Characterization of the Action of Antibiotics and Essential Oils against Bacteria by Surface-Enhanced Raman Spectroscopy and Scanning Electron Microscopy

ABSTRACT

The description of the main structural alterations generated by the interaction between pathogenic microorganisms and antibiotic agents, either standard antibiotics or volatile plant derived oils, is an essential topic in understanding drug action mechanisms at the molecular level. To investigate this effect, an original approach based on ultrasensitive vibrational surface-enhanced Raman spectroscopy (SERS) and scanning electron microscopy (SEM) was used. Single-bacteria SERS spectra, recorded in the 600–1800 cm⁻¹ wavenumber interval are reported for two bacterial strains: Enterococcus durans and Aeromonas media. Spectra-structure correlations for all types of localized vibrations, including bands assigned to proteins, saturated lipids, glycosidic linkages, and nitrogenous bases, are also discussed. SEM images revealed that the mechanism of action of antibiotic agents against the pathogenic microorganisms involves a complete denaturation of the bacterial membrane, which induces bacterial cells apoptosis.

KEYWORDS:

• Antibiotics
• bacterial strains
• essential oils
• inhibition
• scanning electron microscopy
• structure
• surface-enhanced Raman spectroscopy

Additional information

Funding

Financial support from the National Authority for Scientific Research and Innovation-ANCSI, Core Programme, Project PN16-30 02 03 is gratefully acknowledged. The authors also want to thank to the Integrated Laboratory for Electron Microscopy (LIME)—within CETATEA Center, National Institute for Research and Development of Isotopic and Molecular Technologies Cluj-Napoca, for the access to the SEM facility.