Semerci Zeycan, Akıllı Fatih Mehmet, İlki Arzu
Marmara University School of Medicine, Department of Medical Microbiology, Istanbul, Türkiye.
Sincan Training and Research Hospital, Microbiology Laboratory, Ankara, Türkiye.
J Infect Chemother. 2025 Apr;31(4):102643. doi: 10.1016/j.jiac.2025.102643. Epub 2025 Feb 4.
We aimed to evaluate the performance of two methods; disc diffusion and gradient test with the gold standard agar dilution method in determining the susceptibility of fosfomycin, in multidrug-resistant (MDR) K. pneumoniae isolates causing urinary tract infections.
K. pneumoniae producing carbapenemase and extended-spectrum beta-lactamase (ESBL) isolated from urine samples submitted to the clinical microbiology laboratory were included in the study. The isolates were tested using gradient test (MTS, Liofilchem, Italy) and disc diffusion (Oxoid, UK). Agar dilution was employed as the reference method. Since there is no MIC value for K. pneumoniae in EUCAST, epidemiological cut-off values (ECOFFs) were determined and susceptibility and error rates were calculated.
In this study, among the 251 ESBL-positive K. pneumoniae isolates, 20(8 %) were also positive for carbapenemase. The ECOFF was determined as 128 mg/L for K. pneumoniae. When all study isolates (n:251) were considered, 87.6%(220/251) were wild-type (WT) for fosfomycin (MIC≤128 mg/L). Among ESBL-positive but carbapenemase-negative isolates (n:231), 87.8%(203/231) were WT for fosfomycin, and among ESBL and carbapenemase-positive isolates (n:20), 85.0%(17/20) were WT. The MIC values were determined to be 8/256 mg/L. When compared to agar dilution, the categorical agreement was 96.8% for the gradient test and 94.8 % for disc diffusion. While the gradient test showed a 16.1% very major error (VME) rate with no major errors (ME), disk diffusion revealed 35.4 % VME rate and 5.8 % ME rate.
A significant proportion of ESBL-positive K. pneumoniae isolates were WT for fosfomycin. The gradient test with 96.8% categorical agreement appears to be a good alternative, but agar dilution remains the gold Standard for reference laboratories.
我们旨在评估两种方法（纸片扩散法和梯度测试法）与金标准琼脂稀释法在测定耐多药（MDR）引起尿路感染的肺炎克雷伯菌中磷霉素敏感性方面的性能。
从提交到临床微生物实验室的尿液样本中分离出的产碳青霉烯酶和超广谱β-内酰胺酶（ESBL）的肺炎克雷伯菌纳入研究。使用梯度测试法（MTS，Liofilchem，意大利）和纸片扩散法（Oxoid，英国）对分离株进行测试。琼脂稀释法用作参考方法。由于欧洲抗菌药物敏感性试验委员会（EUCAST）中没有肺炎克雷伯菌的最低抑菌浓度（MIC）值，因此确定了流行病学临界值（ECOFFs）并计算了敏感性和错误率。
在本研究中，251株ESBL阳性肺炎克雷伯菌分离株中，20株（8%）碳青霉烯酶也呈阳性。肺炎克雷伯菌的ECOFF确定为128mg/L。当考虑所有研究分离株（n：251）时，87.6%（220/251）对磷霉素为野生型（WT）（MIC≤128mg/L）。在ESBL阳性但碳青霉烯酶阴性的分离株（n：231）中，87.8%（203/231）对磷霉素为WT，在ESBL和碳青霉烯酶阳性的分离株（n：20）中，85.0%（17/20）为WT。MIC值确定为8/256mg/L。与琼脂稀释法相比，梯度测试法的分类一致性为96.8%，纸片扩散法为94.8%。虽然梯度测试法显示非常主要错误（VME）率为16.1%，无主要错误（ME），但纸片扩散法显示VME率为35.4%，ME率为5.8%。
相当一部分ESBL阳性肺炎克雷伯菌分离株对磷霉素为WT。分类一致性为96.8%的梯度测试法似乎是一个很好的替代方法，但琼脂稀释法仍然是参考实验室的金标准。
