Antibacterial Potential of Lucilia sericata (Meigen, 1826) (Diptera: Calliphoridae) Maggot Excretions/Secretions in Presence of Human Tear Fluid.

Lucilia sericata (Meigen, 1826) maggot excretions/secretions (ES) have demonstrated anti-inflammatory and wound healing potential on corneal epithelial cells. This study aimed to evaluate the in vitro antibacterial potential of the ES against clinically relevant Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus epidermidis in the presence of human tear fluid. The ES was collected from sterile first- and second-instar L. sericata maggots. Antibacterial activity was assessed using colony-forming unit (CFU) and turbidimetric (TB) assays. In CFU assays, samples were incubated at 37 °C for 2 h, followed by serial dilutions and agar plate inoculation. For TB assays, samples were incubated for 16 h at 37 °C, with optical density measured at 550 nm. Against P. aeruginosa, maggot ES exhibited a paradoxical effect: growth inhibition was observed at lower concentrations (0.75 and 1.5 µg/mL), whereas higher concentrations (8-130 µg/mL) showed no antibacterial activity. Addition of human tear fluid led to an enhanced antibacterial activity at the lower concentrations, producing an effect stronger than either tears alone or ES alone. The antibacterial activity was consistent across three maggot batches and remained unaffected by reconstituting maggot ES in phosphate-buffered saline. Heat-inactivation of maggot ES resulted in a loss of its antibacterial activity. Against S. epidermidis, maggot ES showed no antibacterial activity at any of the tested concentrations (1.5-92 µg/mL). Lucilia sericata maggot ES exhibits differential antibacterial effects at lower concentrations, which are enhanced in presence of human tear fluid.