# Probiotic and antibacterial properties of recombinant Lactococcus lactis expressing the fusion antimicrobial peptides BMAP18-BSN37 in mice and chickens

## TL;DR

A genetically modified Lactococcus lactis strain was developed to combat Salmonella in animals, showing benefits for gut health and reduced pathogen levels.

## Contribution

A recombinant L. lactis strain expressing fusion antimicrobial peptides was engineered and tested for dual probiotic and antibacterial effects in mice and chickens.

## Key findings

- The recombinant L. lactis NZ-BB strain effectively reduced Salmonella burden in mice and chickens.
- NZ-BB improved intestinal barrier integrity and immune balance through upregulation of tight junction proteins and anti-inflammatory cytokines.
- The strain exhibited stable plasmid maintenance and high peptide expression without metabolic burden.

## Abstract

Antimicrobial resistance poses a serious threat to global food safety and poultry production, prompting the need for effective alternatives to conventional antibiotics in food-producing animals. In this study, a recombinant food-grade strain, L. lactis NZ-BB, was engineered to express a fusion antimicrobial peptide (BMAP18-BSN37), and evaluated its probiotic characteristics and antimicrobial efficacy against Salmonella, a major foodborne pathogen in chicken. The recombinant plasmid pUBB was successfully constructed and introduced into L. lactis NZ9000, with optimal peptide expression achieved following Nisin induction (20 ng/mL, 6 h). NZ-BB demonstrated stable plasmid maintenance, high expression levels, and no detectable metabolic burden. In vivo trials using BALB/c murine and 817 strain avian models showed that NZ-BB enhanced body weight gain, supported immune organ development, and improved intestinal barrier integrity through upregulation of tight junction proteins (occludin, claudin-1, ZO-1) and anti-inflammatory cytokines (TGF-β, IL-4), while reducing pro-inflammatory markers (IL-1β, TNF-α, IL-17a). Importantly, oral administration of NZ-BB significantly reduced intestinal and systemic Salmonella burdens, mitigated tissue damage, and restored immune balance in both mice and chicks. Furthermore, NZ-BB regulated the expression of innate immune receptors (e.g., NLRC3) and matrix metalloproteinases (e.g., MMP-1), highlighting its immunomodulatory potential. These results underscore the dual probiotic and antimicrobial functionality of NZ-BB and support its potential use as a food-safe microbial agent to improve animal health and reduce the risk of Salmonella contamination in the food chain.