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

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 <i>Salmonella</i> spp. in poultry production is particularly important. This study investigated the bactericidal effect of lysozyme on <i>Salmonella</i> Heidelberg and <i>Salmonella</i> 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 <i>S. Heidelberg</i> 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 <i>S. Heidelberg</i> 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.