Gayibova Ülkü, Dalyan Cılo Burcu, Ağca Harun, Ener Beyza
Uludag University Faculty of Medicine, Department of Medical Microbiology, Bursa, Turkey.
Mikrobiyol Bul. 2014 Jul;48(3):438-48. doi: 10.5578/mb.7827.
Opportunistic fungal pathogens are one of the important causes of nosocomial infections, and several different types of yeasts, especially Candida species are increasingly recovered from immunocompromised patients. Since many of the yeasts are resistant to the commonly used antifungal agents, the introduction of appropriate therapy depends on rapid and accurate identification. The aims of this study were to compare the commercial identification systems namely API® ID 32C (bioMerieux, France) and Phoenix™ Yeast ID Panel (Becton Dickinson Diagnostics, USA) for the identification of Candida species and to evaluate the effect of morphological findings in the identification process. A total of 211 yeast strains isolated from different clinical samples (111 urine, 34 blood/vascular catheter, 27 upper/lower respiratory tract, 16 abscess/pus, 13 throat/vagina swabs and 10 sterile body fluids) of 137 patients hospitalized in Uludag University Health and Research Center between October 2013 to January 2014, were included in the study. Samples were cultured on blood agar, chromogenic agar (CHROMagar Candida, BD, USA) and Saboraud's dextrose agar (SDA), and isolated yeast colonies were evaluated with germ tube test and morphological examination by microscopy on cornmeal/Tween-80 agar. The isolates were identified as well by two commercial systems according to the manufacturers' recommendations. Discrepant results between the systems were tried to be resolved by using morphological characteristics of the yeasts. Of the isolates 159 were identified identical by both of the systems, and the concordance between those systems were estimated as 75.4%. According to the concordant identification, the most frequently isolated species was C.albicans (44.1%) followed by C.tropicalis (9.9%), C.glabrata (9.5%), C.parapsilosis (8.5%) and C.kefyr (8.1%). The concordance rate was 81.7% in identification of frequently isolated species (C.albicans, C.tropicalis, C.parapsilosis, C.glabrata, C.kefyr), however it was 38.7% for the rarely isolated ones (C.krusei, C.lusitaniae, C.inconspicua/C.norvagensis, C.catenulata), representing statistical significance (p= 0.034; x2 test). Although not significant (p= 0.31; x2 test), the rate of concordance was increased (88.1%), when adding the morphological findings to the identification process. Of 211 isolates 37 (17.5%), 50 (23.7%) and 124 (58.8%) were identified according to their growth characteristics on chromogenic agar, blood agar and SDA, respectively, indicating no statistically significant difference between the media (p> 0.05). Although genotypic identification is essential, phenotypic methods are more commonly used in routine laboratories for the identification of yeast species. However, since genotypic identification could not be performed in this study, none of the systems were accepted as the standard method and therefore the sensitivity and specificity of the systems were not calculated. On the other hand, our data indicated that the two identification systems were comparable and careful observation of yeast morphology could add confidence to the identification. In conclusion, since the Phoenix™ Yeast ID system was found more practical with easier interpretation, and the results were obtained earlier than those of the API® ID 32C system (16 hours versus 48 hours), it was thought that Phoenix™ Yeast ID system may be used reliably in the routine laboratories. However, as none of the methods evaluated was completely reliable as a stand-alone, careful evaluation is necessary for species identification.
机会性真菌病原体是医院感染的重要原因之一,几种不同类型的酵母,尤其是念珠菌属,越来越多地从免疫功能低下的患者中分离出来。由于许多酵母对常用的抗真菌药物耐药,因此采用适当的治疗方法取决于快速准确的鉴定。本研究的目的是比较商业鉴定系统,即API® ID 32C(法国生物梅里埃公司)和Phoenix™酵母鉴定板(美国BD诊断公司)对念珠菌属的鉴定,并评估形态学结果在鉴定过程中的作用。2013年10月至2014年1月期间,在乌鲁达大学健康与研究中心住院的137例患者的不同临床样本(111份尿液、34份血液/血管导管、27份上/下呼吸道样本、16份脓肿/脓液、13份咽喉/阴道拭子和10份无菌体液)中分离出的211株酵母菌株被纳入研究。样本接种于血琼脂、显色琼脂(CHROMagar念珠菌,美国BD公司)和沙氏葡萄糖琼脂(SDA)上,分离出的酵母菌落通过芽管试验和在玉米粉/吐温80琼脂上的显微镜形态学检查进行评估。根据制造商的建议,使用两种商业系统对分离株进行鉴定。尝试通过酵母的形态学特征解决系统之间的差异结果。在分离株中,159株被两种系统鉴定为相同,这些系统之间的一致性估计为75.4%。根据一致性鉴定,最常分离的菌种是白色念珠菌(44.1%),其次是热带念珠菌(9.9%)、光滑念珠菌(9.5%)、近平滑念珠菌(8.5%)和克菲念珠菌(8.1%)。在鉴定常见分离菌种(白色念珠菌、热带念珠菌、近平滑念珠菌、光滑念珠菌、克菲念珠菌)时一致性率为81.7%,而对于罕见分离菌种(克鲁斯念珠菌、葡萄牙念珠菌、隐匿念珠菌/挪威念珠菌、链状念珠菌)则为3&.7%,具有统计学意义(p = 0.034;卡方检验)。虽然无统计学意义(p = 0.31;卡方检验),但在鉴定过程中加入形态学结果后,一致性率有所提高(88.1%)。在211株分离株中,分别根据其在显色琼脂、血琼脂和SDA上的生长特征鉴定出37株(17.5%)、50株(23.7%)和124株(58.8%),表明不同培养基之间无统计学显著差异(p>0.05)。虽然基因分型鉴定至关重要,但表型方法在常规实验室中更常用于酵母菌种的鉴定。然而,由于本研究无法进行基因分型鉴定,因此没有一个系统被视为标准方法,因此未计算系统的敏感性和特异性。另一方面,我们的数据表明这两种鉴定系统具有可比性,仔细观察酵母形态可以增加鉴定的可信度。总之,由于发现Phoenix™酵母鉴定系统更实用,解释更容易,且结果比API® ID 32C系统更早获得(16小时对48小时),因此认为Phoenix™酵母鉴定系统可在常规实验室中可靠使用。然而,由于所评估的方法中没有一种作为独立方法是完全可靠的,因此菌种鉴定需要仔细评估。
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