A new paper in PNAS from Emory scientists highlights a neat example of bacterial evolution and adaptation related to sexually transmitted infections. Neisseria meningitidis, a bacterium usually associated with meningitis and sepsis, sometimes appears in the news because of cases on college campuses or other outbreaks.
Genetic changes make this clade look more like relatives that are known to cause gonorrhea. Some good news is that these guys are less likely to cause meningitis because they have lost their outer capsule. They have also gained enzymes that help them live in low oxygen.
The DNA analysis helps doctors track the spread of this type of bacteria and anticipate which vaccines might be protective against it. Thankfully, no alarming antibiotic resistance markers are present (yet) and currently available vaccines may be helpful. Full press release here, and information about meningococcal disease from the CDC here.
This looks like a well-worn path in bacterial evolution, since N. gonorrhoeae is thought to have evolved from N. meningitidis and there are recent independent examples of N. meningitidis adapting to the urogenital environment.
If you’ve been following the news about antibiotic resistant bacteria, you may have heard about a particularly alarming plasmid: MCR-1. A plasmid is a circle of DNA that is relatively small and mobile – an easy way for genetic information to spread between bacteria. MCR-1 raises concern because it provides bacteria resistance against the last-resort antibiotic colistin. The CDC reports MCR-1 was found in both patients and livestock in the United States this summer.
This suggests that the pressure of fighting the host immune system may select for MCR-1 to stick around, even in the absence of colistin use, the authors say.
While the findings are straightforward in bacterial culture, Weiss cautions that there is not yet evidence showing that this mechanism occurs in live hosts. For those that really want to get alarmed, he also calls attention to a recent Nature Microbiology paper describing a hybrid plasmid with both MCR-1 and resistance to carbapenem, another antibiotic.
A diagnostic test used by hospitals says a recently isolated strain of bacteria is susceptible to the “last resort” antibiotic colistin. But the strain actually ignores treatment with colistin, causing lethal infections in animals.
Through heteroresistance, a genetically identical subpopulation of antibiotic-resistant bacteria can lurk within a crowd of antibiotic-susceptible bacteria. The phenomenon could be causing unexplained treatment failures in the clinic and highlights the need for more sensitive diagnostic tests, researchers say.
“Heteroresistance has been observed previously and its clinical relevance debated,” Weiss says. “We were able to show that it makes a difference in an animal model of infection, and is likely to contribute to antibiotic treatment failures in humans.”
Weiss is director of the Emory Antibiotic Resistance Center and associate professor of medicine (infectious diseases) at Emory University School of Medicine and Emory Vaccine Center. His laboratory is based at Yerkes National Primate Research Center. The co-first authors of the paper are graduate students Victor Band and Emily Crispell.
The capsule study, published Monday in Journal of Infectious Diseases, represents an important step in moving away from fecal microbiota transplant as a treatment for C. difficile, says Colleen Kraft, MD, assistant professor of pathology and laboratory medicine and medicine (infectious diseases) at Emory University School of Medicine.
While this study involving 30 patients did not include a control group, the reported effectiveness of 96.7 percent compares favorably to published results on antibiotic treatment of C. difficile infection or fecal microbial transplant. Read more
One of the speakers at Thursday’s Antibiotic Resistance Center symposium, Gerald Wright from McMaster University, made the case for fighting antibiotic resistance by combining known antibiotics withÂ non-antibiotic drugs that are used to treat other conditions, which he called adjuvants.
As an example, he cited this paper, in which his lab showed that loperamide, known commercially as the anti-diarrhealÂ Immodium, can make bacteria sensitive toÂ tetracycline-type antibiotics.
Wright said that other commercial drugs and compounds in pharmaceutical companies’ libraries could have similar synergistic effects when combined with existing antibiotics. Most drug-like compounds aimed at human physiology follow “Lipinski’s rule of five“, but the same rules don’t apply to bacteria, he said. What might be a more rewarding place to look for more anti-bacterial compounds? Natural products from fungi and plants, Wright proposed.
“I made a little fist-pump when he said that,” says Emory ethnobotanist Cassandra Quave, whose laboratory specializing in looking for anti-bacterial activities in medicinal plants.
Medical ethnobotanist Cassandra Quave collecting plant specimens in Italy
Indeed, many of the points he made on strategies to overcome antibiotic resistance could apply to Quave’s approach. SheÂ and her colleagues have been investigatingÂ compounds that can disruptÂ biofilms, thusÂ enhancingÂ antibiotic activity. More at eScienceCommonsÂ and at her lab’s site.
To prevent auto-immune attack, our bodies avoid making antibodies against molecules found on our own cells. That leaves gaps in our immune defenses bacteria could exploit. Some of those gaps are filled by galectins, a family of proteins whose anti-bacterial properties were identified by Emory scientists.
