Getting Antibiotics Where They Need To Go

Tacy CalliesHLB Management, Research

Kurt Ristroph holds nanocarrier treatments being tested for treatment of HLB.
(Purdue University photo by Tom Campbell)

Purdue University’s Kurt Ristroph has received a $1 million federal grant to develop nanocarriers as an antibiotic delivery system to help plants fend off citrus greening disease, also known as HLB. The grant is part of the 21.7 million recently awarded for HLB research from the U.S. Department of Agriculture’s National Institute of Food and Agriculture.

“The mixing technology we’re using to make nanocarriers is the same that has been used by pharmaceutical companies like Pfizer,” said Ristroph, assistant professor of agricultural and biological engineering. Collaborating on the project with Ristroph are Greg Lowry, Carnegie Mellon University in Pittsburgh; Arnold Schumann, University of Florida; and Philippe Rolshausen, University of California, Riverside.

HLB bacteria live inside the trunks and roots of trees, attacking their vascular systems. Previous attempts to kill the bacteria with antibiotics have failed. “It’s difficult to reach the location in the tree trunk where the bacteria live,” Ristroph said. The bacteria live in the phloem of a tree’s vascular system.

One approach has been to bore a hole into the tree trunk and inject the antibiotics with a syringe, “but you don’t have a good guarantee that you’re going to the phloem,” Ristroph said. “And if you don’t, then you’ve just done a lot of damage to your tree.”

Another issue: The bacteria live in the phloem of both the trunks and the roots. If an injection kills only the bacteria in the trunk, they can repopulate from the roots back into the tree.

“We’ve shown that our nanocarriers, at least in another plant system, can get into the phloem and down to the roots,” Ristroph said. “If we make our nanocarriers encapsulate an antibiotic that will kill this disease, then put them on the leaves of a tree, we think they’ll go inside the tree, down the phloem to the roots, and they’ll release their antibiotic drug along the way. Maybe it can kill all the bacteria and maybe it can cure the disease.”

“We’re using antibiotics that have already been approved for citrus greening,” Ristroph said. “We have to get them where they need to go in the plant. We’re going to have to be incredibly effective to show that we can cure the trees.”

Ristroph received the USDA grant only two months after he joined Purdue’s faculty last August. He already has built a research group consisting of one postdoctoral scientist, three graduate students and two undergraduates. Half the group works on drugs for plants, while the other half works on drugs for people. 

Source: Purdue University