Prevalence And Screening Methods Investigation Of Local HVISA

Background:Methicillin-resistant staphylococcus aureus (MRSA) were still the main reason of pathopoiesis and fatality rate in infectious diseases clinically. Glycopeptide antibiotics with vancomycin as the representative are the most effective drugs recommended as golden standard by guidelines on the treatment of MRSA infection. However, resently, treatment failure with vancomycin increased year by year. Therefore, drug resistances of Glycopeptide antibiotics, especially vancomycin, have attracted worldwide attention. With regards to this, CLSI (the clinical and laboratory standards institute, original NCCLS) have rectified the critical value of MRSA sensitivity and resistance to vancomycin. MIC of vancomycin sensitive bacteria was adjusted from 4μg/ml to 2μg/ml, and MIC of vancomycin mesomerism bacteria was adjusted from 8～16μg/ml to 4～8μg/ml. Under the new rules, vancomycin resistant MRSA can be divided into two levels:One was VRSA (vancomycin-resistant staphylococcus aureus) of high level resistance, with vancomycin MIC≥16μg/ml; the other was hVISA (heterogeneous vancomycin intermediate resistant staphylococcus aureus) and VISA (vancomycin intermediate resistant staphylococcus areus) of low level resistance. MIC of VISA was between 4μg/ml and 8μg/ml.But the station of hVISA was more special. At present, reports indicated that most vancomycin MIC of hVISA was between 1μg/ml and 4μg/ml, but they can generate subclones in flat plate containing vancomycin, with intermediate level vancomycin MIC in the frequency of 10-6. The fact that hVISA was far more than VRSA/VISA, so the research of hVISA have became the medical hot spot in recent years. So far, there was no report in isolation rate of hVISA in Jinan region. And in the new standard, there was no methods with high sensitivity and specificity for hVISA clinical routine screening.Objestive:(1) To investigate the prevalence of hetero-resistance of to vancomycin (hVISA).(2) To assess three different screening methods of hVISA (BHIV2, BHIV4 and BHIT5).Subjects and Methods:(1) 216 strains of methicillin-resistant staphylococcus aureus (MRSA) were preliminary screened by brain heart infusion agar with 2 mg/liter vancomycin (BHIV2),4 mg/liter vancomycin (BHIV4) or 5 mg/liter teicoplanin (BHIT5).(2) Positive strains were screened by macroEtest (MET).(3) Positive strains through macroEtest (MET) method were confirmed by population analysis profile-area under the curve (PAP-AUC).Results:(1) Of 216 strains clinical MRS A, the numbers of preliminary screened strains were 143,19 and 110 in BHIV2, BHIV4 and BHIT5 methods, respectively.(2) Positive strains screened by macroEtest (MET) were 32,16, and 29, respectively.(3) Final confirmed strains were 23,14, and 21 by population analysis profile-area under the curve (PAP-AUC).(4) 29 strains of hVISA were confirmed finally. And the isolating rate of hVISA was at least 13.4% in Jinan region.Conclusion:(1) Three screening metheds above-mentioned show that some certain isolating rates were existing in hVISA in clinical isolated MRSA. This finding can partly explain the reason of clinical vancomycin treatment failure. (2) Among the three methods, sensitivity has no difference between BHIV2 and BHIT5 method, which was higher than BHIV4 method. In specificity, BHIV4 method was higher than BHIV2,BHIT5 method, and there was no difference between BHIV2 and BHIT5 method.