The Detection Challenge

Bacterial contamination in blood components presents a unique set of characteristics that have thus far eluded complete solution. These include:

• Numerous different species of bacteria have been found to contaminate donated platelets.
• The source of this contamination are typically native flora found on or just below the surface of the skin or low level circulating bacteria that enter the blood component during blood collection.
• The number of contaminating bacteria at the time of collection can be extremely small, literally as few as 2 or 3 bacteria.
• These bacteria can then reproduce in the blood component during storage sometimes achieving levels of 100,000,000, or 10⁸, CFU/mL or even higher.
• The time from initial contamination until log phase growth occurs is highly variable and impossible to predict.

When evaluating strategies for the detection of bacteria, one must remember that they are complex living organisms. Bacteria follow a classic growth cycle: First, there is a lag period in which the bacteria attempt to adapt to a new environment. This is followed by a period of log phase growth, during which the surviving bacteria reproduce exponentially. Finally, there is plateau phase where the number of bacteria stabilizes in relation to the nutrient supply. However, this simple pattern does not fully capture the complexity of bacterial growth in platelets.