Open AccessDoes sub-culturing of positive MRSA blood cultures affect vancomycin MICs?
Author(s) -
Izumo Kanesaka,
Takamitsu Ito,
Ritsuko Shishido,
Makoto Nagashima,
Akiko Kanayama Katsuse,
Hiroshi Takahashi,
Shingo Fujisaki,
Ichiro Kobayashi
Publication year - 2020
Publication title -
journal of medical microbiology/journal of medical microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.91
H-Index - 117
eISSN - 1473-5644
pISSN - 0022-2615
DOI - 10.1099/jmm.0.001225
Subject(s) - microbiology and biotechnology , vancomycin , blood culture , staphylococcus aureus , affect (linguistics) , antibiotics , biology , bacteria , psychology , communication , genetics
. 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.