Overview of Erysipelothrix rhusiopathiae Infection

Erysipelothrix rhusiopathiae is a significant bacterial pathogen of swine, turkeys, and sheep. It is distributed worldwide and has also been isolated from cattle, horses, dogs, cats, mice, rats, fresh and saltwater fish, domestic poultry, and a variety of wild birds and mammals. Erysipeloid, a condition characterized by localized skin infections and cellulitis, may develop in people who work with infected animals, infected carcasses, or infected animal byproducts.

The bacterium can survive in the soil for up to 5 wk; however, soil is not an effective growth medium, and the organism is unable to survive for extended periods of time in the environment. Soil and surface water contamination represent routes of exposure. Asymptomatic carriers are the usual source of infectious organisms, but the bacteria may also be introduced to animal production units by surface water runoff, wild mammals, wild birds, pets, and biting insects. E rhusiopathiae has food safety implications, because it can survive for several months in animal tissues such as frozen or chilled pork, cured and smoked ham, and feed byproducts such as dried blood.

E rhusiopathiae is a nonmotile, gram-positive, facultative anaerobic bacillus. It is catalase negative, coagulase positive, oxidase negative, resistant to high salt concentrations, and produces H₂S on triple sugar iron media. Colonies of E rhusiopathiae are either smooth or rough, with rough colonies being slightly larger, with irregular edges. On agar media, colonies are clear, circular, and very small (0.1–1.5 mm in diameter) after 24 hr of incubation, but they increase in size after 48 hr.

The organism is very hardy and can survive and grow in a wide range of pH and environmental temperatures. E rhusiopathiae has demonstrated the ability to resist the action of several classes of disinfectants used in animal production units, including alcohols, aldehydes, oxidizing agents, and phenols. Classes of disinfectants and/or compounds considered to effectively inactivate E rhusiopathiae include hypochlorites (bleach) and caustic soda (lye; NaOH). The organism is sensitive to the β-lactam (penicillin, ampicillin), cephalosporin (ceftiofur), and tetracycline classes of antibiotics and is resistant to sulfonamides.