Raman Spectroscopy as a Potential Tool for Detection of Brucella spp. in Milk

Detection of Brucella, causing brucellosis, is very challenging, since the applied techniques are mostly time-demanding and not standardized. While the common detection system relies on the cultivation of the bacteria, further classical typing up to the biotype level is mostly based on phenotypic or genotypic characteristics. Results of genotyping do not always fit to the existing taxonomy and misidentifications between genetically closely-related genera cannot be avoided. This gets even worse, when detection from complex matrices, like milk, is necessary. For these reasons, the availability of a method, which allows early and reliable identification of possible Brucella isolates both for clinical and epidemiological reasons, is extremely useful. We evaluated micro-Raman spectroscopy in combination with chemometrical analysis to identify Brucella from agar-plates and directly from milk: Prior to the studies the samples were inactivated via formaldehyde treatment to ensure a higher working safety. Then, single-cell Raman spectra of different Brucella spp., Escherichia ssp., Ochrobactrum spp., Pseudomonas spp. and Yersinia ssp. were measured to create two independent databases for detection from media and milk. Identification accuracies of 92% for Brucella from medium and 94% for Brucella from milk can be obtained while analyzing the single-cell Raman spectra via support vector machine. Even the identification of the other genera yield sufficient results with accuracies over 90%. In summary, micro-Raman spectroscopy is a promising alternative to detect Brucella. The measurements, we performed on single-cell-level, enable a therefore fast identification within few hours without a demanding sample preparation.