Optimization of single plate-serial dilution spotting (SP-SDS) with sample anchoring as an assured method for bacterial and yeast cfu enumeration and single colony isolation from diverse samples

We propose a simple technique for bacterial and yeast cfu estimations from diverse samples with no prior idea of viable counts, designated as single plate-serial dilution spotting (SP-SDS) with the prime recommendation of sample anchoring (10(0) stocks). For pure cultures, serial dilutions were prepared from 0.1 OD (10(0)) stock and 20 μl aliquots of six dilutions (10(1)–10(6)) were applied as 10–15 micro-drops in six sectors over agar-gelled medium in 9-cm plates. For liquid samples 10(0)–10(5) dilutions, and for colloidal suspensions and solid samples (10% w/v), 10(1)–10(6) dilutions were used. Following incubation, at least one dilution level yielded 6–60 cfu per sector comparable to the standard method involving 100 μl samples. Tested on diverse bacteria, composite samples and Saccharomyces cerevisiae, SP-SDS offered wider applicability over alternative methods like drop-plating and track-dilution for cfu estimation, single colony isolation and culture purity testing, particularly suiting low resource settings.