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Antibiotics cure infections by influencing bacterial growth or viability. Antibiotics can be divided to two groups on the basis of their effect on microbial cells through two main mechanisms, which are either bactericidal or bacteriostatic. Bactericidal antibiotics kill the bacteria and bacteriostatic antibiotics suppress the growth of bacteria (keep them in the stationary phase of growth). One of many factors to predict a favorable clinical outcome of the potential action of antimicrobial chemicals may be provided using in vitro bactericidal/bacteriostatic data (e.g., minimum inhibitory concentrations-MICs). Consequently, MICs are used in clinical situations mainly to confirm resistance, and to determine the in vitro activities of new antimicrobials. We report on the combination of data obtained from MICs with information on microorganisms' "fingerprint" (e.g., DNA/RNA, and proteins) provided by Raman spectroscopy. Thus, we could follow mechanisms of the bacteriostatic versus bactericidal action simply by detecting the Raman bands corresponding to DNA. The Raman spectra of Staphylococcus epidermidis treated with clindamycin (a bacteriostatic agent) indeed show little effect on DNA which is in contrast OPEN ACESSMolecules 2013, 18 13189 with the action of ciprofloxacin (a bactericidal agent), where the Raman spectra show a decrease in strength of the signal assigned to DNA, suggesting DNA fragmentation.

Clinical treatment of the infections caused by various staphylococcal species differ depending on the actual cause of infection. Therefore, it is necessary to develop a fast and reliable method for identification of staphylococci. Raman spectroscopy is an optical method used in multiple scientific fields. Recent studies showed that the method has a potential for use in microbiological research, too. Our work here shows a possibility to identify staphylococci by Raman spectroscopy. We present a method that enables almost 100% successful identification of 16 of the clinically most important staphylococcal species directly from bacterial colonies grown on a Mueller-Hinton agar plate. We obtained characteristic Raman spectra of 277 staphylococcal strains belonging to 16 species from a 24-hour culture of each strain grown on the Mueller-Hinton agar plate using the Raman instrument. The results show that it is possible to distinguish among the tested species using Raman spectroscopy and therefore it has a great potential for use in routine clinical diagnostics.

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Advanced optical instruments can serve for analysis and manipulation of individual living cells and their internal structures. We have used Raman microspectroscopic analysis for assessment of β-carotene concentration in algal lipid bodies (LBs) in vivo. Some algae contain β-carotene in high amounts in their LBs, including strains which are considered useful in biotechnology for lipid and pigment production. We have devised a simple method to measure the concentration of β-carotene in a mixture of algal storage lipids from the ratio of their Raman vibrations. This finding may allow fast acquisition of β-carotene concentration valuable, e.g., for Raman microspectroscopy assisted cell sorting for selection of the overproducing strains. Furthermore, we demonstrate that β-carotene concentration can be proportional to LB volume and light intensity during the cultivation. We combine optical manipulation and analysis on a microfluidic platform in order to achieve fast, effective, and non-invasive sorting based on the spectroscopic features of the individual living cells. The resultant apparatus could find its use in demanding biotechnological applications such as selection of rare natural mutants or artificially modified cells resulting from genetic manipulations.