Eur J Cell Biol 2002, 81:203–212.PubMedCrossRef

Competing interests The authors declare that they have no competing interests. Authors’ contributions IIK and GR conceived and designed the study. IIK, MK, MAE, and YMS performed the experiments. JWO provided the mutants. IIK and GR wrote the paper. IIK, GR, JWO, MAE and YMS reviewed and edited the manuscript. All authors read and approved the final manuscript.”
“Background Determination of bacterial cell number is among the most fundamental procedures in microbiology. Several methods are commonly used, each with its characteristic pros and cons (Table 1). The widely used gold standard method is Colonies Forming Units (CFU) counting on plates [1]. The CFU method has two Ceritinib price noteworthy advantages, namely the capacity for counts of any number of bacteria using dilutions, if too many, or concentrations if too few. Second, only viable bacteria are counted with this method as the CFU method excludes dead bacteria and debris. The most important disadvantage of the CFU method is that clumps of bacteria cells can be miscounted as

single colonies; the potential for counting clumps as single units is in fact reason the Sunitinib purchase results are reported as CFU/mL rather than bacteria/mL. In addition, CFU results are usually obtained after 1–3 d, making the method not suitable for serial longitudinal studies. And since the CFU method is also relatively time-consuming and quite tedious, it has limitations for high throughput screening (HTS) studies. Table 1 Bacteria quantification methods Method Range of detection Time to obtain results Distinguishes live vs. dead Persisters below included in quantification Applications Equipment needed Count affected by minor bacterial clumps CFU count Unlimited Days Yes Yes Determination of absolute bacterial number None Yes Absorbance 108–1010 bacteria/mL Immediate No No Follow growth

curves Spectrophotometer or plate reader No Microscopy Unlimited Minutes Yes, with staining No Determination of absolute bacterial number Microscope No Flow cytometry > ~5000 Minutes Yes, with staining Yes, if not below detection Determination of absolute bacterial number FACS Yes MBRT [2] > ~107 Hours Yes No (metabolically quiescent cells missed) MIC and MAC determination Spectrophotometer No SGT Unlimited Hours Yes Yes HTS, persister Quantification Plate reader No The other common method used to estimate bacterial load is reading optical density (OD) at 600 nm. The OD method can be performed automatically in a high throughput manner using a microtiter plate reader and is well suited for experiments requiring continuous growth curve analysis. However, this method does not distinguish live bacteria from dead bacteria or even particles. In addition, its sensitivity is usually limited to concentrations between 108 and 1010 bacteria/mL.