GLA Research Grantees

A mouse model of neurological Lyme disease would be helpful in understanding how patients develop symptoms and how to treat them. Until now, laboratory mice have not developed neuroborreliosis, which mimics human disease with demonstrated colonization of the central nervous system. However, a new report by Divan et al. gives hope that this may be possible. Using two different strains of B. burgdorferi and infecting mice via the skin, the researchers were able to consistently detect spirochetes in the membranes that surround the brain, called the dura and pia mater. Particularly compelling was the fact that they detected spirochetes 75 days after infection, adhering to blood vessels in the dura and pia mater, and that replicating spirochetes could be cultured from these samples. This suggests that long after acute infection, live spirochetes were still present at these sites. There were also more CD3+ T cells present in the dura of infected animals than in uninfected animals, suggesting an immune response. These findings open the door to new ways of studying neuroborreliosis in vivo. By identifying a site in the brain that is consistently colonized by spirochetes, as well as suggesting which immune pathways may be affected, further studies may reveal potential ways to alleviate the suffering of neuroborreliosis patients.

About 10-20% of Lyme disease patients treated with antibiotics continue to suffer debilitating symptoms, known as post-treatment Lyme disease. It is not understood whether this is due to an inappropriate immune response or continued Borrelia bacterial replication. In vitro laboratory experiments have showed that persister forms of bacteria are difficult to eliminate with antibiotics. This is because persisters are very slow-growing, and most antibiotics target actively-replicating bacteria. Limited clinical observations suggested some efficacy of dapsone, a sulfa drug, which belongs to a class of antibiotics not commonly used to treat Lyme disease. To test this drug against persister forms, Dr. Ying Zhang’s group studied sulfamethoxazole, dapsone, and sulfachlorpyridazine singly as well as in combination. By themselves, these drugs had similar efficacy as doxycycline, with 59-92% of stationary bacteria still alive after treatment. Their bacteria-killing activity was weak compared to daptomycin, which when used at the same concentrations, resulted in 26-52% of remaining cell viability. As combinations, they could not completely eradicate persister bacteria, with 74-77% bacteria remaining viable after treatment. But when they were combined with non-sulfa drugs like doxycycline, cefuroxime, ciprofloxacin, rifampin, and azithromycin, the rate of bacterial killing was higher. The most effective combinations included daptomycin. Further research will identify effective combinations that will more completely eradicate persister bacteria in vitro and in patients.

At least 10% of patients treated with antibiotic therapy for Lyme disease continue to suffer persisting symptoms. The reason for this is unknown, but one suspect is the continued survival of persisting forms of B. burgdorferi, the bacterium responsible for Lyme disease. In the test tube, Zhang and colleagues have grown one form of persisting bacteria known as biofilms, and used it to test various combinations of antibiotics. They also compared single continuous dosing versus pulse-dosing, which consists of repeated cycles of adding and removing antibiotics. They found that pulse-dosing was not effective for all antibiotics, and in fact reduced the activity of daptomycin against persisters. The best strategy they found against biofilm-like persisters was a single dose of a combination of daptomycin, doxycycline, and cefuroxime. They also showed that bacteriocidal drugs, which kill bacteria, are better used in pulse dosing than bacteriostatic drugs, which block bacterial replication but do not directly kill them. These promising in vitro data pave the way for animal model studies. If the findings prevail, they may suggest that future human trials are warranted.