Klebsiella pneumoniae carbapenemases in Enterobacteriaceae: history, evolution, and microbiology concerns

Metallo-β-lactamase inhibitors: A continuing challenge for combating antibiotic resistance

β-lactam antibiotics are the most successful and commonly used antibacterial agents, but the emergence of resistance to these drugs has become a global health threat. The expression of β-lactamase enzymes produced by pathogens, which hydrolyze the amide bond of the β-lactam ring, is the major mechanism for bacterial resistance to β-lactams. In particular, among class A, B, C and D β-lactamases, metallo-β-lactamases (MBLs, class B β-lactamases) are considered crucial contributors to resistance in gram-negative bacteria. To combat β-lactamase-mediated resistance, great efforts have been made to develop β-lactamase inhibitors that restore the activity of β-lactams. Some β-lactamase inhibitors, such as diazabicyclooctanes (DBOs) and boronic acid derivatives, have also been approved by the FDA. Inhibitors used in the clinic can inactivate mostly serine-β-lactamases (SBLs, class A, C, and D β-lactamases) but have not been effective against MBLs until now. In order to develop new inhibitors particularly for MBLs, various attempts have been suggested. Based on structural and mechanical studies of MBL enzymes, several MBL inhibitor candidates, including taniborbactam in phase 3 and xeruborbactam in phase 1, have been introduced in recent years. However, designing potent inhibitors that are effective against all subclasses of MBLs is still extremely challenging. This review summarizes not only the types of β-lactamase and mechanisms by which β-lactam antibiotics are inactivated, but also the research finding on β-lactamase inhibitors targeting these enzymes. These detailed information on β-lactamases and their inhibitors could give valuable information for novel β-lactamase inhibitors design.

Identification of Phytochemicals with Inhibitory Potential Against Beta-lactamase Enzymes via Computer-aided Approach

INTRODUCTION

Antibacterial drugs have been widely used for the past century to treat diseases, but their efficacy has been limited by multi-resistant pathogens, particularly those that utilize beta-lactamase enzymes. The inhibition of beta-lactamase enzymes holds great promise for reducing the influence of such pathogens.

OBJECTIVE

This study aims to evaluate the mechanism of inhibition of phytochemicals with antibacterial activity against two classes of beta-lactamases using computational methods.

METHODS

To achieve this objective, a total of thirty phytochemicals were docked against SHV-1 beta-lactamase and AmpC beta-lactamase after procurement from Protein Data Bank. The pharmacokinetics (ADMET) and density functional theory (DFT) analysis study were also conducted to unravel the nature of the top six most promising compounds on each protein.

RESULTS

The results showed that a significant percentage of the compounds had binding affinities greater than that of avibactam, the positive control. Quercetin-3-O-rutinoside showed the most promising results against SHV-1 beta-lactamase with an affinity of -9.4 kcal/mol, while luteolin was found to be the most promising candidate against AmpC beta-lactamase with an affinity of -8.5 kcal/mol. DFT analysis demonstrated the reactivity of these compounds, and the ADMET study indicated that they were relatively safe.

CONCLUSION

In conclusion, the study's findings suggest that the selected compounds have significant potential to inhibit beta-lactamase and may be used in combination with antibiotics against organisms that produce beta-lactamase. This study provides a basis for further research in a wet-lab setting to validate the results.

Redirecting pantoprazole as a metallo-beta-lactamase inhibitor in carbapenem-resistant Klebsiella pneumoniae

The development of resistance to carbapenems in Klebsiella pneumoniae due to the production of metallo-β-lactamases (MBLs) is a critical public health problem because carbapenems are the last-resort drugs used for treating severe infections of extended-spectrum β-lactamases (ESBLs) producing K. pneumoniae. Restoring the activity of carbapenems by the inhibition of metallo-β-lactamases is a valuable approach to combat carbapenem resistance. In this study, two well-characterized clinical multidrug and carbapenem-resistant K. pneumoniae isolates were used. The sub-inhibitory concentrations of pantoprazole and the well-reported metallo-β-lactamase inhibitor captopril inhibited the hydrolytic activities of metallo-β-lactamases, with pantoprazole having more inhibiting activities. Both drugs, when used in combination with meropenem, exhibited synergistic activities. Pantoprazole could also downregulate the expression of the metallo-β-lactamase genes bla NDM and bla VIM. A docking study revealed that pantoprazole could bind to and chelate zinc ions of New Delhi and Verona integron-encoded MBL (VIM) enzymes with higher affinity than the control drug captopril and with comparable affinity to the natural ligand meropenem, indicating the significant inhibitory activity of pantoprazole against metallo-β-lactamases. In conclusion, pantoprazole can be used in combination with meropenem as a new strategy for treating serious infections caused by metallo-β-lactamases producing K. pneumoniae.

Emergence of high-level tigecycline resistance due to the amplification of a tet(A) gene variant in clinical carbapenem-resistant Klebsiella pneumoniae

OBJECTIVE

To investigate the prevalence of a tet(A) gene variant and its role in developing high-level tigecycline resistance among carbapenem-resistant Klebsiella pneumoniae (CRKP) clinical isolates.

METHODS

The mechanism of high-level tigecycline resistance in CRKP mediated by a tet(A) variant was explored by induction experiments, antimicrobial susceptibility testing, whole-genome sequencing and bioinformatics analysis. The amplification and overexpression of the tet(A) variant were measured by the determination of sequencing depth, gene copy numbers, and qRT-PCR.

RESULTS

A high rate (62.1%, 998/1607) of tet(A) variant carriage was observed among 1607 CRKP clinical isolates from Henan Province, China. High-level tigecycline resistance could rapidly develop by the amplification of the tet(A) variant in these isolates. The analysis of the raw sequencing data and the plasmid mapping depth revealed that the ΔtnpA homologous sequence of Tn1721 supports the amplification of the region that harbours the tet(A) variant by forming a large number of repeat arrays through translocatable units (TUs). Moreover, the epidemiological analysis of tet(A) variant-carrying structures among 1607 clinical CRKPs showed that the TU structure is widely present.

CONCLUSION

The presence of a tigecycline resistance-mediating tet(A) variant in CRKP clinical isolates represents a greater health concern than initially thought and should be monitored consistently.

