Lipid A modification of colistin-resistant Klebsiella pneumoniae does not alter innate immune response in a mouse model of pneumonia.

Polymyxin resistance in carbapenem-resistant Klebsiella pneumoniae bacteria is associated with high morbidity and mortality in vulnerable populations throughout the world. Ineffective antimicrobial activity by these last resort therapeutics can occur by transfer of mcr-1, a plasmid-mediated resistance gene, causing modification of the lipid A portion of lipopolysaccharide (LPS) and disruption of the interactions between polymyxins and lipid A. Whether this modification alters the innate host immune response or carries a high fitness cost in the bacteria is not well established. To investigate this, we studied infection with K. pneumoniae (KP) ATCC 13883 harboring either the mcr-1 plasmid (pmcr-1) or the vector control (pBCSK) ATCC 13883. Bacterial fitness characteristics of mcr-1 acquisition were evaluated. Differentiated human monocytes (THP-1s) were stimulated with KP bacterial strains or purified LPS from both parent isolates and isolates harboring mcr-1. Cell culture supernatants were analyzed for cytokine production. A bacterial pneumonia model in WT C57/BL6J mice was used to monitor immune cell recruitment, cytokine induction, and bacterial clearance in the bronchoalveolar lavage fluid (BALF). Isolates harboring mcr-1 had increased colistin MIC compared to the parent isolates but did not alter bacterial fitness. Few differences in cytokines were observed with purified LPS from mcr-1 expressing bacteria in vitro. However, in a mouse pneumonia model, no bacterial clearance defect was observed between pmcr-1-harboring KP and parent isolates. Consistently, no differences in cytokine production or immune cell recruitment in the BALF were observed, suggesting that other mechanisms outweigh the effect of these lipid A mutations in LPS.

Innate Immune Signaling Activated by MDR Bacteria in the Airway.

Health care-associated bacterial pneumonias due to multiple-drug resistant (MDR) pathogens are an important public health problem and are major causes of morbidity and mortality worldwide. In addition to antimicrobial resistance, these organisms have adapted to the milieu of the human airway and have acquired resistance to the innate immune clearance mechanisms that normally prevent pneumonia. Given the limited efficacy of antibiotics, bacterial clearance from the airway requires an effective immune response. Understanding how specific airway pathogens initiate and regulate innate immune signaling, and whether this response is excessive, leading to host-induced pathology may guide future immunomodulatory therapy. We will focus on three of the most important causes of health care-associated pneumonia, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, and review the mechanisms through which an inappropriate or damaging innate immune response is stimulated, as well as describe how airway pathogens cause persistent infection by evading immune activation.

Low Diagnostic Utility of Frequent Serial Tracheal Aspirate Cultures in the PICU.

OBJECTIVES: To determine the diagnostic outcomes of serial tracheal aspirate cultures (TACs) in the PICU. DESIGN: A retrospective chart review of TAC utilization was performed. Items recorded for each TAC included the time and date of culture acquisition, result, changes in microbial resistance patterns, antimicrobial therapy, and patient clinical course. SETTING: A single urban tertiary care children's hospital in the United States. SUBJECTS: Patients admitted to the PICU from January 1, to October 31, 2021, for whom a TAC was performed. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: One hundred fifty unique subjects had 582 TACs performed during the study period, of which 145 (24.9%) were serially repeated within 72 hours. Of these serial TACs, 82 (56.6%) had no growth, 41 (28.3%) grew the same organism as the prior culture, with most (36/41) displaying no major change in antimicrobial susceptibilities, 11 (7.6%) grew a new organism previously grown during the admission, and 11 (7.6%) grew a new organism not previously grown during the admission. Overall, only 26 of these serial TACs (17.9%) provided new diagnostic information, whereas only five (3.4%) led to a change in management. CONCLUSIONS: Frequent serial TAC sampling in the PICU is common and infrequently yields new data that impact clinical decision-making. Considering worsening antimicrobial resistance and the role of diagnostic stewardship in mitigating it, these findings further support a 72-hour reassessment period before performing a repeat TAC in critically ill children.

A Hybrid Model of Pediatric and Adult Critical Care During the Coronavirus Disease 2019 Surge: The Experience of Two Tertiary Hospitals in London and New York.

