Patients with suspected bacterial infection at the time screening are eligible for this study. Patients may participate in this study if they are at least 18 years of age, and most participants will be receiving care at the clinical practices of the University of Pennsylvania. Up to 30 subjects will participate in two different imaging cohorts.

The Biodistribution cohort will include up to 5 patients referred from orthopedics who will undergo a series of vertex to mid-thigh (or feet if indicated) biodistribution [11C]trimethoprim PET/CT scans over a period of approximately 2 ½ hours.

The Dynamic cohort will include up to 25 patients who will undergo approximately 60 minutes of dynamic scanning followed by up to 2 static skull base to mid-thigh (or feet if indicated) scans imaging post injection of [11C]trimethoprim. Some subjects who may be selected clinically to undergo surgical or antibiotic treatment may undergo a second therapy may also undergo an optional second [11C]trimethoprim PET/CT after the initiation of therapy to collect pilot data on the changes in [11C]trimethoprim biodistribution and uptake with therapy, the timing of this scan may vary depending on the type of treatment the patient is receiving.

Patients will also undergo baseline lab tests complete blood count (CBC), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and blood cultures. If these tests are done as part of clinical standard of care they will not need to be repeated for this study.

Inclusion Criteria:

1. Inclusion Criteria at least 18 years of age
2. Known or suspected bacterial infection.
3. Participants must be informed of the investigational nature of this study and provide written informed consent in accordance with institutional and federal guidelines prior to study-specific procedures.

Exclusion Criteria:

1. Antibiotic therapy with trimethoprim within 48h of the baseline PET/CT scan.
2. Inability to tolerate imaging procedures in the opinion of an investigator or treating physician
3. Serious or unstable medical or psychological comorbidities that, in the opinion of the investigator, would compromise the subject's safety or successful participation in the study.
4. Females who are pregnant or breast feeding at the time of screening will not be eligible for this study; a urine pregnancy test will be performed in women of child-bearing potential at screening.