A number of studies have aimed to determine the nature of the antibacterial activity exhibited by maggot excretion/secretion (ES) products. Several reports have described the presence of three categories of antibacterial factors in the ES of maggots, one category with a molecular mass 10 kDa, respectively. Recently lucifensin, a novel larval defensin, has been identified as one of the antibacterial agents of medicinal maggots involved in MDT. Lucifensin was shown to be constitutively produced in the salivary glands of all larval stages during feeding. An infectious environment could induce its production in the fat body from where lucifensin is secreted solely into the haemolymph. Lucifensin possesses antibacterial activity against Gram-positive bacteria, most notably Streptococcus spp. and Staphylococcus spp., but it fails to inhibit the growth of Escherichia coli and Pseudomonas aeruginosa. It also exhibited antibacterial activity against clinical isolates of methicillin-resistant S. aureus (MRSA) – however, the minimal inhibitory concentration of lucifensin against MRSA was significantly higher than for methicillinsensitive S. aureus. Nevertheless, MDT has been successfully used in the treatment of chronic wounds associated with antibiotic-resistant bacteria, including MRSA.