Chromosomal Integration of a Cephalosporinase Gene from Acinetobacter baumannii into Oligella urethralis as a Source of Acquired Resistance to β-Lactams

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Abstract
Clinical Oligella urethralis isolate COH-1, which was uncommonly resistant to penicillins and narrow-spectrum cephalosporins, was recovered from a 55-year-old patient with a urinary tract infection. Shotgun cloning into Escherichia coli and expression experiments gave recombinant clones expressing either an AmpC β-lactamase-type phenotype of resistance or a carbenicillin-hydrolyzing β-lactamase-type phenotype of resistance. The AmpC β-lactamase identified (ABA-1), which had a pI value of 8.2, had 98% amino acid identity with a chromosomally encoded cephalosporinase of Acinetobacter baumannii . A 820-bp insertion sequence element, IS Our1 , belonging to the IS 6 family of insertion sequence elements, was identified immediately upstream of bla ABA-1 , providing a −35 promoter sequence and likely giving rise to a hybrid promoter region. The carbenicillin-hydrolyzing β-lactamase identified (CARB-8), which had a pI value of 6.4, differed from CARB-5 by two amino acid substitutions. Hybridization of Ceu I fragment I-restricted DNA fragments of O. urethralis COH-1 with bla ABA-1 -, bla CARB-8 -, and 16S rRNA-specific probes indicated the chromosomal integration of the β-lactamase genes. PCR and hybridization experiments failed to detect bla CARB-8 - and bla ABA-1 -like genes in three O. urethralis reference strains, indicating that the β-lactamase genes identified were the source of acquired resistance in O. urethralis COH-1. This is one of the few examples of the interspecies transfer and the chromosomal integration of a gene encoding a naturally occurring β-lactamase.

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