J. C. Fernandes, P. Eaton, A. M. Gomes, M. E. Pintado, and F. X. Malcata.
Study of the antibacterial effects of chitosans on Bacillus cereus
(and its spores) by atomic force microscopy imaging and nanoindentation
Ultramicroscopy 109 (8), 854-860 (2009).
Abstract
Bacillus cereus is a Gram-positive, spore-forming bacterium that is widely distributed in nature.
Its intrinsic thermal resistance coupled with the extraordinary resistance against common food
preservation techniques makes it one of the most frequent food poisoning microorganisms causing
both intoxications and infections. In order to control B. cereus growth/sporulation, and hence
minimize the aforementioned hazards, several antimicrobial compounds have been tested. The aim
of this work was to assess by atomic force microscopy (AFM) the relationship between the
molecular weight (MW) of chitosan and its antimicrobial activity upon both vegetative and
resistance forms of B. cereus. The use of AFM imaging studies helped us to understand how
chitosans with different MW act differently upon B. cereus. Higher MW chitosans (628 and
100 kDa) surrounded both forms of B. cereus cells by forming a polymer layer – which eventually
led to the death of the vegetative form by preventing the uptake of nutrients yet didn’t
affect the spores since these can survive for extended periods without nutrients.
Chitooligosaccharides (COS) (<3 kDa) on the other hand, provoked more visible damages in
the B. cereus vegetative form – most probably due to the penetration of the cells by the
COS. The use of COS by itself on B. cereus spores wasn’t enough for the destruction of
large number of cells, but it may well weaken the spore structure and its ability to
contaminate, by inducing exosporium loss.
http://dx.doi.org/10.1021/j.ultramic.2009.03.015
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