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Antimicrobial Agents and Chemotherapy, July 2008, p. 2529-2537, Vol. 52, No. 7
0066-4804/08/$08.00+0     doi:10.1128/AAC.00189-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

SGI2, a Relative of Salmonella Genomic Island SGI1 with an Independent Origin{triangledown}

Renee S. Levings,1 Steven P. Djordjevic,1 and Ruth M. Hall2*

New South Wales Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Microbiology and Immunology Section, Camden, NSW 2570,1 School of Molecular and Microbial Biosciences, The University of Sydney, NSW 2006, Australia2

Received 1 February 2008/ Returned for modification 26 February 2008/ Accepted 18 April 2008

Multiply antibiotic-resistant Salmonella enterica serovar Emek strains isolated in Australia and the United Kingdom had similar features, suggesting that they all belong to a single clone. These strains all contain SGI2 (formerly SGI1-J), an independently formed relative of Salmonella genomic island SGI1. In SGI2, the complex class 1 integron which includes all of the resistance genes is not located between tnpR (S027) and S044 as in SGI1 and SGI1 variants. Instead, tnpR was found to be adjacent to S044, and the integron is located 6.9 kb away, within S023. In both SGI1 and SGI2, the 25-bp inverted repeats that mark the outer ends of class 1 integrons are flanked by a 5-bp duplication of the target, indicating that incorporation of the integron was by transposition. A small number of differences between the sequences of the backbones of SGI1 and SGI2 were also found. Hence, a class 1 integron has entered two different variants of the SGI backbone to generate two distinct lineages. Despite this, the integron in SGI2 has a complex structure that is very similar to that of In104 in SGI1. Differences are in the cassette arrays and in the gene which encodes the chloramphenicol and florfenicol efflux protein. The CmlA9 protein, encoded by InEmek, is only 92.8% identical to FloRc (also a CmlA family protein) from SGI1. A variant form of SGI2, SGI2-A, which has lost the tet(G) and cmlA9 resistance determinants, was found in one strain.

* Corresponding author. Mailing address: School of Molecular and Microbial Biosciences, Biochemistry and Microbiology Building G08, The University of Sydney, NSW 2006, Australia. Phone: 61-2-9351-3465. Fax: 61-2-9351-4571. E-mail: ruth.hall{at}mmb.usyd.edu.au

{triangledown} Published ahead of print on 28 April 2008.

Antimicrobial Agents and Chemotherapy, July 2008, p. 2529-2537, Vol. 52, No. 7
0066-4804/08/$08.00+0     doi:10.1128/AAC.00189-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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