Low-Cost Protocol for Quantitative Measurement of Streptococcus salivarius in Human Saliva

Streptococcus salivarius (S. salivarius) is a prominent oral commensal bacterium with probiotic potential and relevance to both oral and systemic health. Accurate and accessible methods for quantitative measurement of this species are needed to support microbiota studies and clinical interventions. We describe a simple, low-cost, culture-based method for quantifying S. salivarius in human saliva using Mitis-Salivarius Agar. Saliva samples from 18 healthy adult volunteers were analyzed through serial dilutions and selective plating. CFU (colony forming unit)/mL were calculated after 24 and 48 h incubation. The method proved reliable for quantifying S. salivarius in concentrations ranging from 5.8 × 10⁵ to 6.1 × 10⁸ CFU/mL. Although Mitis-Salivarius Agar is a standard medium, we demonstrate its systematic validation and optimization for human saliva in a low-resource clinical setting, where molecular tools are often unavailable.