Identification of Staphylococcus aureus brain abscesses : Rat and human studies with 1H MR spectroscopy

PURPOSE: To determine the feasibility of a statistical classification strategy (SCS) and the identity of metabolites of bacterial and host origins that potentially contributed to the most discriminatory regions of magnetic resonance (MR) spectra from Staphylococcus aureus abscesses of biopsy material from controls, gliomas, and staphylococcal abscesses. MATERIALS AND METHODS: Human and animal study received ethics committee approval, and informed patient consent was obtained. A rat model of S aureus brain abscess was developed. Histologic and microbiologic examination was performed to assess abscess development 3-4, 6-8, and 10-15 days after initiation. Metabolite profiles in pus (n = 62) and controls (n = 37) were characterized with ex vivo MR spectroscopy and compared with data from rat gliomas (n = 27). SCS, optimal region selection, and development of pairwise classifiers allowed MR spectra of abscesses (n = 42, day 6-8) to be distinguished from those of glioblastoma multiforme and controls. MR spectroscopy profiles of pus from animal abscesses were compared with in vivo MR spectra from patients with staphylococcal brain abscesses (n = 7, aged 6-67 years) and ex vivo pus MR spectra from patients with S aureus abscesses. RESULTS: Histologically confirmed abscesses were present 6-8 days after stereotactic injection of S aureus in 42 of 47 rats (89%). MR spectra of abscesses and glioblastoma multiforme in the animal model were similar. Typical metabolites of abscesses due to anaerobe bacteria (acetate, succinate, amino acids) were not detectable in S aureus abscesses in rats or humans. MR spectroscopic findings from controls, abscesses, and gliomas were distinguished by means of SCS with an accuracy of 99%. Analysis of the most discriminatory regions with two-dimensional correlation spectra indicated that glutamine and/or glutamate and aspartate potentially contributed to successful classification. CONCLUSION: S aureus is detectable in abscesses with a non-culture-based method in an animal model.