A comparative 18F-FDG PET/CT imaging of experimental Staphylococcus aureus osteomyelitis and Staphylococcus epidermidis foreign-body-associated infection in the rabbit tibia

Abstract

Background18F-FDG-PET imaging has emerged as a promising method in the diagnosis of chronic osteomyelitis commonly due to Staphylococcus aureus. The inaccuracy of 18 F-FDG-PET in the detection of periprosthetic joint infections may be related to the predominance of low-virulent S. epidermidis strains as the causative pathogen. We have compared the18F-FDG-PET characteristics of S. aureus osteomyelitis and foreign-body-associated S. epidermidis infections under standardized laboratory conditions.MethodsTwenty-two rabbits were randomized into three groups. In group 1, a localized osteomyelitis model induced with a clinical strain of S. aureus was applied. In groups 2 and 3, a foreign-body-associated infection model induced with a clinical or laboratory strain of S. epidermidis was applied. A small block of bone cement was surgically introduced into the medullary cavity of the proximal tibia followed by peri-implant injection of S. aureus (1 × 105 CFU/mL) or one of the two S. epidermidis (1 × 109 CFU/mL) strains with an adjunct injection of aqueous sodium morrhuate. In group 1, the cement block was surgically removed at 2 weeks but left in place in groups 2 and 3 in order to mimic foreign-body-associated S. epidermidis infections. At 8 weeks, the animals were imaged using 18 F-FDG PET/CT. The presence of bacterial infection was confirmed by cultures, and the severity of bone infections was graded by means of radiography, peripheral quantitative CT, and semi-quantitative histology.ResultsThe S. aureus strain caused constantly culture-positive osteomyelitis. The clinical S. epidermidis strain resulted in foreign-body-associated infections, while the laboratory S. epidermidis strain (ATCC 35983) induced only occasionally culture-positive infections. There was a correlation (r = 0.645; P = 0.013) between semi-quantitative score of leukocyte infiltration and the 18 F-FDG uptake in animals with positive cultures. Standardized uptake value (SUV) of the infected bones was twofold (P < 0.001) in S. aureus animals compared with S. epidermidis animals, but there was only a trend (P = 0.053, ANOVA) in the differences of the corresponding SUV ratios. This was due to the altered 18 F-FDG uptake of the contralateral tibias probably reflecting a systemic impact of severe osteomyelitis.ConclusionThe peri-implant inoculation of S. epidermidis, reflecting low virulence of the pathogen and limited leukocyte infiltration, was characterized by low 18 F-FDG uptake.

In Vivo Monitoring of Staphylococcus aureus Biofilm Infections and Antimicrobial Therapy by [ 18 F]Fluoro-Deoxyglucose–MicroPET in a Mouse Model

“…In line with our observations, in a rabbit model detecting bone staphylococcal infections, a direct relationship was found between PET image intensity, degree of leukocyte infiltration, and increased virulence (in S. aureus compared to S. epidermidis) (18). However, detection of S. aureus strain differences and antibiotic monitoring was not attempted.…”

“…Unfortunately, the technique did not distinguish the signal emitted exclusively by bacteria from that generated by inflammatory cells. [ 18 F]FDGMicroPET has also been used in animals, specifically in rabbit staphylococcal osteomyelitis models (18,19). The mouse model, which involved the use of sealed catheters and required a one-step …”

“…The main advantages of PET over other imaging techniques are its high sensitivity and the possibility to perform quantitative measurements in the images generated. In animals, [ 18 F]FDGMicroPET has been used in different rabbit osteomyelitis models (18,19). The most recent one was performed to detect staphylococcal infections in bone and compare S. aureus and S. epidermidis infections (18).…”

“…18 F]FDGMicroPET has been used in different rabbit osteomyelitis models (18,19). The most recent one was performed to detect staphylococcal infections in bone and compare S. aureus and S. epidermidis infections (18).…”

Influence of fracture stability on Staphylococcus epidermidis and Staphylococcus aureus infection in a murine femoral fracture model

“…epidermidis infection resolved in many animals, which was similar to previous implant-associated infection models for this organism (Lankinen et al, 2012;Laure et al, 2008;Lovati et al, 2016b). Higher dose inocula may guarantee a persistent infection; however, as reported recently for S. aureus, infectious dose might alter immune responses and has to be considered carefully (Vidlak and Kielian, 2016).…”