A carbapenemase-resistant Klebsiella pneumoniae strain, clone ST258 producing KPC-3, was fully characterized. The entire plasmid content was investigated, thereby identifying plasmids of the IncFII k (two of them similar to pKPQIL and pKPN3, respectively), IncX, and ColE types, carrying a formidable set of resistance genes against toxic compounds, metals, and antimicrobial drugs and a novel iron(III) uptake system.

Carbapenem-resistant Klebsiella pneumoniae caused an outbreak in a hospital in Rome, Italy. The clinical isolates were tested by antimicrobial susceptibility testing, pulsed-field gel electrophoresis, multilocus sequence typing, plasmid typing, and ␤-lactamase identification. The OmpK35 and OmpK36 porins were analyzed by SDS-PAGE, and their genes were amplified and sequenced. Complementation experiments were performed using a recombinant unrelated ompK36 gene. An ertapenem-resistant and imipenem-and meropenem-susceptible clone was identified and assigned to the sequence type 37 lineage by MLST; it carried SHV-12 and CTX-M-15 ESBLs, did not produce the OmpK35 due to a nonsense mutation, and expressed a novel OmpK36 variant (OmpK36V). This variant showed two additional amino acids located within the L3 internal loop, one of the highly conserved domains of the protein. Two isolates of the same clone also exhibited resistance to imipenem and meropenem, due to the loss of OmpK36 expression by a nonsense mutation occurring in the ompK36V variant gene. These were the first carbapenem-resistant K. pneumoniae isolates identified within the hospital. Screening for the ompK36V gene of unrelated K. pneumoniae isolates derived from patients from 2006 to 2009 demonstrated the high frequency of this gene variant as well as its association with ertapenem resistance, reduced susceptibility to meropenem, and susceptibility to imipenem.The susceptibility to carbapenems in the Enterobacteriaceae family is no longer guaranteed since the increasing occurrence of carbapenem-resistant isolates (26, 38). Carbapenem resistance can arise by acquisition of resistance genes encoding metallo-␤-lactamases (MBLs) and non-metallo-carbapenemases (of the KPC, GES, or OXA type) but has also been associated with the AmpC cephalosporinase or extended-spectrum ␤-lactamase (ESBL) production and alterations of the expression of the major nonspecific porins. The latter mechanism has been reported worldwide in clinical isolates of Klebsiella pneumoniae, Escherichia coli, Enterobacter spp., and others (11, 12, 14-18, 23, 24, 31, 35). The alteration of porin expression may be caused by several different events, including the disruption of the gene by insertion sequences, the termination of translation by nonsense mutations, and the downregulation of transcription by mutations occurring within the promoter (12,18,29). In particular, the effect of the alteration of OmpK35 and OmpK36 expression in ESBL-producing K. pneumoniae isolates has been demonstrated to confer a high level of ertapenem resistance, with the MICs of imipenem and meropenem being raised (11,12,14,16,17,24,39).Sequence analysis of the ompK36 genes of clinical isolates of Enterobacter aerogenes, E. coli, and K. pneumoniae demonstrated the importance of transmembrane ␤-strand loop 3 (L3) in the specific uptake of ␤-lactams (3,8,36). The L3 loop constitutes the channel eyelet of enterobacterial porins, extends inside the barrel, and constricts the pore (1). The mutations occurring in L3 drastic...

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Escherichia coli strains producing extended-spectrum ␤-lactamases (ESBLs) are a major problem in many different hospitals worldwide, causing outbreaks as well as sporadic infections. The prevalence of Escherichia coli ESBL producers was analyzed in a surveillance study performed on the population attending the Policlinico Umberto I, the largest university hospital in Rome, Italy. We also investigated genotypes, pathogenicity islands, and plasmids in the ESBL-positive E. coli isolates as further markers that are useful in describing the epidemiology of the infections. In this survey, 163 nonreplicate isolates of Escherichia coli were isolated from patients from 86 different wards, and 28 were confirmed as ESBL producers. A high prevalence (26/28) of CTX-M-15 producers was observed within the bacterial population circulating in this hospital, and the dissemination of this genetic trait was associated with the spread of related strains; however, these do not have the characteristics of a single epidemic clone spreading. The dissemination was also linked to horizontal transfer among the prevalent E. coli genotypes of multireplicon plasmids showing FIA, FIB, and FII replicons in various combinations, which are well adapted to the E. coli species. The analysis of related bacteria suggests a probable interpatient transmission occurring in several wards, causing small outbreaks.A rapid dissemination of isolates producing CTX-M-type extended-spectrum ␤-lactamases (ESBLs) has recently been reported in some European countries, including Italy, and is a matter of major concern. The bla CTX-M genes have been captured on transferable plasmids from the chromosomes of Kluyvera spp., and their products are becoming the most prevalent ESBLs encountered in Enterobacteriaceae (19). The prevalent bla CTX-M -type genes in Europe have been identified as bla CTX-M-1 , bla CTX-M-3 , bla CTX-M-9 , bla CTX-M-14 , and bla CTX-M-15 (2, 19). Infections caused by enterobacteria producing ESBLs are associated with increased morbidity, mortality, and health care-associated costs (9, 16).In Italy, the presence of CTX-M-type ESBLs in clinical isolates of Enterobacteriaceae examined in a Italian nationwide survey (23,27), as well as in isolates from companion animals (7), was previously reported, and the results showed that CTX-M-type enzymes were common overall (around 20%) among ESBL producers (20). However, the local epidemiology of Escherichia coli producing ESBLs may differ from the national picture, with dominance of different strains. We therefore studied the prevalence and the clonality of the Escherichia coli ESBL producers in the population attending the Policlinico Umberto I, the largest university hospital in Rome, Italy, which had not been included in the nationwide survey. We also investigated virulence factors encoded on pathogenicity islands (PAIs) and plasmids carried by the E. coli ESBL producers as further markers that are useful in describing the epidemiology of nosocomially acquired infections. MATERIALS AND METHODS Clinical i...

This study showed a low risk of donor-recipient CPE transmission, indicating that donor CPE colonization does not necessarily represent a contraindication for donation unless colonization regards the organ to be transplanted. Donor and recipient screening remains essential to prevent CPE transmission and cross-infection in transplantation centres.