Antibody responses in Klebsiella pneumoniae bloodstream infection: a cohort study

Background

Klebsiella pneumonia (Kpn) is the fourth leading cause of infection-related deaths globally, yet little is known about human antibody responses to invasive Kpn. In this study, we sought to determine whether the O-specific polysaccharide (OPS) antigen, a vaccine candidate, is immunogenic in humans with Kpn bloodstream infection (BSI). We also sought to define the cross-reactivity of human antibody responses among structurally related Kpn OPS subtypes and to assess the impact of capsule production on OPS-targeted antibody binding and function.

Methods

We measured plasma antibody responses to OPS (and MrkA, a fimbrial protein) in a cohort of patients with Kpn BSI and compared these with controls, including a cohort of healthy individuals and a cohort of individuals with Enterococcus BSI. We performed flow cytometry to measure the impact of Kpn capsule production on whole cell antibody binding and complement deposition, utilizing patient isolates with variable levels of capsule production and isogenic capsule-deficient strains derived from these isolates.

Findings

We enrolled 69 patients with Kpn BSI. Common OPS serotypes accounted for 57/69 (83%) of infections. OPS was highly immunogenic in patients with Kpn BSI, and peak OPS-IgG antibody responses in patients were 10 to 30-fold higher than antibody levels detected in healthy controls, depending on the serotype. There was significant cross-reactivity among structurally similar OPS subtypes, including the O1v1/O1v2, O2v1/O2v2 and O3/O3b subtypes. Physiological amounts of capsule produced by both hyperencapsulated and non-hyperencapsulated Kpn significantly inhibited OPS-targeted antibody binding and function.

Interpretation

OPS was highly immunogenic in patients with Kpn BSI, supporting its potential as a candidate vaccine antigen. The strong cross-reactivity observed between similar OPS subtypes in humans with Kpn BSI suggests that it may not be necessary to include all subtypes in an OPS-based vaccine. However, these observations are tempered by the fact that capsule production, even in non-highly encapsulated strains, has the potential to interfere with OPS antibody binding. This may limit the effectiveness of vaccines that exclusively target OPS.

Funding

National Institute of Allergy and Infectious Diseases at the National Institutes of Health.

Research in Context

Evidence before this study: Despite the potential of O-specific polysaccharide (OPS) as a vaccine antigen against Klebsiella pneumoniae (Kpn), the immunogenicity of OPS in humans remains largely unstudied, creating a significant knowledge gap with regard to vaccine development. A search of PubMed for publications up to March 18, 2024, using the terms " Klebsiella pneumoniae " and "O-specific polysaccharide" or "O-antigen" or "lipopolysaccharide" revealed no prior studies addressing OPS antibody responses in humans with Kpn bloodstream infections (BSI). One prior study 1 evaluated antibody response to a single lipopolysaccharide (which contains one subtype of OPS) in humans with invasive Kpn infection; however, in this study OPS typing of the infecting strains and target antigen were not described. Added value of this study: Our investigation into OPS immunogenicity in a human cohort marks a significant advance. Analyzing plasma antibody responses in 69 patients with Kpn BSI, we found OPS to be broadly immunogenic across all the types and subtypes examined, and there was significant cross-reactivity among structurally related OPS antigens. We also demonstrated that Kpn capsule production inhibit OPS antibody binding and the activation of complement on the bacterial surface, even in classical Kpn strains expressing lower levels of capsule.Implications of all the available evidence: While the immunogenicity and broad cross-reactivity of OPS in humans with Kpn BSI suggests it is a promising vaccine candidate, the obstruction of OPS antibody binding and engagement by physiologic levels of Kpn capsule underscores the potential limitations of an exclusively OPS-antigen based vaccine for Kpn. Our study provides insights for the strategic development of vaccines aimed at combating Kpn infections, an important antimicrobial resistant pathogen.

Vaccine value profile for Klebsiella pneumoniae

Klebsiella pneumoniae causes community- and healthcare-associated infections in children and adults. Globally in 2019, an estimated 1.27 million (95% Uncertainty Interval [UI]: 0.91-1.71) and 4.95 million (95% UI: 3.62-6.57) deaths were attributed to and associated with bacterial antimicrobial resistance (AMR), respectively. K. pneumoniae was the second leading pathogen in deaths attributed to AMR resistant bacteria. Furthermore, the rise of antimicrobial resistance in both community- and hospital-acquired infections is a concern for neonates and infants who are at high risk for invasive bacterial disease. There is a limited antibiotic pipeline for new antibiotics to treat multidrug resistant infections, and vaccines targeted against K. pneumoniae are considered to be of priority by the World Health Organization. Vaccination of pregnant women against K. pneumoniae could reduce the risk of invasive K.pneumoniae disease in their young offspring. In addition, vulnerable children, adolescents and adult populations at risk of K. pneumoniae disease with underlying diseases such as immunosuppression from underlying hematologic malignancy, chemotherapy, patients undergoing abdominal and/or urinary surgical procedures, or prolonged intensive care management are also potential target groups for a K. pneumoniae vaccine. A 'Vaccine Value Profile' (VVP) for K.pneumoniae, which contemplates vaccination of pregnant women to protect their babies from birth through to at least three months of age and other high-risk populations, provides a high-level, holistic assessment of the available information to inform the potential public health, economic and societal value of a pipeline of K. pneumoniae vaccines and other preventatives and therapeutics. This VVP was developed by a working group of subject matter experts from academia, non-profit organizations, public-private partnerships, and multi-lateral organizations, and in collaboration with stakeholders from the WHO. All contributors have extensive expertise on various elements of the K.pneumoniae VVP and collectively aimed to identify current research and knowledge gaps. The VVP was developed using only existing and publicly available information.

A heptavalent O-antigen bioconjugate vaccine exhibits differential functional antibody responses against diverse Klebsiella pneumoniae isolates

Klebsiella pneumoniae is the leading cause of neonatal sepsis and is increasingly difficult to treat due to antibiotic resistance. Vaccination represents a tractable approach to combat this resistant bacterium; however, there is currently not a licensed vaccine. Surface polysaccharides, including O-antigens of lipopolysaccharide, have long been attractive candidates for vaccine inclusion. Herein we describe the generation of a bioconjugate vaccine targeting seven predominant O-antigen subtypes in K. pneumoniae. Each bioconjugate was immunogenic in isolation, with limited cross-reactivity among subtypes. Vaccine-induced antibodies demonstrated varying degrees of binding to a wide variety of K. pneumoniae strains. Further, sera from vaccinated mice induced complement-mediated killing of many of these strains. Finally, increased capsule interfered with O-antigen antibodies' ability to bind and mediate killing of some K. pneumoniae strains. Taken together, these data indicate that this novel heptavalent O-antigen bioconjugate vaccine formulation exhibits limited efficacy against some, but not all, K. pneumoniae isolates.

