title: Macrolide inactivation gene cluster mphA-mrx-mphR adjacent to a class 1 integron in Aeromonas hydrophila isolated from a diarrhoeic pig in Oklahoma.
abstract: OBJECTIVE
  To characterize a multidrug-resistant Aeromonas hydrophila isolate (CVM861) that possesses a high-level macrolide inactivation gene cluster (mphA-mrx-mphR), previously only reported in Escherichia coli.
  
  
  METHODS
  PCR fragment length mapping, gene sequencing and Southern blotting were used to map the mphA-mrx-mphR gene cluster and flanking elements in CVM861. Conjugation experiments were done to determine whether the multidrug resistance genetic element was mobile.
  
  
  RESULTS
  The mphA-mrx-mphR gene cluster mapped downstream of a class 1 integron and upstream of an aph(3') gene, and was present on a Tn21-like element. The gene order determined by sequencing was intI1-dhfrXII-orfF-aadA2-qacDeltaE-sul1-orf5Delta178-tnpA-mphR-mrx-mphA. Horizontal transmission of high-level macrolide resistance from CVM861 to E. coli 47011 was inconsistent; however, a composite plasmid possessing the mphA gene cluster was transferred at a conjugation frequency of 2.02 x 10(-5) per recipient.
  
  
  CONCLUSIONS
  An mphA-mrx-mphR gene cluster was present downstream of the In2 integron located on a Tn21-like transposon in an A. hydrophila isolate. Whether this recombination event resulted in the truncation of the orf5 sequence is unknown. The presence of other resistance genes downstream of the mphA-mrx-mphR gene cluster suggests that multiple recombination events have occurred on this genetic element. This is the first known report of the mphA-mrx-mphR gene cluster carried by A. hydrophila and the first known isolation of this cluster in the United States.
authors.affiliation: USDA/ARS, Southern Plains Agricultural Research Center, 2881 F&B Road, College Station, TX 77845, USA. poole@ffsru.tamu.edu
authors.forename: T L
authors.initials: TL
authors.lastname: Poole
authors.forename: T R
authors.initials: TR
authors.lastname: Callaway
authors.forename: K M
authors.initials: KM
authors.lastname: Bischoff
authors.forename: C E
authors.initials: CE
authors.lastname: Warnes
authors.forename: D J
authors.initials: DJ
authors.lastname: Nisbet
mesh_terms: D016980:Aeromonas hydrophila / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000302:isolation & purification; D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D004269:DNA, Bacterial / Q000235:genetics; D003967:Diarrhea / Q000382:microbiology* / Q000662:veterinary; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D005798:Genes, Bacterial; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology* / Q000662:veterinary; D032023:Integrons / Q000235:genetics*; D018942:Macrolides / Q000494:pharmacology; D008969:Molecular Sequence Data; D005810:Multigene Family; D009825:Oklahoma; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology*
chemical_list: D004269:DNA, Bacterial; D018942:Macrolides