Binding of nontarget microorganisms from food washes to anti-Salmonella and anti-E-coli O157 immunomagnetic beads:: minimizing the errors of random sampling in extreme dilute systems
Binding of nontarget microorganisms from food washes to anti-Salmonella and anti-E-coli O157 immunomagnetic beads:: minimizing the errors of random sampling in extreme dilute systems
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DOI：
10.1007/s00216-008-1961-8
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发表时间：
2008-05-01
影响因子：
4.3
通讯作者：
Chen, Chin-Yi
中科院分区：
文献类型：
--
作者：
Irwin, Peter;Nguyen, Ly-Huong Thi;Chen, Chin-Yi
对于大多数应用，利用3-5次观察或取样（n）来估计平均群体（mu）中的总需氧平板计数，其大于约50个细胞或菌落形成单位（CFU）/取样体积。我们选择使用6 x 6滴板法进行细菌菌落选择，因为它提供了在96孔格式中快速进行所有必要稀释并使用最少材料将这些稀释液接种在固体培养基上的方法。除了传统的定量目的外，我们还需要选择彼此分离良好的菌落用于细菌鉴定。为了实现这一目标，使用滴板格式需要利用非常稀的溶液（mu < 10 CFU/采样液滴）。在如此低的CFU密度下，取样误差成为问题。为了解决这个问题，我们产生了观察到的和计算机生成的菌落计数数据，并将单个计数的大样本随机分为N个子样本，每个子样本具有n = 2-24个观察结果（N x n = 360）。从这些数据中，我们计算了来自每个第j个子样本估计值（S-j）的总标准差（S-tot）的平均总均值归一化（x（tot），n = 360）偏差，我们称之为。无论是观察还是计算机生成。值作为Xtot的函数进行分析，产生一组关系（α（-2）根X（tot）），其似乎在约18个观测值的n处收敛。在甚至更低的CFU浓度下（x（tot）类似于每次观察1 - 10 CFU），通过分析验证了这一发现。使用落板格式和n = 18采样的额外实验进行了沿着的食品样品与最可能数（MPN）分析，发现这两种计数方法没有显着差异。
For most applications, 3-5 observations, or samplings (n), are utilized to estimate total aerobic plate count in an average population (mu) that is greater than about 50 cells, or colony forming units (CFU), per sampled volume. We have chosen to utilize a 6 x 6 drop plate method for bacterial colony selection because it offers the means to rapidly perform all requisite dilutions in a 96-well format and plate these dilutions on solid media using minimal materials. Besides traditional quantitative purposes, we also need to select colonies which are well-separated from each other for the purpose of bacterial identification. To achieve this goal using the drop plate format requires the utilization of very dilute solutions (mu < 10 CFUs per sampled drop). At such low CFU densities the sampling error becomes problematic. To address this issue we produced both observed and computer-generated colony count data and divided a large sample of individual counts randomly into N subsamples each with n = 2-24 observations (N x n = 360). From these data we calculated the average total mean-normalized (x(tot), n = 360) deviation of the total standard deviation (S-tot) from each jth subsample's estimate (S-j), which we call.. When either observed or computer-generated. values were analyzed as a function of xtot, a set of relationships (alpha(-2)root x(tot)) were generated which appeared to converge at an n of about 18 observations. This finding was verified analytically at even lower CFU concentrations (x(tot) similar to 1 - 10 CFUs per observation). Additional experiments using the drop plate format and n = 18 samplings were performed on food samples along with most probable number (MPN) analyses and it was found that the two enumeration methods did not differ significantly.