Plasmid-encoded tetracycline resistance in Salmonella enterica subsp. enterica serovars choleraesuis and typhimurium: identification of complete and truncated Tn1721 elements

Abstract

During routine screening of Salmonella enterica subsp., S. enterica isolates of animal origin for plasmid-encoded tetracycline resistance, two tetracycline resistance plasmids, the 50 kbp plasmid pGFT3 of Salmonella choleraesuis and the 9.5 kbp plasmid pGFT4 of Salmonella typhimurium var. Copenhagen DT002, were detected. The respective tetracycline resistance genes (tet) were identified by hybridization and PCR analysis to belong to hybridization class A. Conjugation experiments identified plasmid pGFT3 as a conjugative plasmid. Molecular analysis of the tet(A) gene area and the flanking regions identified a complete Tn1721-like transposon on plasmid pGFT3 and a truncated Tn1721-like element on plasmid pGFT4. The complete Tn1721-like element was integrated into a transposase reading frame of a truncated Tn3 transposon also located on plasmid pGFT3. The truncated Tn1721-like element of plasmid pGFT4 lacked the entire transposase part. This Tn1721-relic was integrated in an unknown reading frame which on amino acid level showed homology to the Rop protein of Escherichia coli. A model for the deletion of the transposase part was developed on the basis of the sequences present at the termini of the truncated Tn1721-like element. ß

Distribution of Oxytetracycline Resistance Plasmids between Aeromonads in Hospital and Aquaculture Environments: Implication of Tn 1721 in Dissemination of the Tetracycline Resistance Determinant Tet A

“…Collectively, these findings provide evidence that suggests that we should consider the two environments (fish farm and hospital) one interactive compartment and are therefore contrary to the hypothesis of Smith and coworkers (40). The involvement of Tn1721 and Tn1721-like elements in the dissemination of the Tet A determinant, as demonstrated here and by other workers (13,39), is extremely relevant to this interaction and, globally, to the potential dissemination of these and similar plasmids.…”

Tetracycline and Streptomycin Resistance Genes, Transposons, and Plasmids in Salmonella enterica Isolates from Animals in Italy

“…Thirty-seven of 39 tet(A) genes were found to be located within the Tn1721 transposon by PCR with primers TAF and TetAR3 (12) ( Table 2). Since a Tn1721 deleted version (⌬Tn1721) has been described previously (9), a different primer pair (LAF-LAR [ Table 2]) was used to identify the left arm of the transposon. Only four strains were positive by this PCR assay, indicating that the deletion of the Tn1721 transposon was found widely among the Salmonella strains of our collection ( The strA and strB genes were also highly prevalent in Salmonella strains of our collection, being detected in 46 of 55 (84%) streptomycin-resistant strains.…”

“…The tet gene of class A was found on plasmids as well as on the chromosome, whereas the genes tet(B), tet(C), and tet(D) were detected on the chromosomes of S. enterica bacteria of different serotypes, including Typhimurium, Enteritidis, Hadar, Saintpaul, and Choleraesuis (10). The tet(A) gene is often part of transposon Tn1721, and a truncated version of Tn1721 lacking a portion of the left arm has also been described to occur in Salmonella (1,8,9,21). Recently, a new allele of tet(A), designated tet(A)-1, was identified on the pSSTA-1 plasmid in Shigella spp.…”

Characterization Of Tetracycline Resistance Of Salmonella Enterica Subspecies Enterica Serovar Infantis Isolated From Poultry In The Northern Part Of Serbia

“…It was elucidated that the Tn1721 is located in the 9.5 kbp plasmid designated pGFT4. Additionally, the Escherichia coli transformant JM107:pGFT4 was highly resistant to TET [5]. In S. Typhimurium, isolated from the irrigation water in Culiacan Valley Mexico, the tetA gene and truncated Tn1721 transposon were identifi ed.…”