Othman Hala B, Halim Rania M Abdel, Gomaa Fatma Alzahraa M, Amer Malaka Z
Clinical Pathology Department, Faculty of Medicine, Ain Shams University, Cairo, Egypt.
Microbiology and Immunology Department, Faculty of Pharmacy, Al Azhar University, Cairo, Egypt.
Open Access Maced J Med Sci. 2018 Dec 22;7(1):12-18. doi: 10.3889/oamjms.2019.009. eCollection 2019 Jan 15.
To determine the distribution of vancomycin MIC and the frequency of strains with reduced vancomycin susceptibility among Methicillin-Resistant (MRSA) isolates.
MRSA isolates (n = 100) were tested for reduced susceptibility to vancomycin using MIC broth microdilution method (BMD), vancomycin screening agar with different vancomycin concentrations with and without casein, and Vitek 2 system.
BMD detected (22%) vancomycin-intermediate (VISA) and (78%) vancomycin-susceptible (VSSA) but couldn't detect nine (Heterogeneous VISA) (hVISA) isolates (9%) with MIC ≤ 2 µg/ml that grew on screening agar 4 µg/ml or 6 µg/ml. Adding casein to vancomycin screening agar increased detection rate of VISA by 4.5%. Screening agar with 6 µg/ml vancomycin overall detection rate for VISA was 95.45%. Probable 'pre-hVISA'isolates (17%) showed growth on vancomycin screening agar 2 µg/ml with casein. Vitek 2 system failed to detect any VISA isolates.
Vancomycin screening agar; 2 µg/ml and (4 and 6 µg/ml) were able to detect; probable "pre hVISA and (hVISA and VISA) isolates respectively based on their BMD MIC values. Decreased vancomycin susceptibility in MRSA isolates might be related to MIC creep. Analysis of vancomycin MIC values over longer periods is recommended to further study this phenomenon and its impact on vancomycin treatment failure.
确定耐甲氧西林金黄色葡萄球菌（MRSA）分离株中万古霉素最低抑菌浓度（MIC）的分布情况以及万古霉素敏感性降低菌株的频率。
采用MIC肉汤微量稀释法（BMD）、含不同万古霉素浓度且添加或不添加酪蛋白的万古霉素筛选琼脂以及Vitek 2系统，对100株MRSA分离株进行万古霉素敏感性降低的检测。
BMD检测出22%的万古霉素中介（VISA）菌株和78%的万古霉素敏感（VSSA）菌株，但无法检测出9株（异质性VISA，hVISA）MIC≤2μg/ml且在4μg/ml或6μg/ml筛选琼脂上生长的菌株（9%）。在万古霉素筛选琼脂中添加酪蛋白可使VISA的检出率提高4.5%。含6μg/ml万古霉素的筛选琼脂对VISA的总体检出率为95.45%。可能的“前hVISA”分离株（17%）在含酪蛋白的2μg/ml万古霉素筛选琼脂上生长。Vitek 2系统未能检测出任何VISA分离株。
万古霉素筛选琼脂；2μg/ml以及（4μg/ml和6μg/ml）能够分别根据其BMD MIC值检测出可能的“前hVISA”以及（hVISA和VISA）分离株。MRSA分离株中万古霉素敏感性降低可能与MIC漂移有关。建议对更长时间段内的万古霉素MIC值进行分析，以进一步研究这一现象及其对万古霉素治疗失败的影响。
