The microbiologic method described here is rapid and sensitive, and this method has potential for the screening of PCs contaminated with bacterial cells. Furthermore, this method could contribute to further evaluation of inactivation techniques.

BACKGROUND Transfusion‐transmitted bacterial infections (TTBIs) often have serious consequences for patients. The Japanese Red Cross (JRC) has not implemented culture screening for platelet concentrate (PC), but it has maintained a shelf life of 85 hours for PC. STUDY DESIGN AND METHODS The JRC collected reports of suspected TTBI and investigated causal relationships using PC samples and patient blood samples. PCs showing apparent abnormalities were retrieved and cultured and analyzed for bacterial growth. RESULTS The JRC analyzed 86 samples available from 135 transfused PCs with suspected TTBIs that were collected over the past 12 years; 17 (19.8%) were culture‐positive. One, 6, and 10 TTBIs developed in patients on Days 1, 2, and 3 after PC collection, respectively. Assuming that PC is transfused on the day of issue, the TTBI risk was fourfold higher on Day 3 than on Day 2, after adjusting the TTBI incidence for the number of PCs issued per day. Compared with the model of issuing all PCs on Day 3, issuing PCs with the current distribution of storage time could have decreased the TTBI incidence by 56%. During the past 8 years, the JRC retrieved 960 PC units because of apparent abnormalities, 2.8% of which were culture‐positive. CONCLUSION The short shelf life of PC is associated with a low incidence of reported TTBIs, more than half of which occurred on Day 3 relative to earlier time points. Visual inspection of PC before transfusion is crucial in detecting bacterially contaminated PC despite its low positive predictive value.

We conclude that the isolate was L. garvieae according to molecular identification and its growth characteristic at 10°C. Molecular analysis enabled the identification of this species, which was difficult to classify by biochemical tests. Blood facilities need to be prepared with multiple techniques, including genetic analysis techniques, for identifying contaminating bacterial species. L. garvieae can grow at 10°C and can contaminate both red blood cell concentrates and PCs; thus, this species should be listed as a cryophilic bacterium that could threaten blood safety.

Staphylococcus epidermidis (S. epidermidis) often cause sepsis and related diseases by transfusion of contaminated platelet concentrates (PCs). The proliferation process of this bacterium in PCs has been unclear, thus, bio-imaging system was applied for analyzing the dynamics of S. epidermidis in PCs. S. epidermidis were spiked into PCs or Luria Bertani (LB) broth. These samples were collected at each sampling time during incubation (up to 7 days), and colony-forming-units were counted. Bacterial number and their size distribution in each sample were also determined with a new bio-imaging system. The morphological characters of S. epidermidis growing in the samples were observed precisely by scanning electron microscopy (SEM). The numbers of S. epidermidis were stable for 48 hr after the spiking as lag-phase, while the bio-imaging analysis also showed that aggregates proliferated during "lag-phase." The aggregates were also observed in LB media, however, their sizes were much smaller than those in PCs. SEM suggested that the aggregates were micro-colonies (MCs) of staphylococcal cells and cores of the MCs are composed with platelets (PLTs). Out results suggested that S. epidermidis formed floating MCs in PCs during "lag-phase." Therefore, the term of lag phase of S. epidermidis in PCs should be called as "pseudo-lag phase." The initial processes of forming MCs in PCs are thought to be an interaction between bacterial cells and PLTs. Floating MCs would be the source of biofilms on the inside of PC storage bags. New information obtained in this study would be useful for understanding the dynamics of growing bacteria in PCs.

BACKGROUNDIn 2014, we experienced the first isolation of Lactococcus garvieae from a platelet concentrate (PC). Thereafter, L. garvieae contamination of PCs occurred in two more cases in Japan. It is rare that bacterial contamination with uncommon strains like this species occurs frequently within a short period. Therefore, we performed a detailed analysis of the characteristics of these strains.STUDY DESIGN AND METHODSThree bacterial strains were identified by biochemical testing and molecular analysis. Genomic diversity was characterized by multilocus sequence typing (MLST). To observe growth kinetics in blood components, PCs were inoculated with the three different strains.RESULTSAll three strains were identified as L. garvieae by molecular analysis. Each strain belonged to a different phylogenetic group according to MLST analysis. In the spiking trial, the three strains demonstrated differences in their final concentrations and changes in appearance of PCs.CONCLUSIONIn this study, all three L. garvieae strains were correctly identified by molecular analysis. Since the three strains were collected in different regions of Japan and belonged to different phylogenetic groups according to MLST analysis, it is suggested that L. garvieae have a wide distribution with diversity in Japan. In PCs, the three L. garvieae strains showed clear differences in growth kinetics and changes in appearance of PCs. These differences may have been the primary determinant of whether PC contamination was detected before transfusion. Moreover, L. garvieae represents an emerging foodborne bacterium that can cause transfusion‐transmitted bacteremia. Understanding our cases may help prevent bacterial contamination of blood products.

In clinical settings, false-positive results are treated as positive until bacterial identification. It may result in the discarding of blood products in blood centers or affect clinical decisions in hospitals or testing facilities. Moreover, the management of these samples is usually time- and labor-consuming. The results of our study may help clinicians and laboratory staff in making a more precise evaluation of positive reactions in BacT/Alert.

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