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Improvement of a disk diffusion method for antibiotic susceptibility testing of anaerobic bacteria. French recommendations revisited for 2020.
Anaerobe ( IF 2.3 ) Pub Date : 2020-06-29 , DOI: 10.1016/j.anaerobe.2020.102213
L Dubreuil 1 ,
Affiliation  

The disk diffusion test is very popular but for anaerobes the main pitfalls arise from the significant variation of diameters for an individual MIC and the weak correlation observed between the MIC's values and diameters zone that generates many major and very major errors.

Aims of the study

without any change in the methodology and revisiting only new diameter breakpoints, we try to improve the previous French recommendations and therefore decrease number of errors by introducing recent EUCAST concepts such as ECOFF and ATU Zone.

Method

MIC determination by agar dilution was done on 100 anaerobes against 6 antibiotics. Clinical categorization was based on EUCAST Breakpoints. Disk-diffusion method was realized on the same Brucella blood agar incubated in an anaerobic chamber. 550 categorizations by both methods could be done as amoxicillin was not tested on the 50 B. fragilis group. As anaerobic infections are severe and treated by antibiotics at higher dosage, we focus on resistance breakpoint to avoid mainly very major errors (VME). Distribution of inhibition zones for each MIC allow us to fix the zone diameter breakpoints.

These results were matched to a large data on distribution of zone diameters for each antibiotic collected from two French hospitals from 1990 to 2005. As example for metronidazole and the B. fragilis group, we calculated the cut-off diameter (15 mm) from a wild type population, at a time when there was no resistance to this antibiotic and observed that it was identical to the diameter breakpoint for susceptibility.

Results

For an individual value of MIC, the distribution of diameters is wider for anaerobes especially for clindamycin and metronidazole. Using a 15 mm breakpoint for these two antibiotics limits dramatically the number of very major errors but slowly increases the number of major errors that could be overcome by MIC determination if inhibition zone is less than 15 mm. ATU zones (Area of technical uncertainty) were introduced for amoxicillin-clavulanate (17–20 mm), piperacillin-tazobactam (17–20 mm), imipenem (18–23 mm). Categorization inside the ATU requires MIC determination. Finally, out of 550 determinations, VME were observed in 1.45% of cases, an acceptable rate.

Conclusion

in combination with introduction of ATU zones disk diffusion method allows to detect resistant strains with little MIC determinations and very major errors.



中文翻译:

磁盘扩散法在厌氧菌药敏试验中的改进。法国对2020年的建议进行了重新审查。

圆盘扩散测试非常流行,但对于厌氧菌而言,主要陷阱来自于单个MIC的直径的显着变化以及在MIC的值与直径区域之间观察到的弱相关性,从而产生许多主要和非常主要的误差。

研究目的

在不改变方法的情况下,仅重新考虑新的直径断点,我们尝试通过引入最新的EUCAST概念(例如ECOFF和ATU Zone)来改进以前的法国建议,从而减少错误数量。

方法

通过琼脂稀释法对100种厌氧菌对6种抗生素进行MIC测定。临床分类基于EUCAST断点。圆盘扩散法是在厌氧室中培养的同一布鲁氏菌血琼脂上实现的。可以通过两种方法进行550种分类,因为未在50脆弱的B. gilgilis组上测试过阿莫西林。由于厌氧菌感染很严重,并且可以通过更高剂量的抗生素治疗,因此我们将重点放在耐药性转折点上,以避免主要的重大错误(VME)。每个MIC的抑制区域的分布使我们能够确定区域直径的断点。

这些结果与1990年至2005年从两家法国医院收集的每种抗生素的区域直径分布的大量数据相吻合。例如,对于甲硝唑和脆弱芽孢杆菌组,我们计算了一个细菌的截留直径(15毫米)。野生型种群,此时对这种抗生素没有抗药性,并且观察到其敏感性与直径断点相同。

结果

对于MIC的单个值,厌氧菌的直径分布较宽,尤其是克林霉素和甲硝唑。对于这两种抗生素,使用15 mm的断裂点会极大地限制非常严重的错误的数量,但如果抑制区小于15 mm,则可以通过MIC测定克服的严重错误的数量会缓慢增加。对阿莫西林-克拉维酸盐(17-20毫米),哌拉西林-他唑巴坦(17-20毫米),亚胺培南(18-23毫米)引入了ATU区域(技术不确定性区域)。ATU内部的分类需要确定MIC。最后,在550次测定中,有1.45%的病例观察到VME,这是可以接受的比率。

结论

与ATU区域的引入相结合,圆盘扩散法可以在几乎没有MIC的情况下且非常大的误差下检测耐药菌株。

更新日期:2020-06-29
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