Antibacterial Effect of Three Exotic Carps

Published: 2021-06-17 10:10:32
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Category: Biology, Zoology

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DiscussionIn present study, all selected carps (H. nobilis, C. idella and C. carpio) secreted huge amount of mucus. Also mucus secretion varied among selected fish species. Blackstock and Pickering (1982); Negus (1983) and Nigam, Kumari, Mittal and Mittal (2012) also reported the similar results. This variation in mucus secretion might be due to different ecological and physiological conditions and also different mucus producing cells situated in epidermis and epidermal layers of different fishes. Jung et al. (2012) also revealed the variation in mucus secretion and its component during the summer and winter, which also supports our finding as mucus secretion by fishes was higher in summers than winters. Present study also revealed more dense and increased amount of mucus in all fish species, after challenge with A. hydrophila. Increased amount of mucus might be the indicator of increased stress level and activation of innate immune system against bacterial attack.
Many previous reports by number of authors such as, Subramanian et al.(2008) and Nigam et al.(2012) demonstrated that environmental perturbations such as, pH, temperature, dissolved oxygen etc.; different ecological niches, bacterial stress, different developmental ages influence the amount of mucus secretion in fishes. Our results are in substantial agreement with above studies. Jones (2001) also reported that Gyrodactylus infected fish produced high amount of mucus than normal which also supports our finding that increased bacterial stress enhanced mucus secretion in challenged group. Madetuja, Dalsgaard and Wiklund (2002); Subramanian et al. (2008) and Holm et al. (2015) also observed similar results.It is now well established that fish skin mucus provides mechanical barrier to fishes by lying at interface between them and surrounding pathogens (Shephard, 1993). In addition to trapping and sloughing of infectious pathogens, it is also the reservoir of bioactive components which acts in different way and gifted innate antibacterial properties to mucus (Grinde, Jolles and Jolles, 1998; Nagashima et al., 2001). Present results on antibacterial activity shown by selected exotic carps also confirmed that fish mucus is a source of antimicrobial products. Earlier studies by many authors viz. Austin and Mcintosh (1988); Oren and Shai(1996); Cole, Weis and Diamond (1997); Ellis (2001); Nagashima et al. (2003); Sarmasik (2002); Balasubramanian, Baby Rani, Arul and Prakash (2012); Prakash, Loganathan, Arul, Senthilraja and Gunaesekaran (2013); Nurtamin, Nurman and Hafizah (2016) and many others also demonstrated strong antibacterial activity in several fishes. Ebran et al. (1999) and Ebran, Julien, Orange and Molle (2000) demonstrated that only the hydrophobic components of crude epidermal mucus of fresh water and sea water fish exhibited strong pore-forming properties, which were well correlated with antibacterial activity. Manivasagan, Annamali, Ashokkumar and Sampathkumar (2009) also reported the antibacterial activity in skin mucus soluble and insoluble friction of A. maculatus and A. thallasinus against E. coli and P. aeruginosa. However, ZOIs values against same microbes shown by mucus extracts in our study were higher. Wei et al. (2010) observed that both crude and aqueous mucus extract of C. straitus exhibited inhibitory effect against fish pathogenic bacteria A. hydrophila and no inhibitory effect against human pathogenic bacteria E. coli and K. pneumonia. Bragadeeswaran and Thangraj (2011) noticed that crude mucus extract of eel fish shows a strong inhibitory effect against E. coli, P. aeruginosa and S. aureus and no activity was observed against K. pneumonia. In the same study, they reported that aqueous mucus extract was not effective against P. aeruginosa. However, in the present study, crude mucus, as well as aqueous mucus (HFM and CFM) extracts of all selected fishes, exhibited antibacterial activity against all bacteria. The test species of bacteria were similar to the studies of Wei et al. (2010) and Bragadeeswaran and Thangraj (2011).Variation in antibacterial activity might be due to different fish species, different habitats, different stress levels etc. Also different fishes having different susceptibility against different or same pathogen. Expression of different immune components in different fish species against different pathogen could be one of the reasons responsible for variation in bactericidal effect. Subramanian, Mackinnon and Ross (2007) also investigated the presence of antimicrobial agents in aqueous mucus extract of several fishes. But in their further studies no antibacterial activity was observed in aqueous mucus extract of wider range of fish species S. alpines, S. fontinalis, C. carpio, M. saxatalis, M. aeglefinus and M. glutinosa. The absence of antimicrobial activity of the aqueous extracts in their study could be due to the low level of enzymes or inactivation of these enzymes by the incubation temperature or pH conditions used in the antimicrobial assay. But in present study, aqueous mucus extracts of all selected fishes exhibited bactericidal effect against all pathogenic bacteria taken under study. Anbuchezhian, Gobinath and Ravichandaran (2011) also noticed the similar results which also support our results. Kumari et al. (2011) also reported antibacterial activity of aqueous mucus extract R. rita (9.75 ± 1.70 mm) and C. punctatus (8.00 ± 0.47 mm) against S. arueus. But at the same time, no antibacterial activity was reported against E. coli and P. aeruginosa. However, their report on low ZOIs values against S. aureus was similar to our results. Balasubramanian et al. (2012) demonstrated the antibacterial effect shown by C. idella against E. coli (17mm), K. pneumonia (7mm) and P. aeruginosa (15mm).