Direct monitoring of meropenem therapeutic efficacy against Klebsiella pneumoniae respiratory infection by bioluminescence imaging

Introduction. Klebsiella pneumoniae is a major threat to public health worldwide. It is the causative agent for multiple disease presentations including urinary tract infection, septicemia, liver abscess, wound infection and respiratory tract infection. K. pneumoniae causes community- and hospital-acquired pneumonia, which is a devastating disease associated with high mortality rates.Hypothesis. There is a growing concern about the emergence of multidrug-resistant K. pneumoniae strains complicating the treatment with the current available therapeutics; therefore, there is an urgent need for the development of new antimicrobial agents.Aim. K. pneumoniae causes an acute respiratory disease in mice and in the current work we investigated the capability to perform non-invasive monitoring of bioluminescent Klebsiella to monitor therapeutic efficacy.Methodology. We engineered a bioluminescence reporter strain of K. pneumoniae to monitor the impact of antibiotics in a murine respiratory disease model.Results. We demonstrate that bioluminescence correlates with bacterial numbers in host tissues allowing for a non-invasive enumeration of bacterial replication in vivo. Light production is directly linked to bacterial viability, and this novel bioluminescent K. pneumoniae strain enabled monitoring of the efficacy of meropenem therapy in arresting bacterial proliferation in the lung.Conclusion. The use of non-invasive bioluminescent imaging improves preclinical animal model testing to detect study outcome earlier and with higher sensitivity.

Replacement of the Double Meropenem Disc Test with a Lateral Flow Assay for the Detection of Carbapenemase-Producing Enterobacterales and Pseudomonas aeruginosa in Clinical Laboratory Practice

The prompt detection of carbapenemases among Gram-negative bacteria isolated from patients' clinical infection samples and surveillance cultures is important for the implementation of infection control measures. In this context, we evaluated the effectiveness of replacing phenotypic tests for the detection of carbapenemase producers with the immunochromatographic Carbapenem-Resistant K.N.I.V.O. Detection K-Set lateral flow assay (LFA). In total, 178 carbapenem-resistant Enterobacterales and 32 carbapenem-resistant Pseudomonas aeruginosa isolated in our hospital were tested with both our established phenotypic and molecular testing procedures and the LFA. The Kappa coefficient of agreement for Enterobacterales was 0.85 (p < 0.001) and 0.6 (p < 0.001) for P. aeruginosa. No major disagreements were observed and notably, in many cases, the LFA detected more carbapenemases than the double meropenem disc test, especially regarding OXA-48 in Enterobacterales and VIM in P. aeruginosa. Overall, the Carbapenem-Resistant K.N.I.V.O. Detection K-Set was very effective and at least equivalent to the standard procedures used in our lab. However, it was much faster as it provided results in 15 min compared to a minimum of 18-24 h for the phenotypic tests.

QM/MM Simulations Reveal the Determinants of Carbapenemase Activity in Class A β-Lactamases

β-lactam antibiotic resistance in Gram-negative bacteria, primarily caused by β-lactamase enzymes that hydrolyze the β-lactam ring, has become a serious clinical problem. Carbapenems were formerly considered "last resort" antibiotics because they escaped breakdown by most β-lactamases, due to slow deacylation of the acyl-enzyme intermediate. However, an increasing number of Gram-negative bacteria now produce β-lactamases with carbapenemase activity: these efficiently hydrolyze the carbapenem β-lactam ring, severely limiting the treatment of some bacterial infections. Here, we use quantum mechanics/molecular mechanics (QM/MM) simulations of the deacylation reactions of acyl-enzyme complexes of eight β-lactamases of class A (the most widely distributed β-lactamase group) with the carbapenem meropenem to investigate differences between those inhibited by carbapenems (TEM-1, SHV-1, BlaC, and CTX-M-16) and those that hydrolyze them (SFC-1, KPC-2, NMC-A, and SME-1). QM/MM molecular dynamics simulations confirm the two enzyme groups to differ in the preferred acyl-enzyme orientation: carbapenem-inhibited enzymes favor hydrogen bonding of the carbapenem hydroxyethyl group to deacylating water (DW). QM/MM simulations of deacylation give activation free energies in good agreement with experimental hydrolysis rates, correctly distinguishing carbapenemases. For the carbapenem-inhibited enzymes, free energies for deacylation are significantly higher than for the carbapenemases, even when the hydroxyethyl group was restrained to prevent interaction with the DW. Analysis of these simulations, and additional simulations of mutant enzymes, shows how factors including the hydroxyethyl orientation, the active site volume, and architecture (conformations of Asn170 and Asn132; organization of the oxyanion hole; and the Cys69-Cys238 disulfide bond) collectively determine catalytic efficiency toward carbapenems.

Mortality Risk Factors and Prognostic Analysis of Patients with Multi-Drug Resistant Enterobacterales Infection

Background

The data from the China Network Antibacterial Surveillance Center (http://www.chinets.com) showed that the prevalence of Escherichia coli (E. coli), Klebsiella pneumoniae (KP), and Enterobacter cloacae (ecl), was 18.96%, 14.12%, and 2.74% in 2022, respectively. The resistance rates of E. coli and KP to 3rd or 4th generation cephalosporins were 51.7% and 22.1%, to carbapenems was 1.7% and 3.9%, to quinolones was 55.9% in Shanxi. The generation of extended-spectrum beta-lactamases (ESBLs) is a major mechanism resulting in drug resistance in Enterobacterales. To determine the mortality risk factors of multi-drug resistant Enterobacterales (MDRE) and multi-drug resistant Klebsiella pneumoniae (MDR-KP) infection.

Methods

91 MDR strains from 91 patients were collected from 2015 to 2019 in the second hospital of Shanxi Medical University. The mortality risk factors for the MDRE infections and clinical outcomes were analyzed by univariable and multivariable analysis. The independent predictors of 30-day mortality were analyzed through the Cox regression analysis including the variables with a value <0.2.

Results

The majority of patients were admitted to ICUs. Pulmonary infection was a major infection (43.96%, 40/91). Thirty-three (36.26%, 33/91) strains of MDR-KP were only detected in 2018. The proportion of multi-drug resistant Escherichia coli (MDR E. coli) and multi-drug resistant Enterobacter cloacae (MDR ecl) were 16.48% (15/91) and 17.58% (16/91), respectively. The presence of cerebrovascular diseases (OR, 4.046; 95%Cl, 1.434–11.418; P=0.008) and central venous catheterization (OR, 4.543; 95%Cl, 1.338–15.425; P=0.015) were associated with mortality in patients with MDRE infections. Endotracheal intubation (OR, 4.654; 95%Cl, 1.5–14.438; P=0.008) was an independent mortality risk factor for patients infected with MDR-KP strains. Patients who received aminoglycoside antibiotics (P=0.057) had a higher 30-day survival rate. The β-lactam antibiotics were the major agent in the clinic.

Conclusion

This study implies that patients with cerebrovascular diseases, central venous catheterization, and endotracheal intubation are at risk of carrying MDR isolates.

