Investigating the origins of bacterial SERS responses to antibiotics observed in the extracellular matrix liquid

Abstract

Surface-enhanced Raman spectroscopy (SERS) has been applied to analyze bacterial cells and their responses to antibiotic exposure. However, significant knowledge gaps remain regarding the origins of specific antibiotic response patterns and the necessary experimental steps required to see them clearly in the SERS spectra, particularly involving SERS responses observed in the extracellular matrix liquid of bacterial samples. In this study, a variety of experimental parameters were tested to assess the antibiotic response patterns seen in liquid samples from E. coli under different conditions. These include testing the impact of washing the cells with water after incubating them with antibiotics, as well as the effect of using different types of liquids with varying characteristics for incubating the bacteria with the antibiotics. It was found that the experimental procedure has a significant impact on the resulting SERS signals, and the target patterns could only be observed in specific conditions. In particular, the step of washing the bacteria with water is necessary for observing the antibiotic response patterns, and incubating the bacteria and antibiotics in a nutrient-rich growth medium is preferable to incubating the cells in a buffer or in distilled water. These findings can be used to improve existing methods for testing antibiotic responses with SERS, and could potentially help to further develop and optimize SERS-based procedures for assessing antibiotic sensitivity.