Effect of Resistance Mechanisms on the Inoculum Effect of Carbapenem in Klebsiella pneumoniae Isolates with Borderline Carbapenem Resistance

We aimed to examine the effects of resistance mechanisms on several resistance phenotypes among carbapenem-resistant Klebsiella pneumoniae isolates with borderline carbapenem MICs. We compared carbapenemase-negative K. pneumoniae with carbapenemase-producing K. pneumoniae (CPKP) isolates with similar MICs. CPKP isolates exhibited a marked inoculum effect and were more resistant to the bactericidal effect of meropenem. This suggests that MIC measurements alone may not be sufficient in predicting the therapeutic efficacy of carbapenems against CPKP.     

Ceftazidime-avibactam resistance and restoration of carbapenem susceptibility in KPC-producing Klebsiella pneumoniae infections: A case series

ObjectivesSince the introduction of the β-lactam/β-lactamase inhibitor ceftazidime-avibactam (CZA), rapid evolution of resistance has been reported in different KPC-producing Klebsiella pneumoniae isolates. In this multicenter retrospective study, we describe the emergence of CZA resistance and evaluate the mutations that might be responsible for the restoration of carbapenem susceptibility.MethodsDuring a study period of 18 months, KPC-producing K. pneumoniae isolates of five hospitalized patients were collected with phenotypic development of CZA resistance.ResultsIn vitro restoration of carbapenem susceptibility during treatment was observed in 3 isolates. Whole genome sequencing of these isolates showed a D179Y mutation in the KPC gene of 2 variants and a KPC-2 with a Δ242-GT-243 deletion (KPC-14). Two KPC-3 variants showed CZA resistance with sustained carbapenemase activity without genomic adaptations in the KPC gene.ConclusionsThis study confirms the emergence of CZA resistance in KPC K. pneumoniae. The role of carbapenems in treating patients with these variants is unclear and combination therapies warrant further investigation.     

Emergence in Japan of an imipenem-susceptible, meropenem-resistant Klebsiella pneumoniae carrying blaIMP-6

We identified 5 Klebsiella pneumoniae isolates showing high resistance to β-lactams except imipenem and designated them ISMRK (imipenem-susceptible but meropenem-resistant Klebsiella). They carried the bla_IMP-6 and bla_CTX-M-2 on a self-transmissible plasmid. ISMRK may be falsely categorized as susceptible to carbapenems if imipenem is used to screen carbapenem resistance.     

Efficacy of Humanized Carbapenem Exposures against New Delhi Metallo-β-Lactamase (NDM-1)-Producing Enterobacteriaceae in a Murine Infection Model

Enterobacteriaceae producing the novel carbapenemase New Delhi metallo-β-lactamase (NDM-1) are emerging worldwide. While these organisms often display high levels of in vitro resistance to multiple antibiotics, in vivo efficacy data are lacking. Here, the activities of humanized ertapenem and doripenem exposures were characterized against a wild-type K. pneumoniae and its derived isogenic strains harboring either an NDM-1 or KPC-2 plasmid in immunocompetent mice. In addition, four clinical isolates expressing NDM-1 were evaluated. Human-simulated regimens of ertapenem at 1 g every 24 h and high-dose, prolonged infusion of doripenem at 2 g every 8 h as a 4-h infusion were evaluated over 24 h, and efficacy was determined by the change in bacterial density compared to that in 24-h growth controls. CFU reductions in bacterial density of greater than 1 log unit were observed against the wild-type strain as well as the derived isogenic NDM-1 strain, while no reduction was observed against the derived KPC-2 strain. Postexposure MICs confirmed the in vitro maintenance of the ertapenem resistance marker in both the NDM-1 and KPC-2 strains. Similar to the case for the isogenically derived NDM-1 strain, bacterial density was reduced at 24 h against all four clinical NDM-1 isolates showing variable levels of MICs for carbapenems, with near-maximal activity of both agents occurring when the doripenem MIC was ≤8 μg/ml. While carbapenem monotherapy does not appear to be an option against KPC-based infections, these data suggest that carbapenem monotherapy may be a viable option for treating NDM-1-producing Enterobacteriaceae under certain conditions, and this warrants further in vivo exploration.     

