Rapid, sensitive, and specific detection of bacteria is of great importance. Herein, we developed a versatile biosensing platform for ultrasensitive detection of pathogenic bacteriaPathogenic bacteria, termed as SCENT-Cas (Silver nanoCluster Empowered Nucleic acids Test using CRISPR-Cas12a). Simply, the species-specific invA gene of Salmonella typhi was isothermally amplified using LAMP, which subsequently triggered the trans-cleavage of CRISPR-Cas12a. The trans-cleavage degraded any single-stranded DNA (ssDNA) nonspecifically. A DNA-templated AgNCs probe was then employed, in which green fluorescence-emissive AgNCs effectively converted to red fluorescence-emissive AgNCs when placed in close vicinity to a pre-designed converter ssDNA. As such, the trans-cleavage was utilized for shredding converter ssDNA, enabling the green-to-red fluorescent change to form a ratiometric biosensing platform. With this strategy, target nucleic acid was dexterously converted into ratiometric fluorescence that was recorded to detect as low as 1 CFU/mL S. typhimurium with a dynamic range from 1 to 108 CFU/mL. To our knowledge, this is the first report regarding the use of ratiometric fluorescence in CRISPR-Cas-based detection, which minimizes interference and improves reliability. Lastly, this proposed strategy was challenged by detecting S. typhi contamination in real food samples. Our work enriches CRISPR-Cas toolbox in biosensing by providing a desirable method for bacterial detection.