A heptavalent O-antigen bioconjugate vaccine exhibits differential functional antibody responses against diverse Klebsiella pneumoniae isolates

Klebsiella pneumoniae is a concerning pathogen that is now the leading cause of neonatal sepsis and is increasingly difficult to treat due to heightened antibiotic resistance. Thus, there is an urgent need for preventive and effective immunotherapies targeting K. pneumoniae. Vaccination represents a tractable approach to combat this resistant bacterium in some settings; however, there is currently not a licensed K. pneumoniae vaccine available. K. pneumoniae surface polysaccharides, including the terminal O-antigen polysaccharides of lipopolysaccharide, have long been attractive candidates for vaccine inclusion. Herein we describe the generation of a bioconjugate vaccine targeting seven of the predominant O-antigen subtypes in K. pneumoniae. Each of the seven bioconjugates were immunogenic in isolation, with limited cross-reactivity among subtypes. Vaccine-induced antibodies demonstrated varying degrees of binding to a wide variety of K. pneumoniae strains, including suspected hypervirulent strains, all expressing different O-antigen and capsular polysaccharide combinations. Further, sera from vaccinated mice induced complement-mediated killing of many of these K. pneumoniae strains. Finally, we found that increased quantity of capsule interferes with O-antigen antibodies' ability to bind and mediate killing of some K. pneumoniae strains, including those carrying hypervirulence-associated genes. Taken together, these data indicate that this novel heptavalent O-antigen bioconjugate vaccine formulation exhibits promising efficacy against some, but not all, K. pneumoniae isolates.

Klebsiella pneumoniae: adaptive immune landscapes and vaccine horizons

Klebsiella pneumoniae is among the most common antibiotic-resistant pathogens causing nosocomial infections. Additionally, it is a leading cause of neonatal sepsis and childhood mortality across the globe. Despite its clinical importance, we are only beginning to understand how the mammalian adaptive immune system responds to this pathogen. Further, many studies investigating potential K. pneumoniae vaccine candidates or alternative therapies have been launched in recent years. Here, we review the current state of knowledge on the adaptive immune response to K. pneumoniae infections and progress towards developing vaccines and other therapies to combat these infections.

Replicative Acinetobacter baumannii strains interfere with phagosomal maturation by modulating the vacuolar pH

Bacterial pneumonia is a common infection of the lower respiratory tract that can afflict patients of all ages. Multidrug-resistant strains of Acinetobacter baumannii are increasingly responsible for causing nosocomial pneumonias, thus posing an urgent threat. Alveolar macrophages play a critical role in overcoming respiratory infections caused by this pathogen. Recently, we and others have shown that new clinical isolates of A. baumannii, but not the common lab strain ATCC 19606 (19606), can persist and replicate in macrophages within spacious vacuoles that we called Acinetobacter Containing Vacuoles (ACV). In this work, we demonstrate that the modern A. baumannii clinical isolate 398, but not the lab strain 19606, can infect alveolar macrophages and produce ACVs in vivo in a murine pneumonia model. Both strains initially interact with the alveolar macrophage endocytic pathway, as indicated by EEA1 and LAMP1 markers; however, the fate of these strains diverges at a later stage. While 19606 is eliminated in an autophagy pathway, 398 replicates in ACVs and are not degraded. We show that 398 reverts the natural acidification of the phagosome by secreting large amounts of ammonia, a by-product of amino acid catabolism. We propose that this ability to survive within macrophages may be critical for the persistence of clinical A. baumannii isolates in the lung during a respiratory infection.

Capsular polysaccharide inhibits vaccine-induced O-antigen antibody binding and function across both classical and hypervirulent K2:O1 strains of Klebsiella pneumoniae

Klebsiella pneumoniae presents as two circulating pathotypes: classical K. pneumoniae (cKp) and hypervirulent K. pneumoniae (hvKp). Classical isolates are considered urgent threats due to their antibiotic resistance profiles, while hvKp isolates have historically been antibiotic susceptible. Recently, however, increased rates of antibiotic resistance have been observed in both hvKp and cKp, further underscoring the need for preventive and effective immunotherapies. Two distinct surface polysaccharides have gained traction as vaccine candidates against K. pneumoniae: capsular polysaccharide and the O-antigen of lipopolysaccharide. While both targets have practical advantages and disadvantages, it remains unclear which of these antigens included in a vaccine would provide superior protection against matched K. pneumoniae strains. Here, we report the production of two bioconjugate vaccines, one targeting the K2 capsular serotype and the other targeting the O1 O-antigen. Using murine models, we investigated whether these vaccines induced specific antibody responses that recognize K2:O1 K. pneumoniae strains. While each vaccine was immunogenic in mice, both cKp and hvKp strains exhibited decreased O-antibody binding in the presence of capsule. Further, O1 antibodies demonstrated decreased killing in serum bactericidal assays with encapsulated strains, suggesting that the presence of K. pneumoniae capsule blocks O1-antibody binding and function. Finally, the K2 vaccine outperformed the O1 vaccine against both cKp and hvKp in two different murine infection models. These data suggest that capsule-based vaccines may be superior to O-antigen vaccines for targeting hvKp and some cKp strains, due to capsule blocking the O-antigen.

