hospital acquired infections
Building a Better Bacterial Trap for Sepsis
Posted on by Dr. Francis Collins
Spiders spin webs to catch insects for dinner. It turns out certain human immune cells, called neutrophils, do something similar to trap bacteria in people who develop sepsis, an uncontrolled, systemic infection that poses a major challenge in hospitals.
When activated to catch sepsis-causing bacteria or other pathogens, neutrophils rupture and spew sticky, spider-like webs made of DNA and antibacterial proteins. Here in red you see one of these so-called neutrophil extracellular traps (NETs) that’s ensnared Staphylococcus aureus (green), a type of bacteria known for causing a range of illnesses from skin infections to pneumonia.
Yet this image, which comes from Kandace Gollomp and Mortimer Poncz at The Children’s Hospital of Philadelphia, is much more than a fascinating picture. It demonstrates a potentially promising new way to treat sepsis.
The researchers’ strategy involves adding a protein called platelet factor 4 (PF4), which is released by clot-forming blood platelets, to the NETs. PF4 readily binds to NETs and enhances their capture of bacteria. A modified antibody (white), which is a little hard to see, coats the PF4-bound NET above. This antibody makes the NETs even better at catching and holding onto bacteria. Other immune cells then come in to engulf and clean up the mess.
Until recently, most discussions about NETs assumed they were causing trouble, and therefore revolved around how to prevent or get rid of them while treating sepsis. But such strategies faced a major obstacle. By the time most people are diagnosed with sepsis, large swaths of these NETs have already been spun. In fact, destroying them might do more harm than good by releasing entrapped bacteria and other toxins into the bloodstream.
In a recent study published in the journal Blood, Gollomp’s team proposed flipping the script [1]. Rather than prevent or destroy NETs, why not modify them to work even better to fight sepsis? Their idea: Make NETs even stickier to catch more bacteria. This would lower the number of bacteria and help people recover from sepsis.
Gollomp recalled something lab member Anna Kowalska had noted earlier in unrelated mouse studies. She’d observed that high levels of PF4 were protective in mice with sepsis. Gollomp and her colleagues wondered if the PF4 might also be used to reinforce NETs. Sure enough, Gollomp’s studies showed that PF4 will bind to NETs, causing them to condense and resist break down.
Subsequent studies in mice and with human NETs cast in a synthetic blood vessel suggest that this approach might work. Treatment with PF4 greatly increased the number of bacteria captured by NETs. It also kept NETs intact and holding tightly onto their toxic contents. As a result, mice with sepsis fared better.
Of course, mice are not humans. More study is needed to see if the same strategy can help people with sepsis. For example, it will be important to determine if modified NETs are difficult for the human body to clear. Also, Gollomp thinks this approach might be explored for treating other types of bacterial infections.
Still, the group’s initial findings come as encouraging news for hospital staff and administrators. If all goes well, a future treatment based on this intriguing strategy may one day help to reduce the 270,000 sepsis-related deaths in the U.S. and its estimated more than $24 billion annual price tag for our nation’s hospitals [2, 3].
References:
[1] Fc-modified HIT-like monoclonal antibody as a novel treatment for sepsis. Gollomp K, Sarkar A, Harikumar S, Seeholzer SH, Arepally GM, Hudock K, Rauova L, Kowalska MA, Poncz M. Blood. 2020 Mar 5;135(10):743-754.
[2] Sepsis, Data & Reports, Centers for Disease Control and Prevention, Feb. 14, 2020.
[3] National inpatient hospital costs: The most expensive conditions by payer, 2013: Statistical Brief #204. Torio CM, Moore BJ. Healthcare Cost and Utilization Project (HCUP) Statistical Briefs. Agency for Healthcare Research and Quality (US); 2016 May.
Links:
Sepsis (National Institute of General Medical Sciences/NIH)
Kandace Gollomp (The Children’s Hospital of Philadelphia, PA)
Mortimer Poncz (The Children’s Hospital of Philadelphia, PA)
NIH Support: National Heart, Lung, and Blood Institute
Some ‘Hospital-Acquired’ Infections Traced to Patient’s Own Microbiome
Posted on by Dr. Francis Collins
Caption: New computational tool determines whether a gut microbe is the source of a hospital-acquired bloodstream infection
Credit: Fiona Tamburini, Stanford University, Palo Alto, CA
While being cared for in the hospital, a disturbingly large number of people develop potentially life-threatening bloodstream infections. It’s been thought that most of the blame lies with microbes lurking on medical equipment, health-care professionals, or other patients and visitors. And certainly that is often true. But now an NIH-funded team has discovered that a significant fraction of these “hospital-acquired” infections may actually stem from a quite different source: the patient’s own body.