Metallo-β-lactamases in the Age of Multidrug Resistance: From Structure and Mechanism to Evolution, Dissemination, and Inhibitor Design

Antimicrobial resistance is one of the major problems in current practical medicine. The spread of genes coding for resistance determinants among bacteria challenges the use of approved antibiotics, narrowing the options for treatment. Resistance to carbapenems, last resort antibiotics, is a major concern. Metallo-β-lactamases (MBLs) hydrolyze carbapenems, penicillins, and cephalosporins, becoming central to this problem. These enzymes diverge with respect to serine-β-lactamases by exhibiting a different fold, active site, and catalytic features. Elucidating their catalytic mechanism has been a big challenge in the field that has limited the development of useful inhibitors. This review covers exhaustively the details of the active-site chemistries, the diversity of MBL alleles, the catalytic mechanism against different substrates, and how this information has helped developing inhibitors. We also discuss here different aspects critical to understand the success of MBLs in conferring resistance: the molecular determinants of their dissemination, their cell physiology, from the biogenesis to the processing involved in the transit to the periplasm, and the uptake of the Zn(II) ions upon metal starvation conditions, such as those encountered during an infection. In this regard, the chemical, biochemical and microbiological aspects provide an integrative view of the current knowledge of MBLs.

The Carbapenemase BKC-1 from Klebsiella pneumoniae Is Adapted for Translocation by Both the Tat and Sec Translocons

The cell envelope of Gram-negative bacteria consists of two membranes surrounding the periplasm and peptidoglycan layer. β-Lactam antibiotics target the periplasmic penicillin-binding proteins that synthesize peptidoglycan, resulting in cell death. The primary means by which bacterial species resist the effects of β-lactam drugs is to populate the periplasmic space with β-lactamases. Resistance to β-lactam drugs is spread by lateral transfer of genes encoding β-lactamases from one species of bacteria to another. However, the resistance phenotype depends in turn on these “alien” protein sequences being recognized and exported across the cytoplasmic membrane by either the Sec or Tat protein translocation machinery of the new bacterial host. Here, we examine BKC-1, a carbapenemase from an unknown bacterial source that has been identified in a single clinical isolate of Klebsiella pneumoniae. BKC-1 was shown to be located in the periplasm, and functional in both K. pneumoniae and Escherichia coli. Sequence analysis revealed the presence of an unusual signal peptide with a twin arginine motif and a duplicated hydrophobic region. Biochemical assays showed this signal peptide directs BKC-1 for translocation by both Sec and Tat translocons. This is one of the few descriptions of a periplasmic protein that is functionally translocated by both export pathways in the same organism, and we suggest it represents a snapshot of evolution for a β-lactamase adapting to functionality in a new host.

Mechanistic Basis of OXA-48-like β-Lactamases' Hydrolysis of Carbapenems

Carbapenem-hydrolyzing class D β-lactamases (CHDLs) are an important source of resistance to these last resort β-lactam antibiotics. OXA-48 is a member of a group of CHDLs named OXA-48-like enzymes. On the basis of sequence similarity, OXA-163 can be classified as an OXA-48-like enzyme, but it has altered substrate specificity. Compared to OXA-48, it shows impaired activity for carbapenems but displays an enhanced hydrolysis of oxyimino-cephalosporins. Here, we address the mechanistic and structural basis for carbapenem hydrolysis by OXA-48-like enzymes. Pre-steady-state kinetic analysis indicates that the rate-limiting step for OXA-48 and OXA-163 hydrolysis of carbapenems is deacylation and that the greatly reduced carbapenemase activity of OXA-163 compared to that of OXA-48 is due entirely to a slower deacylation reaction. Furthermore, our structural data indicate that the positioning of the β5-β6 loop is necessary for carbapenem hydrolysis by OXA-48. A major difference between the OXA-48 and OXA-163 complexes with carbapenems is that the 214-RIEP-217 deletion in OXA-163 creates a large opening in the active site that is absent in the OXA-48/carbapenem structures. We propose that the larger active site results in less constraint on the conformation of the 6α-hydroxyethyl group in the acyl-enzyme. The acyl-enzyme intermediate assumes multiple conformations, most of which are incompatible with rapid deacylation. Consistent with this hypothesis, molecular dynamics simulations indicate that the most stable complex is formed between OXA-48 and imipenem, which correlates with the OXA-48 hydrolysis of imipenem being the fastest observed. Furthermore, the OXA-163 complexes with imipenem and meropenem are the least stable and show significant conformational fluctuations, which correlates with the slow hydrolysis of these substrates.

Review of therapeutic options for infections with carbapenem-resistant Klebsiella pneumoniae

Infections with multi-drug resistant (MDR) bacteria including carbapenem-resistant Klebsiella pneumoniae are emerging worldwide but are difficult to treat with the currently available antibiotic compounds and therefore constitute serious threats to human health. This prompted us to perform a literature survey applying the MEDLINE database and Cochrane Register of Controlled Trials including clinical trials comparing different treatment regimens for infections caused by carbapenem-resistant K. pneumoniae. Our survey revealed that a combined application of antibiotic compounds such as meropenem plus vaborbactam, meropenem plus colistin and carbapenem plus carbapenem, resulted in significantly increased clinical cure and decreased mortality rates as compared to respective control treatment. However, further research on novel antibiotic compounds, but also on antibiotic-independent molecules providing synergistic or at least resistance-modifying properties needs to be undertaken in vitro as well as in large clinical trials to provide future options in the combat of emerging life-threatening infections caused by MDR bacteria.

Drugs for Gram-Negative Bugs From 2010-2019: A Decade in Review

A literature review spanning January 1, 2010, to December 31, 2019, was conducted using the PubMed and ISI Web of Science databases to determine the breadth of publication activity in the area of gram-negative bacteria antimicrobial therapy. The number of articles was used as a reflection of scholarly activity. First, PubMed was searched using the following Medical Subject Headings (MeSH): antibacterial agents, Enterobacteriaceae, Acinetobacter, and Pseudomonas. A total of 12 643 articles were identified within PubMed, and 77 862 articles were identified within ISI Web of Science that included these terms. Second, these articles were categorized by antibiotic class to identify relative contributions to the literature by drug category. Third, these studies were used to identify key trends in the treatment of gram-negative bacterial infections from the past decade. This review highlights advances made in the past 10 years in antibacterial pharmacotherapy and some of the challenges that await the next decade of practice.

Food Service Pork Chops from Three U.S. Regions Harbor Similar Levels of Antimicrobial Resistance Regardless of Antibiotic Use Claims

Pork products from animals "raised without antibiotics" (RWA) are assumed to harbor lower levels of antimicrobial resistance (AMR) than conventional (CONV) pork products with no claims regarding use of antimicrobial agents during production. A total of 372 pork chop samples from CONV (n = 190) and RWA (n = 182) production systems were collected over 13 months from three food service suppliers. The following bacteria were cultured: Escherichia coli, tetracycline-resistant (TET^r) E. coli, third-generation cephalosporin-resistant (3GC^r) E. coli, Salmonella enterica, TET^r Salmonella, 3GC^r Salmonella, nalidixic acid-resistant Salmonella, Enterococcus spp., TET^r Enterococcus, erythromycin-resistant Enterococcus, Staphylococcus aureus, and methicillin-resistant S. aureus. Production system did not significantly impact the detection of cultured bacteria (P > 0.05). Metagenomic DNA was isolated from each sample, and equal amounts of metagenomic DNA were pooled by supplier, month, and production system for 75 pooled samples (38 CONV, 37 RWA). Quantitative PCR was used to assess the abundances of the following 10 AMR genes: aac(6')-Ie-aph(2″)-Ia, aadA1, bla_CMY-2, bla_CTX-M, bla_KPC-2, erm(B), mecA, tet(A), tet(B), and tet(M). For all 10 AMR genes, abundances did not differ significantly (P > 0.05) between production systems. These results suggest that use of antimicrobial agents during swine production minimally impacts the AMR of bacteria in pork chops.

