Raman spectroscopic measurement of relative concentrations in mixtures of oral bacteria

In Situ Raman Analysis of Biofilm Exopolysaccharides Formed in Streptococcus mutans and Streptococcus sanguinis Commensal Cultures

This study probed in vitro the mechanisms of competition/coexistence between Streptococcus sanguinis (known for being correlated with health in the oral cavity) and Streptococcus mutans (responsible for aciduric oral environment and formation of caries) by means of quantitative Raman spectroscopy and imaging. In situ Raman assessments of live bacterial culture/coculture focusing on biofilm exopolysaccharides supported the hypothesis that both species engaged in antagonistic interactions. Experiments of simultaneous colonization always resulted in coexistence, but they also revealed fundamental alterations of the biofilm with respect to their water-insoluble glucan structure. Raman spectra (collected at fixed time but different bacterial ratios) showed clear changes in chemical bonds in glucans, which pointed to an action by Streptococcus sanguinis to discontinue the impermeability of the biofilm constructed by Streptococcus mutans. The concurrent effects of glycosidic bond cleavage in water-insoluble α - 1,3-glucan and oxidation at various sites in glucans' molecular chains supported the hypothesis that secretion of oxygen radicals was the main "chemical weapon" used by Streptococcus sanguinis in coculture.

Raman Imaging of Pathogenic Candida auris: Visualization of Structural Characteristics and Machine-Learning Identification

Invasive fungal infections caused by yeasts of the genus Candida carry high morbidity and cause systemic infections with high mortality rate in both immunocompetent and immunosuppressed patients. Resistance rates against antifungal drugs vary among Candida species, the most concerning specie being Candida auris, which exhibits resistance to all major classes of available antifungal drugs. The presently available identification methods for Candida species face a severe trade-off between testing speed and accuracy. Here, we propose and validate a machine-learning approach adapted to Raman spectroscopy as a rapid, precise, and labor-efficient method of clinical microbiology for C. auris identification and drug efficacy assessments. This paper demonstrates that the combination of Raman spectroscopy and machine learning analyses can provide an insightful and flexible mycology diagnostic tool, easily applicable on-site in the clinical environment.

Laser raman spectroscopy as a potential chair-side microbiological diagnostic device

INTRODUCTION

Culture-dependent and -independent techniques are time-consuming processes requiring highly trained personnel to identify microorganisms contained within a sample. Rapid chair-side identification of microorganisms could reduce the lag time between patient presentation and ideal treatment. As a first step toward this goal, this study aims to determine if laser Raman spectroscopy (LRS) can discern uniqueness among 10 different species of bacteria contained within a medium in unprocessed and processed samples.

METHODS

Ten bacterial species were individually grown on blood agar plates for 3 days. Checkerboard DNA-DNA hybridization was used for species verification. For the unprocessed samples, a 1.0-cm diameter agar sample, with undisturbed bacterial growth, was transferred for each species to a barium fluoride crystal (BaF(2)) slide and laser scanned for a total of 15 seconds per sample. For the processed samples, bacterial cells were harvested, washed, and resuspended in phosphate-buffered saline buffer at 10(9) cells/mL concentration. Each suspension was laser scanned for 15 seconds on a BaF(2) slide. Select regions of Raman spectra for each species/agar and species/suspension combination were processed using a two-sided t test.

RESULTS

For the 10 bacterial species, 45 bacteria pair combinations were tested for each group. In both groups, LRS was capable of statistically distinguishing among a majority of bacterial pairings based on RS signature differences of means.

CONCLUSIONS

Results show each bacterial species generated restricted ranges of unique spectral signatures that were not masked by their containing medium. Chair-side LRS is a promising technique that differentiates among oral bacterial species with a high degree of specificity.

Identification of different bacterial species in biofilms using confocal Raman microscopy

Confocal Raman microspectroscopy is used to discriminate between different species of bacteria grown in biofilms. Tests are performed using two bacterial species, Streptococcus sanguinis and Streptococcus mutans, which are major components of oral plaque and of particular interest due to their association with healthy and cariogenic plaque, respectively. Dehydrated biofilms of these species are studied as a simplified model of dental plaque. A prediction model based on principal component analysis and logistic regression is calibrated using pure biofilms of each species and validated on pure biofilms grown months later, achieving 96% accuracy in prospective classification. When biofilms of the two species are partially mixed together, Raman-based identifications are achieved within ∼2 μm of the boundaries between species with 97% accuracy. This combination of spatial resolution and predication accuracy should be suitable for forming images of species distributions within intact two-species biofilms.

A confocal Raman microscopy study of the distribution of a carotene-containing yeast in a living Pseudomonas aeruginosa biofilm

The distribution of a carotene-containing yeast (CCY) in a biofilm formed by a small colony variant (SCV) of Pseudomonas aeruginosa PA01 was followed by confocal Raman microspectroscopy (CRM). SCV PA01 and CCY cells were distinguished by their spectral signatures, and the distribution of the overall biomass was monitored by the C-H bending or stretching signal. The distributions of total biomass, PA01, and CCY cells were compared at various times and positions within the biofilm. The distribution of the CCY was very heterogeneous. It was found in the water channels as well as in regions within biofilm colonies. Many of the yeast cells observed within the biofilm colonies under conditions of low or stopped flow were removed when medium was flowing, suggesting that the yeast was not held in the matrix as tightly as were the bacteria.