Evaluation of an automated microbiological blood culture for detection of bacteria in platelet units

Bacterial contamination of platelet units is an important cause of transfusion-associated morbidity and mortality. Automated bacterial blood culturing system satisfies many of the requirements of an ideal test. In this research we investigated several factors affecting detection by automated culture of bacteria in platelet units. In this study E. coli was selected to model a fast growing organism and Staphylococci epidermidis was used to model a slow growing organism. Staphylococci epidermidis and E. coli were inoculated into freshly prepared platelet units to yield 10 CFU/Ml. At the time of inoculation t=0، t=6، t=24، and t=48 hours، 0. 5، 1. 0 and 2. 0 ml samples of the contaminated platelet units were transferred into culture bottles. E. coli was detected in 100% of experiments when 0. 5، 1. 0 or 2. 0 ml samples were taken at t=0، t=6، t=24، and t=48 hours. For Staphylococci epidermidis 83. 3% of contaminated platelet units was detected when 0. 5 or 1. 0 ml samples were taken at t=0 hours and 91. 6% of units was detected when 2 ml samples were taken at t=0 hours. Staphylococci epidermidis also was detected in 100% of units when 0. 5، 1. 0، or 2 ml samples were taken at t=6، t=24، and t=48 hours. The data from this preliminary evaluation suggest that sampling times of 0 and 6 hours and 0. 5 ml sampling volume are suitable to provide confidence in detection of E. coli and Staphylococci epidermidis in platelet units using this culture method.