Noninvasive pH monitoring for bacterial detection in platelet concentrates.

BACKGROUND: Bacterial contamination of platelet concentrates (PCs) remains the prevalent posttransfusion infectious risk. The pH SAFE system, a noninvasive method used to measure pH of PC for quality control, was evaluated herein as a rapid method to detect bacterial contamination in PCs. STUDY DESIGN AND METHODS: Pairs of ABO-D-matched apheresis and buffy coat PCs were pooled and split into two pH SAFE platelet bags. One of the bags served as the control unit, while the other was inoculated with one of nine clinically relevant bacteria (target concentration approx. 1 colony-forming units [CFUs]/mL). The pH of both PCs was measured over 7 days of storage at approximately 4-hour intervals during daytime. One-milliliter samples were taken at the testing points to determine bacterial concentration. RESULTS: PCs with pH values of less than 6.6 or with a pH change over time (ΔpH/Δtime) greater or equal than 0.046 pH units/hr are suspected of being contaminated. pH decreased significantly during storage in all bacterially inoculated PC at concentrations of more than 10(7) CFUs/mL (p < 0.0001). A significant decrease in pH (p < 0.0001) was noticed as early as 28 hours in units with Bacillus cereus and as late as 125 hours in units containing Staphylococcus epidermidis. Interestingly, PCs containing Gram-negative species showed a decline in pH followed by a rebound. CONCLUSIONS: The pH SAFE system allows for repeated, noninvasive pH screening during PC storage. A significant decrease in pH could serve as an indicator of clinically significant levels of bacterial contamination. Since differences in pH decline were observed among bacterial species, continuous pH monitoring in PCs is recommended.

Multiple pH measurement during storage may detect bacterially contaminated platelet concentrates.

BACKGROUND: Bacterial contamination or platelet (PLT) metabolism can change the pH of stored PLT concentrates (PCs). Measurement of pH for quality control is currently done on a limited basis. An easy noninvasive method was developed to obtain sequential pH measurements over time, without risking contamination and/or consuming PCs. STUDY DESIGN AND METHODS: The objective was to measure pH profiles of bacterially contaminated PCs over 7 days of storage. Small-volume PC storage bags with incorporated pH sensor were prepared and in vitro variables were tested using aliquots of PCs. The pH sensors were used to delineate trends associated with the deterioration of these PCs upon inoculation with 19 different bacterial strains and one yeast. RESULTS: Monitoring the pH trends in real time in a noninvasive fashion, most bacterial strains were detected within 24 to 72 hours after spiking into the bag. At the time of detection, bacterial concentrations had reached levels between 1×10(3) and 1×10(8) colony-forming units/mL. Several strains had pH rebound after initial drop. Multiple noninvasive pH reads allowed bacterial detection whereas single pH reads could give false-negative results. CONCLUSIONS: The noninvasive pH sensor facilitated the detection of most strains of bacterial contaminants within 3 days with no potential for sampling error.

Passivating protein coatings for implantable glucose sensors: evaluation of protein retention.

The long-term function of implantable biosensors is limited by the foreign-body reaction (FBR). Since the acute phase of the FBR involves macrophage attachment mediated by adsorbed fibrinogen, preadsorption, and retention of other proteins might reduce the FBR. The retention of preadsorbed albumin, hemoglobin, von Willebrand's factor, and high-molecular-weight kininogen was therefore measured after exposure to plasma. The retention of preadsorbed proteins after incubation with monocyte cultures and implantation in rats was also measured. Fibrinogen adsorption from plasma to the preadsorbed surfaces was also measured. Hemoglobin adsorption was higher than that for other proteins, and it also had the greatest retention after exposure to blood plasma. When surfaces preadsorbed with hemoglobin were incubated with monocytes, more of the hemoglobin was displaced than that after incubation in plasma, while still more hemoglobin was displaced when the surfaces were implanted in vivo. Protein preadsorption on polystyrene greatly reduced fibrinogen adsorption. However, polyurethane surfaces used for glucose sensors had low fibrinogen adsorption compared with polystyrene, and this low level was not further reduced by preadsorption with other proteins. Preadsorbed proteins on polymers appear to be removed by passive exchange and/or displacement by plasma proteins and by proteases released by monocytes.