Imipenem Resistance in a Salmonella Clinical Strain Due to Plasmid-Mediated Class A Carbapenemase KPC-2

Abstract

A Salmonella enterica serotype Cubana isolate exhibiting resistance to most ␤-lactam antibiotics, including oxyimino-cephalosporins and imipenem, was isolated from a 4-year-old boy with gastroenteritis in Maryland. ␤-Lactam resistance was mediated by a conjugative plasmid that encoded KPC-2, a class A carbapenemase previously found in a Klebsiella pneumoniae isolate from the Maryland area as well. Sequence analysis of the flanking regions indicated a potential association of bla KPC-2 with mobile structures.Resistance to expanded-spectrum oxyimino-cephalosporins among Salmonella strains is mostly due to acquisition of plasmids encoding various class A extended-spectrum ␤-lactamases (1,8,13,17,(19)(20)(21). Production of plasmid-mediated class C ␤-lactamases by Salmonella isolates has also been described previously (4,22,23). The emergence of such strains may have serious implications because of the limitation of therapeutic choices for patients with invasive Salmonella infections and by facilitation of the spread of bla genes in the community. We describe here an imipenem-resistant Salmonella enterica serotype Cubana isolate that produces the recently described KPC-2 ␤-lactamase (E. S. MATERIALS AND METHODSSalmonella serotype Cubana was isolated in December 1998 from a stool specimen of a 4-year-old boy with diarrhea in a hospital in Maryland. The patient was chronically ill with Wiskott-Aldrich syndrome. In the 6 months before isolation of serotype Cubana, he had been hospitalized three times and had received intravenous antibiotics. During each of those hospitalizations he had received intravenous ␤-lactams, including ceftriaxone and ceftazidime, but not carbapenems. There was no history of recent travel. The isolate (AM04707) was submitted to the Centers for Disease Control and Prevention as part of the National Antimicrobial Resistance Monitoring System for enteric bacteria (http://www .cdc.gov/NARMS/) and was subsequently forwarded to the Hellenic Pasteur Institute.Escherichia coli K-12 strain 14R525 (Nal r ) was used as the recipient in conjugation experiments. E. coli DH5␣ (GIBCO-BRL, Carlsbad, Calif.) was used for transformation. Chloramphenicol-resistant plasmid pBCSK(ϩ) (Stratagene, La Jolla, Calif.) was used for cloning and expression of bla genes.The MICs of ␤-lactams were determined by an agar dilution technique (10). Susceptibilities to other antimicrobial agents were assessed by a disk diffusion method (11) and by a partial-range broth microdilution method (Sensititre; Trek Diagnostics; Westlake, Ohio), according to the instructions of the manufacturer.Conjugation experiments were carried out in mixed broth cultures as described previously (5). Transconjugant clones were selected on Mueller-Hinton agar containing ampicillin (50 g/ml) plus nalidixic acid (200 g/ml). Plasmid DNA preparations were obtained by an alkaline lysis technique and resolved in 0.8% (wt/vol) agarose gels. Individual plasmids were excised as discrete bands from low-melting-point agarose (0.8%) and were subjected to partial di...

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SCT in patients with carbapenem resistant Klebsiella pneumoniae: a single center experience with oral gentamicin for the eradication of carrier state

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