Despite the usages of synthetic antibiotics in human and animal practices, emergence of the Antimicrobial resistance (AMR) is predominating. AMR in coming days will be a global threat to the mankind. In order to overcome the potential AMR and also to achieve desired antimicrobial activity, development of safe as well as effective alternative to "synthetic antibiotic" is the need of the hour. In addition, the synthetic antibiotics are potential threat to the environment in causing the biomagnifications and accumulated in the human and animal cells. Moreover, they are not biodegradable and thus altering the ecological balance. In this condition cheap, cost effective and biodegradable potential natural antimicrobial agents are really going to be the next generation hope in order to overcome the existing AMR.
The problem of antibiotic resistance is becoming more and more serious. Insect antimicrobial peptide has been regarded as an important drug to solve antibiotic resistance. In this context, it is necessary to find a simple and easy way to obtain antimicrobial peptides. Recently the quest for the next generation of antibiotics is focused on natural peptides produced by animals or insects. Maggots are recognized as a “treasure house of antimicrobial peptides” as well as a good choice to produce and extract antimicrobial peptides. Maggot has been hailed as the miraculous "medicinal maggot" for its diverse properties including antimicrobial, antibiofilm, anti-inflammatory, and wound healing activities. Current study clearly depicts the use of rat-tailed maggots surviving in the pig excreta as source of antimicrobial peptide in order to potentially exploit as an alternative to the existing synthetic antibiotics.
We identified the antimicrobial property of rat-tailed maggots survived in piggery excreta against two enterobacteria family Escherichia coli and Salmonella typhimurium. Colibacillosis is one of the important diseases of swine industry especially in neonatal mortality caused by pathogenic strain of Escherichia coli (Lupi, 2017). Among different serovars of Salmonella affecting swine population, Salmonella typhimurium stands out due to its zoonotic potential in human salmonellosis1 (EFSA and ECDC, 2015) and its prevalent distribution in pork production (Arguello et al., 2013).
We found that, rat-tailed maggot hemolymph with the concentration of 25–30 µg /100 µl and 35–40 µg / 100 µl, respectively are enough to kill Escherichia coli and Salmonella typhimurium, respectively. Our findings corroborated with earlier studies, identified the role of normal hemolymphs to kill different kinds of bacteria (Sahalan et al., 2006; Basseri et al., 2016; Hirsch et al., 2020; Lee et al., 2020).
To determine the Post Antimicrobial Effect (PAE) of hemolymph against Escherichia coli and Salmonella typhimurium, we have chosen Gentamicin and Streptomycin, respectively as positive controls. Sahalan et al., 2006 used gentamycin as positive control for PAE of hemolymph from larvae and pupae of local fly species, Musca domestica and Chrysomya megacephala, against Escherichia coli. Effect of Streptomycin on the growth of Salmonella typhimurium is well documented. Singh et al., 2015 identified that Streptomycin can induced stress response in Salmonella enterica Serovar Typhimurium. Antibacterial Sensitivity Testing (AST) of various Salmonella enterica serovar typhimurium isolates across 11 antimicrobial compounds revealed that, genotyping performance of the bacterial isolates were improved to 0.89 sensitivity and 0.97 specificity with Streptomycin as antimicrobial agents with minor error rates. Present study envisaged the antibacterial role of rat-tailed maggot hemolymph for both Escherichia coli and Salmonella typhiumurium.
Keeping in view on the role of antimicrobial peptides (AMPs) existing in the hemolymph of maggots, we amplified two AMP genes (Diptericin and Sarcotoxin like peptide) from the isolated hemolymph of rat-tailed piggery waste maggots. Recently, Hirsch et al., 2020 identified number of AMPs from rat-tailed maggots of Eristalis tenax and tested their antibacterial activity against a broad spectrum of microbes, including multidrug-resistant Gram-negative bacteria. From their study, it was speculated that cecropin-like and a diptericin-like peptides having the strong antimicrobial activity against the pathogens, achieved a good therapeutic window. Two maggot derived AMPs like LS-sarcotoxin and LS-stomoxyn were profiled to assess their suitability for systemic application in mouse model, found that these AMPs are suitable as lead candidates for the development of novel antibiotics (Hirsch et al ., 2019). Thomas et al. 1999 confirmed the antibacterial activity of secretions against a range of bacteria, including Streptococcus A and B, Staphylococcus aureus, Pseudomonas and even methicillin resistant S. aureus (MRSA) in a preliminary laboratory study. To study the relevance of AMP gene expression on the antimicrobial property of the rat-tailed maggots, we compared the expression levels of both the AMP genes among the rat-tailed and rice-grain shapped maggot hemolymphs. Our study interestingly insight that, expression levels of AMP genes are significantly higher in the rat-tailed maggots having antibacterial activity in comparison to rice-grain shaped maggots.
Currently in India scanty of systematic reports are available as for as the AMPs related to the fly maggots surviving in pig excreta. Future research needs to be organized for therapeutic evaluation of both the AMPs for their application as natural antibiotics.