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.