Atomic force microscopy study of the antibacterial effects of chitosans on Escherichia coli and Staphylococcus aureus.
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.
Eaton
Peter
P
REQUIMTE, Departamento de Química, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal. peter.eaton@fc.up.pt
Fernandes
João C
JC
Pereira
Eulália
E
Pintado
Manuela E
ME
Xavier Malcata
F
F
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D048271:Chitosan / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D008826:Microbial Sensitivity Tests; D018625:Microscopy, Atomic Force / Q000379:methods*; D009844:Oligosaccharides / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology
D000900:Anti-Bacterial Agents; D009844:Oligosaccharides; D048271:Chitosan