title: Sequence types and pleuromutilin susceptibility of Brachyspira hyodysenteriae isolates from Italian pigs with swine dysentery: 2003-2012.
abstract: Swine dysentery is a mucohaemorrhagic colitis of pigs caused by infection with Brachyspira hyodysenteriae. The disease can be controlled by treatment with antimicrobial agents, with the pleuromutilins tiamulin and valnemulin being widely used. In recent years, the occurrence of B. hyodysenteriae with reduced susceptibility to these drugs has been increasing. The aim of this study was to determine temporal changes in genetic groups and pleuromutilin susceptibility amongst B. hyodysenteriae isolates from Italy. Multilocus sequence typing (MLST) was performed on 108 isolates recovered from 87 farms in different regions of Italy from 2003 to 2012, and their minimum inhibitory concentrations (MICs) for tiamulin and valnemulin were determined. Logistic regression was performed to assess associations between susceptibility to the two antimicrobial agents and genetic group, year and region of isolation. The isolates were allocated to 23 sequence types (STs), with five clonal clusters (Ccs) and seven singletons. More than 50% of isolates were resistant to both pleuromutilins (MIC >2.0 µg/mL for tiamulin and >1.0 µg/mL for valnemulin). All 10 isolates in ST 83 were resistant; these were first isolated in 2011 and came from nine farms, suggesting recent widespread dissemination of a resistant strain. Significant associations were found between the proportion of pleuromutilin susceptible isolates and the genetic group and year of isolation. Although resistant isolates were found in all Ccs, isolates in Ccs 2 and 7 were over five times more likely to be susceptible than those in the other Ccs. A significant trend in the reduction of susceptibility over time also was observed.
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy. Electronic address: gianluca.rugna@izsler.it.
authors.forename: G
authors.initials: G
authors.lastname: Rugna
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Bonilauri
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Carra
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Bergamini
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Luppi
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: Y
authors.initials: Y
authors.lastname: Gherpelli
authors.affiliation: Istituto Zooprofilattico Sperimentale Umbria e Marche, Via G. Salvemini 1, 06126 Perugia, Italy.
authors.forename: C F
authors.initials: CF
authors.lastname: Magistrali
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Nigrelli
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: G L
authors.initials: GL
authors.lastname: Alborali
authors.affiliation: Department of Veterinary Science, University of Parma, Via del Taglio 10, 43126 Parma, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Martelli
authors.affiliation: School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA 6150, Australia.
authors.forename: T
authors.initials: T
authors.lastname: La
authors.affiliation: School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA 6150, Australia.
authors.forename: D J
authors.initials: DJ
authors.lastname: Hampson
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via Bianchi 9, 25124 Brescia, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Merialdi
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017401:Brachyspira hyodysenteriae / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D004224:Diterpenes / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D016905:Gram-Negative Bacterial Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D007558:Italy / Q000453:epidemiology; D017720:Molecular Epidemiology; D058885:Multilocus Sequence Typing; D011083:Polycyclic Compounds; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology*; D000097567:Pleuromutilins
chemical_list: D000900:Anti-Bacterial Agents; D004224:Diterpenes; D011083:Polycyclic Compounds; D000097567:Pleuromutilins
keywords: Brachyspira hyodysenteriae; Multilocus sequence typing; Pleuromutilin susceptibility; Swine dysentery