Does sub-culturing of positive MRSA blood cultures affect vancomycin MICs?. Issue 8 (8th August 2020)

• Record Type: Journal Article
• Authors: Kanesaka, Izumo; Ito, Takamitsu; Shishido, Ritsuko; Nagashima, Makoto; Kanayama Katsuse, Akiko; Takahashi, Hiroshi; Fujisaki, Shingo; Kobayashi, Intetsu
• Is Part Of: Journal of medical microbiology. Volume 69:Issue 8(2020)
• Page Start: 1095
• Page End: 1099
• Publication Date: 2020-08-08
• Subjects: MRSA -- Blood culture -- Vancomycin -- MIC; Medical microbiology -- Periodicals; 616.9041
• DOI: 10.1099/jmm.0.001225
• Languages: English
• ISSNs: 0022-2615

Abstract

Abstract : Introduction . Empirical vancomycin (VAN) treatment failure for methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia, with significantly higher mortality, has been reported for MRSA strains with reduced VAN susceptibility. Aim . Our goal was to study the effect of sub-culture on VAN minimum inhibitory concentration (MIC) values compared to direct susceptibility of MRSA-positive blood cultures. Methodology . Using 19 MRSA-positive blood cultures and 19 seeded MRSA-positive blood cultures, we compared the VAN MICs from direct susceptibility testing of MRSA-positive blood cultures and MRSA sub-cultured from positive blood cultures. Results . In comparing direct VAN MICs from MRSA-positive blood cultures and standard agar dilution, nearly half of the MICs from agar dilution were lower, with one sample decreasing from 1.5 to 0.75 µg ml −1 . Furthermore, in seeded blood cultures, 80 % or more showed lower values from standard agar dilution compared to direct VAN MICs. Conclusion . Our results reveal a trend towards lower MICs after positive blood culture isolates are sub-cultured. Some clinical failures among MRSA infections treated with VAN may result from this phenomenon.