β-Lactamases and β-Lactamase Inhibitors in the 21st Century

The β-lactams retain a central place in the antibacterial armamentarium. In Gram-negative bacteria, β-lactamase enzymes that hydrolyze the amide bond of the four-membered β-lactam ring are the primary resistance mechanism, with multiple enzymes disseminating on mobile genetic elements across opportunistic pathogens such as Enterobacteriaceae (e.g., Escherichia coli) and non-fermenting organisms (e.g., Pseudomonas aeruginosa). β-Lactamases divide into four classes; the active-site serine β-lactamases (classes A, C and D) and the zinc-dependent or metallo-β-lactamases (MBLs; class B). Here we review recent advances in mechanistic understanding of each class, focusing upon how growing numbers of crystal structures, in particular for β-lactam complexes, and methods such as neutron diffraction and molecular simulations, have improved understanding of the biochemistry of β-lactam breakdown. A second focus is β-lactamase interactions with carbapenems, as carbapenem-resistant bacteria are of grave clinical concern and carbapenem-hydrolyzing enzymes such as KPC (class A) NDM (class B) and OXA-48 (class D) are proliferating worldwide. An overview is provided of the changing landscape of β-lactamase inhibitors, exemplified by the introduction to the clinic of combinations of β-lactams with diazabicyclooctanone and cyclic boronate serine β-lactamase inhibitors, and of progress and strategies toward clinically useful MBL inhibitors. Despite the long history of β-lactamase research, we contend that issues including continuing unresolved questions around mechanism; opportunities afforded by new technologies such as serial femtosecond crystallography; the need for new inhibitors, particularly for MBLs; the likely impact of new β-lactam:inhibitor combinations and the continuing clinical importance of β-lactams mean that this remains a rewarding research area.

Similar Levels of Antimicrobial Resistance in U.S. Food Service Ground Beef Products with and without a "Raised without Antibiotics" Claim

U.S. ground beef with "raised without antibiotics" (RWA) label claims are perceived as harboring fewer bacteria with antimicrobial resistance (AMR) than are found in conventional (CONV) ground beef with no such label claim. A total of 370 ground beef samples from CONV ( n = 191) and RWA ( n = 179) production systems were collected over 13 months from three food service suppliers. The following bacteria were cultured: Escherichia coli, tetracycline-resistant (TET^r) E. coli, third-generation cephalosporin-resistant (3GC^r) E. coli, Salmonella enterica, TET^r S. enterica, 3GC^r S. enterica, nalidixic acid-resistant S. enterica, Enterococcus spp., erythromycin-resistant Enterococcus spp., TET^r Enterococcus spp., Staphylococcus aureus, and methicillin-resistant S. aureus. TET^r E. coli was more frequently detected in CONV ground beef (CONV, 54.2%; RWA, 35.2%; P < 0.01), but supplier ( P < 0.01) and production system × suppler interaction ( P < 0.01) effects were also significant. Metagenomic DNA was isolated from each sample, and equal amounts of metagenomic DNA were pooled by supplier, month, and production system for 75 pooled samples (38 CONV, 37 RWA). The abundance of aac(6')-Ie-aph(2″)-Ia, aadA1, bla_CMY-2, bla_CTX-M, bla_KPC-2, erm(B), mecA, tet(A), tet(B), and tet(M) genes was assessed by quantitative PCR. The tet(A) (2.9-log₂-fold change, P = 0.04) and tet(B) (5.6-log₂-fold change) ( P = 0.03) genes were significantly more abundant in RWA ground beef. Phylogenetic analyses revealed that ground beef microbiomes differed more by supplier than by production system. These results were consistent with prior research suggesting antimicrobial use in U.S. beef cattle has minimal impact on the AMR of bacteria found in these products. These results should spur a reevaluation of assumptions regarding the impact of antimicrobial use during U.S. beef production on the AMR of bacteria in ground beef.

[Risk factors and clinical evolution of carbapenemase-producing Klebsiella pneumoniae infections in a university hospital in Spain. Case-control study]

OBJECTIVE

Carbapenemase-producing Enterobacterias is a global health hazard due to their ease of transmission, difficulty of treatment, and their personal and economic impact. We analyze the factors associated with an increased risk of infection by Klebsiella pneumoniae carbapenemase-producing bacteria (KPC) and factors related to poor prognosis.

METHODS

We designed a case-control study. KPC isolates were taken during an outbreak in a hospital in Madrid. A logistic regression was performed with the main variables.

RESULTS

Sixteen cases of clinically documented infections were isolated. Overall mortality rates in the cases group was 25%. The most frequent location was blood (37.5%) followed by urine (25%). All but one were OXA-48. Regarding factors related to an increased risk of developing infection, only previous exposure to antibiotics presented statistical significance difference OR 13 (2.40-70.46). With respect to the overall mortality, the presence of pneumonia OR 25 (1.93-323.55) or the use of invasive mechanical ventilation was associated with greater risk 15 OR 33 (1.92-122.8) For attributable mortality only invasive ventilation had a significant association OR 18 (1.48-218.95).

CONCLUSIONS

Exposure to previous antibiotics is an independent risk factor for developing KPC infection, adjusted for all other clinical and demographic variables. Risk factors such as the presence of pneumonia or the use of invasive mechanical ventilation were associated with a worse prognosis in terms of overall and attributable mortality.

Pulmonary Surfactant Promotes Virulence Gene Expression and Biofilm Formation in Klebsiella pneumoniae

The interactions between Klebsiella pneumoniae and the host environment at the site of infection are largely unknown. Pulmonary surfactant serves as an initial point of contact for inhaled bacteria entering the lung and is thought to contain molecular cues that aid colonization and pathogenesis. To gain insight into this ecological transition, we characterized the transcriptional response of K. pneumoniae MGH 78578 to purified pulmonary surfactant. This work revealed changes within the K. pneumoniae transcriptome that likely contribute to host colonization, adaptation, and virulence in vivo Notable transcripts expressed under these conditions include genes involved in capsule synthesis, lipopolysaccharide modification, antibiotic resistance, biofilm formation, and metabolism. In addition, we tested the contributions of other surfactant-induced transcripts to K. pneumoniae survival using engineered isogenic KPPR1 deletion strains in a murine model of acute pneumonia. In these infection studies, we identified the MdtJI polyamine efflux pump and the ProU glycine betaine ABC transporter to be significant mediators of K. pneumoniae survival within the lung and confirmed previous evidence for the importance of de novo leucine synthesis to bacterial survival during infection. Finally, we determined that pulmonary surfactant promoted type 3 fimbria-mediated biofilm formation in K. pneumoniae and identified two surfactant constituents, phosphatidylcholine and cholesterol, that drive this response. This study provides novel insight into the interactions occurring between K. pneumoniae and the host at an important infection site and demonstrates the utility of purified lung surfactant preparations for dissecting host-lung pathogen interactions in vitro.

