Effect of Sample Preparation on the Discrimination of Bacterial Isolates Cultured in Liquid Nutrient Media Using Laser-Induced Breakdown Spectroscopy (LIBS)

Study on direct identification of bacteria by laser-induced breakdown spectroscopy

Bacteria are everywhere in the natural environment. Although most of them are harmless, there are still some hazardous bacteria that will harm human health, so it is particularly important to identify bacteria quickly. Compared with traditional time-consuming and complicated identification methods, laser-induced breakdown spectroscopy (LIBS) is one of the potential technologies for rapid identification of bacteria. In this paper, six weakly active bacteria, including Escherichia coli, Enterococcus faecalis, Bacillus megaterium, Bacillus thuringiensis, Pseudomonas aeruginosa and Bacillus subtilis, are taken as analysis samples. The thawed bacteria are placed in deionized water, and then uniformly smeared on five kinds of substrates to verify the feasibility of using LIBS to identify these bacteria. Spectrum filtering, normalization and principal component analysis (PCA) are used to preprocess the spectra, and a multi-class identification method based on the one-against-all linear kernel function of support vector machine (SVM) is proposed to establish the prediction model. The identification performance is evaluated by using precision and recall. The experimental results show that high-purity graphite is the best substrate with the least interference to the LIBS spectrum of bacteria. The prediction precision of these six bacteria is 77.27%, 92.86%, 84.21%, 94.12%, 81.82% and 76.92%, respectively, recall is 85%, 100%, 94.12%, 80%, 81.82% and 75% respectively, and the identification rate is 84.17%. It can be seen that the direct identification of bacteria can be preliminarily realized by smearing bacteria on the graphite substrate and analyzing its LIBS spectra, which provides a feasible way for simple, rapid and on-site bacterial identification.

Laser-induced breakdown spectroscopy (LIBS): a novel technology for identifying microbes causing infectious diseases

With the advent of improved experimental techniques and enhanced precision, laser-induced breakdown spectroscopy (LIBS) offers a robust tool for probing the chemical constituents of samples of interest in biological sciences. As the interest continues to grow rapidly, the domain of study encompasses a variety of applications vis-à-vis biological species and microbes. LIBS is basically an atomic emission spectroscopy of plasma produced by the high-power pulsed laser which is tightly focused on the surface of any kinds of target materials in any phase. Due to its experimental simplicity, and versatility, LIBS has achieved its high degree of interest particularly in the fields of agricultural science, environmental science, medical science, forensic sciences, and biology. It has become a strong and sensitive elemental analysis tool as compared to the traditional gold standard techniques. As such, it offers a handy, rapid, and flexible elemental measurement of the sample compositions, together with the added benefits of less cumbersome sample preparation requirements. This technique has extensively been used to detect various microorganisms, extending the horizon from bacteria, molds, to yeasts, and spores on surfaces, while also being successful in sensing disease-causing viruses. LIBS-based probe has also enabled successful detection of bacteria in agriculture as well. In order for good quality processing of food, LIBS is also being used to detect and identify bacteria such as Salmonella enteric serovar typhimurium that causes food contamination. Differences in soil bacteria isolated from different mining sites are a very good indicator of relative environmental soil quality. In this connection, LIBS has effectively been employed to discriminate both the inter- and intra-site differences of the soil quality across varying mining sites. Therefore, this article summarizes the basic theory and use of LIBS for identifying microbes causing serious agricultural and environmental infectious diseases.