Characteristics of KPC-2–producing Klebsiella pneumoniae (ST258) clinical isolates from outbreaks in 2 Mexican medical centers

The KPC-producing Klebsiella pneumoniae sequence type 258 (ST258) is an important pathogen widely spread in nosocomial infections. In this study, we identified the KPC-2–producing K. pneumoniae clinical isolates of 2 unrelated outbreaks that corresponded to pandemic strain ST258. The isolates showed high resistance to cephalosporins, carbapenems, quinolones, and colistin. The KPC-2–producing K. pneumoniae isolates were compared to the previously studied KPC-3–producing K. pneumoniae isolates from an outbreak in Mexico; they showed an unrelated pulsed-field gel electrophoresis fingerprinting pattern and a different plasmid profile. The KPC-2 carbapenemase gene was identified in two 230- and 270-kb non-conjugative plasmids; however, 1 isolate transferred the KPC-2 gene onto an 80-kb plasmid. These findings endorse the need of carrying out a continuous molecular epidemiological surveillance of carbapenem-resistant isolates in hospitals in Mexico.     

Genetic Factors Associated with Elevated Carbapenem Resistance in KPC-Producing Klebsiella pneumoniae

In the United States, the most prevalent mechanism of carbapenem resistance among Enterobacteriaceae is the production of a Klebsiella pneumoniae carbapenemase (KPC). KPC-producing isolates often exhibit a range of carbapenem MICs. To better understand the factors that contribute to overall carbapenem resistance, we analyzed 27 KPC-producing K. pneumoniae isolates with different levels of carbapenem resistance, 11 with low-level (i.e., meropenem or imipenem MIC ≤ 4 μg/ml), 2 with intermediate-level (i.e., meropenem and imipenem MIC = 8 μg/ml), and 14 with high-level (i.e., imipenem or meropenem MIC ≥ 16 μg/ml) carbapenem resistance, that were received from throughout the United States. Among 14 isolates that exhibited high-level carbapenem resistance, Western blot analysis indicated that 10 produced an elevated amount of KPC. These isolates either contained an increased bla_KPC gene copy number (n = 3) or had deletions directly upstream of the bla_KPC gene (n = 7). Four additional isolates lacked elevated KPC production but had high-level carbapenem resistance. Porin sequencing analysis identified 22 isolates potentially lacking a functional OmpK35 and three isolates potentially lacking a functional OmpK36. The highest carbapenem MICs were found in two isolates that lacked both functioning porins and produced elevated amounts of KPC. The 11 isolates with low-level carbapenem resistance contained neither an upstream deletion nor increased bla_KPC copy number. These results suggest that both bla_KPC copy number and deletions in the upstream genetic environment affect the level of KPC production and may contribute to high-level carbapenem resistance in KPC-producing K. pneumoniae, particularly when coupled with OmpK36 porin loss.The occurrence of Gram-negative bacterial infections that are resistant to extended-spectrum β-lactam antimicrobial agents forces clinicians to rely on carbapenems as a “last resort” to combat these resistant pathogens. However, as carbapenems are more frequently utilized, an increasing number of bacteria with various mechanisms of resistance to this class of antimicrobial agents are identified. The most widespread resistance mechanisms include the production of a carbapenemase and the combination of porin loss with the production of either an AmpC enzyme or an extended-spectrum β-lactamase (4, 15). Klebsiella pneumoniae carbapenemase (KPC), an Ambler class A β-lactamase that can hydrolyze most β-lactam agents, including carbapenems, is now the most prevalent carbapenemase found among clinical Gram-negative isolates in the United States (22).KPC was first reported in a K. pneumoniae isolate from North Carolina in 1996 (28). However, recent reports indicate that KPC-producing Gram-negative isolates are being identified throughout the United States as well as parts of Europe, Asia, and South America (13, 20, 22). Although these β-lactamases occur most commonly in K. pneumoniae, they have also been identified in other members of the Enterobacteriaceae family and in Pseudomonas and Acinetobacter species (3, 21, 24, 26, 27). The bla_KPC gene is plasmid mediated and is carried on a Tn3-based transposon, Tn4401 (17), which may account for the high mobility of this resistance mechanism.KPC-producing isolates can