Evaluation of the therapeutic effect of a fly maggot antimicrobial peptide in a Staphylococcus aureus-induced mouse mastitis model.

Background: Antimicrobial peptides (AMPs) have been widely recognized for their robust antimicrobial efficacy and significant activity against diverse pathogens.

Aim: Staphylococcus aureus (S. aureus) is a well-known pathogen associated with mastitis in dairy cows. This study aimed to investigate the therapeutic potential of maggot-derived antimicrobial peptides for treating S. aureus-induced mastitis in a murine model.

Methods: The AMP derived from maggots was isolated, purified, and evaluated for antimicrobial activity. Subsequently, it was applied to treat a murine model of mastitis. A concentration of 25.36 µg/ml AMP was determined as the optimal dose for intramammary administration in mice with S. aureus-induced mastitis. ICR mice were randomly allocated into four groups, with 30 mice in each group: Group I (healthy control), Group II (disease control), Group III (AMP treatment), and Group IV (ciprofloxacin treatment).

Results: The therapeutic efficacy of maggot-derived AMP against S. aureus-induced mastitis was evaluated according to clinical manifestations, mammary gland structure, bacterial load, histopathological analysis, and recovery conditions. During the 7-day treatment period, all mice in Group II (disease control) succumbed to the infection by the afternoon of the fifth day. In contrast, mice in Group III (AMP treatment) exhibited noticeable clinical improvement starting from the third day, characterized by gradual restoration of mental status, food intake, and water consumption. Throughout the treatment period, the bacterial load in Group III was significantly lower than that in Group II but higher than that in Group IV (ciprofloxacin treatment). However, from the fifth to the seventh day, the bacterial load in Group III progressively declined, approaching levels observed in Group IV. Additionally, TNF-ɑ levels in Groups III and IV were significantly reduced compared with Group II, indicating that maggot AMP exerts a suppressive effect on TNF-ɑ production. AMP administration (10 µl at a concentration of 25.36 µg/ml) resulted in alleviation of clinical symptoms, reduction in bacterial load, and decreased TNF-ɑ levels, accompanied by significant amelioration of histopathological alterations compared with the disease control group.

Conclusion: This study demonstrated that maggot-derived AMP holds promise as a potential alternative to conventional antibiotics for the treatment of bovine mastitis, offering a viable therapeutic strategy to address antimicrobial resistance and improve clinical outcomes.