0002). Tick cohorts from individual Δarp3 infected mice contained 9/10, 5/10, 10/10, 6/10 and 10/10 positive ticks. Results demonstrated that Δarp3 can be acquired by ticks from infected C3H mice, but ticks that acquired Δarp3 harbored fewer organisms compared to wild-type. The ability of Δarp3

spirochetes to be transmitted from infected ticks to naïve C3H mice was next evaluated by placing 10 nymphal ticks from the wild-type and Δarp3 positive tick cohorts (above) onto each recipient mouse. Mice were necropsied at 3 weeks following tick feeding, and ear, heart base, ventricular muscle, tibiotarsus and quadriceps muscle were tested by flaB Q-PCR. Among 5 mice fed upon by ticks carrying wild-type spirochetes, 4/5 mice became infected, and all tissue sites Venetoclax solubility dmso from the 4 positive mice were PCR-positive, with high copy numbers of flaB DNA in tissues (Figure 3). In contrast, 2 of the 7 mice that were fed upon by Δarp3 infected ticks were positive, but only a single tissue in each of the positive mice contained low copy numbers of flaB DNA. Results indicated that Δarp3 spirochetes are capable of tick-borne transmission.

Since ticks infected with Δarp3 spirochetes had significantly fewer spirochete loads HSP inhibitor compared to ticks infected with wild-type spirochetes, it could not be concluded that there was less efficient transmission. Figure 3 Borrelia burgdorferi flaB DNA copies per mg tissue weight (means ± standard deviations) in PCR-positive tissues, including ear, heart base (HB), ventricular muscle (VM), quadriceps muscle (QM) and tibiotarsus (Tt) of mice at 3 weeks after feeding of nymphal ticks from tick cohorts

infected with wild-type or arp null Δarp3 B. burgdoferi. Discussion This study examined the effect of targeted deletion of BBF01/arp on infectivity of B. burgdorferi B31. The median infectious dose of B. burgdorferi B31 with an arp null mutation was elevated approximately ten-fold compared to wild-type Sucrase spirochetes, and restored by complementation. Therefore, it is apparent that BBF01/arp is not essential for infectivity of the mammalian host. This is supported by indirect results of others, who demonstrated diminished infectivity in B. burgdorferi spirochetes lacking linear plasmid 28–1 (lp28-1), which encodes only two unique and functional genes, vlsE and arp[25–29]. Furthermore, clones of B. burgdorferi B31 with a deletion of the left side of lp28-1, which contains arp, remained infectious and capable of persistence, similar to wild-type spirochetes [25]. Examination of the pathogenicity of various B. burgdorferi B31 clones lacking lp28-1 has shown that clones lacking lp28-1 were infectious in BALB/c-scid mice and reached similar tissue burdens as wild-type spirochetes, but were incapable of inducing arthritis [29].