[Objectives] To characterize class 1 and class 2 integrons which were simultaneously detected in non-typhoid Salmonella enterica strains of non-prevalent serovars, and to investigate their possible association with transposons and/or plasmids.
[Methods] Eight multidrug-resistant S. enterica strains belonging to serovars Virchow (4), Panama (2), Grumpensis (1) and Worthington (1), each containing a class 1 and a class 2 integron, were analysed. Nested PCR amplification was used to determine the gene-cassette configuration of the integrons. Overlapping PCR amplifications were applied in integron–transposon linkage experiments. Conjugation and hybridization experiments were used to localize integrons and transposons in the bacterial genome (plasmid and chromosome associated).
[Results] One of two different class 1 integrons (with variable regions of 1000 bp/aadA1 and 2300 bp/sat-smr-aadA1) inserted into Tn21-like transposons, were found to coexist with the class 2 integron (2300 bp/dfrA1-sat1-aadA1) of Tn7 in the analysed strains. Class 1 integrons were always found in large conjugative plasmids whereas apparently intact or defective copies of the Tn7 integron could be located on the same plasmid and/or the bacterial chromosome.
[Conclusions] This report describes different associations between mobile genetic elements that play a crucial role in the capture and spread of antimicrobial drug resistance. As far as we are aware, this is the first description of class 2 integrons in serovars Panama, Grumpensis and Worthington.
I. R. is the recipient of a grant from the ‘Fundación para el Fomento en Asturias de la Investigación Científica Aplicada y la Tecnología’ (FICYTBP04-086). This work has been supported by projects from
‘Fondo de Investigación Sanitaria’ (PI02-0172) and ‘Ministerio de Educación y Ciencia’ (SAF-2005-04212) of Spain.
Peer reviewed