Replicative Acinetobacter baumannii strains interfere with phagosomal maturation by modulating the vacuolar pH

Bacterial pneumonia is a common infection of the lower respiratory tract that can afflict patients of all ages. Multidrug-resistant strains of Acinetobacter baumannii are increasingly responsible for causing nosocomial pneumonias, thus posing an urgent threat. Alveolar macrophages play a critical role in overcoming respiratory infections caused by this pathogen. Recently, we and others have shown that new clinical isolates of A. baumannii , but not the common lab strain ATCC 19606 (19606), can persist and replicate in macrophages within spacious vacuoles that we called A cinetobacter C ontaining V acuoles (ACV). In this work, we demonstrate that the modern A. baumannii clinical isolate 398, but not the lab strain 19606, can infect alveolar macrophages and produce ACVs in vivo in a murine pneumonia model. Both strains initially interact with the alveolar macrophage endocytic pathway, as indicated by EEA1 and LAMP1 markers; however, the fate of these strains diverges at a later stage. While 19606 is eliminated in an autophagy pathway, 398 replicates in ACVs and are not degraded. We show that 398 reverts the natural acidification of the phagosome by secreting large amounts of ammonia, a by-product of amino acid catabolism. We propose that this ability to survive within macrophages may be critical for the persistence of clinical A. baumannii isolates in the lung during a respiratory infection.

Airway multidrug-resistant organisms in a population of tracheostomy and chronic ventilator-dependent children at a tertiary care pediatric hospital

OBJECTIVE/BACKGROUND

Children with tracheostomies are at an increased risk of bacterial respiratory tract infections. Infections caused by multidrug-resistant organisms (MDROs) are more difficult to treat and can result in severe complications. This study aimed to investigate the risk factors and sequelae of MDRO positivity in tracheostomy and chronic ventilator-dependent children.

METHODS

We performed a retrospective chart review of 75 tracheostomy and chronic ventilator-dependent children at St. Louis Children's Hospital. Data on demographics, respiratory cultures, hospitalizations, emergency department (ED) visits, and antibiotic usage were collected. We determined the frequency of MDRO positivity and compared the number of hospitalizations, number of ED visits, and antibiotic usage in patients with and without MDRO-positive cultures. Patient clinical variables were analyzed before and after MDRO acquisition.

RESULTS

We found 75.7% (56/74) of our participants had an MDRO-positive culture, with methicillin-resistant Staphylococcus aureus (MRSA, n = 36, 64%) and Pseudomonas aeruginosa (n = 8, 14%) being the most commonly detected organisms. Participants with a greater number of annual nonpulmonary admissions (odds ratio [OR] = 1.99, 95% confidence interval [CI] (1.21-3.29), p = 0.008], inpatient antibiotic courses [OR = 1.27, 95% CI (1.07-1.50), p = 0.006], total antibiotic courses [OR = 1.26, 95% CI (1.08-1.48), p = 0.004], and chronic antibiotic use [OR = 2.31, 95% CI (1.12-4.74), p = 0.03] were at an increased risk for MDRO positivity. Those who were MDRO-positive had more pulmonary admissions following MDRO acquisition compared those who were MDRO-negative [p = 0.005] but not more antibiotic usage or ED visits.

CONCLUSION

Frequent antibiotic usage and hospitalizations increase the risk of MDRO acquisition in children with tracheostomies and ventilator-dependence. Further antibiotic stewardship may help prevent resistant infections in technology-dependent children.

Discovery and characterization of a new class of O-linking oligosaccharyltransferases from the Moraxellaceae family

Bacterial protein glycosylation is commonly mediated by oligosaccharyltransferases (OTases) that transfer oligosaccharides en bloc from preassembled lipid-linked precursors to acceptor proteins. Natively, O-linking OTases usually transfer a single repeat unit of the O-antigen or capsular polysaccharide to the side chains of serine or threonine on acceptor proteins. Three major families of bacterial O-linking OTases have been described: PglL, PglS, and TfpO. TfpO is limited to transferring short oligosaccharides both in its native context and when heterologously expressed in glycoengineered Escherichia coli. On the other hand, PglL and PglS can transfer long-chain polysaccharides when expressed in glycoengineered E. coli. Herein, we describe the discovery and functional characterization of a novel family of bacterial O-linking OTases termed TfpM from Moraxellaceae bacteria. TfpM proteins are similar in size and sequence to TfpO enzymes but can transfer long-chain polysaccharides to acceptor proteins. Phylogenetic analyses demonstrate that TfpM proteins cluster in distinct clades from known bacterial OTases. Using a representative TfpM enzyme from Moraxella osloensis, we determined that TfpM glycosylates a C-terminal threonine of its cognate pilin-like protein and identified the minimal sequon required for glycosylation. We further demonstrated that TfpM has broad substrate tolerance and can transfer diverse glycans including those with glucose, galactose, or 2-N-acetyl sugars at the reducing end. Last, we find that a TfpM-derived bioconjugate is immunogenic and elicits serotype-specific polysaccharide IgG responses in mice. The glycan substrate promiscuity of TfpM and identification of the minimal TfpM sequon renders this enzyme a valuable additional tool for expanding the glycoengineering toolbox.

Classical and γδ T cells are each independently sufficient to establish protection against a classical strain of Klebsiella pneumoniae

Infections with classical strains of the Gram-negative bacterium Klebsiella pneumoniae pose a significant clinical challenge due to rising antibiotic resistance. We previously established a lung inoculation plus challenge model using live, classical K. pneumoniae in order to study host protection. Here, we employ this model to dissect adaptive immune responses to this critical pathogen. First, we performed convalescent serum transfers from inoculated mice to naïve recipients and found that classical K. pneumoniae infection outcomes, unlike hypervirulent K. pneumoniae infection outcomes, were not improved. This suggests that circulating antibody responses alone are not sufficient to mediate protection against this classical strain. Hence, we evaluated the role of T cells in protection against classical K. pneumoniae reinfection and demonstrated that mice lacking T cells are unable to establish a protective response. However, mice individually deficient in either of the major T cell subsets, γδ or αβ (classical T cells), effectively mount a protective response, indicating either subset alone is sufficient to mediate protection. Sequestration of T cells in secondary lymphoid organs during the challenge infection did not ablate protection, indicating the circulating T cell pool is not required for the protective phenotype. Finally, we demonstrate that depletion of T cells during initial infection eliminates protection against challenge. Collectively, these experiments demonstrate the imperative contribution of T cells to protective immunity against classical K. pneumoniae and will guide further inquiries into host effector responses required to control this infection.

