The potential of SERS as an AST methodology in clinical settings

The ability to identify and characterize microorganisms from tiny sample volumes in a rapid and reliable way is the first and crucial step in the diagnostics of microbial infections. Ideal analytical techniques would require minimal and low-cost sample preparation, permit automatic analysis of many serial samples, and allow rapid classification of present microorganisms against a stable database. Current practice, however, is far from this ideal; a typical analytical procedure might require a few days. Delayed laboratory results might lead, for example, to progress/spread of the infection, more serious condition of the patient, even death, prescription of inappropriate antibiotics that could be ineffective against causative agents and may as well contribute to the emerging problem of drug resistance in microorganisms. Several studies confirmed that surface enhanced Raman scattering (SERS) is capable of a rapid identification and discrimination of biological samples including medically relevant bacteria. A typical spectrum contains a wealth of information indicative of the cellular content of nucleic acids, purine bases, proteins, carbohydrates, and lipids. Such a spectrum functions as a cellular 'fingerprint' and serves as a sensitive indicator of the physiological state of the cell which in turn enables to differentiate cell types, actual physiological states, nutrient conditions, and phenotype changes. Consequently, the focus of this review is on the SERS spectra of bacteria which result from secreted metabolic substances - the purine bases - which are a common feature in the label-free SERS research related to clinical diagnostics of pathogens. Here is the review of the current status of SERS applications on bacteria. A special attention is given to the efforts of profiling antimicrobial susceptibility at clinically relevant species, which in turn has a great potential for use in routine point-of-care (POC) tests. Thus, early and accurate infection disease management can be provided at the bedside or at remote care centres.