Chloramphenicol transposons found in Salmonella naestved and Escherichia coli of domestic animal origin

Cloning and sequencing of the class A β-lactamase gene (blaTEM-15) located on a chromosomal Tn801 transposon

Escherichia coli CA0210 was identified in a stool culture of a 03-month-neonate in Tunisia. This strain was resistant to beta-lactams, including ureidopenicillins, ticarcillin-clavulanic acid, cefpirome, ceftazidime, and cefotaxime, but it remained susceptible to imipenem and cefoxitin. The beta-lactam-hydrolyzing beta-lactamase gene of E. coli CA0210 and the upstream and downstream regions were cloned, sequenced, and expressed in E. coli DH5alpha. These resistances were carried by a 1080-bp chromosomal gene that encoded a beta-lactamase with a pI of 6.3. Cloning and sequencing experiments showed that the corresponding blaTEM-15 gene was part of a chromosomally located Tn801 transposon.

Chloramphenicol resistance transposable element TnSs1 of Streptococcus suis, a transposon flanked by IS6-family elements

A new transposon, designated TnSs1, which contains a chloramphenicol acetyltransferase gene flanked by direct repeats of an IS6-family element was found in a field isolate of Streptococcus suis. Polymerase chain reaction and hybridization analyses indicated that another field isolate carried the same transposon in a different location on the chromosome. A transposition assay done with a thermosensitive suicide vector showed that, among the seven TnSs1 mutants tested in this study, six formed a cointegrate between the S. suis genome and the vector with the generation of the third copy of the insertion sequence element, and one harbored one copy of TnSs1 on the chromosome as a result of a subsequent resolution step. On transposition, TnSs1 duplicated an 8-bp sequence at the target site.