Biomedical Engineering Reference
In-Depth Information
UV-resonance Raman spectroscopy is not only used for bacterial identifica-
tion but also to study the influence of antibiotics on bacterial cells. The mode
of action of amikacin on
Pseudomonas aeruginosa
cells was studied by Lopez-
Diez et al. [83]. Neugebauer et al. monitored the effect of ciprofloxacin and
moxifloxacin on the chemical composition of
B. pumilus
and
Staphylococcus
epidermidis
[62, 84].
19.3.4 Surface-Enhanced Raman Spectroscopy of Bacteria
The first SERS spectra of bacterial bulk samples were published in 1998 by
Efrima and Bronk [85]. In this study silver colloids were selectively grown on
or inside
E. coli
cells, depending on the reaction conditions. The method of
silver-coating bacteria was then extended to several other species [86] and al-
ternatively silver or gold colloids were used to coat bacteria [87]. In addition,
it was possible to identify different cell components like FAD (flavin adenine
dinucleotide) [88]. The SERS spectra can also be used to differentiate between
several genera like
E. coli
and
L. monocytogenes
[89]. Laucks et al. investi-
gated mesophilic terrestrial or aquatic bacteria [90]. In this study the content
of unsaturated fatty acids in the bacterial cell wall of
E. coli
and
P. aerugi-
nosa
compared to arctic psychro-active marine bacteria isolated from ice core
samples was investigated. Applying silver colloids the detection limit for the
characterization of
E. coli
was defined to be approximately 10
3
cfu/ml [91].
To minimize the limit of detection Senguputa et al. analyzed bioaerosols by
means of an aerosol sampling system allowing for the identification of bacteria
[92]. The application of gold colloids made the discrimination of
E. coli
and
two bacteriophages possible [93].
Jarvis et al. distinguished between five different bacterial species from
clinical isolates. Here, the silver colloids placed on bacterial layers exhibit
SERS spectra which could mainly be assigned to the bacterial cell wall com-
ponent
N
-acetyl-d-glucosamine [94]. In addition, the combination of a SEM
setup with micro-Raman spectroscopy allows for an identification of SERS-
active spots from silver nanoparticles adsorbed on bacterial layers. With this
method it was possible to enhance the quality of the SERS spectra and to
discriminate between
E. coli
and
B
.
subtilis
[95]. Due to the different SERS
signals of their cell walls Gram-negative and Gram-positive bacteria as well
as different
Bacillus
isolates could be distinguished [96].
The marker substance for
Bacillus
endospores is calcium dipicolinate
(CaDPA). One approach is the isolation of CaDPA from a minimal amount of
spores and its subsequent identification by SERS spectroscopy [97]. The de-
tection of CaDPA in endospores was used for the detection of minimal amount
of spores [98] even in automated mail sorting systems [99]. The detection of
CaDPA does not give any information about the
Bacillus
species present.
The investigation of the components in the outmost layers of the endospores,
the outer sporecoat, or the exosporium will lead to more precise information,
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