Chitosan was chemically modified to produce quaternary ammonium salts in order to improve its antimicrobial activity and physicochemical properties. Quaternization of N-alkyl chitosan derivatives was carried out using alkyl iodide to elaborate water-soluble cationic polyelectrolytes (N,N,N-trimethylchitosan, TMC). TMC was characterized by 1H NMR spectroscopy; the quaternization degree was determined from 1H NMR spectra and by titration of iodide ion. The antibacterial activity of hydroxypropylcellulose (HPC) films or coatings associated with chitosan or TMC as biocide was evaluated against the growth of Listeria monocytogenes and Salmonella typhimurium. The HPC−chitosan and HPC−TMC coatings exhibited a total inhibition on solid medium of both bacterial strains. Experiments conducted in liquid medium showed that the inhibitory activity against the growth of Listeria innocua was improved after chemical modification. Moreover, physicochemical properties of films were evaluated to determine their potential for food applications. The addition of the antibacterial agents showed a significant impact on the moisture barrier and mechanical properties of HPC films.