Potential errors in recognition of Erysipelothrix rhusiopathiae.

Here we describe four isolations of Erysipelothrix rhusiopathiae associated with polyarthralgia and renal failure, septic arthritis, classic erysipeloid, and peritonitis. Although the biochemical identification was straightforward in each case, recognition presented a challenge to the clinical microbiologist, since in three cases E. rhusiopathiae was not initially considered due to unusual clinical presentations, in two cases the significance might not have been appreciated because growth was in broth only, and in one case the infection was thought to be polymicrobic. Because the Gram stain can be confusing, abbreviated identification schemes that do not include testing for H(2)S production could allow E. rhusiopathiae isolates to be misidentified as Lactobacillus spp. or Enterococcus spp. in atypical infections.