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International audience; Surface-enhanced Raman scattering (SERS), based on the enhancement of the Raman signal of molecules positioned within a few nanometres from a structured metal surface, is ideally suited to provide bacterial-specific molecular fingerprints which can be used for analytical purposes. However, for some complex structures such as bacteria, the generation of reproducible SERS spectra is still a challenging task. Among the various factors influencing the SERS variability (such as the nature of SERS-active substrate, Raman parameters and bacterial specificity), we demonstrate in this study that the environment of Gram-positive and Gram-negative bacteria deposited on ultra-thin silver films also impacts the origin of the SERS spectra. In the case of densely packed bacteria, the obtained SERS signatures were either characteristic of the secretion of adenosine triphosphate for Staphylococcus aureus (S. aureus) or the cell wall and the pili/flagella for Escherichia coli (E. coli), allowing for an easy discrimination between the various strains. In the case of isolated bacteria, SERS mapping together with principal component analysis revealed some variabilities of the spectra as a function of the bacteria environment and the bactericidal effect of the silver. However, the variability does not preclude the SERS signatures of various E. coli strains to be discriminated.

Since their discovery, antibiotics have helped treat diseases prior to which many were untreatable, saving millions of lives. However, due to the overuse of antibiotics in medicine and agriculture, the advent of resistant strains of bacteria followed shortly after. The current antibiotic resistance crisis is bringing humanity closer to a post-antibiotic era, when all the advancements made by modern medicine could easily be reversed. Pseudomonas aeruginosa is a Gram-negative, rod-shaped bacterium, ubiquitous owing to its minimal nutritional and growth requirements. P. aeruginosa is one of the pathogens included in the priority list of the WHO, being assessed as critical due to its high antimicrobial resistance, leaving only a few effective treatment options to combat it. As an opportunistic pathogen, P. aeruginosa establishes infection in immunocompromised patients, primarily in hospital settings. In order to initiate infection, it requires several virulence factors that mediate the invasion of the pathogen into host cells. Owing to the multiple resistance mechanisms of P. aeruginosa, it has developed resistance to most classes of antibiotics. Due to its increased resistance, treating P. aeruginosa infections is a great challenge for clinicians. Several β-lactam/β-lactamase combinations have been approved and are available as treatment options, which overall show high efficacy against P. aeruginosa. Moreover, novel antibiotics are currently in development as possible antipseudomonal agents, including a Pseudomonas-specific formulation. In addition, new strategies such as bacteriophage therapy, pyocins or the inhibition of the quorum sensing system are being investigated for the treatment of P. aeruginosa infections.

In the last few decades, methicillin-resistant Staphylococcus aureus (MRSA) strains have become a serious health care problem. However, in the European Union/European Economic Area countries the pr...

The approach of combining different mechanisms of antibacterial action by designing hybrid nanomaterials provides a new paradigm in the fight against resistant bacteria. Here, we present a new method for the synthesis of silver nanoparticles enveloped in the biopolymer chitosan. The method aims at the production of bionanocomposites with enhanced antibacterial properties. We find that chitosan and silver nanoparticles act synergistically against two strains of Gram-positive Staphylococcus aureus (S. aureus). As a result the bionanocomposites exhibit higher antibacterial activity than any component acting alone. The minimum inhibitory (MIC) and minimum bactericidal (MBC) concentrations of the chitosan-silver nanoparticles synthesized at 0 °C were found to be lower than those reported for other types of silver nanoparticles. Atomic force microscopy (AFM) revealed dramatic changes in morphology of S. aureus cells due to disruption of bacterial cell wall integrity after incubation with chitosan-silver nanoparticles. Finally, we demonstrate that silver nanoparticles can be used not only as antibacterial agents but also as excellent plasmonic substrates to identify bacteria and monitor the induced biochemical changes in the bacterial cell wall via surface enhanced Raman scattering (SERS) spectroscopy.