Bacterial infections are one of the major causes of death worldwide. Even in hospitals, patients often contract infections from the bacteria-filled surroundings. Recently, researchers at the Hopkins School of Medicine have developed a diagnostic system that has the potential of pinpointing superbug infection sites within patients, helping doctors combat their spread.
Infections in hospitals are more dangerous than many people realize. Because of the frequent use of antibiotics by doctors, a lot of bacteria have developed drug-resistant traits. These bacteria are often referred to as superbugs because they are hard to treat with medications. A report in Infection Control and Hospital Epidemiology states that there is a five-fold increase in superbug infections from 2008 to 2012. Furthermore, the study reveals that almost 50 percent of patients with superbug infections died. While the study focused on clinics and hospitals in the southeastern U.S., the grim statistics serve as a warning for the risk of infections in hospitals.
Sanjay Jain, a specialist of infectious diseases, and his team combined the characteristics of a positron emission tomography (PET) scan and innovative compounds to mark areas with superbug infections. The imaging system relies on chemical tags that specifically adhere to a subcategory of Gram-negative bacteria. Gram-negative bacteria have a characteristically thin layer of peptidoglycan, a type of polymer, on the outside of their cell membranes. During Gram staining, the thin layer does not take on the stain, giving the bacteria its name. Gram-negative bacteria is further divided into subcategories with Enterobacteriaceae being the most common in human infections. The chemical tags developed by the team targets this class of bacteria.
The innovative tracer relies on the metabolism of Gram-negative bacteria. These bacteria utilize sorbitol for their metabolic functions. Sorbitol, often used in sugar-free gum, is modified with a radio label, which will cause it to show up on a PET scan. The Gram-negative bacteria such as Salmonella and Escherichia coli readily absorb sorbitol while other cells of the body absorb a negligent amount. This creates a sorbitol concentration difference between Gram-negative cells and other cells within the body.
When the radio-labeled sorbitol is imaged with a PET scanner, the areas with high sorbitol concentration show up lighter than places with low or nonexistent sorbitol levels. Furthermore, because the PET scanner lights up areas in which sorbitol is concentrated, it provides a method for doctors to determine whether an inflammation is caused by bacteria. Some infections, such as those that happen from blunt trauma, are referred to as sterile infections; they pose a lower risk since they are not infectious. The new imaging method can allow doctors to distinguish between infectious and noninfectious inflammation because infectious inflammation is caused by the effects of bacteria.
To demonstrate the effectiveness of the system, the researchers induced either infectious or noninfectious inflammation in two groups of mice. After injecting the mice with radio-labeled sorbitol and imaged with a PET scanner, mice with infectious inflammation could be distinguished from those with sterile infections. The mice with infectious inflammation showed an obvious difference in the brightness of the area of infection due to the higher concentration of sorbitol.
In addition, the team tested the method against cancer-induced infections. The PET scan was able to distinguish between tumor-induced and infectious inflammation through comparison of the two images.
The prevalence of superbugs within U.S. hospitals poses an additional risk to patients and their families. Even with a successful operation, the mortality rate of post-operative patients remains high.
However, the new imaging technique offers a way to reduce the overall risks. With a reliable system for detecting infectious inflammation, doctors will be able to more accurately diagnose and treat the disease, providing a higher quality care.
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