The marine environment is a vast source of yet to bediscovered bioactive compounds having the potential to become cure to variousand alarming bacterial diseases. One of the potential sources for suchsubstances is the rich fauna of seas and oceans including the brackish watersof estuaries where mangrove habitats are situated. Endeavors for the search ofantimicrobial substances that preferably are of natural sources, like thosefound in the aquatic environment, is a result of the disturbing reports of therising antibiotic resistance among pathogenic microbes (Argente et al., 2015;Sharma et al., 2009).
This is due to the ability of such microbes to transforminto resistant strains or, possibly, due to evolution as a means to counter thedetrimental effects of antibiotics. This poses great threat to the humanpopulace and, at the same time, opens the opportunity to also have a strikingdevelopment on the previously existing antibiotic drugs in aiming toefficaciously counter the growing issue of antibiotic resistance of microbes.With this, researchers put much effort in searching for novel substances thatcould give solution to the problem of antibiotic resistant microbes. Organismsin the marine environment are always in contact with pathogenic microbes withdifferent levels of virulence as their habitat is a microbe-rich environment(Sathyan et al., 2014). Mangrove ecosystems, which are extended parts of themarine environment, are also a well-known habitat that can harbor variouspathogenic organisms (Argente et al., 2015). One such inhabitant of mangrovesis the Polymesoda sp.
whosefilter-feeding habit causes it to accumulate strains of pathogenic microbesalong with the food that they ingest. Different types of viruses are alsoreported to have been observed in the tissues of marine mollusks includingiridovirus, Herpes virus, plague virus, echo, coxsackie and reo. Moreover,there have also been reports of the presence of a human pathogen, the HepatitisA virus, in the tissues of marine mollusks (Chatterji, 2002). This implies thatother organisms inhabiting these areas are living with the daily high risk ofpossibly acquiring a certain disease from these microbes. On the other hand,this could also mean that these organisms must have a certain defense againstpathogens allowing them to inhabit the mangroves.
Extracting these certainsubstances would allow them to be tested against pathogens and reveal if theycould become potential medicine. Accordingto Ramasamy and Balasubramanian (2014), there are a lot of various bioactivesubstances from the marine environment that are being isolated and characterized.These compounds are being studied further on a global scale for theirprospective contributions to treating human diseases. Marine bivalves areidentified to be one of the various sources of potential anti-viral (Chatterjiet al., 2002), antibacterial and antifungal (Argente and Ilano, 2015) bioactivecompounds.
Certain species of mud clams were included in some of these studiesand were found to exhibit antimicrobial activity against tested microorganisms.P. erosaand P. expansa, which are common bivalves, are one of the mostwell-known species to possess antimicrobial properties against a wide range ofpathogenic microorganisms.
Mollusks, including bivalves, are no exception inlacking a specific adaptive immunity. Therefore, they depend entirely on innateimmunity such as their cellular and humoral immunity to escalate their defenses(Sathyan et al., 2014). Innate immunity is also immediately triggered uponinfection of a certain microbe (Sharma et al.
, 2009). They produce specialtypes of antibodies when they get penetrated by virulent organisms, usuallyviruses, to fight against them (Chatterji, 2002). The bioactive substances thatthey can produce are therefore self-derived and not due to symbioticrelationships with other organisms such as bacteria or fungi. In some cases ofsymbiotic relations, the bacteria or the fungi living within another organismproduces the bioactive compound. But as mentioned earlier, mollusks dependprimarily on innate immunity.
It is their own body that synthesizes thesecompounds, which could, possibly, be never found in other organisms.