Subculturing and Gram staining of blood cultures flagged negative by the BACTEC™ FX system: Optimizing the workflow for detection of Cryptococcus neoformans in clinical specimens

Lingli Liu; Lijun Du; Shuquan He; Tianshu Sun; Fanrong Kong; Yali Liu; Yingchun Xu

doi:10.3389/fmicb.2023.1113817

Subculturing and Gram staining of blood cultures flagged negative by the BACTEC™ FX system: Optimizing the workflow for detection of Cryptococcus neoformans in clinical specimens

Front Microbiol. 2023 Mar 15:14:1113817. doi: 10.3389/fmicb.2023.1113817. eCollection 2023.

Authors

Lingli Liu^{1

2}, Lijun Du^{1

3

4}, Shuquan He^{1

5

6}, Tianshu Sun⁷, Fanrong Kong⁸, Yali Liu^{1

2

9}, Yingchun Xu^{1

2}

Affiliations

¹ Department of Laboratory Medicine, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Chinese Academy of Medical Science and Peking Union Medical College, Beijing, China.
² Beijing Key Laboratory for Mechanisms Research and Precision Diagnosis of Invasive Fungal Diseases, Beijing, China.
³ Department of Clinical Laboratory, Nanchong Central Hospital, the Second Clinical Medical College, North Sichuan Medical College, Nanchong, China.
⁴ Jinan University, Guangzhou, Guangdong, China.
⁵ Department of Clinical Laboratory, Longhua District Central Hospital, Shenzhen, China.
⁶ Teaching Hospital of Guangdong Medical University, Guangdong, China.
⁷ Medical Research Center, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing, China.
⁸ Center for Infectious Diseases and Microbiology Laboratory Services, ICPMR-Pathology West, Westmead Hospital, University of Sydney, Westmead, NSW, Australia.
⁹ Graduate School, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.

Abstract

Objective: To investigate whether an incubation time of 5 days (Aerobic/F, Anaerobic/F) and 14 days (Myco/F) blood culture bottles is sufficient to prevent false-negative results.

Methods: We evaluated 1,244 blood bottles (344 patients) defined as negative by the BACTEC™ FX system. We also reviewed published cases and our own cases of bloodstream infection caused by Cryptococcus neoformans and simulated different scenarios, including different inoculation concentrations, bottle types, and clinical isolates.

Results: Two bottles (0.16%) were found to contain C. neoformans when subcultured and Gram stained. A 5-day protocol with Aerobic/F bottles was insufficient for the growth of C. neoformans in some cases, and C. neoformans grew better in Myco/F bottles than in Aerobic/F bottles.

Conclusion: Subculturing and Gram staining after a 5-day protocol were important for the detection of C. neoformans, and Myco/F bottles should be collected for the blood culture of C. neoformans.

Keywords: BACTEC™ FX; Cryptococcus neoformans; blood culture; bloodstream infection; subculture.