ORIGINAL ARTICLE Novel effect of plant lectins on the inhibition of Streptococcus mutans biofilm formation on saliva-coated surface B. Islam 1 , S.N. Khan 1 , A. Naeem 2 , V. Sharma 3 and A.U. Khan 1 1 Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, Uttar Pradesh, India 2 Department of Biochemistry, Faculty of Life Sciences, Aligarh Muslim University, Aligarh, Uttar Pradesh, India 3 Department of Electron Microscopy, National Jalma Institute of Leprosy and other Mycobacterial Diseases, Agra, Uttar Pradesh, India Introduction Lectins are sugar-binding proteins of nonimmune origin that agglutinate cells and ⁄ or precipitate glycoconjugate molecules (Naeem et al. 2007). Multiple nonspecific pro- tein–protein interactions stabilize the binding of lectin to the cells and therefore the affinity a lectin displays for cells or macromolecules (ligands) is several orders higher than that for single sugars (Liener et al. 1986). The cell surface of micro-organisms is covered with abundant and diverse carbohydrates. The ability of plant lectins to react with surface-exposed carbohydrates of microbes has made it possible to widely employ them as diagnostic and ther- apeutic agents (Munoz-Crego et al. 1999). Plant-associ- ated bacteria interact with plant tissues via adhesins and the specificity of interaction is guarded by lectins present in the plants (Danhorn and Fuqua 2007). Some early studies have reported the inhibition of motility and mul- tiplication of some plant bacterial pathogens by aggluti- nins (Gaidamashvili and van Staden 2002; Karpunina Keywords anti-biofilm, CLSM, plant lectins, SEM, Streptococcus mutans, TFA lectin. Correspondence Asad U. Khan, Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, Uttar Pradesh 202002, India. E-mail: asadukhan72@gmail.com; asad.k@rediffmail.com 2008 ⁄ 1357: received 4 August 2008, revised 19 October 2008 and accepted 27 October 2008 doi:10.1111/j.1365-2672.2008.04135.x Abstract Aims: Dental caries is caused by the disturbance in oral homeostasis, marked by a notable increase in the population of Streptococcus mutans. Lectins are a group of plant proteins that are capable of recognizing the glycoconjugates present on the bacterial surface. The aim of this study was to evaluate the effect of seven plant lectins on the growth and initial adhesion of S. mutans. Methods and Results: Lectins of different carbohydrate specificities were iso- lated from plant sources by conventional methods of protein purification. The effect on growth of S. mutans was evaluated following CLSI guidelines. None of the lectins used in this study inhibited the bacterial growth and multiplica- tion. The adherence and biofilm formation of bacteria to saliva-coated polysty- rene plates was tested in the presence of plant lectins. All the plant lectins tested, inhibited both the adherence and biofilm in a concentration dependent manner. Confocal microscopy and scanning electron microscopy were employed to assess the biofilm formation in the presence of plant lectin (glucose ⁄ mannose-specific) at sub-minimal inhibitory concentrations. These evaluations revealed that lectins inhibited the clumping and attachment of S. mutans. Conclusions: Lectins tested here inhibited initial biofilm formation by S. mutans. Glucose ⁄ Mannose-specific lectin altered the adhesion arrangement of the bacteria on the saliva-coated surfaces. Significance and Impact of the Study: The plant lectins used in this study may offer a novel strategy to reduce development of dental caries by inhibiting the initial adhesion and subsequent biofilm formation of S. mutans. Journal of Applied Microbiology ISSN 1364-5072 1682 Journal compilation ª 2009 The Society for Applied Microbiology, Journal of Applied Microbiology 106 (2009) 1682–1689 ª 2009 The Authors