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

ABSTRACT:The presence of large plasmids in 30 Rhodococcus equi strains isolated from pig lymph nodes with granulomatous changes was investigated. Plasmid DNAs were isolated and digested with the restriction endonucleases BamHI, EcoRI, EcoT22I and HindIII 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 (n = 5) and four new variants that we tentatively designated as type 19 (n = 1), 20 (n = 1), 21 (n = 1) and 24 (n = 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 R. equi strains even in small confined environments such as farms. This is the first molecular epidemiology study of intermediately virulent R. equi isolates from Slovenian pigs.

Prevalence and genetic diversity of Rhodococcus equi in wild boars (Sus scrofa), roe deer (Capreolus capreolus) and red deer (Cervus elaphus) in Poland

“…Unfortunately, in our study complete information about the origin of each positive animal was not available. Comparison of PFGE patterns and plasmid type in this study confirmed previous observation in pigs [ 11 ], horses [ 32 ] and cattle [ 5 ] where R. equi isolates containing the same plasmid type revealed different PFGE patterns and vice versa isolates with identical PFGE patterns contained different virulence plasmids or were plasmid-less.…”

“…Genotypic method often used in the epidemiological investigations of genetic relationships between R. equi isolates was PFGE, however, results were inconclusive [ 5 , 11 , 17 , 30 - 34 ]. In the case of R. equi infection in horses it was shown that many various strains were widespread in horse population but individual farms tended to harbor a particular single strain [ 30 - 32 ].…”

“…Furthermore, using other technique (repetitive sequence-based PCR) it was shown that one foal could be infected with multiple R. equi strains [ 34 ]. Application of PFGE in the investigation of swine R. equi strains showed high genetic diversity of strains not only between farms but also between individual animals on one farm [ 11 ]. It was suggested that infection was not presumably transmitted among animals in the herd but the environment could have been a source of infection.…”

Molecular epidemiology of Rhodococcus equi in slaughtered swine, cattle and horses in Poland

“…However, other studies on swine isolates reported much lower percentage of vapB -positive strains, in approx. 30 % [ 18 , 33 ] or 70 % of isolates [ 1 , 19 ]. The vapB -positive R. equi strains accounted for 25 to 70 % of isolates in wild boar [ 11 , 34 – 36 ].…”

“…Recently, R. equi infection in other species than horse has aroused considerable interest due to its frequent isolation from the lymph nodes and other tissues of apparently healthy animals intended for human consumption. The prevalence of R. equi in swine carcasses varies from 0 % to over 20 % [ 1 , 2 , 11 , 18 – 20 , 28 , 31 – 33 ]. In wild boar the prevalence ranges from 0 % to even 52 % hunted animals [ 34 – 37 ], whereas in the roe deer and red deer it is lower than 1 % [ 37 ].…”