The association of molecular typing, vancomycin MIC, and clinical outcome for patients with methicillin-resistant Staphylococcus aureus infections.
OBJECTIVE
There are reports of an increase in vancomycin minimum inhibitory concentration (MIC) against methicillin-resistant Staphylococcus aureus (MRSA) over time, a phenomenon referred to as "MIC creep", but some studies have conflicting results. The aim of this study is to evaluate the association of molecular typing, vancomycin MIC, and clinical outcome for patients with MRSA infections.


METHODS
Thirty-two MRSA isolates from Taichung Veterans General Hospital (TCVGH), Taichung, Taiwan during the period of 2003 to 2008 were analyzed for the association of sequence typing, vancomycin MIC, and the correlated clinical outcome for patients with MRSA infections. The vancomycin MICs of 28 additional isolates from 2014 were used for the detection of MIC creep.


RESULTS
Among the genotypes of 32 isolates, there were 17 (53.1%) isolates with ST239-SCCmecIII, seven (21.9%) isolates with ST5-SCCmecII, six (18.8%) isolates with ST59-SCCmecIV, and two (6.2%) isolates with ST59-SCCmecVT. Two isolates had an MIC of 2 μg/mL and were identified as ST239-SCCmecIII. No statistically significant change in the distribution of MICs of all isolates was observed between 2003 and 2014 (p = 0.263). There was no significant difference in the mortality rates between two groups of patients with vancomycin MICs < 2 μg/mL and ≥ 2 μg/mL (p = > 0.99).


CONCLUSIONS
There was no vancomycin MIC creep in the period from 2003 to 2014 in this study. Appropriate prognostic models for assessment of the association among sequence types, vancomycin MICs, and clinical outcome warrant further investigation.
Division of Infectious Diseases, Department of Internal Medicine, Taichung Veterans General Hospital, Taichung, Taiwan.
Cheng-Pin
CP
Chen
Division of Infectious Diseases, Department of Internal Medicine, Taichung Veterans General Hospital, Taichung, Taiwan.
Meei-Fang
MF
Liu
Microbiology Section of the Medical Laboratory, Taichung Veterans General Hospital, Taichung, Taiwan.
Chin-Fu
CF
Lin
Division of Infectious Diseases, Department of Internal Medicine, Taichung Veterans General Hospital, Taichung, Taiwan.
Shih-Pin
SP
Lin
Division of Infectious Diseases, Department of Internal Medicine, Taichung Veterans General Hospital, Taichung, Taiwan; School of Medicine, National Yang-Ming University, Taipei, Taiwan; Department of Industrial Engineering and Enterprise Information, Tunghai University, Taichung, Taiwan. Electronic address: zyshi@vghtc.gov.tw.
Zhi-Yuan
ZY
Shi
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004269:DNA, Bacterial / Q000235:genetics; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D058885:Multilocus Sequence Typing / Q000379:methods*; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology / Q000401:mortality; D013624:Taiwan; D016896:Treatment Outcome; D014640:Vancomycin / Q000494:pharmacology* / Q000627:therapeutic use*
D004269:DNA, Bacterial; D014640:Vancomycin
Staphylococcus aureus; clinical outcomes; sequence type