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

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.

Development of a portable SERS method for testing the antibiotic sensitivity of foodborne bacteria.

A method for testing the antibiotic susceptibility of foodborne bacterial samples using a portable Raman spectrometer has been developed. Surface-enhanced Raman spectroscopy (SERS) was used to obtain the spectra from bacterial samples collected on a filter membrane after incubation with antibiotics. The SERS spectra revealed characteristic antibiotic response patterns, which can be used to assess the antibiotic sensitivity of the samples. Several species of bacteria, including Escherichia coli, Bacillus cereus, and Salmonella enterica, were used to test the procedure, as well as multiple classes of antibiotics. Characteristic bacterial SERS peaks could be identified in the spectra, as well as clear antibiotic response patterns that were consistent across the different species of bacteria and could be used to reliably determine the antibiotic sensitivity of the samples. The portable SERS method was then used to test bacteria isolated from ground beef, and the results show the procedure could be used to accurately test the antibiotic sensitivity of bacteria isolated from real food samples. Further optimization of this method to test the filtered liquid obtained from bacterial samples has demonstrated the capability of a simpler approach to identify antibiotic response patterns. The effectiveness and improved accessibility of the portable SERS method indicates that these procedures have great potential for future use in low-resource settings, which will facilitate the monitoring and control of antibiotic resistance.

Assessment of three SERS approaches for studying E. Coli O157:H7 susceptibility to ampicillin.

Antibiotic resistant bacteria pose an increasing threat to global public health, and it is essential that effective detection methods for identifying these organisms. This study assesses the ability of three different analytical approaches that were developed using surface-enhanced Raman spectroscopy (SERS) to differentiate between antibiotic sensitive and resistant bacteria based on their responses to ampicillin exposure, using Escherichia coli O157:H7 as a model bacterium. The approaches tested in this study included a conventional SERS approach of mixing a droplet of bacterial culture with gold nanoparticles, extracellular matrix analysis, and in situ mapping of bacterial cells on a filter membrane. All three of the SERS techniques were able to differentiate between the sensitive and resistant bacterial strains based on peak intensity changes associated with compounds released by the bacteria in response to antibiotic exposure, with extracellular matrix analysis and filter mapping both observed to be more effective than the conventional approach. However, there were significant differences between the spectra obtained from the different techniques and the potential advantages and disadvantages of each approach should be considered when used in the future. This study shows that SERS can be an effective technique for rapid and efficient assessment of ampicillin sensitivity in E. coli, and more work should be done to explore these analytical approaches with other types of bacterial samples.

Cysteamine-Modified Gold Nanoparticles as a Colorimetric Sensor for the Rapid Detection of Gentamicin.

A simple, rapid, and specific colorimetric method for gentamicin detection using cysteamine-modified gold nanoparticles (cys-AuNPs) has been developed. The maximum residue limits of gentamicin allowed in foods are typically below 100 nM, so an effective detection method for low concentrations of the drug is required. The aggregation of gold nanoparticles (AuNPs) was used as the basis for this method, and adding cysteamine to the AuNPs helped to enhance their aggregative abilities. The cys-AuNPs are capable of detecting gentamicin concentrations as low as 12.45 nM in water, which could be quantified using UV-vis spectroscopy. Samples extracted from skim milk with a simple pretreatment showed that gentamicin concentrations down to at least 100 nM could be observed using the cys-AuNPs. This study demonstrates the ability of the cys-AuNPs to rapidly detect and quantify gentamicin in both simple and complex matrices. PRACTICAL APPLICATION: This study demonstrates that cysteamine-modified gold nanoparticles could be used as a rapid and efficient tool for gentamicin detection. This technique is cheaper, simpler, and more effective than many other methods that are currently used for detecting the antibiotic in industrial and commercial applications. It has a great potential to be practically applied as a rapid screening method for gentamicin and gentamicin-like compounds in food and environmental samples.