L. S. Tzouvelekis

Sequence of the Gene Encoding a Plasmid-Mediated Cefotaxime-Hydrolyzing Class A β-Lactamase (CTX-M-4): Involvement of Serine 237 in Cephalosporin Hydrolysis

ABSTRACT The sequence of the gene encoding a novel cefotaxime-hydrolyzing β-lactamase (CTX-M-4) was determined. It was located in a plasmid harbored by a Salmonella typhimurium strain. CTX-M-4 was similar to the plasmidic cefotaxime-hydrolyzing β-lactamases CTX-M-2 and Toho-1 and related to the chromosomal β-lactamase ofKlebsiella oxytoca. A Ser-237→Ala substitution, introduced by site-directed mutagenesis, caused minor alterations in the interaction of CTX-M-4 with β-lactams, reducing slightly the relative hydrolytic activity against cefotaxime and the susceptibility to inhibition by clavulanate.

Extended-spectrum β-lactamase types in Klebsiella pneumoniae and Escherichia coli in two Greek hospitals

Seventy-nine Klebsiella pneumoniae and 124 Escherichia coli clinical strains, isolated consecutively during August-October 2001 in two Greek hospitals, were examined for production of extended-spectrum beta-lactamases (ESBLs). Seventy-one (35%) isolates (46 K. pneumoniae and 25 E. coli) were ESBL-positive by phenotypic methods. Isoelectric focusing of beta-lactamases and PCR assays for bla genes showed that SHV-5-type ESBLs were the most frequent (45 isolates, 22%) followed by CTX-M (24 isolates, 12%) and IBC (three isolates, 1.5%). The latter two ESBL types may have been established recently in this setting.

Outer membrane alterations in multiresistant mutants of Pseudomonas aeruginosa selected by ciprofloxacin.

Spontaneous mutants of Pseudomonas aeruginosa selected by ciprofloxacin were studied for outer membrane alterations. Acquisition of ciprofloxacin resistance was at least partially related to defects in lipopolysaccharide synthesis. When ciprofloxacin resistance was combined with resistance to beta-lactams and aminoglycosides, several alterations in outer membrane proteins were noted. Images

Emergence of CTX-M-15-Producing Enterobacteria in Cameroon and Characterization of a blaCTX-M-15-Carrying Element

ABSTRACT CTX-M-15-producing Klebsiella pneumoniae and Escherichia coli emerged recently in Cameroon. CTX-M-15 was encoded by two different multiresistance plasmids, of which one carried an ISEcp1-blaCTX-M-15 element flanked by a 5-bp target site duplication and inserted within a Tn2-derived sequence. A truncated form of this element in the second plasmid was identified.

CMY-13, a Novel Inducible Cephalosporinase Encoded by an Escherichia coli Plasmid

ABSTRACT An IncN plasmid (p541) from Escherichia coli carried a Citrobacter freundii-derived sequence of 4,252 bp which included an ampC-ampR region and was bound by two directly repeated IS26 elements. ampC encoded a novel cephalosporinase (CMY-13) with activity similar to that of CMY-2. AmpR was likely functional as indicated in induction experiments.

Nucleotide sequence of a plasmid-mediated cephalosporinase gene (blaLAT-1) found in Klebsiella pneumoniae.

The nucleotide sequence of the gene encoding a novel cephalosporinase (LAT-1), carried by a non-self-transferable plasmid from Klebsiella pneumoniae, has been determined. It was found that the sequence shares a high degree of homology with the Citrobacter freundii OS60 ampC structural gene.

KPC-Producing, Multidrug-Resistant Klebsiella pneumoniae Sequence Type 258 as a Typical Opportunistic Pathogen

ABSTRACT The virulence of a KPC-producing Klebsiella pneumoniae sequence type 258 (ST258) strain representing those circulating in Greece was assessed in a mouse septicemia model. The strain was virtually avirulent (50% lethal dose, >108 and 5 × 107 CFU for immunocompetent and neutropenic animals, respectively). Also, it was highly susceptible to serum killing, rapidly phagocytosed in vitro, and classified as K41, which is not among the virulent capsular types. The findings indirectly support the notion that high ST258-associated mortality is largely due to inefficient antimicrobial treatment.

Sequence of pNL194, a 79.3-Kilobase IncN plasmid carrying the blaVIM-1 metallo-β-lactamase gene in Klebsiella pneumoniae.

ABSTRACT The nucleotide sequence of pNL194, a VIM-1-encoding plasmid, is described in this study. pNL194 (79,307 bp) comprised an IncN-characteristic segment (38,940 bp) and a mosaic structure (40,367 bp) including blaVIM-1, aacA7, aadA1, aadA2, dfrA1, dfrA12, aphA1, strA, strB, and sul1. Tn1000 or Tn5501 insertion within fipA probably facilitated recruitment of additional mobile elements carrying resistance genes.

Klebsiella pneumoniae infections in Greek hospitals. Dissemination of plasmids encoding an SHV-5 type β-lactamase☆

A total of 160 Klebsiella pneumoniae clinical strains consecutively isolated in 14 Greek hospitals in a three-month period was examined. Application of capsular typing using 72 monovalent antisera combined with phage-typing using a set of 15 Klebsiella-specific phages showed the absence of epidemic strains. However, 41% of the isolates examined displayed high level resistance to ceftazidime and aztreonam and, in most of the cases, to more than one aminoglycoside as well as to other antibacterial drugs. Nearly all of these multi-resistant strains were epidemiologically distinct on the basis of their capsular serotype and phage reactivity. After examination of 14 distinct strains, it was found that in nine cases, the resistance characters were readily transferred to Escherichia coli recipients through large self-transmissible plasmids (15-100 MDa). Six of the nine plasmids had equal molecular weight (60 MDa) and displayed similar fragment profiles upon digestion with restriction endonuclease EcoRI. Isoelectric focusing and hydrolytic studies showed that the prominent beta-lactamase produced by the transconjugants harbouring the 60 MDa plasmids and the respective K. pneumoniae parent strains, was an extended-spectrum beta-lactamase of the SHV-5 type. It appears that among K. pneumoniae strains isolated in Greek hospitals a significant resistance rate to both newer beta-lactams and amino-glycosides has been established through the acquisition of promiscuous multi-resistant plasmids which share a high degree of similarity.

Characterization of Metallo-β-Lactamase VIM-27, an A57S Mutant of VIM-1 Associated with Klebsiella pneumoniae ST147

ABSTRACT VIM-27 metallo-β-lactamase, an Ala57 → Ser variant of VIM-1, was identified in three Klebsiella pneumoniae isolates belonging to sequence type 147. blaVIM-27 was part of a class 1 integron carried by non-self-transferable plasmids. Kinetic parameters and MIC determinations indicated that VIM-27 hydrolyzed most β-lactams, especially imipenem and cefoxitin, less effectively than VIM-1.