Optimum pH, between 7.0 and 8.0. Via- bility rapidly lost with decrease in pH Pathogenicity: Usually highly virulent for mice, although certain strains of mice may be rather resistant. Intravenous or intraperitoneal inoculation with 0.1 to 0.5 ml of broth culture causes a fatal sepsis, death occurring in 24 to 48 hours, or a chronic disease characterized by purulent polyarthritis, anemia, emaciation, diar- rhea, conjunctivitis and transient or per- manent paralysis involving the hindpart of the body. At necropsy nothing distinctive is found in acute cases; the spleen and lymph nodes are considerably enlarged in subacute and chronic infections, and focal or con- fluent necroses are frequently found in the spleen and liver. Intracutaneous and sub- cutaneous injections cause local abscesses and arthritis and occasionally generalized infection. Bronchopneumonia and sepsis are frequently produced by intranasal in- stillation. Generalized infection has been produced by feeding experiments; the portal of entry in such cases appears to be the sub- ma.xillary and cervical lymph nodes (Freundt, Acta Path, et Microbiol. Scand., 38, 1956, 231.) Passage in 9- to 10-day-old chick embryos causes thickening, edema and hemorrhagic lesions of the chorio-allantoic membrane and invasion of the embryo. Rats, rabbits and guinea pigs are generally resistant, although rabbits have been re- ported to be susceptible to certain strains. Antigenic structure : Mice and rat strains from three different sources (Levaditi et al., op. cit., 1925, 1188; Mackie, van Rooyen and Gilroy, Brit. Jour. Exp. Path., I4, 1933, 132; Strangeways, Jour. Path, and Bact., 37, 1933, 45) were found to be identical by agglutinin absorption tests (van Rooj^en, Jour. Path, and Bact., 43, 1936, 460). L-phase variation: In most bacteria in which the L-phase variation is known, ab- normal culture conditions are generally necessary to induce the development of L-type colonies on solid media. All strains oi Streptobacillus moniliformis, on the other hand, develop L colonies spontaneously, though in a variable number. The L-phase variant of S. moniliformis is known as Li (Klieneberger, Jour. Path, and Bact., 40, 1935, 93). Klieneberger's original theory. that Li was a symbiont of S. moniliformis, was oppo.sed by Dienes (Jour. Inf. Dis., 65, 1939, 24; Jour. Bact., 44, 1942, 37), Dawson and Hobby (Proc. 3rd Internat. Congr. for Microbiol., New York, (1939) 1940, Sect. I, 177), Heilman (op. cit., 1941, 32), Brown and Nunemaker (op. cit., 1942, 201) and 0rskov {op. cit., 1942, 575), among others; it is now generally accepted, also by Klieneberger- Nobel herself (Jour. Gen. Microbiol., 3, 1949, 434), that Li is a variant form of S. moniliformis. L-phase colony: The Li colony is defi- nitely smaller than that of the bacillary form, measuring about 0.1 to 0.2 mm in diameter. It contains a round, dark brown center embedded in the agar and consists of tiny, coccoid or coccobacillary elements. The central spot is surrounded by a delicate, translucent, peripheral zone made up of swollen bodies, extracellular fatty droplets and an amorphous substance. Li is ex- tremely resistant to penicillin, while the streptobacilli are very sensitive to this antibiotic. Cross absorption tests between Li and the bacillary phase have shown that although they share a common antigen, the L phase is deficient in another antigen that is found in the bacillary form (Klieneberger, Jour. Hyg., 42, 1942, 485). Reversion of Li to the streptobacillus form is extremely difficult to obtain on solid media, whereas this reversion generally occurs in fluid or semi-solid media. The stability of Li , even in fluid media, increases with the number of subcultures on solid media. Li cultures are non-pathogenic when reversion to the bacillary form in the inoculated animal is prevented. Vaccines prepared from Li do not protect against infections by streptobacilli (Freundt, op. cit, 1956, 246). Relationships and nomenclature of this species : Streptothrix muris ratti Schottmiiller and Haverhillia multiformis Parker and Hud- son are included here as synonyms of Strep- tobacillus moniliformis Levaditi et al. How- ever, because no comparative studies have been made with authentic cultures of these three organisms, the change in nomencla- ture that would be indicated if it were established that these organisms are iden- tical has not been made at this time. Source: Isolated from cases of sponta-
