Evaluation of the antimicrobial activity of chitosan and its quaternized derivative on E. coli and S. aureus growth

Abstract Chitosan is largely known for its activity against a wide range of microorganisms, in which the most acceptable antimicrobial mechanism is found to include the presence of charged groups in the polymer backbone and their ionic interactions with bacteria wall constituents. This interaction suggests the occurrence of a hydrolysis of the peptidoglycans in the microorganism wall, provoking the leakage of intracellular electrolytes, leading the microorganism to death. The charges present in chitosan chains are generated by protonation of amino groups when in acid medium or they may be introduced via structural modification. This latter can be achieved by a methylation reaction resulting in a quaternized derivative with a higher polymeric charge density. Since the charges in this derivative are permanents, it is expected a most efficient antimicrobial activity. Hence, in the present study, commercial chitosan underwent quaternization processes and both (mother polymer and derivative) were evaluated, in gel form, against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative), as model bacteria. The results, as acquired from turbidity measurements, differ between materials with an expressive reduction on the Gram-positive microorganism (S. aureus) growth, while E. coli (Gram-negative) strain was less sensitive to both polymers. Additionally, the antibacterial effectiveness of chitosan was strongly dependent on the concentration, what is discussed in terms of spatial polymer conformation.

Uso de análise de imagens no acompanhamento de contaminação por fungos em frutos minimamente processados / Use of image analysis in monitoring fungal contamination in minimally processed fruits

Neste trabalho apresentamos uma metodologia bastante simples, fazendo uso de um sistema comercial de captura de imagens, composto de um scanner de mesa que combinado a um programa livre (freeware) da análise de imagens, permite estabelecer qualitativa e quantitativamente a evolução da infestação por fungos sobre frutos fatiados, sendo aqui avaliadas maçãs como exemplo. Penicillium sp e Alternaria sp. foram usados como contaminantes e as imagens geradas duas vezes ao dia empregadas para quantificação. A quitosana, um polissacarídeo com ação fungicida, foi empregado na forma de uma película invisível permitindo, assim, análises comparativas. O método, embora consideravelmente simples, mostrou-se útil sendo indicado para avaliação e prevenção de contaminações de micro-organismos em frutos minimamente processados.

Practical use of immobilized lysozyme for the remediation process of Escherichia coli in aqueous solution

The lysozyme enzyme was immobilized on vitreous surface (fragments with diameters of 0.3 and 1.0 mm) for remediation of the microorganism Escherichia coli JM 109 into fresh water and saline solutions with 0.9 percent NaCl (w/v). Characterization of enzymatic film was carried out by infrared spectroscopy and atomic force microscopy techniques. Bactericide activity of the enzyme was evaluated by spectrophotometric analysis. It was verified that the enzymatic film was strongly coupled with the vitreous surface. The topographic analysis demonstrated that the deposited film was uniform and homogeneous. It was observed bactericide activity of film deposited on vitreous surface with 0.3 mm in fresh and saline solutions. This fact was not verified to vitreous fragments with 1.0 mm of diameter.