A Review of the Antimicrobial Potential of Musca domestica as a Natural Approach with Promising Prospects to Countermeasure Antibiotic Resistance

Drug-resistant pathogens have become a serious public health concern worldwide considering the rapid emergence and distribution of new strains, which outpace the development of antimicrobial drugs. It is a complex and serious clinical problem that can cause an epidemic of a disease; consequently, numerous research studies are conducted to determine the solution to these problems, including the development of new antibiotics derived from natural sources such as insects. The housefly (Musca domestica L.), an insect known as a cosmopolitan pest, possesses several qualities that can ameliorate diseases; consequently, they can be used as a bioactive component in the development of medicines. These qualities include its potential as a source of antibacterial agents. The external surface components, wings, internal organs, and whole body extract of M. domestica can all contribute antimicrobial potential due to bioactive compounds they produce. This article discusses several antimicrobial properties of M. domestica that could be utilized for healthcare benefits.


Introduction
Drug-resistant pathogens present an ever-increasing global health threat due to the rapid emergence and distribution of new strains which is faster than the development of antimicrobial drugs [1][2][3]. Tis circumstance may result in the inappropriate or excessive utilization of antibiotics [4,5]. Tere have been cases recorded of multidrug-resistant bacterial infection caused by Escherichia coli [6], methicillin-resistant Staphylococcus aureus (MRSA), Streptococcus pneumoniae, vancomycin-resistant Enterococcus (VRE), Pseudomonas aeruginosa, Acinetobacter baumannii, and Mycobacterium tuberculosis. Tese antimicrobialresistant superbugs have caused an alarming death rate of over 50% in certain regions [7]. It is a complex and serious clinical problem that can cause an epidemic of a disease, and hence several research studies are conducted to establish the solution to these problems, including the development of new antibiotics derived from nature, such as insects [6,8,9].
Insects and arthropods are considered a vast, unexplored, and underutilized source of potentially useful compounds for contemporary modern medicine [10]. Tey have a long history as a traditional therapy for humans and now have become more popular and are being developed for use in evidencebased practice [11,12], in addition to becoming an important alternative therapy in the modern age in several countries such as India, Mexico, Korea, China, Spain, Brazil, Argentina, Ecuador, and several African countries [10,13].
Te housefy (Musca domestica L.) is among the Dipteran group and is a well-known cosmopolitan pest of livestock, poultry, and human dwellings. Housefies are typically associated with humans or human activity [14]. Female housefies lay countless eggs in animal waste, garbage, and other decaying matter [15]. Te insect undergoes a complete life cycle, consisting of egg, larval, pupal, and adult stages, in 7 to 10 days [14]. Tey will live for 60 days the longest [15]. Tey prefer warm weather for optimal development, and hence they may thrive in the summer [16].
M. domestica is a vector for disease-causing bacteria due to its hopping and feeding behavior on a variety of pathogeninfested substrates [17,18]. Tey also contribute to the spread of antibiotic-resistant bacteria, which can raise public health concerns [19]. However, contrary to the adult's existence as a vector for several diseases, the larvae of M. domestica has been used in the treatment of infectious diseases in Latin America and several other treatments for osteomyelitis, decubitus ulcers, eczema, malnutrition, and gastric cancer in China since the Qing and Ming dynasties until present days [6,10,13]. Due to the fact that scientifc evidence has demonstrated that M. domestica larvae possess a variety of properties that can ameliorate diseases, they can be used as a source of bioactive component for pharmaceutical development [15,20,21]. Tese qualities include potential as antibacterial agents [10], even against bacteria that have developed multidrug resistance [6].
Housefy antimicrobial potential can come from the external surface components [15,20,22] and internal organs such as the digestive tract [6], hemolymph [23], and the insect's whole body extract [24,25]. Terefore, this article focuses on the antimicrobial potentials that can be isolated from M. domestica and utilized for therapeutic purposes.

