Comparison of Standard Plate Counting to Alternative Quantitation Methods for E. coli

The standard plate count method for evaluating colony-forming units (CFU) has long been considered the gold standard for microbial enumeration. However, CFU-based measurements are limited by variability, reproducibility, and the inability to capture viable but non-culturable cells. Alternative methods have been developed to strengthen the reproducibility and understanding of cell physiology. Using Escherichia coli mini packs (ATCC® 8739-MINI-PACK™), ATCC compared the SBT BactoBox and the CytoFLEX flow cytometer to traditional CFU-based measurements. This was performed by serially diluting cells and analyzing by the different instrumentation according to their individual dynamic ranges. Additionally, a live/dead staining kit was used to differentiate between cell types for flow cytometry. 

Though both the BactoBox and CytoFLEX identified intact cell concentrations nearly double those of standard plate counts, each method offered distinct advantages and disadvantages. BactoBox delivered rapid and reproducible measurements but could not distinguish viability or presence of contaminants. CytoFLEX also provided rapid results with greater resolution by separating viable from non-viable cells and, under optimized conditions, even distinguishing organisms; however, this technology was costly and space-intensive.

While these alternative methods detected higher concentrations than the standard plate count method, they can be optimized to more closely align with the traditional method if needed. More importantly, they reveal deeper insights into cellular physiology beyond what CFU can capture. In the end, choosing which method to use will depend on your specific application.