[Enzymatic resistance to beta lactam antibiotics within the genus Proteus and evaluation of Proteus mirabilis phenotypes and genotypes for resistance to third- and fourth-generation cephalosporins]

OXA-258 from Achromobacter ruhlandii: a species-specific marker

A new blaOXA-258 gene is described as a species-specific taxonomic marker for Achromobacter ruhlandii isolates (all recovered from cystic fibrosis patients). Even though OXA-258 differs from OXA-114 variants, isolates could be misidentified as A. xiloxosidans by the amplification of an inner fragment from the OXA-coding gene. A robust identification of A. ruhlandii can be achieved by sequencing this single OXA gene, as well as by a more laborious recently proposed multilocus sequence-typing (MLST) scheme.

Proteus penneri

Proteus penneri, formerly P. vulgaris biogroup 1, was recognized as a new species in 1982. This species is associated with clinical processes similar to those involving P. mirabilis and P. vulgaris and expresses similar pathogenic determinants. In clinical samples, P. penneri is mainly isolated from urine (50%), wound and soft tissue exudates (25%), and blood cultures (15%), mostly of nosocomial origin. Although P. penneri is easy to identify, it can be misidentified as P. vulgaris by automatic systems that do not include the indol test result in the identification process. This species has a characteristic susceptibility profile, essentially due to the production of the chromosomal inducible beta-lactamase HugA, which presents a high homology (86%) with CumA from P. vulgaris. HugA is inhibited by clavulanic acid and determines resistance to aminopenicillins and first- and second-generation cephalosporins, including cefuroxime, but does not affect cephamycins or carbapenems, and is inhibited by clavulanic acid. HugA is derepressed due to mutational processes in gene regulators, affecting the activity of cefotaxime and, to a much lesser extent, that of ceftazidime and aztreonam. This phenotype resembles the production of an extended spectrum beta-lactamase. Like other Proteus species, P. penneri is resistant to tetracyclines and should be considered resistant to nitrofurantoin.

CMY-16, a novel acquired AmpC-type beta-lactamase of the CMY/LAT lineage in multifocal monophyletic isolates of Proteus mirabilis from northern Italy

We report multifocal detection (four different cities in northern Italy) of Proteus mirabilis isolates resistant to both oxyimino- and 7-alpha-methoxy-cephalosporins and producing a novel acquired AmpC-like beta-lactamase. The enzyme, named CMY-16, is a variant of the CMY/LAT lineage, which differs from the closest homologues, CMY-4 and CMY-12, by a single amino acid substitution (A171S or N363S, respectively) and from CMY-2 by two substitutions (A171S and W221R). Expression of the cloned bla(CMY-16) gene in Escherichia coli decreased susceptibility to penicillins, cephalosporins, and aztreonam. Tazobactam was more effective than clavulanate at antagonizing the enzyme activity. Genotyping, by random amplification of polymorphic DNA and pulsed-field gel electrophoresis of genomic DNA digested with SfiI, showed that isolates were clonally related to each other, although not identical. The bla(CMY-16) gene was not transferable to E. coli by conjugation or transformation. In all isolates, it was chromosomally located and inserted in a conserved genetic environment. PCR mapping experiments revealed that the bla(CMY-16) was flanked by ISEcp1 and the blc gene, similar to other genes of this lineage from plasmids of Salmonella enterica, Klebsiella spp., and E. coli. Overall, these results revealed multifocal spreading of a CMY-16-producing P. mirabilis clone in northern Italy. This finding represents the first report of an acquired AmpC-like beta-lactamase in Proteus mirabilis from Italy and underscores the emergence of similar resistance determinants in the European setting.