T cell immunity to a classical strain of Klebsiella pneumoniae

Klebsiella pneumoniae (Kp) is a versatile pathogen capable of causing numerous infections that are becoming increasingly difficult to treat due to increasing antibiotic resistance. Kp strains are categorized into two distinct pathotypes: classical and hypervirulent, which exhibit critical differences in pathogenesis. Despite causing the majority of clinical cases, adaptive immunity resulting from classical Kp infections is poorly understood. Our laboratory has recently developed a model of adaptive immunity to live infection with classical Kp in which wild-type mice surviving primary infection are protected from morbidity and mortality upon rechallenge. Passive transfer of convalescent serum from surviving mice to naïve recipients does not confer protection against cKp infection, suggesting antibody responses alone are inadequate to protect against cKp. CD69+CD4+ T cells and γδ T cells expand dramatically in the lung following primary cKp infection and mice deficient in T cells are not protected from reinfection, indicating a requirement for T cells in the protective response. Further analysis of mice deficient in either classical αβ T cells or γδ T cells indicates that either T cell subset is capable of mediating protective immunity against Kp reinfection. Production of IL-17A by both CD4 and γδ T cells is enhanced during secondary infection. Together these data indicate that a natural course of infection with classical Kp elicits populations of classical T cells and γδ T cells that mediate protection against reinfection, likely through the rapid production of IL-17A. These results will ultimately inform rational design of vaccines and immunotherapies to prevent and treat Kp infection.

Supported by AAI Careers in Immunology Fellowship

Differential Immune Response to Klebsiella pneumoniae O-antigen subtypes O2v1 and O2v2

Klebsiella pneumoniae (Kp) infections are sharply on the rise among at-risk populations. We have previously shown that use of bioconjugate vaccines targeting Kp are beneficial in preventing disease and seek to increase our vaccine breadth of coverage. Kp has nine serogroups of O-antigens. Recently, additional O-antigen subtypes within these serogroups have been identified; yet, the pathogenic fitness, immunogenicity, functional antibody response, and cross-protection between subtypes is unknown. We investigated how the addition of the single branched galactose in O-antigen subtype O2v2 compared to O2v1 changes its bacterial fitness and host immune susceptibility. We knocked out the gmlABC region of an O2v2 strain of Kp, converting it to O2v1. Complementation of this mutant allowed us to identify the specific gene responsible for the addition of the single branched galactose of O2v2. Further, experiments using the O2v1 mutant and its parent O2v2 strain confirmed similar phenotypic expression of virulence factors beyond the O-antigen. Well-established murine models of pneumonia were used to determine the pulmonary fitness of the pathogens and assess the host innate immune responses. Neutrophil and complement-mediated killing assays suggested differences in susceptibility to innate immune defenses. Further, differences in IgG subclass were observed 4 weeks post respiratory infection with the O2v2 parent and O2v1 mutant strains. Lastly, using novel bioconjugate vaccines against these specific O-antigen subtypes, we determined only partial cross-protection is elicited. These studies advance our understanding of the immune response to Kp O-antigens and aid in vaccine design to combat this drug-resistant pathogen.

Supported by the W.M. Keck Postdoctoral Fellowship in Molecular Medicine Dr. Wantuch is a W.M. Keck Fellow

An unconventional T cell population is critical for protection from repeat pulmonary infection with Klebsiella pneumoniae

Due to emerging antibiotic resistance, the nosocomial pathogen Klebsiella pneumoniae is an increasing public health threat. The extent to which survivors are protected against re-infection, or potential correlates of such protection, are poorly understood. We have explored the immunological mechanisms required for protection against K. pneumoniae re-infection using a nonlethal murine model of pulmonary K. pneumoniae challenge. Mice that survive K. pneumoniae TOP52 infection are protected from subsequent re-infection by an adaptive immune response. Genetically modified mice lacking mature lymphocytes or mature T cells were equally susceptible to primary and secondary infection, suggesting that T cells are required for protection. Intriguingly, neither CD4+ nor CD8+ T cells were absolutely required for either the establishment or execution of a protective memory response as depletion of CD4+ and/or CD8+ T cells during either primary or secondary infection did not impair protection against re-infection. However, we observe an expansion of γδ T cells following primary exposure to K. pneumoniae and a profound amplification of this population following secondary infection. Experiments using genetically modified mice deficient in γδ T cells or intact mice treated with γδ T cell depleting antibodies suggest that this T cell subpopulation is important for protection against re-infection. Thus, we hypothesize that K. pneumoniae exposure drives the development of a resident memory-like population of γδ T cells that are maintained in the lung and contribute to the efficient control of secondary K. pneumoniae infection.

Development and organization of pulmonary lymphoid aggregates after Klebsiella pneumoniae infection of the murine respiratory tract

Klebsiella pneumoniae is a worrisome nosocomial pathogen given the widespread emergence of antibiotic resistant strains. Little is known about the host immune response to K. pneumoniae; however, it has recently been shown that aggregates of lymphoid cells can be found in murine lungs 4 weeks after surviving K. pneumoniae pulmonary infection. Others have characterized pulmonary collections of lymphoid cells in response to other pathogens and coined them induced bronchus-associated lymphoid tissue (iBALT). iBALT is believed to assist in protection against re-infection. In our nonlethal model of K. pneumoniae, mice that survive the primary infection and exhibit these structures are indeed protected from K. pneumoniae challenge. To further characterize the development and organization of these structures, pulmonary immune cell populations were analyzed post-infection by flow cytometry, histology, and immunofluorescence. As expected, pulmonary neutrophil populations increase over the first 10 days post-infection. T cells appear to rapidly expand between 7 and 10 days post-infection and both CD4+ and γδ T cell subsets make up the majority of this population. Immunofluorescent imaging of lymphoid aggregates demonstrate that CD4+ and γδ T cells are found within these structures at early time-points. Experiments using TCRβδ−/− mice lacking T cells reveals the absence of lymphoid aggregates 28 days post-infection, suggesting that T cells are essential in the initial formation and development of these structures.

A murine model demonstrates capsule-independent adaptive immune protection in survivors of Klebsiella pneumoniae respiratory tract infection

Klebsiella pneumoniae represents a growing clinical threat, given its rapid development of antibiotic resistance, necessitating new therapeutic strategies. Existing live-infection models feature high mortality rates, limiting their utility in the study of natural adaptive immune response to this pathogen. We developed a preclinical model of pneumonia with low overall mortality, in which previously exposed mice are protected from subsequent respiratory tract challenge with K. pneumoniae Histologic analyses of infected murine lungs demonstrate lymphocytic aggregates surrounding vasculature and larger airways. Initial exposure in RAG1 knockout mice (lacking functional B and T cells) failed to confer protection against subsequent K. pneumoniae challenge. While administration of isolated K. pneumoniae capsule was sufficient to provide protection, we also found that initial inoculation with K. pneumoniae mutants lacking capsule (Δcps), O-antigen (ΔwecA) or both conferred protection from subsequent wild-type infection and elicited K. pneumoniae-specific antibody responses, indicating that non-capsular antigens may also elicit protective immunity. Experiments in this model will inform future development of multivalent vaccines to prevent invasive K. pneumoniae infections.

