Assessing the Potential of Five Strains of Different Lactic Acid Bacterial Species as a Microbial Chassis for Oral Drug Delivery

Lactic acid bacteria (LAB) are promising oral drug delivery systems due to their probiotic properties, safety, and ability to stimulate mucosal immunity. In this study, we characterized five LAB strains, Lacticaseibacillus casei ATCC 393, Lacticaseibacillus paracasei UST1611, Lactiplantibacillus plantarum UST1611, Limosilactobacillus reuteri LR08, and Lacticaseibacillus rhamnosus GG, to assess their potential as a microbial chassis for oral drug delivery. We tested competence for transformation, plasmid stability, GFP expression under a constitutive promoter, survival under simulated gastrointestinal conditions, and survival in the gut of Danio rerio larvae. Successful transformation with the pTRKH3-ermGFP plasmid was achieved in L. casei ATCC 393, L. paracasei UST1611, and L. reuteri LR08. We also showed that the L. casei ATCC 393 strain had significantly higher protein expression than its L. paracasei UST1611 and L. reuteri LR08 counterparts. In the absence of selection, L. casei ATCC 393 and L. paracasei UST1611 retained their plasmid for 48 h. L. reuteri LR08 retained it for up to 72 h. The three transformed strains showed comparable tolerance to simulated gastrointestinal pH, though L. casei and L. reuteri were more resistant to 0.3% greater bile. In vivo testing showed the highest survival for L. casei ATCC 393 and L. paracasei UST1611 in the gut of zebrafish (Danio rerio) larvae. Overall, our results suggest that, among the five strains tested, L. casei ATCC 393 is the most promising candidate for an LAB-based microbial system for oral drug delivery.