Ng Qin Xiang, National University of Singapore
In recent years, there is a rapid emergence of multiple-drug resistant bacterial strains. The increasing occurrence of antibiotic resistance has made bacterial infections a greater health risk and threat than before. Thus, there is an immediate need to research new and more effective antimicrobial agents. Maggot debridement therapy is an up-and-coming therapeutic treatment involving the introduction of live, sterile maggots (the species used most frequently is Lucilia sericata, the common green bottle fly) into the festering wounds of a patient for cleaning out the necrotic tissues and disinfection. Although there is anecdotal evidence to support the efficacy of the treatment, limited studies have been done to investigate the exact antiseptic mechanisms. This project therefore aimed to investigate the antimicrobial effects of excretions/secretions and gas flatulence produced by Lucilia sericata larvae on Escherichia coli, Staphylococcus epidermidis and Micrococcus luteus.
Lucilia sericata larvae were reared on a diet of ad libitum pig’s liver; third-instar larvae (3-day-old) were used for all experiments. Briefly, overnight excretions/secretions (ES) were collected from third-instar larvae, centrifuged and filter-sterilized before use. 1000 µl of 10^3 colony forming units (cfu)/ml bacterial broth culture was combined with 100 µl of sterile ES extract, antibiotic ampicillin or sterile water. Subsequently, 10 µl of the mixture was plated onto a new sterile Luria Bertani (LB) agar plate for enumeration of bacterial colonies after overnight incubation at 37oC. In addition, using an air-tight setup, gas flatulence produced by 500 third-instar larvae was applied to bacterial culture plates (plated with 10 µl of 10^3 cfu/ml of E. coli, S. epidermidis, or M. luteus) and an accompanying control plate (with no bacteria plated) for an hour. The plates were then incubated overnight at 37oC for enumeration of bacterial colonies.
The excretions/secretions and gas flatulence produced by L. sericata larvae showed significant inhibitory actions against both Gram-positive and Gram-negative bacteria tested in this experiment (p<0.05 when compared to the control using Student’s t-test). Furthermore, the antimicrobial effects of the excretions/secretions were comparable to that of ampicillin; in fact, it exhibited a more pronounced antimicrobial effect against S. epidermidis than ampicillin. The gas flatulence also caused a significant reduction in size and number of bacterial colonies.
The results showed that natural products from L. sericata larvae hold great promise for development of potent antimicrobial therapeutics. Future work entails testing the larval excretions/secretions and flatulence on other bacteria and further chemical analyses.