Potential errors in recognition of Erysipelothrix rhusiopathiae

Here we describe four isolations of Erysipelothrix rhusiopathiae associated with polyarthralgia and renal failure, septic arthritis, classic erysipelo id, and peritonitis. Although the biochemical identification was straightfo rward in each case, recognition presented a challenge to the clinical micro biologist, since in three cases E. rhusiopathiae was not initially consider ed due to unusual clinical presentations, in two cases the significance mig ht not have been appreciated because growth was in broth only, and in one c ase the infection was thought to be polymicrobic. Because the Gram stain ca n be confusing, abbreviated identification schemes that do not include test ing for H2S production could allow E. rhusiopathiae isolates to be misident ified as Lactobacillus spp. or Enterococcus spp. in atypical infections.