Suboptimal PAM Enables One-Pot RPA-CRISPR/Cas12a Detection of Clostridium perfringens in Food Samples

The strict requirement for a canonical TTTV protospacer adjacent motif (PAM) restricts target-site selection in clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 12a (CRISPR/Cas12a)-based diagnostics and limits the flexibility of assay design. Whether suboptimal PAMs can be effectively incorporated into one-pot detection systems for Clostridium perfringens has not been systematically examined. Here, we developed two one-pot recombinase polymerase amplification (RPA)-CRISPR/Cas12a assays targeting the plc and cpe toxin genes of C. perfringens and systematically evaluated 28 crRNAs spanning canonical (TTTV) and suboptimal (VTTV, TCTV) PAMs in both trans-cleavage and one-pot formats. Several suboptimal-PAM crRNAs, including crRNA 4 for plc (PAM: GTTG) and crRNA 7 for cpe (PAM: CTTA), maintained efficient detection in the one-pot system, whereas crRNA performance between the two formats was not predictable, underscoring the need for direct one-pot screening. The optimized assays achieved limits of detection of 50 copies (plc) and 10 copies (cpe), showed no cross-reactivity against four non-target bacterial species. The plc assay was successfully validated in pork, chicken, and beef samples spiked with C. perfringens, with results readable within 40 min using a simple isothermal device and naked-eye readout. The cpe assay was confirmed as a proof-of-concept at the genomic DNA level. These results demonstrate that suboptimal PAMs can serve as a deliberate design strategy to expand target accessibility in one-pot CRISPR/Cas12a diagnostics.