Antimicrobial peptides and bacteria: Scanning and Transmission Electron Microscopical Investigations

Session

LSA.12 - Application of EM in health industry

Authors

assist. prof. dr merve elmas (2), ASSOC. PROF. DR. OZGE CAN (1), prof. dr. tanıl kocagoz (3), PROF. DR. SERAP ARBAK (2)

Affiliations

1. Faculty of Engineering, Department of Medical Engineering, Acibadem Mehmet Ali Aydinlar University
2. School of Medicine, Department of Histology and Embryology, Acibadem Mehmet Ali Aydinlar University
3. School of Medicine, Department of Medical Microbiology Acibadem Mehmet Ali Aydinlar University

Keywords

SEM, TEM, Morphology, AMPs

Abstract text

Background and Aim: Many living organisms produce antimicrobial peptides (AMPs) as a part of their innate immune system against bacteria, viruses, and fungi.  These peptides are cationic and amphipathic.  Because of the ability to interact with bacterial membrane,   negatively charged lipids leads to destabilization and permeabilization of the cell membrane. Regarding increased resistance of pathogenic bacteria to traditional antibiotics and medications, AMPs are a promising alternative to treat infections. Studies with transmission electron microscopic analysis revealed a morphological variety of bacteria with various internal and external structures, such as wide variation of the cell envelope and thickness of the capsules. So,   the aim of the present study is to investigate ultrastructural changes in the bacteria trigerred by antimicrobial peptides (AMPs) by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Methods: As a gram-negative strain, Escherichia coli were exposed to the AMPs and untreated controls were used to compare morphological changes with SEM (Thermo Scientific- Quattro SEM)  and TEM (Thermo Scientific- Talos L120C ) analysis. For the SEM analysis dialysis membrane was used to capture E.coli cells. Then, routine SEM preperation techniques were used. For the TEM analysis, firstly E.coli were fixed with glutaraldehyde and following  the fixation liquid samples were embedded in agar. At the end of this procedure  evenly distributed specimens could   be treated like easily handled tissue blocks. Then, these tissue blocks were processed for epoxy resin embedding. Thin sections, stained with uranyl acetate.

Results:  SEM analysis of  untreated E.coli cells revealed  a smooth cell surface  morphology. Different shapes of blisters and  numerous small bubbles were obviously seen in AMPs treated  E.coli cells. TEM analysis showed that the morphology of the bacteria treated with AMPs was altered dramatically. Cell membranes which had an intact ultrastructure in untreated group, were damaged and the cellular contents were released outsideof the cell   in AMPs treated  E.coli cells.

Conclusion: Comprehensive EM analysis revealed that AMPs cause multiple stresses on the membranes of E. coli. So, these results suggest that AMPs play antibacterial role by destroying the integrity of the membrane and this molecule has a promising role to develop a potent antimicrobial agent.

Acknowledgements: This study was financed by The Scientific and Technological Research Council of Turkey (TUBITAK), project number 217S060

References

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