Parts of M. domestica
Housefies have a close association with microorganisms and their environments, especially at a crucial moment in each developmental stage [26]. Te internal bacterial community of housefies from various locations is similar and relatively stable, whereas the external bacterial community is afected by geography and habitat [27]. Several specifc microbiota species isolated from various body parts of M. domestica are depicted in Table 1.
Bahrndorf et al. [28] reported that Firmicutes, Actinobacteria, Proteobacteria, and Bacteroidetes are phyla that dominate the entire microbiota of housefies from 10 dairy farms in Denmark. In addition, Laziz et al. [22] isolated and identifed 300 samples of housefies (M. domestica) collected from diferent areas in Kirkuk City (Iraq) and found several species of Gram-positive and Gram-negative bacteria associated with body surface on the head, thorax, and abdomen (45.2%), right wing (35.7%), and left wing (19.1%). de Jonge et al. [29] revealed that M. domestica, both female and male, have a diferent population of bacteria in every segment of their digestive tracks.
Te crop segment is abundant with Streptococcus, Lactococcus, Leuconostoc, and Chishuiella; the midgut segment is rich with Delftia, Chryseobacterium, Acidovorax, Comamonas, Spirosoma, and Sphingomonas; meanwhile other bacterial colonies found in both segments are Pelagibacterium, Fructobacillus, Lactobacillus, Dyadobacter, and Novosphingobium. Te following bacterial phyla are present in accordance with the life cycle of the housefy: Firmicutes are abundant during the larval stages and are considered early colonizers, but as they mature into adults, Proteobacteria and Bacteroidetes take over. On the other hand, bacteria that exist throughout all stages are Lactococcus, Lactobacillus, and Enterococcus, while Weissella and Chishuiella were found in newly hatched larvae and adults, respectively.

Antimicrobial Potentials of M. domestica
Secondary metabolites account for the majority of antimicrobials produced by microorganisms [9]. Insect physiology, such as resistance to pathogenic organisms, is infuenced by numerous factors, including the gut microorganisms within the insect body [28]. M. domestica is known to have a diverse microbiome with antagonistic or antimicrobial properties that can impede the growth of pathogenic bacteria originating from the previous substrate [33]. Antagonistic activities from these bacteria may be associated with their abilities to secrete enzymes or compounds that function antagonistically and/or as an antimicrobial [18]. Table 2 and Figure 1 show various antimicrobial components belonging to M. domestica, which are derived from various parts of their body, and the bacteria that are the targets of these antimicrobials.
Te production of early antimicrobial compounds by M. domestica larvae may protect the housefy from pathogenic microbes during the next developmental stages until it becomes an adult. Tese early antimicrobial compounds could be the primary antimicrobial compounds in their defense [43][44][45]. Te presence of bacteria in the digestive system of a housefy indicates that M. domestica digestive tract produces antimicrobial compounds. Tese antimicrobial-producing bacteria in the wings and guts of insects are linked to their feeding behavior on microbecontaminated substrates and stimulate the resistance response [18]. Laziz et al. [22] discovered that B. subtilis isolated from the right wing and body surface of M. domestica efectively inhibited the growth of Pseudomonas spp. B. subtilis plays an important role in the   Veterinary Medicine International production of antibiotics, enzymes, and other secondary metabolites that possess a broad spectrum of antimicrobial activities against pathogenic microbes [46]. Te right wing of M. domestica contains B. subtilis and B. circulans that can neutralize E. coli contaminated drinks due to their antibiotic efects. Te enzymes and other secondary metabolites they produce can inhibit activities of several pathogenic microbes such as bacteria, fungi/yeasts, and parasites [20,34]. Furthermore, the right wing contains bacteriophage, which is thought to produce endolysins (phage lysins), which causes bacterial cell lysis [20]. Another component of M. domestica that acts as a defense against microbes is hemolymph. Tis bactericidal effect from the hemolymph may counter-attack several bacteria including Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa [42]. Hemolymph is a clear fuid (with or without greenish-yellow pigmentation) that contains very complex chemicals, mostly consisting of immune proteins and carbohydrates such as antimicrobial peptides (AMP), lysozyme, and agglutinins [23,40,47]. AMP is an innate immunity efector against bacteria, fungi, parasites, and viruses that possess several common properties such as cationicity, hydrophobicity, and amphipathicity for their antimicrobial activities [33]. A number of AMPs found in housefies are cecropin [37], defensins [39,48], MDAP-2 [40], and Hf-1 [10], as well as a cationic antimicrobial protein with a molecular weight of 16,315 D that is thermally stable and resistant to freezing and thawing [41]. AMPs are synthesized by immune and epithelial cells and secreted into hemolymph in response to infection and the presence of pathogenic bacteria [18]. Te mechanisms of AMPs include binding to DNA, RNA, or intracellular protein [9] as well as inhibition of membrane protein and cell wall synthesis, altering the permeability of target cells [41]. Additionally, AMPs also induce apoptosis in eukaryotic cells and autolysis in bacterial cells and inhibit enzymes produced by some microbes, thereby reducing their virulence [9].
Another vital AMP is bacteriocin [35,36]. Bacillus spp. found in the wings, digestives tract, and entire body of M. domestica produces bacteriocins such as mersacidin, subpeptin JM4-B, subtilosin A, and sublancin [35]. On the other hand, Enterococcus sp., which is found in the entire body and body surface, produces enterpco E-760 [35]. Lactococcus spp., which is found throughout the body, produces the lactic clinic Q. Body surfaces, the right wing, and the digestive tract harbor E. coli that produce microcin L, microcin J25, and colicin [35,36].

