e Klebsiella pneumoniae strains producing KPC-type carbapenemases (KPC-KP) are challenging multidrug-resistant pathogens due to their extensively drug-resistant phenotypes and potential for epidemic dissemination in health care settings. Colistin is a key component of the combination antimicrobial regimens used for treatment of severe KPC-KP infections. We previously reported that insertional inactivation of the mgrB gene, encoding a negative-feedback regulator of the PhoQ-PhoP signaling system, can be responsible for colistin resistance in KPC-KP, due to the resulting upregulation of the Pmr lipopolysaccharide modification system. In this work we investigated the status of the mgrB gene in a collection of 66 colistin-resistant nonreplicate clinical strains of KPC-KP isolated from different hospitals in Italy and Greece. Overall, 35 strains (53%) exhibited alterations of the mgrB gene, including insertions of different types of mobile elements (IS5-like, IS1F-like, or ISKpn14), nonsilent point mutations, and small intragenic deletions. Four additional strains had a larger deletion of the mgrB locus, while the remaining 27 strains (41%) did not show mgrB alterations. Transcriptional upregulation of the phoQ and pmrK genes (part of the phoPQ and pmrHFIJKLM operon, respectively) was observed in all strains with mgrB alterations. Complementation experiments with a wild-type mgrB gene restored colistin susceptibility and basal expression levels of phoQ and pmrK genes in strains carrying different types of mgrB alterations. The present results suggest that mgrB alteration can be a common mechanism of colistin resistance among KPC-KP in the clinical setting.

fWe describe a large hospital outbreak (93 bloodstream infections) of colistin-resistant Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae isolates which was mirrored by increased colistin consumption. The outbreak was mostly traced to the clonal expansion of an mgrB deletion mutant of an ST512 strain that produced KPC-3.

Although a trend to a polyclonal evolution of the Italian KPC-KP was noted, this study showed that the KPC-KP population remained largely oligoclonal with the wide diffusion of an ST512 lineage carrying cps-2 capsular type and producing the KPC-3 enzyme.

Carbapenem-resistant Enterobacteriaceae (CRE) are emerging as a public health problem in various settings. In Italy, a rapid and remarkable increase of carbapenem-non-susceptible Klebsiella pneumoniae has been reported since 2010. Here we report on the results of a countrywide cross-sectional survey, carried out from 15 May to 30June 2011 to investigate the diffusion of CRE in Italy and to characterise the most prevalent resistance mechanisms and their dissemination patterns. CRE were reported from most (23 of 25) participating laboratories, with an overall proportion of 3.5% and 0.3% among consecutive non-duplicate clinical isolates of Enterobacteriaceae from inpatients (n=7,154) and outpatients (n=6,595), respectively. K. pneumoniae was the most frequent species (proportion of carbapenem-non-susceptible isolates: 11.9%), while a minority of CRE of other species were detected. Carbapenemase production was detected in the majority (85%) of CRE. KPC-type enzymes were by far the most common (89.5% of carbapenemase producers), followed by VIM-1 (9.2%) and OXA-48 (1.3%). KPC-producing K. pneumoniae (KPC-KP) were detected in most centres and contributed majorly to the epidemic dissemination of CRE recently observed in our country. Dissemination of KPC-KP was mostly sustained by strains of clonal complex 258 (ST-258 producing KPC-2 or KPC-3, and ST-512 producing KPC-3), while a minority belonged to ST-101.

Strains of Klebsiella pneumoniae producing KPC-type beta-lactamases (KPC-Kp) are broadly disseminating worldwide and constitute a major healthcare threat given their extensively drug resistant phenotypes and ability to rapidly disseminate in healthcare settings. In this work we report on the characterization of two different capsular polysaccharide (CPS) gene clusters, named cps BO-4 and cps 207-2, from two KPC-Kp clinical strains from Italy belonging in sequence type (ST) 258, which is one of the most successful ST of KPC-Kp spreading worldwide. While cps BO-4 was different from known 78 K-types according to the recently proposed typing schemes based on the wzi or wzc gene sequences, cps 207-2 was classified as K41 by one of these methods. Bioinformatic analysis revealed that they were represented in the genomic sequences of KPC-Kp from strains of ST258 from different countries, and cps BO-4 was also detected in a KPC-Kp strain of ST442 from Brazil. Investigation of a collection of 46 ST258 and ST512 (a single locus variant of ST258) clinical strains representative of the recent Italian epidemic of KPC-Kp by means of a multiplex PCR typing approach revealed that cps BO-4 was the most prevalent type, being detected both in ST258 and ST512 strains with a countrywide distribution, while cps 207-2 was only detected in ST258 strains with a more restricted distribution.