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Journal of Electron Microscopy Advance Access published online on May 18, 2009
Journal of Electron Microscopy, doi:10.1093/jmicro/dfp024
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Morphological and ultrastructural changes in the cell structure of enterohaemorrhagic Escherichia coli O157:H7 following treatment with Quercus infectoria nut galls

Sakol Suwalak1,2 and Supayang P. Voravuthikunchai2,3*

1 Electron Microscopy Unit, Department of Pathology, Faculty of Medicine
2 Department of Microbiology, Faculty of Science
3 Natural Products Research Center, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand

* To whom correspondence should be addressed. E-mail: supayang.v{at}psu.ac.th

Some information is available on the oak (Quercus infectoria) nut gall as an effective medicinal plant against Shiga toxin-producing Escherichia coli (STEC) O157:H7. However, its antibacterial mechanisms have not yet been elucidated. In this study, some antibacterial actions against STEC O157:H7 were investigated by observing cell viability as well as morphological and ultrastructural changes. An ethanolic extract of Q. infectoria demonstrated inhibitory and bactericidal effects on all of the strains tested with minimal inhibition concentrations (MICs) at 0.78–1.56 mg ml–1 and minimal bactericidal concentrations (MBCs) at 1.56–3.12 mg ml–1. Cell numbers treated with 4MIC of the extract decreased at least two log-fold within 4 h and were completely killed within 12 h. Scanning electron microscopy illustrated a complete loss of surface appendages and pronounced morphological changes at MIC and 2MIC. The whole cell collapsed at 4MIC. Ultrastructural changes from corresponding transmission electron micrographs further verified that damages in the treated cells increased with the increase in the extract concentrations. At MIC (0.78 mg ml–1), there was some evidence that the cytoplasmic membranes of the treated E. coli were bulging and/or ruptured, and the cells appeared to be discharging intracellular materials. At 2MIC, the outer membrane of the treated E. coli which was attached to the cell wall became separated from the wall. Disruption in the outer wall and cytoplasmic membranes, especially at the polar regions of the cells occurred and some vacuolization appeared. At 4MIC, the damage to E. coli cells was extensive, and there was loss of their cellular integrity.

Keywords     Quercus infectoria, enterohaemorrhagic Escherichia coli O157:H7, ultrastructure, morphology, cell membrane, electron microscopy

Received      2 March 2009, accepted 16 April 2009


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