People make antibodies on their own all the time, when they’re vaccinated or infected, but in many Klebsiella infections, Fries said, the antibodies come too late. “If you can make the antibodies in the laboratory and give them to the patient early in the infection, when they haven’t made their own yet, you can help them fight the infection.” So far, her team has produced monoclonal Klebsiella antibodies in mice, and are now investigating ways of “humanizing” the antibody, or changing its protein structure to make it match the structure of a human B cell. “Once you humanize the antibodies,” she said, “then you have a product you can get FDA approved for use in human patients.”
Acinetobacter baumannii: An Immunologist’s Nightmare
An ESKAPE pathogen of particular concern to VA researchers is Acinetobacter baumannii, a Gram-negative bacterium that can form biofilms and adhere to surfaces for extended periods of time, or become airborne in water vapor. A. baumannii’s natural habitat is still unknown, as it’s rarely found outside hospital environments. Last year, the World Health Organization named multidrug-resistant A. baumannii as one of its three most critical priorities. In health care settings, the organism is notoriously difficult to eradicate, and has evolved a vigorous resistance to antibiotics, including carbapenems.
In the mid-2000s, A. baumannii was the cause of an outbreak among wounded service members returning from the Middle East, particularly from Iraq, earning it the nickname “Iraqibacter.” As patients moved from one level of care to another – from forward facilities to Landstuhl Regional Medical Center in Germany to stateside hospitals such as Walter Reed Army Medical Center and Brooke Army Medical Center – many became infected and brought the organism with them, where it infected others.
Last year, the World Health Organization named multidrug-resistant A. baumannii as one of its three most critical priorities. In health care settings, the organism is notoriously difficult to eradicate, and has evolved a vigorous resistance to antibiotics, including carbapenems.
A. baumannii’s strong antibiotic resistance has turned an organism with a relatively low level of virulence into a killer, said Philip Rather, Ph.D., professor of microbiology at Emory University School of Medicine and a research career scientist at the Atlanta VA Medical Center. Estimates of the mortality rates of A. baumannii-infected patients vary widely; Rather puts it at between 25 and 60 percent, depending on the patient population. Most who are infected with A. baumannii are already sick or wounded, “so, they’re already weakened to begin with,” Rather said. “And some of these strains now are just very difficult to treat with antibiotics. And in fact, some strains are completely resistant to every available antibiotic.”
As Rather and his investigative team have discovered, one of the features that makes A. baumannii so dangerous is its ability to switch back and forth from an avirulent form – one that does not cause disease – to a virulent pathogen. Either form will be attacked by the body’s immune system, he said, but the virulent form typically survives by throwing up defenses. At lower temperatures in the surrounding environment, Rather’s team believes, the avirulent form has a survival advantage, lying low until it’s taken up by a host.
In spring 2018, Rather and his team at Emory’s Antibiotic Resistance Center, which includes another VA investigator, David Weiss, Ph.D., reported not only that they’d discovered how A. baumannii performs this switch – with a regulatory gene, ABUW_1645 – but also that they’d figured out how to manipulate that switch, turning the virulent form back into an avirulent one. “We’ve now been able to show that when you lock cells into that avirulent form,” Rather said, “they act as an incredibly effective vaccine, at least in animal models.”
After Rather’s team has demonstrated the vaccine’s effectiveness and ability to keep the avirulent cells “locked” in animal models, it hopes to move on to clinical trials. The ability to flip A. baumannii’s virulence switch may also enable treatments for already infected patients. “We could identify chemicals we could treat humans with,” he said, “and if the chemical causes all the virulent cells to switch to avirulent, our immune system would clear them almost immediately, and it could be a next generation of therapies for this bacterium.”
Among the first VA researchers to study A. baumannii isolates from U.S. military hospitals was Robert A. Bonomo, M.D., professor at Case Western Reserve University (CWRU) School of Medicine and chief of medical service at the Louis Stokes Cleveland VA Medical Center. By mapping the genes of these organisms, Bonomo and Dr. Mark Adams, also of CWRU, found that not only were A. baumannii strains evolving to become more resistant, but that several strains had multiple genes conferring resistance to multiple antibiotics. “There were some isolates that had never seen certain antibiotics before,” he said, “that were already resistant to them, even before those antibiotics were used to treat them.”
The ability to flip A. baumannii’s virulence switch may also enable treatments for already infected patients.
Bonomo and Adams mapped out the entire genome of one of these early multidrug-resistant organisms from the outbreak at Walter Reed Army Medical Center, and have now published about 70 papers on A. baumannii, attempting to understand its resistance genes and looking at novel combinations to treat multidrug-resistant strains. Two years ago, they were part of a U.S.-Argentinian study that discovered how an A. baumannii bacillus and other MDROs could make themselves immune to antibiotics they had never seen before: They had devised several ways of sharing genes with other bacteria, one of which was a new wrinkle in bacterial genetic exchanges. The team, led by Dr. Alejandro Vila, observed MDROs sloughing off little bits of their protective outer membranes and sharing them with other bacteria: “… kind of like little blebs of lipids, with enzymes or genes in them,” said Bonomo, “that go off the surface of MDROs onto the surface of another cell and fuse with the surface of that cell, and directly transfer the gene, as well as the protein, over to the other recipient.”
Understanding this particular defense mechanism may aid researchers in designing an attack, and Bonomo, Vila, and colleagues have since widened their focus. “We’ve also, with the support of the VA, tried to understand how other carbapenem-resistant bacteria, or bacteria that are resistant to our last-resort antibiotics, evolved.” They’ve studied carbapenem-resistant K. pneumoniae and P. aeruginosa, and recently began working with Brad Spellberg, M.D., an immunologist at the University of Southern California, to generate a monoclonal antibody that might be used as a vaccine against A. baumannii. In collaboration with Rather at Emory, Bonomo also studies the impact of new drugs on bacteria with altered transport systems.
Bonomo is a standout among VA researchers: In 2017, he received the William S. Middleton Award, the highest honor awarded annually by the department’s Biomedical Laboratory R&D Service to senior research scientists for their outstanding contributions in areas of prime importance to the VA research mission. But like many VA investigators, Bonomo is also a clinician, and he and his colleagues never lose sight of what this micro-level research is all about: “The people who do research in the VA are very dedicated to the welfare of their patients, and are hopeful of eventual cures. Our lab is driven not just by science, but by a desire to bring good therapies to patients, to prolong life, and mitigate suffering,” he said. “We’re privileged to take care of veterans.”
This article was originally published in the 2018 Fall edition of Veterans Affairs & Military Medicine Outlook By Faircount, LLC