Erysipelothrix rhusiopathiae: Morphology and Identification, Pathogenesis and Clinical Findings, Treatment.

Question 1

Morphology and identification

Answer 1

Erysipelothrix rhusiopathiae is a gram-positive, non-spore-forming, non-motile rod that can appear filamentous or in short chains. It is catalase negative and produces hydrogen sulfide (H2S) on triple sugar iron (TSI) agar, which helps differentiate it from other gram-positive rods. It is facultatively anaerobic and grows slowly on blood agar, forming small, alpha-hemolytic colonies. It is resistant to harsh environmental conditions and can survive in soil or animal products for weeks.

Question 2

Pathogenesis and clinical findings

Answer 2

E. rhusiopathiae is a zoonotic pathogen found in animals like pigs, fish, and turkeys. Humans are usually infected through occupational exposure (e.g., butchers, fish handlers, veterinarians) via broken skin. It causes three clinical syndromes: 1) Erysipeloid: localized skin infection with painful, violaceous, raised lesion on fingers or hands, often mistaken for cellulitis but without pus. 2) Diffuse cutaneous form: rare, generalized skin lesions. 3) Septicemic form: rare, associated with endocarditis, usually in immunocompromised patients or those with prosthetic valves.

Question 3

Treatment

Answer 3

Erysipeloid is treated with penicillin or ampicillin. For penicillin-allergic patients, erythromycin or clindamycin may be used. E. rhusiopathiae is resistant to vancomycin, which is unusual for a gram-positive rod. Endocarditis requires prolonged penicillin therapy. Early diagnosis and treatment prevent complications.