1. Listeria monocytogenes (Murray et al., 1926) Pirie, 1940. {Bacterium monocyto- genes Murray, Webb and Swann, Jour. Path, and Bact., 29, 1926, 407; Pirie, Science, 91, 1940, 383.) mo.no.cy.to'ge.nes. Gr. adj. menus alone, single; Gr. noun cytus a hollow, a vessel; M.L. noun cytus a cell; M.L. noun monocytum a blood cell, monocyte; Gr. v. gennaio to produce; M.L. adj. monocytogenes monocyte-producing. Small rods, 0.4 to 0.5 by 0.5 to 2.0 microns, with rounded ends, slightly curved in some culture media, occurring singly and in V-shaped or parallel pairs. Motile by means of peritrichous flagella (Paterson, Jour. Path, and Bact., 48, 1939, 25) at 2.5° C. to room temperatures with a tendency to re- duced motility in time at 37° C. (Griffin, Jour. Bact., 48, 1944, 114). Not acid-fast. Gram-positive. Gelatin: Growth is confined to the needle track. No liquefaction. In 0.25 per cent agar, 8.0 per cent gelatin, 1.0 per cent glucose semisolid medium, growth along the stab in 24 hours at 37° C. followed by irregular, cloudy e.xtensions into the medium; growth spreads slowly through the entire medium. This is charac- teristic (Seastone, Jour. Exp. Med., 62, 1935,203). Sheep liver extract agar colonies: Circu- lar, smooth, butyrous, slightly flattened, transparent by transmitted and milky by reflected light. Sheep liver extract agar slant: Confluent, flat, transparent, butyrous growth. Peptone agar: Growth is thinner than on liver extract agar. Blood agar: Improved growth with zone of hemolysis around colonies varjang with the species of blood. Peptone broth: Turbid; flocculent sedi- ment. Litmus milk: Slightly acid, decolorized. No coagulation. Glycerol-potato: No apparent growth. Inspissated ox serum: Grows as a very thin, transparent film. Dorsett's egg medium: Very thin film. Indole not produced. Hydrogen sulfide not produced. Acid but no gas from glucose, salicin and trehalose promptly, more slowly or variable from maltose, lactose, dextrin, sucrose, rhamnose, melezitose, soluble starch and glycerol. Tends to be negative on arabinose and galactose. No action on xylose, manni- tol, dulcitol, inulin or inositol. Esculin hydrolyzed in 24 hours (Sohier, Ann. Inst. Past., 74, 1948, 57). All cultures give off a penetrating, rather acid smell. Nitrites not produced from nitrates. Catalase-positive. Aerobic, facultatively anaerobic. Optimum temperature, 37° C; grows at all temperatures down to 2.5° C. Thermal death point, 58° to 59° C. in 10 minutes. Survives eight weeks in 20 per cent NaCl at 4° C. (Wramby, Skandinavisk Vetinartid- skriften, 34, 1944, 279). Animal inoculations: Intravenous or intraperitoneal injection of rabbits with cultures results in a very marked increase in monocytes circulating in the blood. This is the most striking character of the organ- ism, and it is exhibited by strains derived from all sources. Monocytosis is induced by extracted chloroform-soluble lipid (Stan- ley, Australian Jour. Exp. Biol, and Med., 27, 1949, 123). Infection is characterized by necrotic or granulomatous foci in various organs. Causes conjunctivo-keratitis when instilled into the conjunctiva of rabbits and guinea pigs (Anton, Zent. f. Bakt., I Abt., Orig., 131, 1934, 89; also see Julianelle, Proc. Exp. Biol, and Med., 40, 1939, 362); also produces this effect in the horse and ham- ster. Serological characters: Paterson (Jour. Path, and Bact., 51, 1940, 427) and Seeliger and Linzenmeier (Ztschr. f. Hyg., 136, 1953, 335) conclude from studies of the flagellar and somatic antigens that four types may be recognized in this species; these do not bear any relation to the host species or to the geographical area from which they were isolated. Relationships to other species: Possibly identical with Bacterium hepatis Hiilphers (Sven. Vet. Tidskrift,^, 1911,271) according to Nyfeldt (Sven. Vet. Tidskrift, 30, 1940, 280). Further comparative studies are needed, however, before this can be deter-
