Antimicrobial Peptides for Detection and Diagnostic Assays - Designing Receptors for the Next Generation of Biosensors - page 89

Fig. 1 Concept of AMP-based screening for detection and categorization of microbial species.
The semi-selective binding characteristics of AMPs are used to detect many different species of
microbes. The information provided by the overall pattern of binding is used to classify the
detected species into different families of targets. Once the appropriate category of target is
known, follow-on testing (such as immunoassay, PCR) can be used to identify which species is
present
Using a 3-pronged approach encompassing both in vitro and multiple in vivo
screening models, Welling's group at Leiden University has led the field in
discovery, development, and use of radiolabeled AMPs for in vivo detection and
imaging of microbial infections [ 24 , 25 ]. They have identified a number of
promising technetium-99m (Tc)-labeled peptides with different spectra of binding
and pharmokinetic properties when tested in different in vivo models [ 26 ]. The most
promising Tc-labeled compound could detect Gram-negative, Gram-positive, and
fungal infections in vivo and discriminate them from sterile inflammations induced
by LPS or heat-killed bacteria [ 24 - 26 ]. This material has been used in several
clinical studies with promising results as a negative predictor of infection [ 27 , 28 ].
Derivatives with improved pharmokinetic properties are currently under develop-
ment [ 29 ].
While radiolabeled AMPs are intended as imaging agents for point-of-care use,
AMPs tagged with other labels (e.g., Ru(bpy) 3 - or fluorophore-labeled) offer
tremendous potential for use as “tracer” molecules in biosensors. Olstein and Albert
developed copolymers with repeating polymyxin B (PMB) “recognition” units
and biotin “label” units and demonstrated binding to Gram-negative, but not
Gram-positive cells. Improved sensitivity was demonstrated by increasing the
“label” moieties in the copolymer [ 30 ]. Rocco [ 31 ] conjugated PMB directly to a
fluorophore and demonstrated broadly specific binding to different bacteria
with minimal binding/staining of eukaryotic cells. Lim's group used an analogous
PMB-dye conjugate in biosensor assays where PMB was also used for microbial