In the accompanying video, Sean Stowell, MD, PhD and colleagues explain how galectins can be compared to sheep dogs, which are vigilant in protecting our cells (sheep) against bacteria that may try to disguise themselves (wolves).
The video was produced to showcase the breadth of research being conducted within Emoryâ€™s Antibiotic Resistance Center. Because of their ability to selectively target some kinds of bacteria, galectins could potentially be used as antibiotics to treat infections without wiping out all the bacteria in the body. Read more
Part of the problem of antibiotic resistanceÂ involves physiciansâ€™ habits. Doctors are used to prescribing antibiotics in certain situations, even when they may be inappropriate or when alternatives may be best. However, they may be susceptible to â€œnudgesâ€, even if health care organization policies donâ€™t formally restrict their choices. Former White House regulatory policy guru Cass Sunstein has written several books on this concept.
In March 2015, MD/PhD student Kira Newman and colleagues published a studyÂ in Journal of General Internal Medicine that has some bearing on this idea, althoughÂ it doesnâ€™t address antibiotic resistance directly:
The authors describe a shift involving the Emory University hospital electronic health record and order entry system. When a patient has systemic or urinary tract bacterial infection, the system shows a table of antibiotic sensitivity data alongside blood or urine culture results.
Beginning in May 2010, cost category data for antibiotics were added. Explicit numbers were not included â€“ too complicated. Instead, the information was coded in terms of $ to $$$$. For the year after the change, the authors report a 31 percent reduction in average cost per unit of antibiotics prescribed. Read more
Evolutionary theory says mutations are blind and occur randomly. But in theÂ controversialÂ phenomenon of adaptive mutation, cells can peek under the blindfold, increasing their mutation rate in response to stress.
Scientists at Winship Cancer Institute, Emory University have observed that an apparent “back channel” for genetic information called retromutagenesis can encourage adaptive mutation to take place in bacteria.
“This mechanism may explain how bacteria develop resistance to some types of antibiotics under selective pressure, as well as how mutations in cancer cells enable their growth or resistance to chemotherapy drugs,” says senior author Paul Doetsch, PhD.
Doetsch is professor of biochemistry, radiation oncology and hematology and medical oncology at Emory University School of Medicine and associate director of basic research at Winship Cancer Institute. The first author of the paper is Genetics and Molecular Biology graduate student Jordan Morreall, PhD, who defended his thesis in April.
Retromutagenesis resolves the puzzle: if cells arenâ€™t growing because theyâ€™re under stress, which means their DNA isnâ€™t being copied, how do the new mutants appear?
The answer: a mutation appears in the RNA first. Read more
Emory is preparing to launch a center devoted to antibiotic resistance. On Wednesday, Arjun Srinivasan, one of the CDCâ€™s point people for antibiotic use and hospital acquired infections, kicked off the preparations with a talk on the multifaceted nature of this problem.
Without attempting to cover everything related to antibiotic resistance (that would take a bookÂ — or several), I willÂ note in an upcoming post how Emory and partners such asÂ Childrenâ€™s Healthcare of Atlanta already haveÂ begun assembling many of the necessary tools.
Tackling antibiotic resistance has to take into account the habits of physicians, the expectations of patient, improved surveillance and antibiotic overuse in agriculture, as well as research on new antibiotics and detecting dangerous bacteria. In short, itâ€™s both a science and policy issue — captured well by the documentary Resistance.
At the end of his talk, Srinivasan made a remark that brought this home for me, saying â€œWe just have to push all the boulders up the hill at the same timeâ€ in response to a question about balancing effort on science vs policy. Allusions to Sisyphus!
Yet he provided some hope too, highlighting a recent CDC studyÂ that models how a coordinated response to antibiotic resistance in health care facilities could substantially cut infections. Read more
Resistance to an entire class of antibiotics â€“ aminoglycosides — has the potential to spread to many types of bacteria, according to new biochemistry research.
A mobile gene called NpmA was discovered inÂ E. coliÂ bacteria isolated from a Japanese patient several years ago. Global spread of NpmA and related antibiotic resistance enzymes could disable an entire class of tools doctors use to fight serious or life-threatening infections.
Using X-ray crystallography, researchers at Emory made an atomic-scale snapshot of how the enzyme encoded by NpmA interacts with part of the ribosome, protein factories essential for all cells to function. NpmA imparts a tiny chemical change that makes the ribosome, and the bacteria, resistant to the drugsâ€™ effects.
The results, published in PNAS, provide clues to the threat NpmA poses, but also reveal potential targets to develop drugs that could overcome resistance from this group of enzymes.
First author of the paper is postdoctoral fellow Jack Dunkle, PhD. Co-senior authors are assistant professor of biochemistry Christine Dunham, PhD and associate professor of biochemistry Graeme Conn, PhD. Read more