Chromosomal integration of a cephalosporinase gene from Acinetobacter baumannii into Oligella urethralis as a source of acquired resistance to beta-lactams.

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 beta-lactamase-type phenotype of resistance or a carbenicillin-hydrolyzing beta-lactamase-type phenotype of resistance. The AmpC beta-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, ISOur1, belonging to the IS6 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 beta-lactamase identified (CARB-8), which had a pI value of 6.4, differed from CARB-5 by two amino acid substitutions. Hybridization of CeuI 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 beta-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 beta-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 beta-lactamase.