title: Multiresistance in Pasteurella multocida is mediated by coexistence of small plasmids.
abstract: In most gram-negative bacteria, acquired multiresistance is conferred by large plasmids compiling numerous antimicrobial resistance genes. Here, we show an evolutionary alternative strategy used by Pasteurella multocida to become resistant to multiple clinically relevant antibiotics. Thirteen beta-lactam-resistant clinical isolates, concomitantly resistant to tetracyclines and/or streptomycin as well as to sulfonamides, were studied. Pulsed-field gel electrophoresis analysis revealed different profiles among the isolates, showing that clonal dissemination was not the sole event responsible for the spread of multiresistance. Each P. multocida strain carried two or three small plasmids between 4 and 6 kb in size. A direct association between resistance profile and plasmid content was found. Complete nucleotide sequencing of all plasmids revealed seven different replicons, six of them belonging to the ColE1 superfamily. All plasmids carried one, or a maximum of two, antimicrobial resistance determinants. Plasmids pB1000 and pB1002 bore bla(ROB-1), pB1001 carried tet(B), pB1003 and pB1005 carried sul2 and strA, pB1006 harbored tet(O), and p9956 bore the tet(H) gene. All plasmids except pB1002 and pB1006 were successfully transformed into Escherichia coli. pB1000, also involved in beta-lactam resistance in Haemophilus parasuis (A. San Millan et al., Antimicrob. Agents Chemother. 51:2260-2264, 2007), was mobilized in E. coli using the conjugation machinery of an IncP plasmid. Stability experiments proved that pB1000 was stable in P. multocida but highly unstable in E. coli. In conclusion, bla(ROB-1) is responsible for beta-lactam resistance in P. multocida in Spain. Coexistence and the spread of small plasmids are used by P. multocida to become multiresistant.
authors.affiliation: Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: Alvaro
authors.initials: A
authors.lastname: San Millan
authors.forename: Jose Antonio
authors.initials: JA
authors.lastname: Escudero
authors.forename: Belen
authors.initials: B
authors.lastname: Gutierrez
authors.forename: Laura
authors.initials: L
authors.lastname: Hidalgo
authors.forename: Nerea
authors.initials: N
authors.lastname: Garcia
authors.forename: Montserrat
authors.initials: M
authors.lastname: Llagostera
authors.forename: Lucas
authors.initials: L
authors.lastname: Dominguez
authors.forename: Bruno
authors.initials: B
authors.lastname: Gonzalez-Zorn
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D015139:Blotting, Southern; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016979:Pasteurella multocida / Q000187:drug effects* / Q000235:genetics; D010957:Plasmids / Q000235:genetics / Q000502:physiology*; D017422:Sequence Analysis, DNA; D013307:Streptomycin / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology; D013754:Tetracyclines / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D013449:Sulfonamides; D013754:Tetracyclines; D013307:Streptomycin