Dr. Catherine Logue addressed the 2017 Iowa Egg Symposium with enthusiasm as she discussed some of the advances being made in poultry infectious disease work. Logue, who moved from Iowa State University to the College of Veterinary Medicine at the University of Georgia, is excited to be working with veterinarians and researchers around the world to characterize the genomic data surrounding Avian Pathogenic Escherichia coli (APEC). This work has led to research regarding the mechanisms by which organisms cause disease and their resistance to things like antibiotics and disinfectants.
“The idea has always been that E. coli comes in as a secondary pathogen,” said Logue. “However, we now actually know that E. coli itself can be a primary pathogen.” She explained that approaches to deal with this are management, such as stress reduction, and improvement of overall flock health, as well as disinfectants and antibiotics. While vaccines have also been used, they can have limited success because of the diversity of the E. coli they are fighting.
To help address the growing concern of APEC, her team helped develop a quick and effective diagnostic test to determine if a flock has APEC. “We found that if we look at the top five genes we could develop a test that was accurate 80-85% of the time in identifying an E. coli as an APEC.” The parameter for the test is that if three of the five genes are present in the sample, then it is considered APEC.
But why APEC is now considered a primary pathogen and it wasn’t this type of issue years ago is the bigger question. Logue stated that while FDA has chosen to focus on antibiotics as the issue, that approach does not necessarily address some of the biology that is occurring. Logue’s research has dug into those details.
Logue explained that bacteria have various methods of resistance. Mechanisms developed by E. coli to ensure treatments of any kind don’t work include: changes in cell wall permeability, active ejection of the drug back out of the cell, modification or degradation of the treatment to the point that it is ineffective, creation of alternative pathways within the cell instead of using those targeted by the treatment, modification of actual targets the treatment will use, and overproduction of the treatment targets within the cell.
Given all these methods, Logue’s lab started asking if these traits to render antimicrobials useless were being transferred. Research found that there are two types of DNA in bacteria. The first is chromosomal DNA and the second are smaller pieces of DNA called plasmids. Some plasmids are related to virulence (how severe a disease is) and others are focused on antimicrobial resistance. “Some of our work has also found some plasmids that are hybrids consisting of both virulence and resistance genes.”
Logue clarified that other organisms can pick up these plasmids from their environment and keep it, if they deem it beneficial, or they can mate with other bacteria and pass the traits back and forth. “If it is an important enough plasmid and it doesn’t take a lot of energy, then they keep it,” clarified Logue. And that can be a concern when it comes to the resistance traits.
Logue’s research has used past samples ranging over ten-plus years, to determine that a given plasmid with resistance properties is more common now than in the past. “There is an increase in the risk that there is going to be an increase in the prevalence of resistant organisms,” she said. “And I don’t just mean APEC. We have already proven there is clear possibility that these resistances move.” Logue pointed out that this could mean increased risks for Salmonella or Campylobacter.
Logue concluded by explaining that her work really means that on the horizon could be a time someday when producers face an increased risk of diseases in their animals even though we continue to do what we know is right today. In 2017, the industry faces reduced options for antibiotic use. Logue said, “the real challenge will be if we have ill animals and we have nothing left in our arsenal to treat them with.”