Scientists, clinicians, seed companies and others may soon have a new tool in their belt for detecting bacterial pathogens, thanks to a new study by researchers in Penn State's College of Agricultural Sciences.
The research - available online now and slated for publication in the November issue of the Journal of Microbiological Methods - details a new method for detecting Pseudomonas syringae, common bacteria that infect a wide variety of crops, vegetables and woody ornamentals.
The cost is similar to the traditional method, called enzyme-linked immunosorbent assay or ELISA. However, the researchers' new method - called enzyme-linked chaperone assay or ELCA - has the potential to detect only living bacteria, making it more sensitive and accurate.
Rachel Herschlag, lead author on the paper who earned her doctorate in plant pathology at Penn State, said the study is a proof of concept, with opportunity in the future to adapt the method for detecting other pathogens.
"Now that we've documented this method, researchers can adapt it for other bacteria that have a similar system," she said. "This could include some animal and human pathogens in addition to those affecting plants, expanding its potential utility in clinical, agricultural, environmental and biotechnology applications."
Carolee Bull, professor of bacterial systematics and plant pathology and co-author of the paper, said that many current diagnostic tests like ELISA work by using animal-derived antibodies produced to fight an infection. However, the new method uses a different mechanism.
"I asked Dr. Herschlag to think creatively about bacterial pathogen detection to develop novel strategies for detecting Pseudomonas strains, and potentially, other types of bacteria," Bull said. "She went on to develop this technique by using the same mechanism that many pathogens use to invade their hosts to allow us to recognize them."
When bacteria attack plants, animals or people, they deliver specialized proteins called effectors into the host's cells, she explained. These proteins help the bacteria overcome the host's immune system and invade the organism.
To do this efficiently, many bacteria rely on helper proteins called chaperones that recognize and bind - like a lock and key - to these effectors with high specificity. The chaperones protect the effectors, which are vulnerable to degradation.
The new method relies on this process, rather than the labor-intensive process of harvesting antibodies in a lab.
"Different from other diagnostics, this new method uses a bacterial chaperone to recognize and bind to its matching effector protein," Herschlag said. "This then triggers a colorless solution to turn yellow, providing an easy visual signal that the target is present. And because this interaction is highly specific, the method can reliably detect its intended target."
Other diagnostic approaches, the researchers explained, work by detecting specific parts of the cell such as DNA. However, since these parts exist even after bacteria have died, this can produce false positives. The researchers said what's most helpful about this new technique is that effectors are only produced by living bacteria.
"Because effectors are thought to degrade quickly, effectors from dead bacteria likely do not survive very long," Herschlag said. "Thus, ELCA can detect living bacteria, or in other words, those that are actually capable of causing infections. Indeed, we showed that living bacteria had higher levels of detection than dead bacteria."
In the future, the researchers said next steps will be to optimize the test by reducing background signal, along with adapting the concept for other pathogens that have comparable chaperone-effector systems, including some that are relevant to agriculture, veterinary science and human health.
This research was supported by the U.S. Department of Agriculture National Institute of Food and Agriculture Federal Appropriations under project number PEN04926 and accession number 7006350 and Specialty Crop Research Initiative grants 2019-51181-30019 and 2026-51181-46425. This content is solely the responsibility of the authors and does not necessarily represent the official views of the funders.