Whole-Genome Sequencing of Klebsiella pneumoniae Isolates to Track Strain Progression in a Single Patient With Recurrent Urinary Tract Infection

Klebsiella pneumoniae is an important uropathogen that increasingly harbors broad-spectrum antibiotic resistance determinants. Evidence suggests that some same-strain recurrences in women with frequent urinary tract infections (UTIs) may emanate from a persistent intravesicular reservoir. Our objective was to analyze K. pneumoniae isolates collected over weeks from multiple body sites of a single patient with recurrent UTI in order to track ordered strain progression across body sites, as has been employed across patients in outbreak settings. Whole-genome sequencing of 26 K. pneumoniae isolates was performed utilizing the Illumina platform. PacBio sequencing was used to create a refined reference genome of the original urinary isolate (TOP52). Sequence variation was evaluated by comparing the 26 isolate sequences to the reference genome sequence. Whole-genome sequencing of the K. pneumoniae isolates from six different body sites of this patient with recurrent UTI demonstrated 100% chromosomal sequence identity of the isolates, with only a small P2 plasmid deletion in a minority of isolates. No single nucleotide variants were detected. The complete absence of single-nucleotide variants from 26 K. pneumoniae isolates from multiple body sites collected over weeks from a patient with recurrent UTI suggests that, unlike in an outbreak situation with strains collected from numerous patients, other methods are necessary to discern strain progression within a single host over a relatively short time frame.

Ureaplasma urealyticum pyelonephritis presenting with progressive dysuria, renal failure, and neurologic symptoms in an immunocompromised patient

Ureaplasma urealyticum is a bacterial species correlated with urethritis in healthy individuals and invasive infections in immunocompromised patients. We describe a 20-year-old female with a history of remote heart transplant on everolimus, mycophenolate, and rituximab presenting with progressive urinary tract symptoms, renal failure, and neurologic symptoms. An extensive workup ultimately identified U urealyticum infection, and the patient successfully recovered after a course of azithromycin and doxycycline.

In silico discovery of small molecules that inhibit RfaH recruitment to RNA polymerase

RfaH is required for virulence in several Gram-negative pathogens including Escherichia coli and Klebsiella pneumoniae. Through direct interactions with RNA polymerase (RNAP) and ribosome, RfaH activates the expression of capsule, cell wall and pilus biosynthesis operons by reducing transcription termination and activating translation. While E. coli RfaH has been extensively studied using structural and biochemical approaches, limited data are available for other RfaH homologs. Here we set out to identify small molecule inhibitors of E. coli and K. pneumoniae RfaHs. Results of biochemical and functional assays show that these proteins act similarly, with a notable difference between their interactions with the RNAP β subunit gate loop. We focused on high-affinity RfaH interactions with the RNAP β' subunit clamp helices as a shared target for inhibition. Among the top 10 leads identified by in silico docking using ZINC database, 3 ligands were able to inhibit E. coli RfaH recruitment in vitro. The most potent lead was active against both E. coli and K. pneumoniae RfaHs in vitro. Our results demonstrate the feasibility of identifying RfaH inhibitors using in silico docking and pave the way for rational design of antivirulence therapeutics against antibiotic-resistant pathogens.

The utility of accelerometers to predict stroke rate in captive fur seals and sea lions

The energy expenditure of free-living fur seals and sea lions is difficult to measure directly, but may be indirectly derived from flipper stroke rate. We filmed 10 captive otariids swimming with accelerometers either attached to a harness (Daily Diary: sampling frequency 32 Hz, N=4) or taped to the fur (G6a+: 25 Hz, N=6). We used down sampling to derive four recording rates from each accelerometer (Daily Diary: 32, 16, 8, 4 Hz; G6a+: 25, 20, 10, 5 Hz). For each of these sampling frequencies, we derived 20 combinations of two parameters (RMW, the window size used to calculate the running mean; and m, the minimum number of points smaller than a local maxima used to detect a peak) from the dynamic acceleration of x, z and x+z, to estimate stroke rate from the accelerometers. These estimates differed by up to ∼20% in comparison to the actual number of foreflipper strokes counted from videos. RMW and the choice of axis used to make the calculations (x, z or x+z) had little effect on the overall differences, though the variability was reduced when using x+z. The best m varied depending on the axis used and the sampling frequency; a larger m was needed for higher sampling frequencies. This study demonstrates that when parameters are appropriately tuned, accelerometers are a simple yet valid tool for estimating the stroke rates of swimming otariids.

Summary: Accelerometer data collected from captive fur seals and sea lions swimming were used to determine the best method for processing raw data to achieve the highest accuracy of stroke rate.

Klebsiella pneumoniae FimK Promotes Virulence in Murine Pneumonia

Klebsiella pneumoniae, a chief cause of nosocomial pneumonia, is a versatile and commonly multidrug-resistant human pathogen for which further insight into pathogenesis is needed. We show that the pilus regulatory gene fimK promotes the virulence of K. pneumoniae strain TOP52 in murine pneumonia. This contrasts with the attenuating effect of fimK on urinary tract virulence, illustrating that a single factor may exert opposing effects on pathogenesis in distinct host niches. Loss of fimK in TOP52 pneumonia was associated with diminished lung bacterial burden, limited innate responses within the lung, and improved host survival. FimK expression was shown to promote serum resistance, capsule production, and protection from phagocytosis by host immune cells. Finally, while the widely used K. pneumoniae model strain 43816 produces rapid dissemination and death in mice, TOP52 caused largely localized pneumonia with limited lethality, thereby providing an alternative tool for studying K. pneumoniae pathogenesis and control within the lung.

