Atomic force microscopy study of the antibacterial effects of chitosans on Escherichia coli and Staphylococcus aureus

Abstract

Chitosan has been reported to be a non-toxic, biodegradable antibacterial agent. The aim of this work was to elucidate the relationship between the molecular weight of chitosan and its antimicrobial activity upon two model microorganisms, one Gram-positive (Staphylococcus aureus) and one Gram-negative (Escherichia coli). Atomic force microscopy (AFM) imaging was used to obtain high-resolution images of the effect of chitosans on the bacterial morphology. The AFM measurements were correlated with viable cell numbers, which show that the two species reacted differently to the high- and low-molecular-weight chitosan derivatives. The images obtained revealed not only the antibacterial effects, but also the response strategies used by the bacteria; cell wall collapse and morphological changes reflected cell death, whereas clustering of bacteria appeared to be associated with cell survival. In addition, nanoindentation experiments with the AFM revealed mechanical changes in the bacterial cell wall induced by the treatment. The nanoindentation results suggested that despite little modification observed in the Gram-positive bacteria in morphological studies, cell wall damage had indeed occurred, since cell wall stiffness was reduced after chitooligosaccharide treatment.

A review of the antimicrobial activity of chitosan

“…This supports the evidence that the leakage of intracellular material observed by chitosan in gram-negative is superior to that reported in gram-positive bacteria [21][22][23] . [28][29][30][31] .…”

“…These findings are confirmed by several in vitro experiments in which gram-negative bacteria appear to be very sensitive to chitosan, exhibiting increased morphological changes on treatment when compared to gram-positives [22,23,[33][34][35] . The charge density on the cell surface is a determinant factor to establish the amount of adsorbed chitosan.…”

“…The detachment generates ions and water efflux, provoking decreases on the internal bacteria pressure [16] . Visual confirmation of an effective membrane lysis been also reported on gram-negative and gram-positive bacteria [21][22][23] . Since such mechanism is based on electrostatic interaction, it suggests that the greater the number of cationized amines, the higher will be the antimicrobial activity [24,25] .…”

Atomic force microscopy study of the antibacterial effect of fosfomycin on methicillin-resistant Staphylococcus pseudintermedius

“…Fosfomycin has the ability to penetrate into the fluid of the interstitial space of soft tissues (Frossard et al 2000) to reach levels sufficient to substantially inhibit the growth of relevant bacteria at the target site. The pharmacokinetic and pharmacodynamic properties of fosfomycin facilitate design of drug doses with clinically relevant concentrations for sites such as lungs, bone, soft tissue, and serum and heart valves (Roussos et al 2009 (Eaton et al 2008), kyotorphin peptide (Ribeiro et al 2012), carvacrol (Storia et al 2011) on Staphylococcal aureus biofilms. The nanoscale visualization and characterization of Staphylococcus aureus cells (Ribeiro et al 2012) demonstrated that kyotorphin perturbed the bacterial cell-wall membrane by blebbing, lysis and disruption.…”

Influence of the Chemical Structure and Physicochemical Properties of Chitin- and Chitosan-Based Materials on Their Biomedical Activity

“…Bactericidal activity of the gluten peptide-chitosan conjugates was observed when both types of chitosan were used, but the presence of HMWC in a conjugate made this more active, especially at low temperatures. Atomic force spectroscopy was also used to investigate the molecular weight dependency of the antibacterial effect of chitosans, but this time against Escherichia coli and Staphylococcus aureus (Eaton et al, 2008). These studies also allowed the response strategies used by Gram-negative and Gram-positive bacteria to be compared.…”