TABLE 3.

Classification of Yersinia pestis subgroups by M. I. Levi^a

Y. pestis variety	Differential characteristics
	Fermentation of:		Nitrate reduction	Virulence for guinea pigs	Infectious bacteriemiab
	Glycerol	Rhamnose			Pygmy suslik	Left-bank midday gerbilc	Common vole
Rat's	−	−	+	+	NDe	ND	ND
Marmot's	+	−	+	+	+	−	+
Suslik's	+	−	−	+	+	−	+
Gerbil's	+	−	−	+	+	+	+
Vole's	+	+	±d	−	−	−	+

^aThis table was compiled from reference 11 and M. I. Levi (Abstr. Sci. Conf. Nat. Focality Prophyl. Plague Tularemia, 1962), modified from reference 11, and used with the permission of the copyright holder (G. P. Aparin and E. P. Golubinskii).

^bMaintenance of plague in nature is completely dependent on cyclic transmission between fleas and rodents. An infectious bacteremia of at least 10⁴ CFU/ml can ensure ingestion of a number of bacteria sufficient for flea blockage, leading to infection of a new mammalian host (7-9, 11,13, 28, 30, 31, 34, 49, 55, 56, 104, 132, 135, 141, 146,179).

^cMidday gerbils living on the opposite banks of the Volga river differ in their susceptibilities to lethal plague infection. LD₅₀s for the left-bank midday gerbils, which are living in the natural plague focus, are 2 orders of magnitude more than those of the right-bank population (56).

^dPresence of a character but not in all strains.

^eND, no data.