Molecular detection and antimicrobial resistance of Klebsiella pneumoniae from house flies (Musca domestica) in kitchens, farms, hospitals and slaughterhouses

Identifying disease vectors and pathogens is one of the key steps in controlling vector-borne diseases. This study investigated the possible role of house flies (Musca domestica) as vectors in the transmission of Klebsiella pneumoniae in Chaharmahal VA Bakhtiari and Isfahan provinces of Iran. House flies were captured from household kitchens, cattle farms, chicken farms, animal hospitals, human hospitals and slaughterhouses. Isolation of K. pneumoniae from external surfaces and guts of the flies was performed using MacConkey agar (MA) and thioglycollate broth (TGB). Identification of the isolates was performed with phenotypic techniques and polymerase chain reaction (PCR). A total of 600 house flies were sampled during the study period from different locations in four different seasons. Overall, 11.3% of the captured house flies were positive for K. pneumoniae. In Chaharmahal VA Bakhtiari province, the prevalence was 12.7%, while in Isfahan province, 10.0% of the sampled house flies were infected with K. pneumoniae. Season-wise, the highest prevalence of infections among the house flies was in summer. The organisms were highly resistant to ampicillin, amoxicillin, cefotaxime and piperacillin. A lowest level of resistance was observed for imipenem/cilastatin. The findings of this study demonstrated that house flies are potential vectors of antibiotic-resistant K. pneumoniae in Isfahan and Chaharmahal provinces, Iran. Control efforts for infections caused by this particular bacterium should take M. domestica into account.

Carbapenem resistance: overview of the problem and future perspectives

Carbapenem resistance, mainly among Gram-negative pathogens, is an ongoing public-health problem of global dimensions. This type of antimicrobial resistance, especially when mediated by transferable carbapenemase-encoding genes, is spreading rapidly causing serious outbreaks and dramatically limiting treatment options. In this article, important key points related to carbapenem resistance are reviewed and future perspectives are discussed.

Induction and nosocomial dissemination of carbapenem and polymyxin-resistant Klebsiella pneumoniae

INTRODUCTION

Polymyxins are antimicrobial agents capable of controlling carbapenemase-producing Klebsiella pneumoniae infection.

METHODS

We report a cluster of four patients colonized or infected by polymyxin-resistant and Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae.

RESULTS

Three patients were hospitalized in adjacent wards, and two were admitted to the intensive care unit. The index case maintained prolonged intestinal colonization by KPC-producing K. pneumoniae. Three patients received polymyxin B before the isolation of polymyxin-resistant K. pneumoniae.

CONCLUSIONS

Colonization by KPC-producing K. pneumoniae and previous use of polymyxin B may be causally related to the development of polymyxin-resistant microorganisms.

Septicemia and Infection due to ESBL-producing K. pneumoniae Following Feline Renal Allograft Transplantation

A 12 yr old castrated male domestic longhair underwent renal transplantation for treatment of chronic interstitial nephritis. Full-thickness intestinal biopsies obtained prior to transplantation revealed mild enteritis. Twelve months following transplantation, the patient underwent surgery for resection of a mesenteric mass causing septic peritonitis. The mesenteric mass was resected and an intestinal resection and anastomosis was performed. Extended-spectrum-β-lactamase producing Klebsiella pneumoniae was cultured from the resected tissue and urinary tract. Bacterial rods were noted to be circulating in the bloodstream, causing septicemia. Despite aggressive treatment of the septic peritonitis and septicemia using surgical debridement, drain placement, aggressive antibiotic therapy with IV meropenem, and vasopressor support, the patient succumbed to persistent hypotension and suffered cardiopulmonary arrest. Extended-spectrum-β-lactamase-producing bacteria are of growing concern in human and veterinary medicine, maintaining susceptibility often only to carbapenem and aminoglycoside antibiotics. Resistance to even those antibiotics is emerging. Veterinary patients with a history of antibiotic therapy, central venous or urinary catheterization, immunosuppression, enteric surgery, and an extended stay in the intensive care unit may be predisposed.

Colistin resistance mechanisms in Klebsiella pneumoniae strains from Taiwan

Colistin is one of the antibiotics of last resort for the treatment of carbapenem-resistant Klebsiella pneumoniae infection. This study showed that capsular type K64 (50%) and ST11 (53.9%) are the prevalent capsular and sequence types in the colistin-resistant strains in Taiwan. The interruption of transcripts (38.5%) and amino acid mutation (15.4%) in mgrB are the major mechanisms contributing to colistin resistance. In addition, novel single amino acid changes in MgrB (Stop48Tyr) and PhoQ (Leu26Pro) were observed to contribute to colistin resistance.

No carbapenem resistance in pneumonia caused by Klebsiella species

Klebsiella species are a common cause of community- and nosocomial-acquired pneumonia. Antibiotic resistance to the class of carbapenem in patients with pneumonia caused by Klebsiella species is unusual. New studies report carbapenem resistance in patients with pneumonia caused by Klebsiella species.This article examines, retrospectively, antibiotic resistance in patients with community- and nosocomial-acquired pneumonia caused by Klebsiella species.The data of all patients with community- and nosocomial-acquired pneumonia caused by Klebsiella species were collected from the hospital charts at the HELIOS Clinic, Witten/Herdecke University, Wuppertal, Germany, within the study period 2004 to 2014. An antibiogram was created from all of the study patients with pneumonia caused by Klebsiella species. Sensitivity and resistance profiles were performed for the different antibiotics that have been consistently used in the treatment of patients with pneumonia caused by Klebsiella species. All demographic, clinical, and laboratory data of all of the patients with pneumonia caused by Klebsiella species were collected from the patients' records.During the study period of January 1, 2004, to August 12, 2014, 149 patients were identified with community- and nosocomial-acquired pneumonia affected by Klebsiella species. These patients had a mean age of 70.6 ± 13 (107 [71.8%, 95% CI 64.6%-79%] men and 42 [28.2%, 95% CI 21%-35.4%] women). In all of the patients with pneumonia caused by Klebsiella species, there was resistance to ampicillin (P < 0.0001). Many patients with pneumonia caused by Klebsiella species (75.3%) also showed resistance to piperacillin (P < 0.0001). However, no patients with pneumonia caused by Klebsiella species showed resistance to imipenem or meropenem (P < 0.0001).Antibiotic resistance to the antibiotic class of carbapenem was not detected in patients with pneumonia caused by Klebsiella species.

