Investigation of diversity of plasmids carrying the blaTEM-52 gene

OBJECTIVES: To investigate the diversity of plasmids that carry blaTEM-52 genes among Escherichia coli and Salmonella enterica originating from animals, meat products and humans. METHODS: A collection of 22 blaTEM-52-encoding plasmids was characterized by restriction fragment length polymorphism (RFLP), replicon typing (by PCR or replicon sequencing), susceptibility testing, assessment of plasmid ability to self-transfer by conjugation and typing of the genetic environment of the blaTEM-52 gene.

Detected IncI1 plasmids underwent further plasmid multilocus sequence typing. RESULTS: RFLP profiles demonstrated dissemination of blaTEM-52 in Denmark (imported meat from Germany), France, Belgium and the Netherlands from 2000 to 2006 by mainly two different plasmids, one encoding blaTEM-52b (IncX1A, 45 kb) and the other blaTEM-52c (IncI1, 80 kb).

In addition, blaTEM-52b was also found to be located on various other plasmids belonging to IncA/C and IncL/M, while blaTEM-52c was found on IncN-like as well as on IncR plasmids. In the majority of cases (n = 21) the blaTEM-52 gene was located on a Tn3 transposon. Seven out of 10 blaTEM-52 plasmids tested in conjugation experiments were shown to be capable of self-transfer to a plasmid-free E. coli recipient.

CONCLUSIONS: The blaTEM-52 gene found in humans could have been transmitted on transferable plasmids originating from animal sources. Some of the blaTEM-52 plasmids carry replicons that differ from the classical ones. Two novel replicons were detected, IncX1A and IncN-like. Unlike its predecessor blaTEM-1, the blaTEM-52 gene was not detected on F-type replicons suggesting that this gene evolved on other types of plasmid scaffolds.