five times higher in pools than in single units (p < 0.05). Between Days 3 and 5 of storage, in 23 of 27 paired samples, nonfiltered pools containing S. aureus had greater total bacteria levels than the single PCs. By Day 5, 15 of 16 non-white-cell reduced pools had total levels of Staphylococcus epidermidis bacteria approximately five times those in the paired single PCs. Greater total bacteria levels in pooled units than in single units generally occurred when bacteria in pools reached the stationary phase of growth (when bacteria concentration became constant), and they were well correlated with the sixfold volume of pooled units. White cell reduction did not substantially affect the time required to attain stationary phase.
Conclusion:
The potential during storage for greater total bacteria levels in pools than in single PCs is a consequence of the greater volume of the pool.
Insights
Pooling platelet concentrates (PCs) can increase total bacteria levels compared to single units due to larger volumes, posing a risk for bacterial contamination during storage. This highlights the need for careful monitoring of pooled blood products.
Area of Science:
- Transfusion Medicine
- Microbiology
- Blood Banking
Background:
- Storing pooled platelet concentrates (PCs) offers logistical advantages but raises concerns about bacterial contamination.
- Previous adverse reactions linked to contaminated PCs necessitate an investigation into bacterial growth in pooled versus unpooled units.
Purpose of the Study:
- To compare total bacteria levels in pooled PCs versus single PCs after deliberate inoculation with bacteria.
- To assess the impact of pooling on bacterial proliferation during storage.
Main Methods:
- Platelet concentrates were deliberately inoculated with one of three bacterial species.
- Inoculated PCs were either pooled with multiple units or kept as controls, with some pooled units undergoing white cell reduction.
- Sterile connections and modified storage containers were utilized.
Main Results:
- Pooled, non-white cell-reduced PCs showed significantly higher total bacteria levels than single units, particularly with Escherichia coli and Staphylococcus aureus.
- Bacterial levels in pools were approximately five times higher than in single units by Day 2 or Day 3.
- The increased bacterial load in pools correlated with the larger volume and bacterial growth reaching the stationary phase; white cell reduction had minimal impact.
Conclusions:
- The greater storage volume of pooled platelet concentrates is a primary factor contributing to higher total bacteria levels.
- This finding underscores the potential for increased bacterial contamination risk in pooled blood products during storage.
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