Critical issues for Klebsiella pneumoniae KPC-carbapenemase producing K. pneumoniae infections: a critical agenda

ABSTRACT 

The wide dissemination of carbapenemase producing K. pneumoniae (KPC-Kp) has caused a public health crisis of global dimensions, due to the serious infections in hospitalized patients associated with high mortality. In 2014, we aim to review clinical data on KPC-Kp at a time when a pro-active strategy (combating the problem before it is established) is no longer useful, focusing on epidemiology, patient risk profile, infection control, digestive tract colonization and treatment issues such as the role of carbapenems or carbapenem sparing strategies, colistin and resistance, dual carbapenem administration and the role of tigecycline. All these issues are illustrated prospectively to provide a forum for a Consensus strategy when not only intensive care units but also medical and surgical wards are affected by the epidemics.

Rapid detection of the Klebsiella pneumoniae carbapenemase (KPC) gene by loop-mediated isothermal amplification (LAMP)

Klebsiella pneumoniae carbapenemases (KPC), which are associated with resistance to carbapenem, have recently spread worldwide and have become a global concern. It is necessary to detect KPC-producing organisms in clinical settings to be able to control the spread of this resistance. We have developed a loop-mediated isothermal amplification (LAMP) method for rapid detection of KPC producers. LAMP primer sets were designed to recognize the homologous regions of blaKPC-2 to blaKPC-17 and could amplify blaKPC rapidly. The specificity and sensitivity of the primers in the LAMP reactions for blaKPC detection were determined. This LAMP assay was able to specifically detect KPC producers at 68 °C, and no cross-reactivity was observed for other types of β-lactamase (class A, B, C, or D) producers. The detection limit for this assay was found to be 10(0) CFU per tube, in 25 min, which was 10-fold more sensitive than a PCR assay for blaKPC detection. Then, the sensitivity of the LAMP reactions for blaKPC detection in human specimens (sputum samples, urine samples, fecal samples and blood samples) was analyzed; it was observed that the LAMP assay had almost the same sensitivity in these samples as when using purified DNA. The LAMP assay is easy to perform and rapid. It may therefore be routinely applied for detection of KPC producers in the clinical laboratory.

Combating the spread of carbapenemases in Enterobacteriaceae: a battle that infection prevention should not lose

The emergence of carbapenemases in Enterobacteriaceae has raised global concern among the scientific, medical and public health communities. Both the CDC and the WHO consider carbapenem-resistant Enterobacteriaceae (CRE) to constitute a significant threat that necessitates immediate action. In this article, we review the challenges faced by laboratory workers, infection prevention specialists and clinicians who are confronted with this emerging infection control issue.

Klebsiella: a long way to go towards understanding this enigmatic jet-setter

Klebsiella pneumoniae is the causative agent of a variety of diseases, including pneumonia, urinary tract infections, septicemia, and the recently recognized pyogenic liver abscesses (PLA). Renewed efforts to identify and understand the bacterial determinants required to cause disease have come about because of the worldwide increase in the isolation of strains resistant to a broad spectrum of antibiotics. The recent increased isolation of carbapenem-resistant strains further reduces the available treatment options. The rapid geographic spread of the resistant isolates and the spread to other pathogens are of particular concern. For many years, the best characterized virulence determinants were capsule, lipopolysaccharide, siderophores, and types 1 and 3 fimbriae. Recent efforts to expand this list include in vivo screens and whole-genome sequencing. However, we still know little about how this bacterium is able to cause disease. Some recent clonal analyses of K. pneumoniae strains indicate that there are distinct clonal groups, some of which may be associated with specific disease syndromes. However, what makes one clonal group more virulent and what changes the disease pattern are not yet clear and remain important questions for the future.

Trends in multidrug-resistant gram-negative bacilli and the role of prolonged β-lactam infusion in the intensive care unit

Multidrug-resistant gram-negative bacilli are emerging threats in the intensive care unit setting worldwide. Extended-spectrum β-lactamases, AmpC β-lactamases, and carbapenem-resistant Enterobacteriaceae are increasing at an alarming rate, leaving limited therapeutic options. In addition, multidrug resistance among Pseudomonas aeruginosa and Acinetobacter baumannii has widely disseminated and become a frequent cause of nosocomial infections within many intensive care units. Therefore, resistance is increasing to all currently available antibiotics, including cephalosporins, penicillins, aztreonam, carbapenems, fluoroquinolones, and aminoglycosides. Some multidrug-resistant gram-negative bacteria remain susceptible to only a few antibiotics such as tigecycline, fosfomycin, and polymyxins. The steady trend of increasing resistance coupled with the lack of novel antibiotics targeting resistant gram-negative bacilli has forced clinicians to increasingly apply more aggressive dosing strategies, such as prolonged and continuous infusion of β-lactam antibiotics to address the challenges associated with these difficult-to-treat pathogens. Nurses who have a thorough understanding of antibiotic resistance patterns, infection control procedures, and appropriate antibiotic use and dosing regimens, particularly the method of administration, are essential in the battle to preserve the usefulness of antibiotics and prevent further antibiotic resistance.

Role of novel multidrug efflux pump involved in drug resistance in Klebsiella pneumoniae

Background

Multidrug resistant Klebsiella pneumoniae have caused major therapeutic problems worldwide due to the emergence of the extended-spectrum β-lactamase producing strains. Although there are >10 major facilitator super family (MFS) efflux pumps annotated in the genome sequence of the K. pneumoniae bacillus, apparently less is known about their physiological relevance.

Principal Findings

Insertional inactivation of kpnGH resulting in increased susceptibility to antibiotics such as azithromycin, ceftazidime, ciprofloxacin, ertapenem, erythromycin, gentamicin, imipenem, ticarcillin, norfloxacin, polymyxin-B, piperacillin, spectinomycin, tobramycin and streptomycin, including dyes and detergents such as ethidium bromide, acriflavine, deoxycholate, sodium dodecyl sulphate, and disinfectants benzalkonium chloride, chlorhexidine and triclosan signifies the wide substrate specificity of the transporter in K. pneumoniae. Growth inactivation and direct fluorimetric efflux assays provide evidence that kpnGH mediates antimicrobial resistance by active extrusion in K. pneumoniae. The kpnGH isogenic mutant displayed decreased tolerance to cell envelope stressors emphasizing its added role in K. pneumoniae physiology.

Conclusions and Significance

The MFS efflux pump KpnGH involves in crucial physiological functions besides being an intrinsic resistance determinant in K. pneumoniae.

First identification of coexistence of blaNDM-1 and blaCMY-42 among Escherichia coli ST167 clinical isolates

Background

Emergence of multidrug resistance in Enterobacteriaceae limits the selection of antimicrobials for treatment of infectious diseases. Identification of NDM-1 makes more difficulty in treating multidrug-resistant Enterobacteriaceae infections. Carbapenem-resistant Escherichia coli clinical isolates from a tertiary hospital in Wenzhou, east China, were investigated for NDM-1 production.

