Characterization of Erysipelothrix rhusiopathiae isolates from poultry, pigs, emus, the poultry red mite and other animals

Erysipelothrix rhusiopathiae is the causative agent of erysipelas in mammals and birds, especially pigs and poultry. In order to investigate the suitability of different subtyping methods for genetic and phenotypic similarities among Swedish isolates of the organism, 45 isolates from poultry (n=23), pigs (n=17), emus (n=2) and the poultry red mite Dermanyssus gallinae (n=3) were investigated by serotyping, pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing.

Sequence analysis of the 16S rRNA gene was performed on eleven isolates from nine animal species. The results indicated a random scattering of serotypes throughout the dendrogram based on PFGE banding patterns following SmaI digestion. In three cases, isolates with an identical PFGE pattern were of differing serotypes.

No differentiation into subgroups by antimicrobial susceptibility testing by broth microdilution was possible as results were similar for all isolates. The Minimum Inhibitory Concentrations for most antimicrobials, including penicillin and oxytetracycline, were low. The 16S rRNA gene sequences (1443 nts) from eight of eleven selected isolates of Erysipelothrix spp. were identical to that of the type strain E. rhusiopathiae ATCC 19414(T).

The other three isolates differed from the type strain by two or three nucleotides. While this method may be useful for identification of Erysipelothrix spp., it is unsuitable for epidemiological investigations. Similarities in PFGE banding patterns between isolates from chickens and mites supported the hypothesis that D. gallinae may act as a reservoir and vector for E. rhusiopathiae.

Further PFGE studies on E. rhusiopathiae isolates are appropriate to investigate the epidemiology of poultry erysipelas.