Abbas and team use chemiluminescence to detect, identify harmful bacteria within one hour

July 31, 2018
black and white cell shielding photo captured by abbas lab, sized 900 px acrossMacromolecular shielding of microorganisms using polymer conjugated antibodies. These pictures show transmission electron microscopy images of bare (left) and fully shielded (right) bacteria.

Assistant Professor Abdennour Abbas and his research team have developed a method to screen and identify harmful or antibiotic-resistant bacteria within one hour using a portable luminometer. Traditional diagnostic methods often require complex equipment and lab work that can take days.

The new method uses chemiluminescence and was developed with the food industry in mind.

two vials of gold nanoparticles, one is green and one is pinkAssistant Professor Abdennour Abbas and his research team have been conducting basic research on the interactions between gold nanoparticles and cell surfaces to create novel sensors. Differently shaped gold nanoparticles like the flat triangular gold (green solution on left) and spherical gold (red-pink solution on right) not only appear different, but can have very unique interactions with cells that can be exploited to create novel reactions that yield detectable signals like color changes or glowing reactions.

"The big barrier for microbial detection in the food industry is cost and the inability to detect harmful bacteria in a reasonable time," said John Brockgreitens, a graduate student involved in the study with Postdoctoral Research Associate Minh-Phuong Ngoc Bui in Abbas’ research laboratory in the Department of Bioproducts and Biosystems Engineering. "We’re trying to develop an inexpensive and rapid way for microbial detection that can be used without needing extensive training."

In addition to its uses in the food industry, this method could also be used in healthcare settings. "Rapid microbial detection in less than two hours is not only vital to prevent food poisoning, but also to fight antimicrobial resistance by helping physicians make informed decisions before prescribing antibiotics," Abbas said.

According to the Centers for Disease Control and Prevention (CDC), "At least 2 million people become infected with bacteria that are resistant to antibiotics and at least 23,000 people die each year in the United States as a direct result of these infections."

In the study published as a frontispiece article in Advanced Healthcare Materials, the researchers demonstrated the new technology by analyzing surface swabs and urine samples for the presence of small concentrations of methicillin-resistant Staphylococcus aureus (MRSA), a bacteria that causes more than 11,000 deaths in the U.S. every year.

"More work is needed to apply this technology to more complex samples such as food and crops," Abbas said.

"Our initial inspiration was to look at nanoparticle interactions with cells and how we can translate that to a sensing reaction, specifically sensors for food safety," Brockgreitens said.

To screen for microorganisms, triangular gold nanoplates were combined with a reducing agent and luminol. This caused a strong chemiluminescent reaction that was stable for as long as 10 minutes. When researchers introduced MRSA and other microorganisms into the combination, they consumed the gold nanoplates, causing the chemiluminescent intensity to decrease proportionally to the microbial concentration. This indicated a presence of microorganisms.

frontispiece image of abbas research in advanced healthcare materialsThe frontispiece of "Advanced Healthcare Materials" featuring a new rapid microbial detection method developed by Professor Abbas and his research team.

To take it one step further, researchers introduced a new concept called microbial macromolecular shielding to specifically identify MRSA. A polymer specific to MRSA was added to the same sample where it engulfed and surrounded the MRSA bacteria, preventing them from consuming the gold nanoplates. This increased chemiluminescence intensity, indicating the presence of MRSA.

"We know our direction is to keep looking at some of these cellular interactions and how to make this whole process either automated or a one-step process," Brockgreitens said.

Another big challenge is improving how specific cells can be removed or isolated from other cells or parts.

"In the food industry, items like processed meat, cheese, yogurt, and milk have a lot of other competing parts such as proteins and other cells that you need to effectively filter out before you could actually detect what you’re looking for," Brockgreitens said.

Though more work is needed, Brockgreitens believes it is promising. "I do think this is definitely a few years down the line."

Funding for this project includes the National Science Foundation, the University of Minnesota MnDRIVE Global Food Venture, the USDA National Institute of Food and Agriculture, General Mills, Schwan Food Company Graduate Fellowship, and the Midwest Dairy Association.

Read the full published report

Bui MN, Brockgreitens J, Abbas A. Gold Nanoplate-Enhanced Chemiluminescence and Macromolecular Shielding for Rapid Microbial Diagnostics. Advanced Healthcare Materials. 2018;7(13):e1701506. doi: 10.1002/adhm.201701506.