Our findings on aqueous HFM and CFM also similar to above said study. It is evident from this discussion that different fish species exhibit variation in their antibacterial activity against similar or different microbial strains which might be due to difference in quality and quantity of proteins/ enzymes in secreted mucus. Contradictory to our results Hellio et al. (2002) reported no antibacterial activity in aqueous mucus extracts of 13 fish species. However, they did not study crude mucus extract. Similarly, Rao et al. (2015) observed the antibacterial activity in acidic extracts of Tilapia and bigrid cat fish against human pathogenic bacteria. Whereas, no bactericidal effect was noticed in crude and aqueous extracts.Current investigation revealed the change in antibacterial activity (either increased or decreased) after bacterial challenge. Subramanian et al. (2008) also reported that extruded slime produce by bacterial stress showed higher bactericidal effect than normal mucus in M. glutinosa L. Raj et al. (2011) observed increased antibacterial activity in mucus of C. carpio after virus infection. Our studies are in agreement with these studies. Futhermore, this increased or decreased inhibitory effect in fish species might be due to different enzymes level or different protein secretion in same/ different fish, during adverse conditions. Antibacterial activities shown by HFM and CFM of exotic carps, suggesting the presence of one or more antibacterial components in fish skin mucus. Oren and Shai (1996); Cole et al.(1997) and Ebran et al. (1999) isolated antibacterial peptides such as Paradaxin and pleurocidin and many others from epidemal mucus of different fishes. Andreu and Rivas (1999) demonstrated that the action of these antibacterial peptides is non-specific and rapid; they kill pathogenic microbes by a pore formation in cell membranes followed by disruption and solubilization. Thus, we may assume that strong antimicrobial activity of epidermal mucus extracts of exotic carps against microbial strains may be due to pore formation ability of their antibacterial peptides in target cell membrane.
Many authors such as Wei et al. (2010); Vennila et al. (2011) and Rao et al. (2015) carried out MIC assay on mucus extracts of some fishes viz. C. statius, Desyatis sephen and Himantura gerradi, tilapia, C. nigrodigitatus against many human and fish pathogenic bacterial strains. Ebran et al. (1999) revealed the MICs of epidermal mucus of O. mykiss exhibited MIC at 50 µgml-1 against S. aureus, T. ticna at 60 µgml-1 against A. hydrophila and crude mucus supernatant of C. carpio at 50 µgml-1 against S. aureus, supporting the present results. Also Hellio et al. (2002) reported the MICs value of 13 fish species against different pathogen ranged from 25μgml-1 to 48 μgml-1. Our results are in agreement with above study. Contradictory to our findings, Oren and Shai (1996) and Cole et al. (1997) reported that the mucus extracts of winter flounder and moses fish have been found to inhibit the growth of P. aeruginosa, E. coli and A. hydrophila and the MIC values obtained were in range of 40mgl-1 to 200 mgl-1. Lemaitre et al. (1996) reported that glycosylated proteins of MW 27kDa and 31kDa isolated from C. carpio strongly inhibits the growth of all tested microbial strains at approximately 5 µgml-1. similarily, Ebran et al. (2000) noticed that three proteins (45kDa, 49kDa and 65 kDa) from hydrophobic supernatant of skin mucus of eel, tench and trout showed MICs values ranging from 1 µgml-1 to 5 µgml-1. However, same fish or different fishes exhibited different MIC against different or same bacterial strains. This may be due to difference in their age, geological and physiological conditions. Thus, skin mucus extract of these carps species need to be characterized further, and can be explored as a potent antimicrobial against infectious bacteria.ConclusionIn the present study, the increase in amount of mucus secretion after exposure to bacterial challenges indicates its involvement in protection against pathogenic attacks. High mucus secretion could be utilized as an indicator of increased stress level in fishes. Both crude and aqueous mucus extracts of healthy and challenged fishes showed broad spectrum of antibacterial activity against tested human and fish pathogenic bacteria. Therefore, fish skin mucus might posses bioactive components and could be utilized as a novel alternative of antibiotic used in aquaculture and for humans. Being a natural product, it could be helpful in reducing the antibiotic resistance and would be a cost effective.

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