Distribution and characteristics of heterogeneous vancomycin-intermediate Staphylococcus aureus in blood culture / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To investigate the epidemiological and molecular biological characteristics of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) in blood culture. Methods:hVISA was detected using Mueller-Hinton agar containing 5 μg/ml of teicoplanin (MHA5T) and Populats profiles/area under the curve (PAP/AUC). Staphylococcal cassette chromosome mec ( SCCmec), Staphylococcus aureus protein A ( spa) and accessory gene regulator ( agr) typing and multilocus-sequence typing (MLST) were analyzed using PCR. Difference in autolysis between hVISA and vancomycin-sensitive Staphylococcus aureus (VSSA) isolates were evaluated with Triton X-100-inducd autolysis. Expression of vraR, mgrA, icaA, icaR, pbp4 and agr genes in hVISA and VSSA strains were detected by real-time PCR. Results:The positive detection rate of methicillin-resistant Staphylococcus aureus (MRSA) in blood culture was 39.5% (136/344) in our hospital. Among the MRSA strains, there were 31 strains of hVISA (22.8%). The minimum inhibitory concentrations (MIC) of vancomycin were mainly 1.5 μg/ml (54.8%) and 2 μg/ml(25.8%)against hVISA isolates, and 0.5 μg/ml (46.7%) and 0.75 μg/ml (39.0%) against VSSA isolates. The predominant clone of hVISA was ST239- SCCmecⅢ-t030- agrⅠ accounting for 71.0% (22/31). The autolysis of hVISA isolates decreased significantly as compared with that of VSSA isolates ( χ2=13.583, P=0.032). Compared with VSSA strains, the expression of vraR, mgrA and icaA genes in hVISA strains increased by 1.58, 1.53 and 1.06 times ( P<0.01), while the expression of icaR, agr and pbp4 genes decreased by 0.85, 0.61 and 1.03 times ( P<0.05). Conclusions:The prevalence rate of hVISA in our hospital reached 22.8% and the main epidemic clone was ST239- SCCmecⅢ-t030- agrⅠ, which should be paid great attention to clinically. Rational use of antibiotics, strengthening the prevention and control of nosocomial infection, and avoiding the spread of hVISA strains and the emergence of VISA and VRSA (vancomycin-resistance Staphylococcus aureus) were also necessary.