Meighan Paul
J AOAC Int. 2014 Mar-Apr;97(2):453-78.
The MicroSnap Coliform and E. coli system was devised to give rapid enumeration and detection of coliforms and/or Escherichia coli strains in a sample of food within an 8 h working shift. The method measures beta-galactosidase and beta-glucuronidase enzymes using novel bioluminogenic substrates which develop an output light signal proportional to the concentration of enzyme discovered. The assay uses two different phases to determine the enzyme concentration. The first phase is an enrichment of the sample in a nutrient-rich broth device at 37 +/- 0.5 degrees C. After 6 or 8 h, an aliquot is taken from the enrichment device and injected into the Coliform Detection Device, which is assayed in a luminometer after 10 min of incubation at 37 +/- 0.5 degrees C. Samples testing positive in the Coliform Detection Device can be subsequently assayed specifically for E. coli using the E. coli Detection Device. The relative light unit output from the detection device is proportional to the bacterial concentration when the incubation was initiated, which is proportional to the contamination level in the matrix being assessed. The MicroSnap Coliform and E. coli system was evaluated for both quantitative and qualitative analysis of coliforms and E. coli in a variety of foods. Three different luminometers were used in the analysis, each of which has different functionalities and different sensitivities. The MicroSnap method showed good correlation with the appropriate corresponding reference method for enumeration of coliforms and E. coli. A statistically significant difference was seen in detection of E. coli in milk, as reported by the independent laboratory. The reference method reported higher mean Log10 CFU counts than the MicroSnap method; however, no significant differences were seen between the MicroSnap system and reference methods for any of the other matrixes. Inclusivity testing was conducted on 25 different non-E. coli coliforms and 25 different E. coli strains, and exclusivity testing was conducted on 30 different species of nontarget organisms. Two E. coli strains were not detected in the Coliform Detection Device after 8 h on one of the instruments. All other inclusivity strains tested were detected after 8 h of incubation. None of the exclusivity strains were detected. The lot-to-lot and kit stability studies showed no statistical differences between lots or over the term of the shelf-life. Robustness studies indicate that the timing of incubation for the detection phase is critical for correct system functioning.
MicroSnap大肠菌群和大肠杆菌检测系统旨在在8小时工作班次内快速计数和检测食品样品中的大肠菌群和/或大肠杆菌菌株。该方法使用新型生物发光底物测量β-半乳糖苷酶和β-葡萄糖醛酸酶，产生与发现的酶浓度成比例的输出光信号。该测定使用两个不同阶段来确定酶浓度。第一阶段是在37±0.5摄氏度的富含营养的肉汤装置中对样品进行富集。6或8小时后，从富集装置中取出一份样品注入大肠菌群检测装置，在37±0.5摄氏度孵育10分钟后在发光计中进行检测。在大肠菌群检测装置中检测呈阳性的样品随后可使用大肠杆菌检测装置专门检测大肠杆菌。当开始孵育时，检测装置的相对光单位输出与细菌浓度成比例，而细菌浓度又与所评估基质中的污染水平成比例。对MicroSnap大肠菌群和大肠杆菌检测系统进行了评估，以对各种食品中的大肠菌群和大肠杆菌进行定量和定性分析。分析中使用了三种不同的发光计，每种发光计具有不同的功能和不同的灵敏度。MicroSnap方法与用于计数大肠菌群和大肠杆菌的相应参考方法显示出良好的相关性。如独立实验室报告的那样，在牛奶中检测大肠杆菌时存在统计学上的显著差异。参考方法报告的平均Log10 CFU计数高于MicroSnap方法；然而，对于任何其他基质，MicroSnap系统与参考方法之间均未观察到显著差异。对25种不同的非大肠杆菌大肠菌群和25种不同的大肠杆菌菌株进行了包容性测试，并对30种不同的非目标生物进行了排他性测试。在其中一台仪器上，8小时后在大肠菌群检测装置中未检测到两种大肠杆菌菌株。所有其他包容性菌株在孵育8小时后均被检测到。未检测到任何排他性菌株。批次间和试剂盒稳定性研究表明，不同批次之间或在保质期内均无统计学差异。稳健性研究表明，检测阶段的孵育时间对于系统的正确运行至关重要。
