Potential antimicrobial activity of marine molluscs from tuticorin, southeast coast of India against 40 biofilm bacteria

Journal of Shellfisheries Research, Jan, 2005 by M. Santhana Ramasamy, A. Murugan

With regard to the bivalves, 70.6% of the whole body extracts showed activity, almost equal to that of gastropod. But, no high activity (not more than 60% strains inhibited) was observed for bivalve extracts. Nearly 91.7% of the bivalve species showed activity against less than 50% biofilm bacteria and 29.4% showed no activity. Among the bivalves, the methanol: dichloromethane extract of Pinna bicolor (72) showed high inhibitory activity against 55% biofilm bacteria. The activity of two cephalopod whole body extracts was not prominent and they exhibited inhibition of less than 40% of biofilm bacteria (Table 1).

Antibacterial Assay of Digestive Gland, Ink, and Opercula Extracts

The digestive gland extracts of the 10 gastropods did not show much activity. Only the methanol extracts of Melo melo (81) and Haliotis varia (78) exhibited activity, with the remaining digestive gland extracts showing no activity (Table 2).

The ink extracts of two gastropods and two cephalopods, screened for antibacterial activity, did not show promising inhibitory activity either. Only the methanolic extracts of Aplysia extraordinaria (88), Dolabella auricularia (89) inks showed activity, but against less than 50% of biofilm bacteria (Table 3).

Among the five opercula screened, only that of Lambis lambis (93) and Chicoreus virgineus (95) showed activity (Table 4). The activity exhibited by opercula of Lambis lambis (93) was not prominent because it inhibited only 15% of biofilm bacteria.

Antibacterial Assay of Molluscan Egg Mass Extracts

Interestingly, all encapsulated egg masses of the 10 gastropods exhibited inhibitory activity (Table 5). Sixty percent of the egg masses showed activity against more than 50% of biofilm bacteria. The egg masses of the family Muricidae inhibited the highest number of biofilm bacteria, with, Chicoreus virgineus, C. ramosus, and Rapana rapiformis showing broad spectrum antibacterial activity against all the 40 biofilm bacterial strains (Table 6). The methanolic extract of Chicoreus virgineus egg mass showed an inhibition zone ranging from 1-10 mm against different bacteria. The acetone extract of the egg mass of Rapana rapiformis showed an inhibition zone of 1-7 mm. The methanolic extract of Chicoreus ramosus egg mass showed an inhibition zone of 1-5 mm. The extracts of these three egg masses showed high inhibitory activity against the biofilm bacteria Vibrio sp. 2 (Table 6). The extracts of empty egg masses did not show any activity.

DISCUSSION

Forty biofilm bacterial strains belonging to 10 genera were isolated and used in antibacterial assays. The strains are the common marine biofilm bacteria in India (Santhana Ramasamy & Murugan 2003). It is well known that many fouling invertebrates require the presence of a microbial surface film as a prerequisite for settlement (Scheltema 1974). Many marine organisms produce bioactive metabolites, which may play a direct role in preventing fouling (Pawlik 1993) and their production can be considered as a kind of autogenic protection (Wahl et al. 1998). In this study, some marine molluscs were shown to inhibit the growth of biofilm bacteria, although since the activity was not associated with surface tissues, the ecologic role is uncertain. Nevertheless, the extracts of marine organisms showing antimicrobial activity against biofilm bacteria could have potential applications as antifouling agents, irrespective of their ecologic function.