Class 1 and class 2 integrons in non-prevalent serovars of Salmonella enterica: structure and association with transposons and plasmids.
OBJECTIVE
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.
Rodríguez
Irene
I
Departamento de Biología Funcional-Microbiología, Universidad de Oviedo and Instituto Universitario de Biotecnología de Asturias, 33006-Oviedo, Spain.
Martín
M Cruz
MC
Mendoza
M Carmen
MC
Rodicio
M Rosario
MR
D002876:Chromosomes, Bacterial / Q000235:genetics; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics*; D024901:Drug Resistance, Multiple, Bacterial; D016680:Genome, Bacterial; D032023:Integrons / Q000235:genetics*; D020071:Interspersed Repetitive Sequences; D009693:Nucleic Acid Hybridization; D010957:Plasmids / Q000235:genetics*; D016133:Polymerase Chain Reaction; D019779:Salmonella enterica / Q000235:genetics*
D004251:DNA Transposable Elements; D004269:DNA, Bacterial