Validation of a Blood Culture System Via Correlation Between Microorganism Concentration and Positive Result
Introduction: Quick and accurate determination of the pathogens that invade the circulatory system requires the validation of the blood culture system used in the laboratory. In this study, the growth of microorganisms in different concentrations that were experimentally inoculated into BACTEC blood...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Bilimsel Tip Yayinevi
2009-09-01
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| Series: | Flora Infeksiyon Hastalıkları ve Klinik Mikrobiyoloji Dergisi |
| Subjects: | |
| Online Access: | http://www.floradergisi.org/getFileContent.aspx?op=REDPDF&file_name=2009-14-3-105-112.pdf |
| Summary: | Introduction: Quick and accurate determination of the pathogens that invade the circulatory system requires the validation of the blood culture system used in the laboratory. In this study, the growth of microorganisms in different concentrations that were experimentally inoculated into BACTEC blood culture media was monitored by BACTEC 9240 blood culture system, and relations between microorganism species, concentration and time to positivity signal were investigated. Materials and Methods: A total of 239 strains isolated from clinical specimens, including Enterobacteriaceae, Staphylococcus aureus and Staphylococcus spp., Enterococcus spp., beta-hemolytic streptococci, Candida spp., and nonfermentative bacilli were included in this study. A decreasing order of six dilutions were prepared from the strains, and blood culture bottles were experimentally inoculated by these dilutions within 10 mL of expired, volunteer donor whole blood, and the times to positivity were monitored. Results: The relation between bacterial concentration and time to positivity signal was statistically significant for Enterobacteriaceae and gram-positive cocci (p< 0.05). The relation between bacterial genus/species for Enterobacteriaceae and gram-positive cocci and time to positivity was statistically significant for all bacterial concentrations (p< 0.05). A total of 26 of 180 (14.4%) blood culture vials experimentally inoculated with Candida species and 43 of 180 (23.9%) vials inoculated with nonfermentative bacilli were found to be negative by BACTEC 9240 blood culture system. These false-negative results of BACTEC 9240 were confirmed by subculturing. The average time to positivity did not correlate with the concentration of Candida and nonfermentative bacilli in some of the dilutions. The relation between the concentration and time to positivity was statistically significant (p< 0.05) for Candida species but not statistically significant for nonfermentative bacilli (p> 0.05). Conclusion: BACTEC 9240 blood culture system was validated for Enterobacteriaceae and gram-positive cocci. Validation of the system for Candida species and nonfermentative bacilli was not accomplished. The system has been shown to have a limitation regarding its inability to detect growth of some dilutions of Candida and nonfermentative bacilli. It was thought that the microscopic examination of the blood culture bottles that tested negative by the system or subculturing may be useful in the routine laboratory procedure and may avoid this limitation of the automated blood culture system. Furthermore, if there is a suspicion of fungal infection, using selective fungal medium and following cultures up to 21 days would be appropriate. |
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| ISSN: | 1300-932X 1300-932X |