Proteus mirabilis clinical isolate harbouring a new variant of Salmonella genomic island 1 containing the multiple antibiotic resistance region

Objectives: A clinical isolate of Proteus mirabilis strain 18306, which displayed the multidrug resistance phenotype of Salmonella genomic island 1 (SGI1), was examined for the presence of this island including its multiple antibiotic resistance genomic region. Methods: P. mirabilis 18306 was isolated in March 2006 from a patient in Palestine with diabetic foot infection. Antibiotic susceptibility tests and various molecular techniques, including PCR, cloning and DNA sequencing were used for detection and characterization of SGI1 in P. mirabilis 18306. Results: P. mirabilis 18306 showed the typical multidrug resistance phenotype of SGI1 as it was resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides and tetracycline, in addition to trimethoprim and nalidixic acid. Molecular characterization showed that P. mirabilis 18306 harboured a structure similar to SGI1, except that the aadA2 gene, which confers resistance to streptomycin and spectinomycin, of standard SGI1 had been replaced with dfrA15, which confers resistance to trimethoprim. Furthermore, the nucleotide sequence of the extrachromosomal circular form of SGI1 in P. mirabilis was found to be identical to that of Salmonella Typhimurium DT104. However, PCR results showed that P. mirabilis 18306 was negative for the left and right junctions which represent the integration sites of SGI1 into Salmonella enterica chromosome. Hence, this new variant of SGI1 may be integrated at a different site into the chromosome of P. mirabilis 18306. Tn 1826-derived class 2 integron, which carries only two gene cassettes, sat2 and aadA 1, was also identified in this strain. Conclusions: In this study, we identified a new variant SGI1 containing the multiple resistance genomic region in a multidrug-resistant strain of P. mirabilis. This is the first report for SGI1 in a genus other than Salmonella.