Results

The two tested isolates were negative for modified Hodge test, but positive for a double-disc synergy test used for detecting metallo-β-lactamase production. E. coli WZ33 and WZ51 exhibited discrepant-level resistance to most clinically frequent used antimicrobials, but still susceptible to trimethoprim/sulfamethoxazole, amikacin, fosfomycin, tigecycline and polymyxin B. E. coli WZ33 and WZ51 were positive for bla_NDM-1 determined by PCR and DNA sequencing. Other than bla_NDM-1, E. coli WZ33 also harbored bla_CTX-M-14 and bla_CMY-42, while E. coli WZ51 simultaneously harbored bla_SHV-12,bla_CTX-M-14 and bla_CMY-42. Carbapenem resistance for E. coli WZ51 and WZ33 could not be transferred to E. coli recipients through conjugation, but could be transferred to E. coli recipients by chemical transformation. The EcoR1-digested DNA pattern of plasmids from the transformant of E. coli WZ51 was different from that of E. coli WZ51. MLST showed that E. coli WZ33 and WZ51 belonged to an animal-associated clone (ST167).

Conclusion

The present study is the first report of bla_NDM-1 carriage in E. coli ST167 isolates and coexistence of bla_NDM-1 and bla_CMY-42 in same isolate. Systemic surveillance should focus on the dissemination of bla_NDM-1 among Enterobacteriaceae, especially E. coli ST167 clone associated with animal infection.

The prevalence of carbapenemase genes and plasmid-mediated quinolone resistance determinants in carbapenem-resistant Enterobacteriaceae from five teaching hospitals in central China

We investigated the prevalence of β-lactamase genes and plasmid-mediated quinolone resistance (PMQR) determinants in 51 carbapenem-resistant Enterobacteriaceae (CRE) from five teaching hospitals in central China. The prevalence of carbapenem resistance in Enterobacteriaceae was 1·0% (51/5012). Of 51 CRE, 31 (60·8%) isolates were positive for one tested carbapenemase gene, while 10 (19·6%) were simultaneously positive for two tested carbapenemase genes. The positive rates of bla KPC-2, bla NDM-1, bla IMP-4, bla IMP-26 and bla IMP-8 were 54·9%, 17·6%, 11·8%, 11·8% and 3·9%, respectively. Of 10 CRE with two carbapenemase genes, three, five, one and one were positive for bla KPC-2 and bla IMP-4, bla KPC-2 and bla IMP-26, bla KPC-2 and bla IMP-8, and bla KPC-2 and bla NDM-1, respectively. Eight of nine bla NDM-1-positive isolates lacked carbapenemases by the modified Hodge test, while 27/28 isolates harbouring bla KPC-2 were positive for carbapenemases determined by this test; 41·2% of the CRE-positive isolates also harboured ESBL genes in various combinations (three and two positive for bla KPC-2 also carried bla DHA-1 and bla CMY-2). The positive rates of qnrS1, qnrA1, qnrB and aac-(6/)-Ib-cr in CRE were 25·5%, 9·8%, 23·5% and 15·7%, respectively. In particular, 7/9 isolates harbouring bla NDM-1 were positive for these quinolone resistance genes, of which five carried qnrS1 and two carried qnrS1 and qnrB4. All but two of 29 Klebsiella pneumoniae isolates were grouped into 20 clonal clusters by PFGE, with the predominant cluster accounting for four bla KPC-2-positive isolates distributed in the same hospital. We conclude that there is a high prevalence of bla NDM-1 and PMQR determinants in CRE isolates in central China. Multiple resistance determinants in various combinations co-exist in these strains and we report for the first time the co-existence of bla KPC-2 and bla IMP-26 in a strain of Klebsiella oxytoca.

Klebsiella spp. in endoscopy-associated infections: we may only be seeing the tip of the iceberg

PURPOSE

Two endoscopy-associated nosocomial outbreaks caused by carbapenemase-producing Klebsiella pneumoniae (CPKP) were recently observed in two German hospitals. In this study, we performed a systematic search of the medical literature in order to elucidate the epidemiology of Klebsiella spp. in endoscopy-associated outbreaks.

METHODS

Medline, the Outbreak Database ( http://www.outbreak-database.com ) and reference lists of articles extracted from these databases were screened for descriptions of endoscopy-associated nosocomial outbreaks. The data extracted and analysed were: (1) the type of medical department affected; (2) characterisation of pathogen to species and conspicuous resistance patterns (if applicable); (3) type of endoscope and the grade of its contamination; (4) number and the types of infections; (5) actual cause of the outbreak.

RESULTS

A total of seven nosocomial outbreaks were identified, of which six were outbreaks of endoscopic retrograde cholangiopancreatography-related infections and caused by contaminated duodenoscopes. Including our own outbreaks in the analysis, we identified one extended-spectrum beta-lactamase-producing K. pneumoniae strain and six CPKP strains. Insufficient reprocessing after the use of the endoscope was the main reason for subsequent pathogen transmission.

CONCLUSIONS

There were only two reports of nosocomial outbreaks due to Klebsiella spp. in the first three decades of endoscopic procedures, but seven additional outbreaks of this kind have been reported within the last 4 years. It is very likely that many of such outbreaks have been missed in the past because this pathogen belongs to the physiological gut flora. However, with the emergence of highly resistant (carbapenemase-producing) strains, strict adherence to infection control guidelines is more important than ever.

Non-phenotypic tests to detect and characterize antibiotic resistance mechanisms in Enterobacteriaceae

In the past 2 decades, we have observed a rapid increase of infections due to multidrug-resistant Enterobacteriaceae. Regrettably, these isolates possess genes encoding for extended-spectrum β-lactamases (e.g., blaCTX-M, blaTEM, blaSHV) or plasmid-mediated AmpCs (e.g., blaCMY) that confer resistance to last-generation cephalosporins. Furthermore, other resistance traits against quinolones (e.g., mutations in gyrA and parC, qnr elements) and aminoglycosides (e.g., aminoglycosides modifying enzymes and 16S rRNA methylases) are also frequently co-associated. Even more concerning is the rapid increase of Enterobacteriaceae carrying genes conferring resistance to carbapenems (e.g., blaKPC, blaNDM). Therefore, the spread of these pathogens puts in peril our antibiotic options. Unfortunately, standard microbiological procedures require several days to isolate the responsible pathogen and to provide correct antimicrobial susceptibility test results. This delay impacts the rapid implementation of adequate antimicrobial treatment and infection control countermeasures. Thus, there is emerging interest in the early and more sensitive detection of resistance mechanisms. Modern non-phenotypic tests are promising in this respect, and hence, can influence both clinical outcome and healthcare costs. In this review, we present a summary of the most advanced methods (e.g., next-generation DNA sequencing, multiplex PCRs, real-time PCRs, microarrays, MALDI-TOF MS, and PCR/ESI MS) presently available for the rapid detection of antibiotic resistance genes in Enterobacteriaceae. Taking into account speed, manageability, accuracy, versatility, and costs, the possible settings of application (research, clinic, and epidemiology) of these methods and their superiority against standard phenotypic methods are discussed.

