Distribution of oxytetracycline resistance plasmids between aeromonads in hospital and aquaculture environments: Implication of Tn1721 in dissemination of the tetracycline resistance determinant Tet A

Oxytetracycline-resistant (OTT) mesophilic aeromonads were recovered from u ntreated hospital effluent (72 isolates) and from fish farm hatchery tanks (91 isolates) at sites within the English Lake District, Cumbria, England. The transfer of OTr plasmids from these isolates was investigated. Using Es cherichia coli J53-1 as a recipient, 11 isolates from the hospital site and 6 isolates from the fish farm site transferred OTr plasmids (designated pF BAOT1 to 17), Original isolates were identified using fatty acid methyl est er and fluorescent amplified fragment length polymorphism comparisons as ei ther Aeromonas hydrophila HG3 (eight isolates), A. veronii b.v. sobria HG8 (six isolates), and A. caviae HGB5 (one isolate). One isolate remained unid entified, and one could not be assigned a taxonomic designation beyond the genus level, Plasmids pFBAOT1 to -17 were screened for the presence of the tetracycline resistance determinants Tet A to E and Tet G. Only determinant Tet A (10 plasmids) was detected in these plasmids, with 7 tet gene determ inants remaining unclassified, In all cases, Tet A was located on a 5.5-kb EcoRI restriction fragment, Hybridization with inc-rep probes N, P, Q, W, a nd U shelved pFBAOT3, -4, -5, -6, -7, -9, and -11, from the hospital enviro nment, to be IncU plasmids, Further, restriction fragment length polymorphi sm (RFLP) analyses and DNA probing demonstrated that pFBAOT plasmids were c losely related to IncU OTr plasmids pASOT, pASOT2, pASOT3, pRAS1 (originall y isolated from A, salmonicida strains from fish farms in Scotland and Norw ay, respectively), and pIE420 (isolated from a German hospital E, coli stra in). In addition, DNA analyses demonstrated that plasmids pRAS1 and pIE420 had identical RFLP profiles and that all fragments hybridized to each other . The presence of tetracycline resistance transposon Tn1721 in its entirety or in a truncated form in these plasmids was demonstrated. These results p rovided direct evidence that related tetracycline resistance-encoding plasm ids have disseminated between different Aeromonas species and E, coli and b etween the human and aquaculture environments in distinct geographical loca tions. Collectively, these findings provide evidence to support the hypothe sis that the aquaculture and human compartments of the environment behave a s a single interactive compartment.