Generality of Post-Antimicrobial Treatment Persistence of Borrelia burgdorferi Strains N40 and B31 in Genetically Susceptible and Resistant Mouse Strains

Abstract

A basic feature of infection caused by Borrelia burgdorferi, the etiological agent of Lyme borreliosis, is that persistent infection is the rule in its many hosts. The ability to persist and evade host immune clearance poses a challenge to effective antimicrobial treatment. A link between therapy failure and the presence of persister cells has started to emerge. There is growing experimental evidence that viable but noncultivable spirochetes persist following treatment with several different antimicrobial agents. The current study utilized the mouse model to evaluate if persistence occurs following antimicrobial treatment in disease-susceptible (C3H/HeJ [C3H]) and disease-resistant (C57BL/6 [B6]) mouse strains infected with B. burgdorferi strains N40 and B31 and to confirm the generality of this phenomenon, as well as to assess the persisters' clinical relevance. The status of infection was evaluated at 12 and 18 months after treatment. The results demonstrated that persistent spirochetes remain viable for up to 18 months following treatment, as well as being noncultivable. The phenomenon of persistence in disease-susceptible C3H mice is equally evident in disease-resistant B6 mice and not unique to any particular B. burgdorferi strain. The results also demonstrate that, following antimicrobial treatment, both strains of B. burgdorferi, N40 and B31, lose one or more plasmids. The study demonstrated that noncultivable spirochetes can persist in a host following antimicrobial treatment for a long time but did not demonstrate their clinical relevance in a mouse model of chronic infection. The clinical relevance of persistent spirochetes beyond 18 months following antimicrobial treatment requires further studies in other animal models.

Keywords: Borrelia burgdorferi; antimicrobial tolerance; mouse model; persistence.

FIG 1

Copy numbers of B. burgdorferi DNA of flaB-ospA genes in heart base (HB), ventricular muscle (VM), and tibiotarsus (TT) of C3H and B6 mice infected with either strain N40 or B31 at 12 (A) and 18 (B) months after ceftriaxone and saline solution treatment. *, significantly higher copy number (P < 0.05). The error bars indicate SD.

FIG 2

Dark-field images of B. burgdorferi spirochetes cultured from mouse tissues necropsied 18 months after completion of treatment. Magnification, ×400. (A) Note the numerous spirochetes from ear culture of a saline solution-treated C3H mouse infected with strain N40. (B) Ear culture of a ceftriaxone-treated B6 mouse infected with strain B31. (C) Front joint of a ceftriaxone-treated B6 mouse infected with strain N40.

FIG 3

Comparisons of carditis severity between ceftriaxone-treated and saline-treated C3H and B6 mice infected with either B. burgdorferi strain N40 or B31 necropsied at 12 and 18 months after treatment. (A1 to A4) C3H/N40. (B1 to B4) C3H/B31. (C1 to C4) B6/N40. (D1 to D4) B6/B31. (Column 1) Ceftriaxone treated/12 months. (Column 2) Saline treated/12 months. (Column 3) Ceftriaxone treated/18 months. (Column 4) Saline treated/18 months.

FIG 4

(A and B) Chronic periarteritis observed in a C3H mouse infected with B. burgdorferi B31 and then treated with saline solution and necropsied 18 months after treatment. (C) Tenosynovitis observed in a B6 mouse infected with B. burgdorferi N40 and then treated with saline solution and necropsied 18 months after treatment.