Objective To study the correlation between mutant selection window (MSW) and selective enrichment of Staphylococcus aureus resistant mutants in vivo. Methods Tuberculosis patients colonized with S. aureus in anterior nares were selected as experimental group. The susceptibility of S. aureus to rifampicin was determined at the beginning of and 2,4 and 5 weeks after the anti-tuberculosis therapy with rifampicin-containing regimens. S. aureus isolates developing acquired resistance were examined by molecular strain typing. Diabetes patients colonized with S. aureus served as an untreated control. Results The S. aureus isolated from 5 patients acquired rifampicin resistance in 58 tuberculosis patients. It was determined by pulsed-field gel electrophoresis and protein A repeat sequence the strains of S. aureus were different, but the isolates obtained from the same patient before and after acquisition of resistance were the same strains. No resistance was acquired in 39 untreated control patients, which differed statistically from treated patients. Conclusion The selective enrichment of rifampicin-resistant S. aureus mutants occurred when rifampicin concentration was in the mutant selection window.

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Objective To explore the clinical characteristics, risk factors of mortality and antimicrobial therapy of carbapenemresistant Klebsiella pneumoniae (CRKP) bloodstream infections. Methods A 5-year retrospective study was conducted for 60 patients with CRKP bloodstream infection, who were treated in Chinese People's Liberation Army (PLA) General Hospital during the period from June 2011 to August 2016. The patients were assigned to death (n=24) or survival (n=36) group according to 28-day survival after bloodstream infection to identify the predictors of mortality. The patients treated with combination antimicrobial therapy (n=32) were compared with those received monotherapy (n=14). Results A total of 60 nonduplicate CRKP blood isolates were identified. The 28-day mortality was 40.0％ (24/60). High APACHE Ⅱ score (OR=1.15, 95％ CI 1.0-1.3, P=0.048) was identified as an independent risk factor for 28-day mortality in patients with CRKP bloodstream infection. The 46 patients receiving antimicrobial therapy showed 28-day mortality of 34.8％. Univariate analysis indicated that the 28-day mortality rate was similar between the patients receiving combination antimicrobial therapy and those receiving monotherapy. Conclusions Bloodstream infection due to CRKP is associated with high mortality. APACHE II score is an independent predictor for mortality in patients with CRKP bloodstream infection.