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Te peritrophic matrix/membrane (PM protein) in a housefy's midgut plays a crucial role in preventing infection from outside microbes. Te novel PM protein, MdPM-17, has been isolated from the housefy larvae. Several essential components of AMPs, including defensins, cecropins, and diptericin, are expressed by MdPM-17 recombinant protein silencing via RNA interference. Tis mechanism encourages the association between the MdPM-17 protein and the antibacterial response of housefies [38]. Lysozymes are considered one of the innate immune effectors in fies that function in degrading pathogenic microbes [49]. As an antibacterial enzyme, lysozyme cleaves the β-1.4 glycosidic bond between N-acetylmuramic acid and Nacetylglucosamine, which are major components of the peptidoglycan structure of a bacterial cell wall [18]. Lysozyme activity is afected by several factors, including enzyme activity, pH level, and some efectors such as AMPs, which function to combat bacterial infections when the number is at an alarming level [44]. Lysozyme exerts its complex antibacterial defense strategies in response to infections [23]. Besides antibacterial proteins and carbohydrates in the hemolymph, it is possible that bactericidal potential is related to the acidity level (pH) through the increase of bacterial activities because of the decrease in pH level.
Additionally, other antimicrobial potentials of housefy can be seen from the butanol fraction obtained from ethanol extract of its larvae which demonstrate antibacterial activity against the methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE strains) [25]. Housefy is also efciently protected from infection by common pathogens inhabiting similar habitats through the association between the innate immunity mechanisms with mixtures of alcohols found in cuticular lipids of all stages (larvae, pupae, and adults) [14]. Moreover, 1-lysophosphatidylethanolamine (C 16:1 ) (1-LPE) which is extracted from healthy uninfected last instar larvae can interfere with the growth of the Gram-positive bacteria (Bacillus thuringiensis) and the yeast Saccharomyces cerevisiae [24].

Conclusion
Evidence from a number of studies indicates that the common house fy, Musca domestica, possesses bioactive compounds with antimicrobial potential. Tese compounds originate from its organ components and the diverse microbiomes it harbors. Te antagonistic activities of the diverse microbiome isolated from insect body parts are thought to be related to the ability to secrete enzymes or compounds that function as antimicrobial. Bacteriophage, AMP, lysozyme, pH, and alcohols contained in this insect have a direct or indirect bactericidal efect. However, a substantial amount of research is still required to investigate and develop the antimicrobial potentials of housefies.

Data Availability
Te research data are presented in the article. Tese data are publicly available and accessible online. Detailed sources are provided in References of the article.

Conflicts of Interest
Te authors declare that they have no conficts of interest.

Authors' Contributions
Nurdjannah Jane Niode was responsible for conceptualisation, investigation, formal analysis, original draft preparation, and review and editing. Trina Ekawati Tallei was responsible for conceptualisation, investigation, formal analysis, and review and editing. Billy Johnson Kepel was responsible for conceptualisation, investigation, and formal analysis. Charles Kurnia Mahono was responsible for investigation, validation, and review and editing. Felicia Maria Lolong was responsible for investigation, validation, and original draft preparation. Merina Pingkan Matheos was responsible for validation and original draft preparation.