Navy Researchers Identify Bacteria in Human Serum

By Christian Kotanen, Ph.D.
Postdoctoral Fellow, NAMRU-SA

The rate of infectious complications in the U.S. military is approximately 35 percent for combat casualties. Early diagnosis of bacterial agents in the field is critical for the survival and care of wounded warfighters. Advances in diagnostic capabilities that are well suited to field conditions can aid in prevention of infectious complications.

Scientists at the Naval Medical Research Unit-San Antonio (NAMRU-SA) are investigating novel techniques and platforms for rapid and effective infectious pathogen diagnosis.

NAMRU-SA Bioengineer and postdoctoral fellow, Christian N. Kotanen, Ph.D., holds a battery-powered, handheld Raman spectrometer that can display biomolecular “fingerprints” of an infectious pathogen in less than a minute. (Photo: Flisa Stevenson/NAMRU-SA Public Affairs/Released)

NAMRU-SA Bioengineer and postdoctoral fellow, Christian N. Kotanen, Ph.D., holds a battery-powered, handheld Raman spectrometer that can display biomolecular “fingerprints” of an infectious pathogen in less than a minute. (Photo: Flisa Stevenson/NAMRU-SA Public Affairs/Released)

One such technique, known as surface enhanced Raman scattering (SERS) spectroscopy, has the ability to generate unique spectral biomolecular “fingerprints” of microbes such as bacteria and viruses.

Ultimately, researchers want to see a fully-functional biosensor system deployed that will actually have an impact on improving trauma-related outcomes.

NAMRU-SA scientists recently demonstrated that the SERS device was able to identify five bacterial species of military interest from pure culture and bacteria recovered from human serum using a NAMRU-SA designed lysis filtration procedure.

The spectra of each bacterial species represent shifts in the frequency of monochromatic (fixed frequency) light caused by the biological structures of the bacterial cell wall. Hydrophilic bacterial species of Staphylococcus aureus and Acinetobacter baumannii were easily detected and identified from serum samples without significant changes occurring to their spectra due to sample processing. Shifts in relative peak intensities of SERS spectra were observed primarily for hydrophobic bacterial species of Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli. Using this technique, libraries of bacterial SERS spectra can be prepared in advance to generate reference criteria for identification of several bacterial species and strains from blood and tissue samples.

The SERS biosensor can also aid caregivers in administering appropriate antibiotic treatments. After successful identification of an infecting microbe, drug resistance can be assessed by observing shifts in SERS peak intensity after incubation on antibiotic coated nanoparticles.

Preliminary studies at NAMRU-SA have shown mixtures of Gramnegative and Gram-positive bacterial species can be differentiated from either species alone. Improvements to the methods of separation for sample preparation to increase bacterial extraction yields and reduce component requirements are currently underway.

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