Live Attenuated Borrelia burgdorferi Targeted Mutants in an Infectious Strain Background Protect Mice from Challenge Infection.

Borrelia burgdorferi, B. garinii, and B. afzelii are all agents of Lyme disease in different geographic locations. If left untreated, Lyme disease can cause significant and long-term morbidity, which may continue after appropriate antibiotic therapy has been administered and live bacteria are no longer detectable. The increasing incidence and geographic spread of Lyme disease are renewing interest in the vaccination of at-risk populations. We took the approach of vaccinating mice with two targeted mutant strains of B. burgdorferi that, unlike the parental strain, are avirulent in mice. Mice vaccinated with both strains were protected against a challenge with the parental strain and a heterologous B. burgdorferi strain by either needle inoculation or tick bite. In ticks, the homologous strain was eliminated but the heterologous strain was not, suggesting that the vaccines generated a response to antigens that are produced by the bacteria both early in mammalian infection and in the tick. Partial protection against B. garinii infection was also conferred. Protection was antibody mediated, and reactivity to a variety of proteins was observed. These experiments suggest that live attenuated B. burgdorferi strains may be informative regarding the identification of protective antigens produced by the bacteria and recognized by the mouse immune system in vivo Further work may illuminate new candidates that are effective and safe for the development of Lyme disease vaccines.

The ß3-integrin ligand of Borrelia burgdorferi is critical for infection of mice but not ticks.

P66 is a Borrelia burgdorferi surface protein with ß3 integrin binding and channel forming activities. In this study, the role of P66 in mammalian and tick infection was examined. B. burgdorferiΔp66 strains were not infectious in wild-type, TLR2⁻/⁻- or MyD88⁻/⁻-deficient mice. Strains with p66 restored to the chromosome restored near wild-type infectivity, while complementation with p66 on a shuttle vector did not restore infectivity. Δp66 mutants are cleared quickly from the site of inoculation, but analyses of cytokine expression and cellular infiltrates at the site of inoculation did not reveal a specific mechanism of clearance. The defect in these mutants cannot be attributed to nutrient limitation or an inability to adapt to the host environment in vivo as Δp66 bacteria were able to survive as well as wild type in dialysis membrane chambers in the rat peritoneum. Δp66 bacteria were able to survive in ticks through the larva to nymph moult, but were non-infectious in mice when delivered by tick bite. Independent lines of evidence do not support any increased susceptibility of the Δp66 strains to factors in mammalian blood. This study is the first to define a B. burgdorferi adhesin as essential for mammalian, but not tick infection.