exhibit a range of carbapenem MICs, thus making their detection a significant challenge for clinical laboratories. By using 2009 Clinical and Laboratory Standards Institute (CLSI) breakpoints and testing methods (1, 6), some KPC-producing isolates may be identified as susceptible to carbapenems. The clinical significance of carbapenem-susceptible isolates with elevated carbapenem MICs is unclear (6), and the cellular changes that may convert a susceptible KPC-producing isolate to one with MICs indicating resistance to carbapenem are not well described. From previous reports, we know that KPC production combined with porin loss can result in higher carbapenem MICs (10, 14, 29). This finding suggests that the KPC enzyme alone is not always sufficient to confer carbapenem resistance, as defined by the 2009 CLSI breakpoints.Other factors likely result in higher carbapenem MICs for KPC-producing isolates. For example, isolates with an increased expression of bla_KPC were previously shown to have increased rates of hydrolysis of imipenem and meropenem (14). Directly upstream of the bla_KPC gene is a nonconserved region of the Tn4401 transposon, located between the istB and the bla_KPC genes (17). Previous reports describe four isoforms in this variable region: Tn4401a contains a 100-bp deletion, Tn4401b contains no deletion (17), and isoforms with 215-bp (GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"DQ989640","term_id":"116263782","term_text":"DQ989640"}}DQ989640) and 255-bp (13) deletions were recently reported. Additional studies of this variable region suggest that the 100-bp deletion may result in a different −35 promoter region of the bla_KPC gene (11). Upstream deletions that affect the promoter may impact the level of bla_KPC expression and thus would influence the overall level of carbapenem resistance. Also, KPC-producing isolates may contain different levels of bla_KPC dosage based on the presence of multiple copies of a bla_KPC-carrying plasmid, multiple bla_KPC-carrying plasmids, or multiple copies of the bla_KPC gene located within the same plasmid (11). Increasing the bla_KPC gene copy number could result in increased enzyme production and higher carbapenem MICs. Understanding the impact of these factors may help to predict the potential for KPC-producing isolates susceptible to carbapenems to convert to isolates resistant to carbapenems.In this study, we examined genetic factors that may enhance the level of carbapenem resistance. We selected 27 KPC-producing K. pneumoniae isolates that were obtained from clinical patients in different areas of the country and exhibited a range of carbapenem MICs. These isolates were characterized by determining the sequences of the two main porins, OmpK35 and OmpK36 (9), examining levels of KPC production by Western blot analysis, comparing relative bla_KPC copy numbers using quantitative real-time PCR, and analyzing sequence variations in the genetic environment directly upstream of the bla_KPC gene.     

Outer Membrane Profiles of Clonally Related Klebsiella pneumoniae Isolates from Clinical Samples and Activities of Cephalosporins and Carbapenems

Fifteen isolates of Klebsiella pneumoniae producing extended-spectrum β-lactamases (ESBLs) isolated during a nosocomial outbreak were studied. The strains belonged to the same clonal type, as shown by pulsed-field gel electrophoretic analysis of chromosomal DNA. All the isolates were resistant to extended-spectrum cephalosporins, aztreonam, gentamicin, and fluoroquinolones and were susceptible to carbapenems, tobramycin, netilmicin, and amikacin. None of the isolates expressed the OmpK36 porin. Eight isolates, for which the MICs of cefoxitin were ≥64 μg/ml, showed a diminished level or no expression of a 35-kDa porin. The MICs of meropenem, cefotaxime, and cefpirome were three to eight times higher for porin-deficient isolates than for isolates expressing the 35-kDa porin, but the MICs of imipenem increased two times for porin-deficient isolates compared to those for isolates expressing the porin. This MIC increase reverted to a level similar to that for the parental strain when porin-deficient isolates were transformed with the gene coding for the K. pneumoniae porin OmpK36. It is concluded that the high level of resistance to cefoxitin and the increase in the MICs of meropenem, cefotaxime, and cefpirome for the ESBL-producing K. pneumoniae isolates studied are associated with porin deficiency.     

