Table 1.

Overview of infections, with most common causative micro-organisms, and potentially suitable tracers for detection

Infection	Common causative micro-organisms (>10 %)	Potential tracers for detection	Remarks
Necrotizing fasciitis	Streptococcus pyogenes, other β-hemolytic streptococci, Staphylococcus aureus; (an)aerobic mixed flora, Clostridium perfringens a, other clostridiaa	CEF, CIP, FIAU, MALT, UBI, VAN
Septic arthritis	Staphylococcus aureus, streptococci, N. gonorrhoeae	CEF, CIP, FIAU, FLER, MALT, NUC, PRO, UBI, VAN
Infective endocarditis	S. aureus, coagulase negative staphylococci, viridans streptococci, enterococci, HACEK organismsa	CEF, CIP, FIAU, MALT, NUC, PRO, UBI, VAN
Infected surgical meshes	S. aureus, coagulase negative staphylococci, streptococci, enterococci	CEF, CIP, FIAU, MALT, NUC, PRO, UBI, VAN
Infected surgical grafts and meshes	S. aureus, coagulase negative staphylococci, streptococci, enterococci	CEF, CIP, FIAU, MALT, NUC, PRO, UBI, VAN
Meningitis	Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae, Listeria monocytogenes a	CEF, FIAU, MALT, UBI	The tracer has to cross the blood–brain barrier
Bacteremia	Miscellaneous	CEF, CIP, FIAU, MALT, NUC, PRO, SOR, UBI, VAN, BLA
Pneumonia	Streptococcus pneumoniae, Haemophilus influenzae, S. aureus. Hospital-acquired pneumonia: miscellaneous	CEF, CIP, FIAU, MALT, NUC, PRO, SOR, UBI, BLA

Tracers can be suitable in two possible ways, namely (1) detection of infection by targeting the vast majority of causative pathogens, or (2) by detection of particular species, which would have direct implications for the choice of therapy. Ideally, future approaches would offer both possibilities. Potentially usable tracers not only include the tracers in their current published structures but also future variants (e.g., modification from radiolabeled to optically labeled, or vice versa). Microorganisms and tracers are mentioned in alphabetical order

^aMicro-organisms that occur in less than 10 % of the cases, but are classically associated with the respective infection. The specific tracers listed are: ^99mTc-ceftriaxone (CEF), ^99mTc-ciprofloxacin/¹⁸F-ciprofloxacin (CIP), ¹²⁴Iodine-FIAU (FIAU), ¹⁸F-fleroxacin (FLER), 6-[¹⁸F]-fluoromaltose/maltodextrin-based optical tracer (MALT), activatable nuclease-targeted optical tracer (S. aureus-directed; NUC), prothrombin-based optical/radiolabeled tracer (PRO), 2-[¹⁸F]-fluoro-deoxy-sorbitol (SOR), ^99mTc-ubiquicidin (UBI), vancomycin-IRDye 800CW (VAN), activatable β-lactamase-targeted optical tracer (BLA). HACEK organisms (fastidious Gram-negative bacilli): Haemophilus spp., Aggregatibacter actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae/Kingella denitrificans