Jett B, Free L, Sahm D F
Department of Opthalmology, Dean A. McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City 73104, USA.
J Clin Microbiol. 1996 Mar;34(3):701-6. doi: 10.1128/jcm.34.3.701-706.1996.
Studies were conducted to identify factors contributing to the inability of the Vitek Gram-Positive Susceptibility system (GPS; bioMerieux, Vitek, Inc., Hazelwood, Mo.) to reliably detect vanB-mediated vancomycin resistance among enterococci. To some extent the accuracy of the GPS depended on a particular strain's level of resistance, as all isolates for which vancomycin MICs were > or = 128 mu g/ml were readily detected but detection of resistance expressed by several strains for which MICs were < or = 64 mu g/ml was sporadic. Factors besides the level of resistance were studied in two vanB strains. For one strain (Enterococcus faecium U8304), the ability of GPS to detect resistance was accurate and consistent, while for the other (Enterococcus faecalis V583), GPS results were inconsistent and unreliable. Using these isolates, we established that growth medium had the most notable effect on the detection of resistance. In the absence of vancomycin, Vitek GPS broth supported growth comparable to that obtained with brain heart infusion broth for both E. faecium U8304 and E. faecalis V583. However, in the presence of vancomycin the growth patterns changed dramatically so that neither VanB strain grew well in Vitek broth, and growth of V583 was barely detectable after 8 h of incubation. In contrast, good growth of both strains was observed in brain heart infusion broth supplemented with vancomycin. Additionally, the same medium effect was observed with other inducibly resistant VanB strains. In conclusion, although Vitek broth can support good enterococcal growth, this medium does not sufficiently support expression of vancomycin resistance by certain strains to allow them to be detected by the Vitek automated system. Furthermore, this observation establishes that the type of growth medium used can substantially influence the expression of vancomycin resistance and indicates that medium-based strategies should be explored for the enhancement of resistance detection among commercial systems.
开展了多项研究，以确定导致Vitek革兰氏阳性药敏系统（GPS；生物梅里埃公司，Vitek公司，密苏里州黑兹尔伍德）无法可靠检测肠球菌中vanB介导的万古霉素耐药性的因素。在某种程度上，GPS的准确性取决于特定菌株的耐药水平，因为所有万古霉素MIC≥128μg/ml的分离株都能很容易地被检测到，但对于几种MIC≤64μg/ml的菌株所表现出的耐药性检测却是零星的。除耐药水平外，还对两株vanB菌株的其他因素进行了研究。对于一株菌株（屎肠球菌U8304），GPS检测耐药性的能力准确且一致，而对于另一株（粪肠球菌V583），GPS的结果不一致且不可靠。利用这些分离株，我们确定生长培养基对耐药性检测的影响最为显著。在没有万古霉素的情况下，Vitek GPS肉汤支持屎肠球菌U8304和粪肠球菌V583的生长，其生长情况与脑心浸液肉汤相当。然而，在有万古霉素的情况下，生长模式发生了巨大变化，以至于两株VanB菌株在Vitek肉汤中都生长不佳，孵育8小时后V583的生长几乎无法检测到。相比之下，在添加了万古霉素的脑心浸液肉汤中观察到两株菌株都生长良好。此外，在其他诱导型耐药VanB菌株中也观察到了相同的培养基效应。总之，尽管Vitek肉汤可以支持肠球菌良好生长，但这种培养基不能充分支持某些菌株表达万古霉素耐药性，从而无法通过Vitek自动化系统进行检测。此外，这一观察结果表明，所用生长培养基的类型可显著影响万古霉素耐药性的表达，并表明应探索基于培养基策略以提高商业系统中耐药性检测水平。