Characterization of BKC-1 Class A Carbapenemase from Klebsiella pneumoniae Clinical Isolates in Brazil

Three Klebsiella pneumoniae clinical isolates demonstrating carbapenem resistance were recovered from different patients hospitalized at two medical centers in São Paulo, Brazil. Resistance to all β-lactams, quinolones, and some aminoglycosides was observed for these isolates that were susceptible to polymyxin B. Carbapenem hydrolysis, which was inhibited by clavulanic acid, was observed for all K. pneumoniae isolates that belonged to the same pulsed-field gel electrophoresis (PFGE) type and a novel sequence type (ST), ST1781 (clonal complex 442 [CC442]). A 10-kb nonconjugative incompatibility group Q (IncQ) plasmid, denominated p60136, was transferred to Escherichia coli strain TOP10 cells by electroporation. The full sequencing of p60136 showed that it was composed of a mobilization system, ISKpn23, the phosphotransferase aph3A-VI, and a 941-bp open reading frame (ORF) that codified a 313-amino acid protein. This ORF was named bla_BKC-1. Brazilian Klebsiella carbapenemase-1 (BKC-1) showed a pI of 6.0 and possessed the highest identity (63%) with a β-lactamase of Sinorhizobium meliloti, an environmental bacterium. Hydrolysis studies demonstrated that purified BKC-1 not only hydrolyzed carbapenems but also penicillins, cephalosporins, and monobactams. However, the carbapenems were less efficiently hydrolyzed due to their very low k_cat values (0.0016 to 0.031 s⁻¹). In fact, oxacillin was the best substrate for BKC-1 (k_cat/K_m, 53,522.6 mM⁻¹ s⁻¹). Here, we report a new class A carbapenemase, confirming the diversity and rapid evolution of β-lactamases in K. pneumoniae clinical isolates.     

Characteristics of carbapenem-resistant Enterobacteriaceae isolates from Korea

In this study, the characteristics of carbapenem-resistant Enterobacteriaceae (CRE) isolates from Korea was investigated. A total of 22 CRE isolates were investigated, and most were identified as Klebsiella pneumoniae (16 isolates). In vitro antimicrobial susceptibility testing, multilocus sequence typing, and pulsed-field gel electrophoresis were performed. Extended-spectrum β-lactamase (ESBL) and carbapenemase genes were detected using gene amplification and sequencing. Efflux pump activity and inactivating mutations in OmpK35/36 were also investigated. Among 22 CRE isolates, only 5 produced metallo-β-lactamases (3 NDM-1, one VIM-2 and one IMP-1). Four and 2 K. pneumoniae and Serratia marcescens isolates showed resistance to polymyxins, respectively, and 2 CRE isolates (1 K. pneumoniae and C. freundii) were resistant to tigecycline. The prevalent carbapenem resistance mechanism found in K. pneumoniae might be porin defects. The most prevalent clone of carbapenem-resistant K. pneumoniae was ST11 (56.3%), which is the most frequently identified clone among ESBL-producing K. pneumoniae isolates from Korea. Three NDM-1-producing K. pneumoniae isolates belonged to a single clone (ST340) despite their different antimicrobial susceptibilities. In the present study, the clonal dissemination of carbapenem-resistant K. pneumoniae isolates (ST11) and NDM-1-producing K. pneumoniae isolates (ST340) was determined. Polymyxin- and tigecycline-resistant CRE isolates were also identified, which limits treatment options for infections causes by these organisms.     

