# Activity of Lysozyme Against Multidrug-Resistant Salmonella Heidelberg and Salmonella Minnesota Isolated from Broilers

## TL;DR

Lysozyme, a natural enzyme, effectively reduces multidrug-resistant Salmonella in chickens, offering a potential alternative to antibiotics.

## Contribution

Demonstrates lysozyme's efficacy against antibiotic-resistant Salmonella in poultry, both in vitro and in vivo.

## Key findings

- Lysozyme inhibited 86.36% of Salmonella isolates at concentrations ≤ 15 ppm in vitro.
- Chickens treated with lysozyme had significantly fewer Salmonella-positive birds at slaughter (26.08% vs. 63.63%).

## Abstract

The presence of Salmonella in food can result in diseases, including diarrhea and fever. The consumption of chicken meat contaminated with the bacteria is a concern worldwide. Therefore, there is great interest in finding alternatives to antibiotics to keep poultry healthy and prevent food contamination. In this study, we tested whether lysozyme, a natural enzyme, could kill Salmonella, a common bacterium in chicken production in Brazil. We analyzed 44 Salmonella isolates from poultry feces in four Brazilian states. The two most common variants were Salmonella Heidelberg and Salmonella Minnesota, both resistant to several antibiotics. In the laboratory, we found that small amounts of lysozyme were sufficient to kill most of these bacteria. We then tested the product on infected chickens and observed that those treated with lysozyme had less Salmonella in their intestines after 21 days. These results show that lysozyme can help reduce the presence of Salmonella in poultry, indicating that it may be a promising alternative to antibiotics in chicken production.

Bacterial resistance in foodborne pathogens is a global concern and has stimulated the search for alternative compounds to antimicrobials. In this context, the prevention of colonization by Salmonella spp. in poultry production is particularly important. This study investigated the bactericidal effect of lysozyme on Salmonella Heidelberg and Salmonella Minnesota. A total of 44 serotyped isolates were subjected to minimum inhibitory concentration (MIC) testing against 17 distinct antibiotics. Subsequently, the same isolates were subjected to minimal bactericidal concentration (MBC) with lysozyme at concentrations ranging from 15 to 2000 ppm. One strain of S. Heidelberg was selected for an in vivo challenge. Seventy-two male chicks were randomly divided into three experimental groups, and two of them were challenged on the second day with 0.5 mL of an inoculum containing 1 × 105 CFU/mL. One of these groups was treated with lysozyme at a concentration of 1000 ppm per bird for 21 days. MIC tests showed that the multidrug resistance rate was 97.72%, with susceptibility only to fosfomycin, florfenicol, and meropenem. After the in vitro exposure of these isolates to lysozyme, 86.36% were inhibited at concentrations ≤ 15 ppm. The in vivo tests showed a significant reduction in the total number of chickens colonized by S. Heidelberg at 2, 5, 7, 14, 18, and 21 days of farming. On the day of slaughter, the percentage of positive birds in the inoculated group was 63.63%, while that in the group treated with lysozyme was 26.08%. These data highlight the potential use of lysozyme as an alternative to antibiotics in poultry production.