The Occupational Opportunist: An Update on Erysipelothrix rhusiopathiae Infection, Disease Pathogenesis, and Microbiology

The genus Erysipelothrix currently consists of four named species, the most clinically significant of which is E. rhusiopathiae. E. rhusiopathiae is found ubiquitously in the environment, with worldwide prevalence. The organism is identified as both a pathogen and a saprophyte for diverse hosts, ranging from fish and amphibians to birds, mammals, and insects. E. rhusiopathiae is recognized as the etiological agent of swine erysipelas, a disease of significant economic consequence. Human clinical infections are generally the result of occupational zoonotic exposure to infected animal tissues or by-products. Although rare, three distinct clinical forms of human E. rhusiopathiae disease are recognized: a localized cutaneous cellulitis (human erysipeloid), a disseminated cutaneous infection, and an infectious endocarditis that is usually secondary to sepsis. Diagnosis of E. rhusiopathiae infection can be complicated, particularly with limited clinical history; therefore, the microbe may be under-recognized. From a laboratory perspective, diagnostic challenges include the bacterium's Gram stain variability and variable cellular and colony morphologies that can occur during identification. While the disease is treatable with routine antimicrobials, empiric therapeutic interventions can be hampered due to intrinsic vancomycin resistance. The recent availability of the E. rhusiopathiae genome will strengthen our understanding of the organism's disease pathogenesis and expand our knowledge about the spectrum of E. rhusiopathiae infections.