Antibiofilm Peptides Increase the Susceptibility of Carbapenemase-Producing Klebsiella pneumoniae Clinical Isolates to β-Lactam Antibiotics

Multidrug-resistant carbapenemase-producing Klebsiella pneumoniae (KpC) strains are becoming a common cause of infections in health care centers. Furthermore, Klebsiella can develop multicellular biofilms, which lead to elevated adaptive antibiotic resistance. Here, we describe the antimicrobial and antibiofilm activities of synthetic peptides DJK-5, DJK-6, and 1018 against five KpC isolates. Using static microplate assays, it was observed that the concentration required to prevent biofilm formation by these clinical isolates was below the MIC for planktonic cells. More-sophisticated flow cell experiments confirmed the antibiofilm activity of the peptides against 2-day-old biofilms of different KpC isolates, and in some cases, the peptides induced significant biofilm cell death. Clinically relevant combinations of DJK-6 and β-lactam antibiotics, including the carbapenem meropenem, also prevented planktonic growth and biofilm formation of KpC strain1825971. Interestingly, peptide DJK-6 was able to enhance, at least 16-fold, the ability of meropenem to eradicate preformed biofilms formed by this strain. Using peptide DJK-6 to potentiate the activity of β-lactams, including meropenem, represents a promising strategy to treat infections caused by KpC isolates.     

In vivo selection of carbapenem-resistant Klebsiella pneumoniae by OmpK36 loss during meropenem treatment

We recovered a carbapenem-resistant Klebsiella pneumoniae isolate H224 under in vivo meropenem selection pressure. Insertional inactivation of a major porin gene, ompK36, by IS5 element might play a role in acquiring carbapenem resistance in this strain harboring plasmid-borne DHA-1 AmpC β-lactamase.     

Genomic Epidemiology of Klebsiella pneumoniae in Italy and Novel Insights into the Origin and Global Evolution of Its Resistance to Carbapenem Antibiotics

Klebsiella pneumoniae is at the forefront of antimicrobial resistance for Gram-negative pathogenic bacteria, as strains resistant to third-generation cephalosporins and carbapenems are widely reported. The worldwide diffusion of these strains is of great concern due to the high morbidity and mortality often associated with K. pneumoniae infections in nosocomial environments. We sequenced the genomes of 89 K. pneumoniae strains isolated in six Italian hospitals. Strains were selected based on antibiotypes, regardless of multilocus sequence type, to obtain a picture of the epidemiology of K. pneumoniae in Italy. Thirty-one strains were carbapenem-resistant K. pneumoniae carbapenemase producers, 29 were resistant to third-generation cephalosporins, and 29 were susceptible to the aforementioned antibiotics. The genomes were compared to all of the sequences available in the databases, obtaining a data set of 319 genomes spanning the known diversity of K. pneumoniae worldwide. Bioinformatic analyses of this global data set allowed us to construct a whole-species phylogeny, to detect patterns of antibiotic resistance distribution, and to date the differentiation between specific clades of interest. Finally, we detected an ∼1.3-Mb recombination that characterizes all of the isolates of clonal complex 258, the most widespread carbapenem-resistant group of K. pneumoniae. The evolution of this complex was modeled, dating the newly detected and the previously reported recombination events. The present study contributes to the understanding of K. pneumoniae evolution, providing novel insights into its global genomic characteristics and drawing a dated epidemiological scenario for this pathogen in Italy.     

Severe Sepsis Facilitates Intestinal Colonization by Extended-Spectrum-β-Lactamase-Producing Klebsiella pneumoniae and Transfer of the SHV-18 Resistance Gene to Escherichia coli during Antimicrobial Treatment

