The discovery of penicillin began the age of antibiotics, which was a turning point in human healthcare. However, to this day, microbial infections are still a concern throughout the world, and the rise of multidrug-resistant organisms is an increasing challenge. To combat this threat, diagnostic imaging tools could be used to verify the causative organism and curb inappropriate use of antimicrobial drugs. Nuclear imaging offers the sensitivity needed to detect small numbers of bacteria in situ. Among nuclear imaging tools, radiolabeled antibiotics traditionally have lacked the sensitivity or specificity necessary to diagnose bacterial infections accurately. One reason for the lack of success is that the antibiotics were often chelated to a radiometal. This was done without addressing the ramifications of how the radiolabeling would impact probe entry to the bacterial cell, or the mechanism of binding to an intracellular target. In this review, we approach bacterial infection imaging through the lens of bacterial specific molecular targets, their intracellular or extracellular location, and discuss radiochemistry strategies to guide future probe development.

Recently, several molecular imaging strategies have developed to image bacterial infections in humans. Nuclear approaches, specifically positron emission tomography (PET), affords sensitive detection and the ability to non-invasively locate infections deep within the body. Two key radiotracer classes have arisen: metabolic approaches targeting bacterial specific biochemical transformations, and antibiotic-based approaches that have inherent selectivity for bacteria over mammalian cells. A critical question for clinical application of antibiotic radiotracers is whether resistance to the template antibiotic abrogates specific uptake, thus diminishing the predictive value of the diagnostic test. We recently developed small-molecule PET radiotracers based on the antibiotic trimethoprim (TMP), including [11C]-TMP, and have shown their selectivity for imaging bacteria in preclinical models. Here, we measure the in vitro uptake of [11C]-TMP in pathogenic susceptible and drug-resistant bacterial strains. Both resistant and susceptible bacteria showed similar in vitro uptake, which led us to perform whole genome sequencing of these isolates to identify the mechanisms of TMP resistance that permit retained radiotracer binding. By interrogating these isolate genomes and a broad panel of previously sequenced strains, we reveal mechanisms where uptake or binding of TMP radiotracers can potentially be maintained despite the annotation of genes conferring antimicrobial resistance. Finally, we present several examples of patients with both TMP-sensitive and drug-resistant infections in our first-in-human experience with [11C]-TMP. This work underscores the ability of an antibiotic radiotracer to image bacterial infection in patients, which may allow insights into human bacterial pathogenesis, infection diagnosis, and antimicrobial response monitoring.

Iivanainen, E., Northrup, J., Arbeit, R. D., Ristola, M., Katila, M.-L. 8t von Reyn, C. E Isolation of mycobacteria from indoor swimming pools in Finland. APMIS 1999: 107: 193-200.The presence of mycobacteria in seven indoor pools in Finland was evaluated by multiple culture methods. Replicate samples, with and without inactivation of chlorine by sodium thiosulfate, were cultured in two laboratories. Laboratory I used two methods: (A) no decontamination and (B) cetylpyridinium chloride (0.005%, 20 min); and Laboratory I1 two methods: (C) cetylpyridinium chloride (0.005Y0, 18 h) and (D) oxalic acid (5%, 15 min). Samples processed by methods (A) and (B) were cultured on different egg media of pH 6.3 or 5.8; by method (C) on Middlebrook and Cohn 7H10 (+OADC) agar of pH 5.5; and by method (D) on Middlebrook and Cohn 7H10 agar (+OADC) with cycloheximide (500 pg/ml). Mycobacteria were recovered from five (71%) of seven pools. Detection of mycobacteria depended on the method used. High isolation rates (3&46% of the samples) were obtained by methods (A), (B) and (D). Contamination was a problem only with method (A). Inactivation of chlorine had a variable impact on mycobacterial detection. Isolates included M. kansasii, M. gordonae, M. fortuitum complex, M . sphagni, and M. vaccae, as well as M. simiae-like and M. chubuenselike organisms. In addition, a group of slowly growing and a group of rapidly growing isolates with previously unknown fatty acid and alcohol composition were isolated. No M . avium was detected. Mycobacterial counts were highest in a small pool with high temperature, low pH, and low content of free available chlorine.

Herein, we introduce the efficient synthesis of Q-proline (Q-Pro) based, metal-binding macrocycles (QPM), which can display up to nine functional groups. Synthesis of eight QPM was achieved through standard Fmoc-SPPS and peptoid chemistry. QPM are disordered in the absence of a metal cation, as evidenced by NMR and a crystal structure of <b>QPM-3</b> obtained through racemic crystallization. Addition of metal cations cause these macrocycles to adopt ordered, uniform core structures regardless of the functional groups. Alkylation of QPM allows for addition of reactive functional groups as the final step in a synthesis. Interestingly, the addition of secondary functional groups to the hydantoin amide position (R₂) converts the proline ring from Cg-endo to Cg-exo, due to steric interactions.