New Spectroscopic Approach Explores How Antibiotics Alter E. coli at the Molecular Level

Recently, a team of scientists from Putian University investigated the effectiveness of antibiotics in combating Escherichia coli (E. coli). Using a dual spectroscopic approach that combined Fourier transform infrared (FT-IR) spectroscopy with surface-enhanced Raman spectroscopy (SERS), the researchers demonstrated how their method can lead to improved methods for assessing antibiotic resistance (1). This study’s findings were published in the journal Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (1).

What are the current challenges regarding antibiotic resistance?

Antibiotics are designed to fight bacterial infections that occur in the human body (2). These drugs target the bacteria that is causing the infection and prevent it from multiplying (2). Effective antibiotic treatments kill the bacteria, resulting in the patient recovering from the infection.

A doctor's or researcher's hand holding a Petri dish with a culture of bacteria on which an antibiotic disc test is performed. Antimicrobial resistance concept. | Image Credit: © TopMicrobialStock - stock.adobe.com

However, the main challenge is that bacteria can resist antibiotic treatment. As bacteria adapt to evade drugs, researchers need better tools to understand how these microorganisms respond to different classes of antibiotics (1). In this study, the research team investigated subtle biochemical changes in E. coli when exposed to both β-lactam and quinolone antibiotics, including ampicillin (AMP), enrofloxacin (ENR), ciprofloxacin (CIP), and norfloxacin (NFX) (1).

As part of the experimental procedure, the researchers first determined the optimal concentration for SERS analysis to be 50 μL of bacterial suspension diluted six times to achieve an optical density (OD600) of approximately 0.1 (1). The SERS measurements revealed that ampicillin treatment led to primary changes at 1267 cm⁻¹, a spectral region linked to the amide III band in proteins, indicating disruptions to bacterial protein structure (1). In contrast, FT-IR analysis of the AMP-treated bacteria revealed significant changes between 1200–900 cm−1, corresponding to carbohydrate components, suggesting that ampicillin impacts both protein and carbohydrate metabolism (1).

For quinoline antibiotics, the molecular signatures varied depending on the antibiotic. These drugs are known to inhibit DNA synthesis, and the SERS spectra of antibiotic-resistant E. coli showed notable peaks at 760 cm⁻¹ (cytosine and uracil), 960 cm⁻¹ (C–N stretching and C––C deformation), and 1140 cm⁻¹ (C–O–C stretching and ring breathing) (1). With FT-IR analysis, the research team detected major shifts at 1655 cm⁻¹, 1544 cm⁻¹, and 1239 cm⁻¹, corresponding to amide I, II, and III bands, respectively (1).

What was a key innovation of the study?

A key innovation of the study was the fabrication of a dual-enhanced SERS substrate. By combining gold nanorod (AuNR) and gold nanosphere (AuNS) arrays, the team achieved significant SERS signal amplification compared to monometallic substrates (1). This signal amplification was key in detecting the Raman “fingerprints” from bacterial cells (1). Optimizing the experimental procedure also allowed the team to identify the ideal substrate preparation parameters, bacterial concentration, and ratio of bacteria to AuNRs.

Another important innovation was the use of statistical methods. In the study, the researchers used principal component analysis (PCA) to help simplify data interpretation. The researchers demonstrated that PCA could differentiate between different antibiotic treatments and exposure times, revealing clear molecular trends associated with both susceptible and resistant E. coli strains (1).

By merging the complementary strengths of SERS and FT-IR, the team demonstrated that it is possible to build a comprehensive biochemical profile of bacterial responses to antibiotics. SERS excelled at detecting specific vibrational modes associated with nucleic acids, proteins, and cell wall components, whereas FT-IR offers broader insights into overall biomolecular composition (1). Together, they create a multidimensional “fingerprint” that captures the dynamic molecular changes that occur as bacteria encounter and adapt to antibiotic stress (1).

What are the key takeaways from this study?

This study presents a dual-spectroscopy approach that can investigate bacterial resistance mechanisms. The researchers demonstrated that the method is non-destructive and has the sensitivity required to identify molecular shifts that accompany resistance (1). This is important because this information can help clinicians and biologists understand how antibiotics are working and what can be done to make them more effective.

This study used E. coli as the test subject, but its methodology can be applied to other pathogens. Such rapid and detailed resistance profiling could help clinicians choose the most effective treatments sooner, reducing the misuse of antibiotics and slowing the spread of resistant strains (1).

Antibiotic resistance remains an ongoing problem that scientists are attempting to solve. Technological developments, such as the SERS–FTIR–PCA platform presented in the study, helps advance this cause by providing real-time diagnostics to improve our understanding of bacterial survival and molecular behavior in microbiology.

References

1. Rao, Y.; Li, H.; Ding, X.; et al. Detection of Antibiotic-resistant Escherichia coli Using Surface-enhanced Raman Spectroscopy and Infrared Spectroscopy. Spectrochimica Acta Part A: Mol. Biomol. Spectrosc. 2025, 345, 126759. DOI: 10.1016/j.saa.2025.126759
2. Medline Plus, Antibiotics. National Library of Medicine. Available at: https://medlineplus.gov/antibiotics.html (accessed 2025-08-11).