Infections caused by multidrug-resistant pathogens are frequent and life threatening in critically ill patients. To investigate whether severe sepsis affects gut colonization by resistant pathogens and genetic exchange between opportunistic pathogens, we tested the intestinal-colonization ability of an extended-spectrum beta-lactamase-producing Klebsiella pneumoniae strain carrying the SHV-18 resistance gene and the transfer ability of the resistance gene to endogenous Escherichia coli under ceftriaxone treatment in rats with burn injury only or severe sepsis induced by burns plus endotoxin exposure. Without ceftriaxone treatment, the K. pneumoniae strain colonized the intestine in both septic and burned rats for a short time, with clearance occurring earlier in burn-only rats but never in sham burn rats. In both burned and septic rats, the colonization level of the challenge strain dropped at the beginning and then later increased during ceftriaxone treatment, after which it declined gradually. This pattern coincided with the change in resistance of K. pneumoniae to ceftriaxone during and after ceftriaxone treatment. Compared with burn-only injury, severe sepsis had a more significant effect on the change in antimicrobial resistance to ceftriaxone. Only in septic rats was the resistance gene successfully transferred from the challenge strain to endogenous E. coli during ceftriaxone treatment; the gene persisted for at least 4 weeks after ceftriaxone treatment. We concluded that severe sepsis can facilitate intestinal colonization by an exogenous resistant pathogen and the transfer of the resistance gene to a potential endogenous pathogen during antimicrobial treatment.     

In vitro antibacterial activities of doripenem, imipenem, and meropenem against recent Streptococcus pneumoniae isolates

We investigated the in vitro activities of carbapenems against 347 Streptococcus pneumoniae isolates from Korea. While doripenem and imipenem resistance was displayed by only 1.2% and 3.2%, respectively, 21.3% of the isolates were resistant to meropenem. One isolate displaying very high carbapenem MICs and susceptibility only to vancomycin was also identified.     

A new carbapenem drug dosage metric for carbapenem usage and correlation with carbapenem resistance of Pseudomonas aeruginosa

The emergence and dissemination of antimicrobial resistance is a worldwide problem. Inappropriate antimicrobial use contributes to this resistance, and several metrics of drug usage have been used to monitor their consumption and rational use. We examined several existing drug metrics, and developed a new one, dose/duration-density (D/d²), for a the best correlation between carbapenem usage and carbapenem resistance of Pseudomonas aeruginosa. The annual changes of antimicrobial use density (AUD), days of therapy (DOT), daily dose (DD) and D/d² for meropenem, imipenem and total carbapenems was analyzed for a correlation with carbapenem susceptibility of P. aeruginosa from 2006 through 2015 at a university hospital. The substitution of meropenem for imipenem usage, and an approximate 10% increase in carbapenem susceptibility of P. aeruginosa occurred over the study period. There were significant correlations of the meropenem susceptibility of P. aeruginosa and meropenem usage as measured by the meropenem DD, of imipenem susceptibility and imipenem AUD and DOT, and overall carbapenem susceptibility and imipenem DOT. The D/d² for meropenem, imipenem and total carbapenems had significant correlations with individual and all carbapenem susceptibility of P. aeruginosa. These D/d² is the best single carbapenem use metric for correlating carbapenem usage with P. aeruginosa resistance. Further studies are warranted to consider the value of D/d² for other antimicrobials and bacteria.     

Relationship of Carbapenem Restriction in 22 University Teaching Hospitals to Carbapenem Use and Carbapenem-Resistant Pseudomonas aeruginosa

