Table 1. Y. pestis strains used in this study for Caf1 isolation, serologic cross-reactivity tests, and virulence experiments.

Y. pestis strain		Relevant characteristics	Source/reference
subsp. pestis bv. antique
231	Wild type strain; universally virulent (LD50 for mice ≤ 10 CFU, for guinea pigs ≤ 10 CFU); NT1 allele of caf1; Aksai mountain natural plague focus # 33		SCPM-O* [20]
subsp. pestis bv. orientalis
EV line NIIEG	The Russian vaccine strain (GenBank: JBOL00000000.1); avirulent); NT1 allele of caf1; Madagascar		SCPM-O
subsp. microtus bv. caucasica (0.PE2)
C-376	Naturally pPst− strain C-376 virulent for voles and mice (LD50 for mice ≤ 5.0 × 102 CFU, for guinea pigs ≥ 106 CFU); NT2 allele of caf1; Leninakan mountain natural plague focus # 04		SCPM-O
C-376pCD1−	pCD1− derivative of naturally pPst− strain C-376; avirulent		The authors' collection
C-824	Naturally pPst− strain C-824 virulent for voles and mice(LD50 for mice ≤ 2.0 × 103 CFU, for guinea pigs ≥ 106 CFU); NT3 allele of caf1; Dagestan-highland natural plague focus # 39		SCPM-O
C-824pCD1−	pCD1− derivative of naturally pPst− strain C-824; avirulent		The authors' collection

*The State Collection of Pathogenic Microbes and Cell Cultures on the base of the State Research Center for Applied Microbiology and Biotechnology (“SCPM-Obolensk”; http://obolensk.org/center/state-collection.htm).