Modeling the optical properties of bowtie antenna generated by self-assembled ag triangular nanoprisms

Self-organized metal nanoparticles often possess assembly defects that can have a profound impact on the optical properties of the resulting nanoparticle assembly. Modeling these defects and evaluating their optical outcomes can provide a better understanding of how to design the assembly process and can evaluate the quality of the resulting materials. Here, we use finite element methods to examine the fabrication of bowtie nanoantenna, a commonly sought-after plasmonic structure with resonances in the visible and near-infrared wavelengths, through the self-assembly of colloidal triangular Ag nanoprisms. We model perfect and defective antenna structures and examine the effects of commonly observed assembly defects such as imperfect nanoprism shapes, off-axis antenna structures, and trimer or tetramer formation. We also evaluate the ability to fabricate antenna structures that possess comparable structural parameters (e.g., thickness, gap distance) to top-down lithographic techniques. We find that structural defects in self-assembled bowties can shift the resonant wavelength of the antenna by as much as 200 nm. Our models also indicate that self-assembled bowties possess high defect tolerances with respect to near-field enhancement, suggesting that they are viable structures for nanophotonic and nanoplasmonic applications.

An institutional experience with epidural analgesia in children and young adults undergoing cardiac surgery

BACKGROUND

Allowing spontaneous respiration after cardiac surgery eliminates complications related to mechanical ventilation and optimizes cardiopulmonary interaction. Epidural analgesia has been proposed to promote early extubation after cardiac surgery.

OBJECTIVE

To identify the characteristics of patients with epidural analgesia and safety profiles with respect to the timing of extubation following cardiac surgery.

DESIGN AND METHOD

A retrospective chart review of patients who underwent cardiac surgery during a 5-year period. Demographic, procedural, and perioperative variables were analyzed to investigate factors that affect the timing of extubation.

RESULTS

A total of 750 records were reviewed. The patients' median age was 12 months, and 52% were infants (<1 year). Seventy-five percent of the patients utilized cardiopulmonary bypass. The study population was classified into three groups according to the timing of extubation: 66% were extubated in the operating room or upon arrival at the PICU (Immediate), 15% were extubated within 24 h (mean, 10.8 h; 95% CI, 9.0-12.6) (Early), and 19% were extubated after 24 h (Delayed). For the Immediate and Early groups, multivariate logistic regression identified young age, increased cross-clamp time, and inotrope score as independent risk factors for the need for mechanical ventilation. Postextubation respiratory acidosis (mean P(a)CO(2), 50 mmHg; 95% CI, 49-51) was well tolerated by all patients. There were no neurologic complications related to the epidural technique.

CONCLUSION

Epidural analgesia in children undergoing cardiac surgery provides stable analgesia without complications in our experience.

Preliminary Experience With Nesiritide in Pediatric Patients Less Than 12 Months of Age

The natriuretic peptide system plays an active role in the regulation of fluid balance and systemic vascular resistance. Advances in recombinant technology have provided the opportunity for the exogenous administration of a recombinant form of B-type natriuretic peptide (nesiritide). To date, reports of its use in the pediatric population are limited, with limited information regarding its use in patients less than 12 months of age. We retrospectively reviewed our experience with nesiritide in infants less than 12 months of age to determine its efficacy and adverse effect profile. The study cohort included 22 patients, ranging in age from 4 days to 12 months. The starting dose of the nesiritide infusion ranged from 0.01 to 0.05 µg/kg/min (0.015 ± 0.01µg/ kg/min) and was administered for a total of 3 to 264 hours (85.2 ± 75.0 hours). Nesiritide resulted in a significant increase in urine output even in the face of decreased fluid intake. Mean urine output increased from 3.1 ± 2.5 mL/kg/h before nesiritide to 5.7 ± 4.5 mL/kg/h ( P = .03) during the initial 24 hours after starting the infusion. Fluid intake before and after the infusion were 126 ± 60 mL/kg/d and 108 ± 56 mL/kg/d, respectively. There were no statistically or clinically significant changes in hemodynamic parameters (heart rate, blood pressure, and central venous pressure) during the nesiritide infusion. No change in electrolytes, blood urea nitrogen, and creatinine were noted. No adverse effects of the nesiritide infusion were noted. No infusion was stopped due to adverse effects. These data suggest that nesiritide is a safe method of improving urine output in pediatrics patients less than 12 months of age and that the adverse effect profile does not appear to be different than that reported in older children.

Detection of intracellular bacterial communities in human urinary tract infection

BACKGROUND

Urinary tract infections (UTIs) are one of the most common bacterial infections and are predominantly caused by uropathogenic Escherichia coli (UPEC). While UTIs are typically considered extracellular infections, it has been recently demonstrated that UPEC bind to, invade, and replicate within the murine bladder urothelium to form intracellular bacterial communities (IBCs). These IBCs dissociate and bacteria flux out of bladder facet cells, some with filamentous morphology, and ultimately establish quiescent intracellular reservoirs that can seed recurrent infection. This IBC pathogenic cycle has not yet been investigated in humans. In this study we sought to determine whether evidence of an IBC pathway could be found in urine specimens from women with acute UTI.

METHODS AND FINDINGS

We collected midstream, clean-catch urine specimens from 80 young healthy women with acute uncomplicated cystitis and 20 asymptomatic women with a history of UTI. Investigators were blinded to culture results and clinical history. Samples were analyzed by light microscopy, immunofluorescence, and electron microscopy for evidence of exfoliated IBCs and filamentous bacteria. Evidence of IBCs was found in 14 of 80 (18%) urines from women with UTI. Filamentous bacteria were found in 33 of 80 (41%) urines from women with UTI. None of the 20 urines from the asymptomatic comparative group showed evidence of IBCs or filaments. Filamentous bacteria were present in all 14 of the urines with IBCs compared to 19 (29%) of 66 samples with no evidence of IBCs (p < 0.001). Of 65 urines from patients with E. coli infections, 14 (22%) had evidence of IBCs and 29 (45%) had filamentous bacteria, while none of the gram-positive infections had IBCs or filamentous bacteria.

CONCLUSIONS

The presence of exfoliated IBCs and filamentous bacteria in the urines of women with acute cystitis suggests that the IBC pathogenic pathway characterized in the murine model may occur in humans. The findings support the occurrence of an intracellular bacterial niche in some women with cystitis that may have important implications for UTI recurrence and treatment.