Many hospital antimicrobial stewardship programs restrict the availability of selected drugs by requiring prior approval. Carbapenems may be among the restricted drugs, but it is unclear if hospitals that restrict availability actually use fewer carbapenems than hospitals that do not restrict use. Nor is it clear if restriction is related to resistance. We evaluated the relationship between carbapenem restriction and the volume of carbapenem use and both the incidence rate and proportion of carbapenem-resistant Pseudomonas aeruginosa isolates from 2002 through 2006 in a retrospective, longitudinal, multicenter analysis among a consortium of academic health centers. Carbapenem use was measured from billing records as days of therapy per 1,000 patient days. Hospital antibiograms were used to determine both the incidence rate and proportion of carbapenem-resistant P. aeruginosa isolates. A survey inquired about restriction policies for antibiotics, including carbapenems. General linear mixed models were used to examine study outcomes. Among 22 hospitals with sufficient data for analysis, overall carbapenem use increased significantly over the 5 years of study (P < 0.0001), although overall carbapenem resistance in P. aeruginosa did not change. Hospitals that restricted carbapenems (n = 8; 36%) used significantly fewer carbapenems (P = 0.04) and reported lower incidence rates of carbapenem-resistant P. aeruginosa (P = 0.01) for all study years. Fluoroquinolone use was a potential confounder of these relationships, but hospitals that restricted carbapenems actually used fewer fluoroquinolones than those that did not. Restriction of carbapenems is associated with both lower use and lower incidence rates of carbapenem resistance in P. aeruginosa.Hospital antimicrobial stewardship programs (ASPs) attempt to improve antibacterial prescribing, commonly using formulary restrictions and by requiring preauthorization (7). Carbapenems are restricted in some hospitals for treatment of gram-negative bacterial infections resistant to first-line drugs, although carbapenem resistance among Pseudomonas aeruginosa and Enterobacteriaceae is increasing (3, 14, 18-20).Individual hospitals have reported improvement in bacterial susceptibilities to carbapenems after implementing ASPs that restricted carbapenem use (1, 11, 22). However, these “before and after” study designs have been criticized, and it is not known if the results are generalizable (6). There are no multihospital investigations that have assessed the effect of carbapenem restriction on carbapenem use and carbapenem-resistant P. aeruginosa over multiple years. In this study we evaluated the association between carbapenem restriction in academic health centers and the volume of carbapenem use and both the incidence rate and proportion of carbapenem-resistant P. aeruginosa from 2002 through 2006.(This study was presented in part at the 47th Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, IL, September 2007.)     

Activity of Imipenem against Klebsiella pneumoniae Biofilms In Vitro and In Vivo

Encapsulated Klebsiella pneumoniae has emerged as one of the most clinically relevant and more frequently encountered opportunistic pathogens in combat wounds as the result of nosocomial infection. In this report, we show that imipenem displayed potent activity against established K. pneumoniae biofilms under both static and flow conditions in vitro. Using a rabbit ear model, we also demonstrated that imipenem was highly effective against preformed K. pneumoniae biofilms in wounds.     

Molecular characterization of carbapenem-resistant Klebsiella pneumoniae ST14 and ST512 causing bloodstream infections in ICU and surgery wards of a tertiary university hospital of Verona (northern Italy): co-production of KPC-3, OXA-48, and CTX-M-15 β-lactamases

Klebsiella pneumoniae strain is an important opportunistic pathogen that causes severe nosocomial infections. In the present study a molecular characterization of carbapenem resistant K. pneumoniae, isolated from blood samples of hospitalized patients of Verona University Hospital, was performed. The simultaneous presence of SHV-1/CTX-M-15/KPC-3 and SHV-1/CTX-M-15/OXA-48 serin-β-lactamases was ascertained in the 89% and 11% of K. pneumoniae ST512 and K. pneumoniae ST14, respectively. Molecular characterization of bla genes showed that bla_KPC-3 was found in Tn4401a transposon with the tnpR, tnpA, ISKpn6, and ISKpn7 mobile elements whereas bla_CTX-M-15 was detected downstream ISEcp1 genetic element. A class 1 integron with a gene cassette of 780 bp corresponding to aadA2 gene was identified in 33 K. pneumoniae ST512 isolates.     

First Report of KPC-2 Carbapenemase-Producing Klebsiella pneumoniae in Japan

We investigated a novel Japanese isolate of sequence type 11 (ST11), the Klebsiella pneumoniae carbapenemase-2 (KPC-2)-producing K. pneumoniae strain Kp3018, which was previously obtained from a patient treated at a Brazilian hospital. This strain was resistant to various antibiotic classes, including carbapenems, and harbored the gene bla_KPC-2, which was present on the transferable plasmid of ca. 190 kb, in addition to the bla_CTX-M-15 gene. Furthermore, the ca. 2.3-kb sequences (ISKpn8-bla_KPC-2–ISKpn6-like), encompassing bla_KPC-2, were found to be similar to those of K. pneumoniae strains from China.