Phage endolysin specific binding characteristics and killing activity support their potential use in biotechnological applications, such as potency and purity testing of live biotherapeutic products (LBP). LBPs contain live organisms, such as Lactic acid bacteria (LAB), and are intended for use as drugs. Our approach is to use endolysin cell wall binding domains (CBD) for LBP potency assays and endolysin killing activity for purity assays. CBDs of 5 lactobacilli phage lysins, CL1, Jlb1, Lj965, LL-h, and ɸJB were characterized. They exhibited different binding to 27 LAB strains and were found to bind peptidoglycan or surface polymers. Flow Cytometry based on CBD binding was used to enumerate viable counts of two strains in mixture. CL1-lys, jlb1-lys, and ɸJB-lys and their EADs exhibited cell wall digestive activity and lytic activity against LAB. Jlb1-EAD and ɸJB-EAD were more sensitive than their respective hololysins to buffer pH and NaCl concentration changes. The ɸJB-EAD exhibited stronger lytic activity than ɸJB-lys, possibly due to ɸJB-CBD-mediated sequestration of ɸJB-lys by cell debris. CBD multiplex assays indicate that these proteins may be useful LBP potency reagents and the lytic activity suggests that CL1-lys, jlb1-lys, and ΦJB-lys and their EDs are good candidates for LBP purity reagent development.