SHORT COMMUNICATION In vitro activity of water-soluble quaternary chitosan chloride salt against E. coli Leandro Prezotto da Silva • Douglas de Britto • Mirna Helena Regali Seleghim • Odilio B. G. Assis Received: 26 November 2009 / Accepted: 1 March 2010 / Published online: 11 March 2010 Ó Springer Science+Business Media B.V. 2010 Abstract The antibacterial effect of the N,N,N-trimethyl chitosan chloride salt (TMC) was evaluated against the bacterium Escherichia coli. The derivative was prepared via reaction of chitosan with dimethyl sulfate in the pres- ence of NaOH and the Minimum Inhibitory Concentration was assessed by measuring the changes in turbidity and by counting of Colony Forming Units (c.f.u.). The results indicated good antibacterial activity against E. coli for all concentration of TMC tested (20.0; 7.5 and 3.5 mg/l) over 7 h of incubation. From the data, the ideal lethal concen- tration was determined as 20.0 mg/l. Keywords Escherichia coli  Chitosan  Water-soluble chitosan  Minimum inhibitory concentration Introduction Chitosan is an unbranched homopolymer of glucosamine that occurs naturally or can be derived from chitin, an abundant by-product of seafood processing, via deacetyla- tion in the presence of alkali. The term chitosan is usually referred to a family of copolymers with predominant frac- tions of deacetylated units with structure consisting of poly(2-amino-2-deoxy-D-glucopyranose) bonded by b(1 ? 4) linkages, although, a completely deacetylated material is rarely obtained and small fractions of 2-acetamido-2-deoxy- D-glucopyranose units are generally present. Since chitosan is a biocompatible, biodegradable, antimicrobial and non- cytotoxic polymer, it has been extensively evaluated as a potential material for uses in food, agriculture and biomed- ical applications (Kumar 2000; Marques et al. 2008). When submitted to intensive methylation, chitosan generates a trimethylated derivative characterized by hav- ing permanent positive charges in the chains as a conse- quence of the quaternization of the amino groups in the C-2 position in the chitosan backbone (Britto et al. 2008). This modification can be accomplished, for instance, by the methylation of nitrogen atoms (in the amino groups) via reaction with dimethyl sulfate, NaOH and NaCl resulting in N,N,N-trimethyl chitosan (TMC) (Britto and Assis 2007a), Fig. 1. One of the advantages of TMC is that this derivative is a cationic polyelectrolyte soluble over a wide pH range, while the parent chitosan is a weak base soluble only in dilute aqueous acidic solutions below its pKa (*6.3), i.e., it is insoluble in water. TMC has good biocompatibility and shows excellent intestinal absorption, being suggested for uses as a carrier for oral drug delivery (Bowman and Leong 2006) and for support for intranasal vaccine (Amidi et al. 2007). The antibacterial effect of methylated chitosan has been also reported to be more pronounced than the parent chitosan against a broad spectrum of bacteria (Jia et al. 2001; Sadeghi et al. 2008). Several mechanisms have been suggested for the anti- microbial activity of these polysaccharides, but the most accepted model is that related to their polycationic nature (Shahidi et al. 1999; Goy et al. 2009). In this sense, the electrostatic interaction between positively charged qua- ternary R–N(CH 3 ) 3 ? sites and negatively charged microbial cell membranes is the driving force for this antimicrobial L. P. d. Silva  D. de Britto  O. B. G. Assis (&) Embrapa Instrumentac ¸a ˜o Agropecua ´ria, Rua XV de Novembro 1452, 13560-970 Sa ˜o Carlos, SP, Brazil e-mail: odilio@cnpdia.embrapa.br L. P. d. Silva  M. H. R. Seleghim Universidade Federal de Sa ˜o Carlos, UFSCar, Sa ˜o Carlos, SP, Brazil 123 World J Microbiol Biotechnol (2010) 26:2089–2092 DOI 10.1007/s11274-010-0378-7