Streptobacillus moniliformis
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CHAPTER 14.5 su l l i cabotper tS
s imrof i l i nom
Streptobacillus moniliformis JAMES R. GREENWOOD AND SYDNEY M. HARVEY
Introduction The genus Streptobacillus is presently represented by one species, Streptobacillus moniliformis, the etiologic agent of rat-bite fever and Haverill fever. S. moniliformis has also been known as Haverhillia multiformis, Actinomyces muris, Actinobacillus muris, and Haverhillia moniliformis. Although the genus Streptobacillus was described in the 1920s, taxonomically it continues to be a genus of uncertain affiliation. Previously this genus was placed in the families Parvobacteriaceae (Tribe Haemophileae) and Bacteroidaceae. Since the 8th edition of Bergy’s Manual, Streptobacillus has been described as a genus of “uncertain affiliation.” It was recently suggested (Savage, 1989) that S. moniliformis is more similar to some of the Mycoplasmatales. This suggestion is based on the low GC content of the DNA (24–26 mol%), serum or blood requirements for growth, cholesterol incorporation into the cell membrane, animal parasitism, and production of L-phase organisms. Further clarification of the taxonomic position of this genus awaits genetic studies, such as DNA-RNA hybridizations.
Habitats S. moniliformis is found in the nasopharynx of laboratory and wild rats, with some studies reporting as many as 50–100% of wild rats carrying it as a commensal organism and excreting it in their urine (McHugh et al., 1985). It is reported to have caused tendon sheath infections in turkeys, cervical abscesses in guinea pigs, epizootics in laboratory mice, and lesions in laboratory rats with bronchopneumonia. Humans become involved in the transmission cycle through rat bites or from the bites of squirrels, weasels, and such rat-eating carnivores as dogs, cats, and pigs. Rat bite fever has also been This chapter was taken unchanged from the second edition.
reported following the handling of dead rats. Haverhill fever may result from the ingestion of milk to which rats have had access.
Selective Enrichment S. moniliformis is both fastidious and slow growing; consequently it is frequently overgrown by normal flora. Because it is an uncommon human pathogen, little work has been done to develop a selective culture medium. Recently, however, colistin nalidixic acid agar (CNA) was used in conjunction with other media to isolate Gramnegative S. moniliformis from a 2-month old with a fatal infection following a bite by a wild rat (Sens et al., 1989). CNA is inhibitory for many other Gram-negative bacteria and the use of this medium or a modification combining colistin, nalidixic acid and serum might provide a new approach to isolation of S. moniliformis from nonsterile body sites.
Isolation S. moniliformis growth media should be supplemented with blood, serum, or ascitic fluid. Because L-phase variants might be present in clinical samples, media formulations must also take the specialized growth requirements of these forms into account. The bacterial phase has been isolated on media with either a meat infusion or trypt
