Figure 1.
Yersinia pestis KIM D27 and UC91309 are attenuated for virulence due to a defect in iron scavenging. A, Y. pestis strains CO92 (virulent wild-type plague isolate), KIM D27 (nonpigmented vaccine type strain), and UC91309 (clinical isolate from a case of fatal plague septicemia) were spread on Congo red agar plates and incubated at 26°C for 3 days, after which colonies were photographed. B, Culture medium (supernatant [S]) and bacterial extract (pellet [P]) of Y. pestis strains CO92, KIM D27, and UC91309 were analyzed by immunoblotting with antibodies specific for LcrV (V antigen), Caf1 (F1 or capsular fraction 1 antigen) and RNA polymerase subunit A (RpoA), as a loading control. KIM D27 variants with a mutation in the lcrV gene (lcrV1) or a deletion of caf1 (Δcaf1) were included as controls. C, Cohorts of Swiss Webster mice (n = 10) were challenged by subcutaneous injection with suspensions of Y. pestis strains CO92 (100 colony-forming units [CFUs]), KIM D27 (105 or 106 CFUs), or UC91309 (105 or 106 CFUs). For each challenge experiment, inocula were verified by plating aliquots of bacterial suspensions on agar plates and enumerating CFUs. Animals were monitored over 14 days after challenge for survival. Results are representative of at least 3 independent experimental determinations. D, Mice were treated 24 hours before challenge with 0.1 mL 50% (v/v) iron dextran (100 mg/mL) and 50 mg/mL desferrioxamine B mesylate into the peritoneal cavity (+). Cohorts of Swiss Webster mice (n = 10) were challenged by subcutaneous injection with 105 CFUs of Y. pestis KIM D27 or UC91309. For each challenge experiment, inocula were verified by plating aliquots of bacterial suspensions on agar plates and enumerating CFUs. Animals were monitored for 14 days after challenge. Results are representative of 2 independent experimental determinations.