Intermediately virulent Rhodococcus equi isolates from pigs in Slovenia: discovery of new plasmid types and assessment of genetic diversity by pulsed-field gel electrophoresis

Abstract

The presence of large plasmids in 30 <I>Rhodococcus equi</I> strains isolated from pig lymph nodes with granulomatous changes was investigated. Plasmid DNAs were isolated and digested with the restriction endonucleases <I>Bam</I>HI, <I>Eco</I>RI, <I>Eco</I>T22I and <I>Hind</I>III for detailed comparison and estimation of plasmid sizes. A total of nine isolates were identified as intermediately virulent (VapB-positive), harbouring large plasmids of type 5 (<I>n</I> = 5) and four new variants that we tentatively designated as type 19 (<I>n</I> = 1), 20 (<I>n</I> = 1), 21 (<I>n</I> = 1) and 24 (<I>n</I> = 1). All isolates were subjected to genotyping with pulsed-field gel electrophoresis (PFGE). High genetic diversity was observed: 21 distinct genotypes were detected; five were found in multiple isolates and the others were unique. Isolates of the same plasmid type exhibited different PFGE profiles and vice versa. In a few cases, multiple strains from certain farms were analysed, the majority of which exhibited diverse PFGE profiles. Our findings demonstrate the presence of a wide variety of <I>R. equi</I> strains even in small confined environments such as farms. This is the first molecular epidemiology study of intermediately virulent <I>R. equi</I> isolates from Slovenian pigs.