Short Duration Large Dose Dexmedetomidine in a Pediatric Patient During Procedural Sedation

We describe an infusion of dexmedetomidine at 1.0 microg.kg(-1).min(-1) for 10 min (total dose, 144 microg) sedation in a 3-yr-old child weighing 14 kg. The large dose of dexmedetomidine produced a hemodynamically stable patient who was deeply sedated for approximately 4 h after discontinuing the infusion.

Nesiritide during extracorporeal membrane oxygenation

Nesiritide is a recombinant formulation of B-type natriuretic peptide (BNP). Preliminary experience in the adult population has shown nesiritide to be an effective agent in the treatment of decompensated congestive heart failure (CHF) in adults. Given its physiological effects, it may be an effective agent in other clinical scenarios. We report the use of nesiritide in two infants during extracorporeal membrane oxygenation (ECMO). In one patient, nesiritide in doses up to 0.09 microg.kg(-1).min(-1) were used to control mean arterial pressure while in the other patient, doses of 0.01-0.03 microg.kg(-1).min(-1) were used to augment urine output. The potential applications of nesiritide and dosing regimens for this agent in the ECMO population are discussed.

An Epidural Hematoma in an Adolescent Patient After Cardiac Surgery

An 18-yr-old patient had a thoracic epidural placed under general anesthesia preceding an uneventful aortic valve replacement with a bioprosthetic valve. On the second postoperative day, he was anticoagulated and also received an antithrombotic medication. While ambulating, he experienced pain in his back, and there was blood in his epidural catheter. The catheter was removed, and he developed motor and sensory loss. Rapid surgical decompression resulted in recovery of his lost neurological function. Management and strategies for preventing this problem are discussed.

IMPLICATIONS

Epidural hematoma is a rare complication of epidural anesthesia and has not been reported in pediatric patients undergoing cardiac surgery. The successful treatment of this complication requires swift recognition, diagnosis, and surgical intervention.

Nonsteroidal anti-inflammatory agents in neonates

The use of NSAIDs has become routine for adults and children in the management of pain. NSAIDs (other than aspirin [acetylsalicylic acid]) are also enjoying greater popularity as antipyretics since the recognition of Reye's syndrome's putative association with aspirin. In neonates, NSAIDs have been used for many years in an attempt to pharmacologically close the ductus arteriosus. This review examines the various NSAIDs and their potential and real applications in the neonatal population. For completeness, acetaminophen (paracetamol), which has weak NSAID activity and is a widely used analgesic and antipyretic in this patient group, was also included. The prostaglandin system is important for healthy development, and conversely there are unique risks posed by pharmacologic interference with this system in the neonatal period. The prostanoid system in neonates has the capacity to modulate nociception, but comes at the expense of interfering with nearly every organ system. Physiologic effects of inhibition of prostaglandin synthesis applicable to neonates include disruption of the sleep cycle, increased risk of pulmonary hypertension, alterations in cerebral blood flow, decreased renal function, disrupted thermoregulation, and alterations in hemostasis balance, among others. Prostaglandins are also important for the normal development of the central nervous, cardiovascular, and renal systems, and there is evidence that the proper genesis of these systems may be adversely effected by NSAID exposure in utero and in the neonatal period. Gastrointestinal adverse effects have provided the impetus for the development and marketing of selective cyclo-oxygenase type 2 (COX-2) inhibitors. These agents' reputation for safety in adults may not be applicable to neonates. COX-2 is involved in the development of several organ systems, and its inhibition may induce a prothrombotic state. The advent of parenteral formulations of cyclo-oxygenase inhibitors, including COX-2-selective agents, increases the therapeutic flexibility of NSAIDs. However, objective data on the safety of these agents have not kept pace with their clinical availability.

Gingival colonization with selective HACEK microbes in children with congenital heart disease

It was previously shown that children with congenital heart disease (CHD) harbored Hemophilus, Actinobacillus, Cardiobacter, Eikenella, and Kingella (HACEK) microbes to a greater extent and had more severe gingival inflammation than a normal group of children. The purpose of this study was to determine if HACEK microbes are more prevalent in children with CHD than in normal children when there is no difference in gingival inflammation. Two groups of 12 children were matched with respect to gingival inflammation. Each child had a gingival index recorded as described by Massler. The experimental group consisted of 12 children with CHD 2.5-10 years old (average 5.5) and the control group consisted of 12 healthy children 2-13 years old (average 5.6). Subgingival samples were obtained and cultured for HACEK microbes. Fischer's exact test was performed with the significance level defined at P<0.05. The average gingival indices for the experimental and control groups were 6.5 and 6.4, respectively (N.S.). Nine of 12 children with CHD had Eikenella corrodens (E.c.) compared to 3/12 control patients ( P<0.05). Three of 12 CHD patients but no control patient had Actinobacillus actinomycetemcomitans (A.a.) (N.S.). There were no significant differences in E.c. or A.a. presence between cyanotic and acyanotic CHD patients. This study found that the greater extent of specific HACEK microbes harbored by children with CHD is not associated with cyanosis or the degree of gingival inflammation. Further study is needed to delineate fully the medical significance of this observation.

Extracorporeal CO2 removal in a child with a single ventricle by the addition of an oxygenator to a dialysis circuit

OBJECTIVE

To optimize CO2 removal in a child with a single ventricle.

DESIGN

Case report.

SETTING

A ten-bed pediatric intensive care unit in a university-affiliated hospital.

PATIENT

A 6-yr-old boy with a single ventricle who underwent a Fontan procedure.

INTERVENTIONS

Addition of a membrane oxygenator to a venovenous hemodialysis circuit.

MEASUREMENTS

Patient respiratory variables were measured.

MAIN RESULTS

A clinically significant improvement in CO2 removal was achieved.

CONCLUSIONS

Addition of a membrane oxygenator to a dialysis circuit facilitates CO2 removal.

Nalmefene to prevent epidural narcotic side effects in pediatric patients: a pharmacokinetic and safety study

STUDY OBJECTIVE

To determine the pharmacokinetics and preliminary efficacy of nalmefene in children in preventing epidural-induced narcotic side effects.

DESIGN

Double-blind, placebo-controlled study.

SETTING

University-affiliated children's hospital.

PATIENTS

Thirty-four children (aged 2-12 yrs) undergoing cardiothoracic surgery with epidural anesthesia.

INTERVENTIONS

Patients were randomized to receive intravenous bolus nalmefene 1 microg/kg or placebo.

