Page 272 - Vibrational Spectroscopic Imaging for Biomedical Applications

248 Cha pte r Ei g h t

which is presently the major drawback of antimalarial therapy. Using
resonance Raman spectroscopy the characterization of hemozoin
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under different physiological conditions, as well as the influences of
45
46
quinoline additives or chloroquine to β-hematin were investi-
gated. The structural changes of hemozoin during chloroquine expo-
sure were monitored by RR spectroscopy. 47
8.4 Raman Spectroscopy of Bacteria
Prokaryotic bacteria are generally smaller than single (eukaryotic)
cells. While some of them can cause serious infectious diseases, oth-
ers are vital parts of the gut flora or live on the skin; again other bac-
teria can spoil food, while other strains are utilized in food,
pharmaceutical and chemical industry to produce cheese, vinegar,
yoghurt, antibiotics, hormones, lactic acids, and many other prod-
ucts. Fast and reliable identification methods are needed to distin-
guish the useful and harmless bacteria from the unwanted and toxic
ones, and to provide an efficient and appropriate treatment of infec-
tions. In times of growing antibiotic resistances it is furthermore
desirable to identify new target structures for new and effective
drugs.
Besides the classical microbiological identification a variety of
alternative methods has evolved, ranging from immunological assays
with different labeling techniques to molecular biological methods.
An overview of the identification of microorganisms using infrared
spectroscopy has recently been given. Simultaneous to the micro-
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bial classification by infrared spectroscopy, Raman spectroscopy was
used as a nondestructive fingerprint method to identify and classify
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bacteria. In general, sample preparation is easier than for infrared
spectroscopy because bacteria grown in liquid cultures as well as bac-
50
teria on agar plates can directly be investigated. Different wave-
lengths can be employed for resonance and nonresonance excitation
and only a minimal sample volume, down to a single cell, is neces-
sary, which means a tremendous reduction in analysis time. An
important target structure of many antibiotics is the bacterial cell
wall. Tip-enhanced Raman spectroscopy is a relatively new way how
to assess information about the outer bacterial layer with lateral reso-
lution down to few nanometers and with high chemical specificity.

8.4.1 Species Classification
In medicine the exact identification of bacteria is necessary in order to
provide the appropriate therapy and to prevent antibiotic resistance
which may further delay administration of the most appropriate nar-
row-spectrum antibiotic. 51 Traditional microbiological identification
and infection diagnoses are time-consuming and labor-intensive pro-
cesses: at least 12- to 24 hour incubation is required to obtain an accurate