Identification of new phages to type strains and comparison with a genotypic method

The aim of this study was to optimize the epidemiological monitoring of strains of Staphylococcus aureus, a major cause of hospital-acquired infections. From September to December 1998 47 S. aureus strains isolated from swabs taken from orthopaedic and trauma patients were in studied. Thirty-five isolates were sensitive to methicillin (MSSA) and 12 were methicillin-resistant (MRSA). Ten of the 47 isolates could not be phage-typed using the international set of typing phages: five of these isolates were MSSA and five were MRSA. These MRSA isolates, which were also not typeable by the phages currently recommended for phage-typing MRSA, were lysed by locally isolated experimental phages 584 and 1814. Phage 1814 lysed the gentamicin-resistant MRSA and phage 584 acted on the gentamicin-sensitive MRSA. Both new phages were inactive against the methicillin-sensitive isolates. Cloning of certain isolates was confirmed by macrorestriction genomic profiles obtained by pulsed-field gel electrophoresis analysis (PFGE). The results showed good discriminatory ability of antibiotic-resistance pattern phenotyping and phage-typing when the phages used were adapted to epidemic-associated MRSA strains.

AmpD is required for regulation of expression of NmcA, a carbapenem-hydrolyzing beta-lactamase of Enterobacter cloacae

To further elucidate the induction process of the carbapenem-hydrolyzing beta-lactamase of Ambler class A, NmcA, ampD genes of the wild-type (WT) strain and of ceftazidime-resistant mutants of Enterobacter cloacae NOR-1 were cloned and tested in transcomplementation experiments. Ceftazidime-resistant E. cloacae NOR-1 mutants exhibited derepressed expression of the AmpC-type cephalosporinase and of the carbapenem-hydrolyzing beta-lactamase NmcA. The ampD genes of Escherichia coli and E. cloacae WT NOR-1 transcomplemented the ceftazidime-resistant E. cloacae NOR-1 mutants to the WT level of beta-lactamase expression, while the mutated ampD alleles of E. cloacae NOR-1 failed to do so. The deduced E. cloacae NOR-1 WT AmpD protein exhibited 95 and 91% amino acid identity with the E. cloacae O29 and E. cloacae 14 WT AmpD proteins, respectively. Of the 12 ceftazidime-resistant E. cloacae NOR-1 strains, 3 had AmpD proteins with amino acid changes, while the others had truncated AmpD proteins. Most of these mutations were located outside the conserved regions that link the AmpD proteins to the cell wall hydrolases. AmpD from E. cloacae NOR-1 is involved in the regulation of expression of both beta-lactamases (NmcA and AmpC), suggesting that structurally unrelated genes may be under the control of an identical genetic system.

Integron-located VEB-1 extended-spectrum beta-lactamase gene in a Proteus mirabilis clinical isolate from Vietnam

A clinical isolate of Proteus mirabilis Lil-1 was obtained from a Vietnamese patient hospitalized in Paris, France. This isolate was resistant to cephalosporins, and there was marked synergy between cephalosporins and clavulanic acid together with unusual synergy between cefoxitin and cefuroxime. PCR analysis revealed the presence of blaVEB-1, an integron-located gene coding for an extended-spectrum beta-lactamase (ESBL) identified previously in an Escherichia coli isolate MG-1 from Vietnam. Using class 1 integron primers and blaVEB-1 intragenic primers, the insert region of the blaVEB-1-containing integron along with flanking sequences were amplified from P. mirabilis Lil-1 whole-cell DNA. A novel class 1 integron, In55, was identified that contained, in addition to intI1, qacEDelta1, sul1 and Orf5 genes, an 8 kb variable region. This region was comparable in size to that found previously in E. coli MG-1, but different from those previously identified in two Pseudomonas aeruginosa isolates from Thailand. In55 was located on a 190 kb self-transferable plasmid, which was different in size and structure from that found in E. coli MG-1. The finding of blaVEB-1 on different plasmids and integrons in enterobacterial isolates underlines the interspecies spread of this novel ESBL gene.