MEASUREMENTS AND MAIN RESULTS

Six blood samples (one before nalmefene administration and five from 13 randomly designated time points) from each patient were assayed to determine plasma nalmefene concentrations. Patients were assessed for pain, nausea, vomiting, and urinary retention for 24 hours after administration. Concentration-time data were analyzed by a limited sampling strategy with adult pharmacokinetic parameters used as Bayesian priors. A two-compartment, first-order model was fitted to the data using ADAPT II. Pharmacokinetic parameter estimates in these patients were similar to values reported in adults. The initial disposition half-life (t(1/2alpha)) was 0.36+/-0.11 hour, the terminal elimination half-life (t(1/2beta)) 8.7+/-2.3 hours, clearance 0.729+/-0.172 L/kg/hr, and steady-state volume of distribution 7.21+/-2.49 L/kg. Ability to prevent epidural narcotic-induced side effects could not be documented at the 1-microg/kg dose. No statistically significant differences were noted between study and placebo groups with regard to pain, nausea, vomiting, or urinary retention.

CONCLUSION

Nalmefene has similar pharmacokinetics in children as in adults. It was administered safely to these patients and did not produce unmanageable pain.

Analgesia for pediatric thoracostomy tube removal

Eutectic mixture of local anesthetics (EMLA; Astra Pharmaceuticals, Wayne, PA) has been shown to reduce the pain of blood draws in children. We investigated the use of EMLA versus IV morphine for providing analgesia during chest tube removal (CTR) in children. One hundred twenty pediatric cardiothoracic surgery patients were enrolled. Patients were randomly assigned to receive either morphine (0.1 mg/kg up to 10 mg IV 30 min before CTR) or EMLA cream (5 g per chest tube cutaneously 3 h before CTR). A single, trained observer rated the patient's pain before, during, and after CTR using a 10-cm visual analog scale. The sites were evaluated for adverse effect. Methylhemoglobin levels were monitored in infants. Before CTR, the pain scores of the children who received morphine were rated lower than those who received EMLA (P < 0.01). During CTR, there was no difference in the pain score between the morphine or EMLA group. The change from baseline pain score in the morphine group was significantly larger than in the EMLA group (P < 0.01). We conclude that EMLA is safe and useful for blunting the pain of CTR.

Metabolic effects of low-energy diet on steller sea lions, Eumetopias jubatus

Diets of six Steller sea lions (Eumetopias jubatus) were switched between a high (herring) and a low (squid) energy density food for 14 d to determine the effects on ingested prey mass, body mass, resting metabolic rate, and the heat increment of feeding. Body mass was measured daily, and resting metabolism was measured weekly by gas respirometry. Ingested food mass did not differ significantly between the squid diet and the control or the recovery herring diet periods. As a result of differences in energy density, gross energy intake was significantly lower during the squid diet phase than during either the control or recovery periods. As a result, sea lions lost an average of 1.1 kg/d, totaling 12.2% of their initial body mass by the end of the experimental period. The heat increment of feeding for a 4-kg squid meal was significantly lower than for a similarly sized meal of herring. Decreases in both absolute (24.0 to 18.0 MJ/d, -24%) and mass-corrected (903 to 697 kJ/d/kg0.67, -20%) metabolism were observed by the end of the squid feedings. This study suggests that sea lions can depress their resting metabolism in response to decreases in energy intake or body mass, regardless of satiation level.

Topical lidocaine-prilocaine cream (EMLA) for thoracostomy tube removal

We prospectively studied topical lidocaine-prilocaine cream (EMLA) versus IV morphine in a double-blinded, randomized fashion for pain relief during thoracostomy tube (chest tube; CT) removal. Adult patients who had undergone thoracotomy or median sternotomy were randomized to receive either EMLA cream over CT sites transdermally for 3 h or IV morphine 0.5 h before CT removal. Pain behavior was observed and rated before, during, and after CT removal. Pain behavior increased less in the topical EMLA group (mean +/- SE, 4.4+/-0.39) compared with the IV morphine group (6.0+/-0.38; P < 0.01). No signs of infection were noted at the CT sites 24 or 48 h after CT removal. We conclude that EMLA cream is more effective than IV morphine in preventing the pain associated with CT removal.

IMPLICATIONS

Postoperatively applying a topical anesthetic cream onto chest tube sites of chest surgery patients 3 h before chest tube removal is more effective than IV morphine in blunting pain response.

A guide to the EEOC's final regulations on the Americans with Disabilities Act

The Equal Employment Opportunity Commission (EEOC) recently issued its final regulations on the Americans with Disabilities Act (ADA). Although the regulations offer some guidance for employers on how to comply with the Act, they fail to provide specific answers to the many complicated compliance questions that will surely arise. Further, the regulations are almost totally silent on certain critical issues related to insurance, workers' compensation, and potential conflicts between ADA obligations and terms of collective bargaining agreements. The EEOC has essentially left the resolution of many important ADA questions to case-by-case determination and the litigation process.

Correlates of seasonal changes in metabolism in Atlantic harbour seals (Phoca vitulina concolor)

This study tested the hypothesis that seasonal variation in resting metabolic rate (RMR) was more closely related to changes in total energy use than to energy intake. It also quantified the extent to which variation in metabolism contributed to changes in total energy expenditure. RMR, gross energy intake, and body mass and composition were measured in six captive Atlantic harbour seals (Phoca vitulina concolor) over 16 months. Gross energy intake during the year (across all seals) averaged 25.4 ± 4.1 MJ/d (mean ± SD). The energy used by the seals Eused a composite measure of energy expenditure from ingested energy and tissue catabolism) averaged 19.2 ± 3.4 MJ/d. RMR averaged 11.2 ± 1.5 MJ/d during the year, while mass-corrected metabolism declined with age. The seals displayed significant changes in both absolute and mass-corrected metabolism during the year. Overall, Eused was a stronger predictor of changes in metabolism than either gross energy intake or body mass. Mass-corrected metabolic rate was more closely related to Eused than was absolute metabolism. Energy changes in metabolism during the year (range = 6.9 ± 1.9 MJ/d) were minor compared with those in Eused (27.8 ± 7.3 MJ/d). These results suggest that seasonal changes in metabolism were a response to, or facilitated by, concurrent changes in Eused but were not the cause of variation in Eused. Rather, variation in both RMR and Eused was the result of changes in other bioenergetic components of the seals' energy budget, such as activity.