Erysipelothrix rhusiopathiae and Zoonotic Occupational Infection

Erysipelothrix rhusiopathiae is a Gram-positive rod-shaped bacterium belonging to the genus Erysipelothrix. The cells are straight or slightly curved and may form elongated filamentous structures in aging cultures or infected tissues.

The organism does not produce spores and lacks flagella, rendering it non-motile. It grows under microaerophilic or facultatively anaerobic conditions and can be cultivated on routine laboratory media, although growth is enhanced by the presence of blood or serum.

A distinctive biochemical feature is the production of hydrogen sulfide (H₂S) in triple sugar iron (TSI) agar, which serves as an important laboratory identification marker. On blood agar, colonies are typically small and circular, sometimes surrounded by a narrow zone of α-hemolysis.

The bacterium is relatively resilient in environmental reservoirs such as soil, decaying organic matter, and animal tissues. However, it remains susceptible to heat and standard disinfectants.

Erysipelothrix rhusiopathiae is widely distributed among animals, including pigs, sheep, poultry, fish, and shellfish. Human infection typically results from occupational exposure.

Transmission generally occurs when individuals handling contaminated animal products sustain minor skin injuries, allowing bacterial entry through damaged skin or mucous membranes. Occupations at higher risk include veterinarians, fishermen, butchers, and workers in meat or seafood processing industries.

Several virulence factors contribute to its pathogenicity:

• Capsular components that assist in resisting phagocytosis.
• Neuraminidase and hyaluronidase enzymes that facilitate tissue invasion and bacterial spread.
• Surface protective antigen A (SpaA), which mediates adhesion to host cells and contributes to host immune responses.

These factors allow the organism to establish localized infection and, in rare cases, disseminate into the bloodstream.

Human infection with E. rhusiopathiae can present in several clinical forms.

• Localized cutaneous infection (erysipeloid): The most common presentation. Within 1–7 days after exposure, a sharply demarcated violaceous or purplish skin lesion develops near the site of injury, usually on the hands or fingers. The lesion may be painful or pruritic but typically does not suppurate.
• Diffuse cutaneous form: Less common, involving multiple skin lesions or progressive spread of the initial lesion.
• Systemic infection: Rare but potentially severe. Bacteremia may lead to infective endocarditis, septic arthritis, or meningitis. Endocarditis associated with this organism frequently involves the aortic valve.

In animals—particularly pigs—the organism causes swine erysipelas, which may manifest as septicemia, characteristic diamond-shaped skin lesions, or chronic arthritis and endocarditis.

Laboratory identification plays an essential role in differentiating infections caused by E. rhusiopathiae from other skin and soft tissue infections such as streptococcal erysipelas or cellulitis.

For cutaneous disease, biopsy of the affected skin area or sampling of lesion exudate provides higher diagnostic yield than superficial aspiration. In suspected systemic infection, blood cultures should be obtained.

Bacterial culture remains the diagnostic reference method, although growth may require extended incubation. Molecular diagnostic techniques targeting specific bacterial gene sequences, including probe-based real-time PCR assays, provide rapid and specific detection.

Accurate identification is clinically important because E. rhusiopathiae displays intrinsic resistance to certain antibiotics, including vancomycin, which is frequently used empirically for Gram-positive infections.

Antimicrobial therapy is generally effective when appropriate antibiotics are used.

The organism typically exhibits resistance to vancomycin, sulfonamides, and aminoglycosides, highlighting the importance of accurate laboratory identification and susceptibility testing.

Erysipelothrix rhusiopathiae is a zoonotic pathogen with a broad ecological distribution among animals and environmental reservoirs. Although most human infections remain localized to the skin, systemic disease can occur in rare cases.

Effective prevention relies primarily on occupational protective measures, including the use of gloves, proper wound care, and hygiene practices when handling animals or animal products. Continued improvements in diagnostic technologies and surveillance are important for timely identification and management of zoonotic infections associated with this organism.