Promoter deletions of Klebsiella pneumoniae carbapenemase (KPC)-encoding genes (blaKPC -2) and efflux pump (AcrAB) on β-lactam susceptibility in KPC-producing Enterobacteriaceae

Klebsiella pneumoniae carbapenemase (KPC)-encoding genes containing promoter-deletions (bla(KPC-2a), bla(KPC-2b), and bla(KPC-2c) have disseminated in Enterobacteriaceae. The minimal inhibitory concentrations (MICs) to β-lactams in clinical KPC-producing Enterobacteriaceae range from susceptible to high-level resistant, resulting in diagnostic problems. To better understand the variability in β-lactam MICs among KPC-producing Enterobacteriaceae, three isoforms of bla(KPC-2) gene were used to transform Escherichia coli W4573 and its deletion mutant of an efflux pump (AcrAB) to examine the effects on β-lactam susceptibility. MICs to β-lactams in E. coli W4573 and its acrAB mutant strain increased 1- to 500-fold (MIC from 0.125 to 64 μg mL(-1) of aztreonam) in the bla(KPC-2a), bla(KPC-2b), and bla(KPC-2c) transformants compared with the cloning vector alone. However, transformants of the acrAB mutant strain remained susceptible to all β-lactams tested except for aztreonam and carbenicillin. Levels of the three promoters' length and carbapenemase activities in the transformants harboring the bla(KPC-2a), bla(KPC-2b), and bla(KPC-2c) were correlated to the levels of β-lactam MICs in both E. coli W4573 and its mutant of an efflux pump (AcrAB). Overall, these results suggest that promoter-deletions of bla(KPC-2) gene and AcrAB may be associated with the variability in β-lactam MICs in KPC-producing Enterobacteriaceae.

Modulation of respiratory dendritic cells during Klebsiella pneumonia infection

Background

Klebsiella pneumoniae is a leading cause of severe hospital-acquired respiratory tract infections and death but little is known regarding the modulation of respiratory dendritic cell (DC) subsets. Plasmacytoid DC (pDC) are specialized type 1 interferon producing cells and considered to be classical mediators of antiviral immunity.

Method

By using multiparameter flow cytometry analysis we have analysed the modulation of respiratory DC subsets after intratracheal Klebsiella pneumonia infection.

Results

Data indicate that pDCs and MoDC were markedly elevated in the post acute pneumonia phase when compared to mock-infected controls. Analysis of draining mediastinal lymph nodes revealed a rapid increase of activated CD103⁺ DC, CD11b⁺ DC and MoDC within 48 h post infection. Lung pDC identification during bacterial pneumonia was confirmed by extended phenotyping for 120G8, mPDCA-1 and Siglec-H expression and by demonstration of high Interferon-alpha producing capacity after cell sorting. Cytokine expression analysis of ex vivo-sorted respiratory DC subpopulations from infected animals revealed elevated Interferon-alpha in pDC, elevated IFN-gamma, IL-4 and IL-13 in CD103⁺ DC and IL-19 and IL-12p35 in CD11b⁺ DC subsets in comparison to CD11c⁺ MHC-class II^low cells indicating distinct functional roles. Antigen-specific naive CD4⁺ T cell stimulatory capacity of purified respiratory DC subsets was analysed in a model system with purified ovalbumin T cell receptor transgenic naive CD4⁺ responder T cells and respiratory DC subsets, pulsed with ovalbumin and matured with Klebsiella pneumoniae lysate. CD103⁺ DC and CD11b⁺ DC subsets represented the most potent naive CD4⁺ T helper cell activators.

Conclusion

These results provide novel insight into the activation of respiratory DC subsets during Klebsiella pneumonia infection. The detection of increased respiratory pDC numbers in bacterial pneumonia may indicate possible novel pDC functions with respect to lung repair and regeneration.

Carbapenemases: Partners in crime

Carbapenemases, β-lactamases that inactivate carbapenems and most β-lactam antibiotics, are most widely known for their ability to confer resistance to β-lactams. They include serine carbapenemases, such as the widespread KPC family of enzymes, and the metallo-β-lactamases that contain the IMP, NDM and VIM enzyme families acquired by Gram-negative bacteria on transferable elements. These enzymes are almost always produced by organisms that encode at least one other β-lactamase, with as many as eight different β-lactamase genes detected in a single isolate. This consortium of β-lactamases includes a full spectrum of molecular and biochemical characteristics, providing the producing organism with a range of catalytic activities. In addition to the variety of β-lactamases found in carbapenemase-producing Gram-negative pathogens are multiple other resistance factors, especially aminoglycoside-modifying enzymes and 16S rRNA methylases that confer resistance to aminoglycosides. Other acquired genes encode fluoroquinolone, trimethoprim, sulfonamide, rifampicin and chloramphenicol resistance determinants on mobile elements that travel together with β-lactamase genes. Thus, the recent proliferation of transferable carbapenemases serves to magnify resistance to virtually all antibiotic classes. Judicial use of current antibiotics and a quest for novel antibacterial agents are necessary, as multidrug-resistant bacteria continue to multiply.

Extended-spectrum cephalosporin-resistant Gram-negative organisms in livestock: an emerging problem for human health?

Escherichia coli, Salmonella spp. and Acinetobacter spp. are important human pathogens. Serious infections due to these organisms are usually treated with extended-spectrum cephalosporins (ESCs). However, in the past two decades we have faced a rapid increasing of infections and colonization caused by ESC-resistant (ESC-R) isolates due to production of extended-spectrum-β-lactamases (ESBLs), plasmid-mediated AmpCs (pAmpCs) and/or carbapenemase enzymes. This situation limits drastically our therapeutic armamentarium and puts under peril the human health. Animals are considered as potential reservoirs of multidrug-resistant (MDR) Gram-negative organisms. The massive and indiscriminate use of antibiotics in veterinary medicine has contributed to the selection of ESC-R E. coli, ESC-R Salmonella spp. and, to less extent, MDR Acinetobacter spp. among animals, food, and environment. This complex scenario is responsible for the expansion of these MDR organisms which may have life-threatening clinical significance. Nowadays, the prevalence of food-producing animals carrying ESC-R E. coli and ESC-R Salmonella (especially those producing CTX-M-type ESBLs and the CMY-2 pAmpC) has reached worryingly high values. More recently, the appearance of carbapenem-resistant isolates (i.e., VIM-1-producing Enterobacteriaceae and NDM-1 or OXA-23-producing Acinetobacter spp.) in livestock has even drawn greater concerns. In this review, we describe the aspects related to the spread of the above MDR organisms among pigs, cattle, and poultry, focusing on epidemiology, molecular mechanisms of resistance, impact of antibiotic use, and strategies to contain the overall problem. The link and the impact of ESC-R organisms of livestock origin for the human scenario are also discussed.