B. burgdorferi strain | No. of infected mice/no. of mice fed on by 20 infected nymphs^{a} | No. of tissue reisolates/no. of mice fed on by infected ticks (ear, bladder, joint)^{b} | No. of spirochetes/nymphal tick (mouse 1; mouse 2; mouse 3)^{c} |
---|---|---|---|

A3 | 3/3 | 3/3, 3/3, 3/3 | 100,000; 130,000; 140,000 |

A3ΔA1-7 | 4/7 | 4/7, 4/7, 4/7 | 100,000; 140,000; 130,000 |

A3ΔA7-14 | 3/3 | 3/3, 3/3, 3/3 | 140,000; 120,000; 140,000 |

↵

*a*Seroconversion was determined by immunoblot analysis with*B. burgdorferi*lysate 3 weeks postfeeding. The number of mice infected by either A3- or A3ΔA1-7-infected ticks was not significantly different using 20 ticks per mouse (*P*= 0.48, performed by Fisher's two-tailed exact-probability test).↵

*b*Number of tissue reisolates/number of mice fed on by infected ticks, for ear, bladder, and joint. All three tissues from infected mice were positive.↵

*c*Twenty infected nymphal ticks were fed to repletion on three naïve mice per strain. Ten days postfeeding, three fed nymphs from each mouse were pooled, crushed, and plated to determine the number of viable spirochetes. The average number of spirochetes per tick was calculated from the total number of colonies obtained per pool of three nymphs. Mean numbers of spirochetes per tick were not significantly different between strains as determined by one-way analysis of variance (ANOVA) (*P*= 0.75), performed by use of GraphPad Prism 5 software.