title: Characterization of a large outbreak by CTX-M-1-producing Klebsiella pneumoniae and mechanisms leading to in vivo carbapenem resistance development.
abstract: All extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae isolates from patients admitted to and adult intensive care unit were prospectively documented from 2002 to 2005, when a large outbreak (51 patients affected) of multiresistant ESBL-producing Klebsiella pneumoniae infection was detected. The involvement of a single K. pneumoniae clone was demonstrated by pulsed-field gel electrophoresis. In addition to the ESBL-mediated resistance, the epidemic strain uniformly showed cross-resistance to ciprofloxacin, gentamicin, tobramycin, trimethoprim-sulfamethoxazole, and tetracycline, whereas resistance to the beta-lactam-beta-lactamase inhibitor combinations was variable. The ESBL involved was CTX-M-1, as demonstrated by isoelectric focusing, PCR amplification, and sequencing. CTX-M-1 as well as the aminoglycoside resistance determinants were encoded in a 50-kb plasmid that could be transferred to Escherichia coli only by transformation. In two of the infected patients, carbapenem resistance development (MICs of 8 to 12, 16, and >32 microg/ml for imipenem, meropenem, and ertapenem, respectively) was documented, both in clinical samples and in intestinal colonization studies. The analysis of the outer membrane proteins of the carbapenem-susceptible and -resistant isolates revealed that the former expressed only one of the two major porins, OmpK36, whereas the latter did not express either of them. In one of the cases, the lack of expression of OmpK36 was demonstrated to be mediated by the interruption of the coding sequence by the insertion sequence IS26. This is the first report of a large outbreak of CTX-M-1-producing Enterobacteriaceae and, curiously, the first documented description in the literature of CTX-M-1 in K. pneumoniae, despite the fact that this enzyme has been found in multiple species. Furthermore, we document and characterize for the first time carbapenem resistance development in CTX-M-1-producing Enterobacteriaceae.
authors.affiliation: Servicio de Microbiología, Hospital Son Dureta and Instituto Universitario de Investigación en Ciencias de la Salud, Palma de Mallorca, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Mena
authors.forename: Virginia
authors.initials: V
authors.lastname: Plasencia
authors.forename: Laura
authors.initials: L
authors.lastname: García
authors.forename: Olga
authors.initials: O
authors.lastname: Hidalgo
authors.forename: José Ignacio
authors.initials: JI
authors.lastname: Ayestarán
authors.forename: Sebastián
authors.initials: S
authors.lastname: Alberti
authors.forename: Nuria
authors.initials: N
authors.lastname: Borrell
authors.forename: José L
authors.initials: JL
authors.lastname: Pérez
authors.forename: Antonio
authors.initials: A
authors.lastname: Oliver
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000032:analysis / Q000302:isolation & purification; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification; D015153:Blotting, Western; D016172:DNA Fingerprinting; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics; D004196:Disease Outbreaks; D024901:Drug Resistance, Multiple, Bacterial; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics; D022761:Gene Transfer, Horizontal; D006801:Humans; D007525:Isoelectric Focusing; D007710:Klebsiella Infections / Q000453:epidemiology* / Q000382:microbiology*; D007711:Klebsiella pneumoniae / Q000145:classification / Q000187:drug effects* / Q000201:enzymology / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D018272:Porins / Q000032:analysis / Q000235:genetics / Q000302:isolation & purification; D014169:Transformation, Bacterial; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D018272:Porins; C055184:beta-lactamase TEM-3; D001618:beta-Lactamases