SGI1-K, a Variant of the SGI1 Genomic Island Carrying a Mercury Resistance Region, in Salmonella enterica Serovar Kentucky

Abstract

A multiple-antibiotic-resistant Salmonella enterica serovar Kentucky strain was found to contain SGI1-K, a variant form of the Salmonella genomic island 1 (SGI1) with an In4-type class 1 integron that contains only one cassette array, aacCA5-aadA7, and an adjacent mercury resistance module. Part of the 3 -conserved segment (3 -CS) of the integron, together with the inverted short segment from the right-hand end of the integron transposition module normally found between the 3 -CS and IS6100 in In4 family integrons, has been removed by an IS6100-mediated deletion. IRt, the right-hand inverted repeat found at the outer end of the integron, abuts a mercury resistance region instead of the usual SGI1 backbone segment. The mer module is a hybrid of those found in Tn501 and Tn21. This mer region and a further uncharacterized segment of at least 10 kb appear to have been incorporated between IRt and the SGI1 backbone. These findings demonstrate that the multidrug resistance region in SGI1 can incorporate new DNA segments in the same way as multiple antibiotic resistance regions in plasmids.

Persistence of fluoroquinolone-resistant Salmonella enterica serovar Kentucky from poultry and poultry sources in Nigeria

“…This study documented a significant contamination of poultry with multidrug-resistant S. Kentucky, which reaffirmed the initial speculation of the existence of a prevailing circulating poultry-associated STI98-X1 CIP R S. Kentucky in Africa, including Nigeria [2]. We speculate that one or more traits must be present in this serovar that underlie its success as colonizer of chickens; perhaps among these traits are those facilitating specific host-bacterial interactions and those that survive in modern poultry farm environments [10,11]. Further studies will be needed to confirm these hypotheses.…”

“…Beyond quinolone resistance, additional resistance to streptomycin, spectinomycin, gentamicin, sulfamethoxazole, and tetracycline were observed in some CIP R S. Kentucky isolates, which points to the presence of SGI (9,10,11); further studies are required to confirm this speculation. The lack of effective policy to regulate the use of fluoroquinolones, including ciprofloxacin, enrofloxacin, and ofloxacin, in chicken production in Nigeria (unpublished data) may have contributed to the dissemination of multidrug-resistant non-typhoidal Salmonella; rapid spread has also been observed in Southeast Asia [2].…”

SGI2, a Relative ofSalmonellaGenomic Island SGI1 with an Independent Origin

“…CR1 and CR3 are related elements that draw a variety of resistance genes into the complex class 1 integrons that contain them (31). All of these deletion, insertion, and exchange events could have occurred by homologous recombination (3,15,22,23), as the wild-type strains are usually recombination proficient and such events have been shown to occur (28,30,31).…”

“…1). In Salmonella serovar Typhimurium strains, 99 bp of sequence found between the end of the thdF gene and yidY in the other serovars (23) is replaced by a second integrated element (called a "retron phage") (4,5). The In104 integron is found near the right end of the SGI backbone, between the tnpR (S027) and S044 genes, and is flanked by a 5-bp duplication of the target sequence, indicating that it took up this position by transposition.…”

Salmonella Genomic Island 1 (SGI1), Variant SGI1-I, and New Variant SGI1-O in Proteus mirabilis Clinical and Food Isolates from China

“…1). SGI1 and variants of it named SGI1-A to SGI1-N have been described for other Salmonella enterica serovars (5,11,12,14,17,18). In Salmonella SGI1 is integrated in the last 18 bp of the thdF gene (specific attB site) (7,14).…”