Detection of Erysipelothrix rhusiopathiae in clinical and environmental samples

Erysipelothrix rhusiopathiae is pathogenic for both animals and humans, causing erysipelas in swine and erysipeloid in humans. In swine, disease may be either acute or chronic, resulting in the development of arthritis and endocarditis. In Japan, erysipelas remains an animal hygiene problem causing great economic loss as infected swine are disused. Human infection closely resembles that seen in swine, with both acute and chronic forms also. The most common presentation is erysipeloid, a localized cutaneous infection. In Western Australia, an erysipeloid-like infection referred to as "crayfish poisoning" occurs in lobster fishermen and handlers. A second type of presentation is a generalized cutaneous form involving lesions that progress from the initial site of infection or appear in remote areas. The third and most serious form of disease is a septicemia that is almost always linked to endocarditis. The mortality rate in Erysipelothrix endocarditis is still high (38%) and can be explained by the use of vancomycin (to which Erysipelothrix spp. are inherently resistant) as empirical therapy. Therefore, it is critical to have an early diagnosis of E. rhusiopathiae infection.Unfortunately, several problems exist with the diagnosis of E. rhusiopathiae infections by conventional cultural procedures, and these infections are often incorrectly diagnosed. First, because of their very small colony size and slow growth rates, it is difficult to isolate E. rhusiopathiae from heavily contaminated specimens. Various selective media have been described to improve the isolation of E. rhusiopathiae from contaminated specimens; however, not all contaminants are inhibited. The development of two polymerase chain reaction (PCR) methods has created an opportunity to greatly improve the efficiency with which these organisms are detected and identified. Makino et al. designed a PCR method that amplifies a 407-bp DNA fragment derived from the 16S rRNA coding sequence. The primers in this method are specific for the genus Erysipelothrix and do not differentiate between the species. A second set of primers designed by Shimoji et al. amplifies a 937-bp DNA fragment which is derived from a sequence associated with virulence of E. rhusiopathiae. These primers are specific for E. rhusiopathiae only. Shimoji et al. also utilized a selective enrichment medium based on tryptic soy broth containing ethidium bromide and sodium azide.