In a study of 30 bone-marrow transplant patients suffering from bloodstream infections, researchers used a newly developed computational tool called StrainSifter to match microbial DNA from close to one-third of the infections to bugs already living in the patients’ large intestines [1]. In contrast, the researchers found little DNA evidence to support the notion that such microbes were being passed around among patients.
Has an Alternative to Table Sugar Contributed to the C. Diff. Epidemic?
Posted on by Dr. Francis Collins
Thinkstock/piyaphat50
Most of us know how hard it is to resist the creamy sweetness of ice cream. But it might surprise you to learn that, over the past 15 years or so, some makers of ice cream and many other processed foods—from pasta to ground beef products—have changed their recipes to swap out some of the table sugar (sucrose) with a sweetening/texturizing ingredient called trehalose that depresses the freezing point of food. Both sucrose and trehalose are “disaccharides.” Though they have different chemical linkages, both get broken down into glucose in the body. Now, comes word that this switch may be an important piece of a major medical puzzle: why Clostridium difficile (C. diff) has emerged as a leading cause of hospital-acquired infections.
A new study in the journal Nature indicates that trehalose-laden food may have helped fuel the recent epidemic spread of C. diff., which is a microbe that can cause life-threatening gastrointestinal distress, especially in older patients getting antibiotics and antacid medicines [1, 2]. In laboratory experiments, an NIH-funded team found that the two strains of C. diff. most likely to make people sick possess an unusual ability to thrive on trehalose, even at very low levels. And that’s not all: a diet containing trehalose significantly increased the severity of symptoms in a mouse model of C. diff. infection.
Snapshots of Life: Portrait of a Bacterial Biofilm
Posted on by Dr. Francis Collins
Credit: Scott Chimileski and Roberto Kolter, Harvard Medical School, Boston
In nature, there is strength in numbers. Sometimes, those numbers also have their own unique beauty. That’s the story behind this image showing an intricate colony of millions of the single-celled bacterium Pseudomonas aeruginosa, a common culprit in the more than 700,000 hospital-acquired infections estimated to occur annually in the United States. [1]. The bacteria have self-organized into a sticky, mat-like colony called a biofilm, which allows them to cooperate with each other, adapt to changes in their environment, and ensure their survival.
In this image, the Pseudomonas biofilm has grown in a laboratory dish to about the size of a dime. Together, the millions of independent bacterial cells have created a tough extracellular matrix of secreted proteins, polysaccharide sugars, and even DNA that holds the biofilm together, stained in red. The darkened areas at the center come from the bacteria’s natural pigments.
Portable System Uses Light to Diagnose Bacterial Infections Faster
Posted on by Dr. Francis Collins
Caption: PAD system. Left, four optical testing cubes (blue and white) stacked on the electronic base station (white with initials); right, a smartphone with a special app to receive test results transmitted by the electronic base station.
Credit: Park et al. Sci. Adv. 2016
Every year, hundreds of thousands of Americans acquire potentially life-threatening bacterial infections while in the hospital, nursing home, or other health-care settings [1]. Such infections can be caused by a variety of bacteria, which may respond quite differently to different antibiotics. To match a patient with the most appropriate antibiotic therapy, it’s crucial to determine as quickly as possible what type of bacteria is causing his or her infection. In an effort to improve that process, an NIH-funded team is working to develop a point-of-care system and smartphone app aimed at diagnosing bacterial infections in a faster, more cost-effective manner.
The portable new system, described recently in the journal Science Advances, uses a novel light-based method for detecting telltale genetic sequences from bacteria in bodily fluids, such as blood, urine, or drainage from a skin abscess. Testing takes place within small, optical cubes that, when placed on an electronic base station, deliver test results within a couple of hours via a simple readout sent directly to a smartphone [2]. When the system was tested on clinical samples from a small number of hospitalized patients, researchers found that not only did it diagnose bacterial infections about as accurately and more swiftly than current methods, but it was also cheaper. This new system can potentially also be used to test for the presence of antibiotic-resistant bacteria and contamination of medical devices.
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