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

Clinical Oligella urethralis isolate COH-1, which was uncommonly resistant to penicillins and narrowspectrum 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 -lactamase-type phenotype of resistance or a carbenicillin-hydrolyzing -lactamase-type phenotype of resistance. The AmpC -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 blaABA-1, providing a 35 promoter sequence and likely giving rise to a hybrid promoter region. The carbenicillin-hydrolyzing -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 blaABA-1-, blaCARB-8-, and 16S rRNA-specific probes indicated the chromosomal integration of the -lactamase genes. PCR and hybridization experiments failed to detect blaCARB-8and blaABA-1-like genes in three O. urethralis reference strains, indicating that the -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 -lactamase.