OBJECTIVES: The current novel severe acute respiratory syndrome coronavirus 2 outbreak has caused an unprecedented demand on global adult critical care services. As adult patients have been disproportionately affected by the coronavirus disease 2019 pandemic, pediatric practitioners world-wide have stepped forward to support their adult colleagues. In general, standalone pediatric hospitals expanded their capacity to centralize pediatric critical care, decanting patients from other institutions. There are few units that ran a hybrid model, managing both adult and pediatric patients with the same PICU staff. In this report, we describe the hybrid model implemented at our respective institutions with shared experiences, pitfalls, challenges, and adjustments required in caring for both young and older patients. DESIGN: Retrospective cohort study. SETTING: Two PICUs in urban tertiary hospitals in London and New York. PATIENTS: Adult and pediatric patients admitted to the PICU in roughly a 6-week period during the coronavirus disease 2019 surge. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The PICU at King's College Hospital admitted 23 non-coronavirus disease adult patients, while whereas the PICU at Morgan Stanley's Children Hospital in New York admitted 46 adults, 30 of whom were coronavirus disease positive. The median age of adult patients at King's College Hospital was higher than those admitted in New York, 53 years (19-77 yr) and 24.4 years (18-52 yr), respectively. Catering to the different physical, emotional, and social needs of both children and adults by the same PICU team was challenging. One important consideration in both locations was the continued care of patients with severe non-coronavirus disease-related illnesses such as neurosurgical emergencies, trauma, and septic shock. Furthermore, retention of critical specialists such as transplant services allowed for nine and four solid organ transplants to occur in London and New York, respectively. CONCLUSIONS: This hybrid model successfully allowed for the expansion into adult critical care while maintaining essential services for critically ill children. Simultaneous care of adults and children in the ICU can be sustained if healthcare professionals work collaboratively, show proactive insight into anticipated issues, and exhibit clear leadership.

The Effects of IFN-λ on Epithelial Barrier Function Contribute to Klebsiella pneumoniae ST258 Pneumonia.

IFN-λ and IL-22, cytokines that share the coreceptor IL-10RB, are both induced over the course of Klebsiella pneumoniae ST258 (KP35) pneumonia. IL-22 is known to protect mucosal barriers, whereas the effects of IFN-λ on the mucosa are not established. We postulated that IFN-λ plays a role in regulating the airway epithelial barrier to facilitate cellular trafficking to the site of infection. In response to IFN-λ, the transmigration of neutrophils across a polarized monolayer of airway epithelial cells was increased, consistent with diminished epithelial integrity. KP35 infection increased epithelial permeability, and pretreatment with IFN-λ amplified this effect and facilitated bacterial transmigration. These effects of IFN-λ were confirmed in vivo, in that mice lacking the receptor for IFN-λ (Ifnlr1-/-) were protected from bacteremia in a murine model of KP35 pneumonia. Conversely, the integrity of the epithelial barrier was protected by IL-22, with subsequent impairment of neutrophil and bacterial transmigration in vitro. Maximal expression of IL-22 in vivo was observed later in the course of infection than IFN-λ production, with high levels of IL-22 produced by recruited immune cells at 48 hours, consistent with a role in epithelial barrier recovery. The divergent and opposing expression of these two related cytokines suggests a regulated interaction in the host response to KP35 infection. A major physiological effect of IFN-λ signaling is a decrease in epithelial barrier integrity, which facilitates immune cell recruitment but also enables K. pneumoniae invasion.

Interleukin-10 Produced by Myeloid-Derived Suppressor Cells Provides Protection to Carbapenem-Resistant Klebsiella pneumoniae Sequence Type 258 by Enhancing Its Clearance in the Airways.

Carbapenem-resistant Klebsiella pneumoniae sequence type 258 (CRKP-ST258) can cause chronic infections in lungs and airways, with repeated episodes of bacteremia. In this report we addressed whether the recruitment of myeloid cells producing the anti-inflammatory cytokine interleukin-10 (IL-10) modulates the clearance of CKRP-ST258 in the lungs and establishes bacterial persistence. Our data demonstrate that during pneumonia caused by a clinical isolate of CRKP-ST258 (KP35) there is an early recruitment of monocyte-myeloid-derived suppressor cells (M-MDSCs) and neutrophils that actively produce IL-10. However, M-MDSCs were the cells that sustained the production of IL-10 over the time of infection evaluated. Using mice unable to produce IL-10 (IL-10-/-), we observed that the production of this cytokine during the infection caused by KP35 is important to control bacterial burden, to prevent lung damage, to modulate cytokine production, and to improve host survival. Importantly, intranasal transfer of bone marrow-derived M-MDSCs from mice able to produce IL-10 at 1 day prior to infection improved the ability of IL-10-/- mice to clear KP35 in the lungs, decreasing their mortality. Altogether, our data demonstrate that IL-10 produced by M-MDSCs is required for bacterial clearance, reduction of lung tissue damage, and host survival during KP35 pneumonia.

Host-Pathogen Interface: Progress in Understanding the Pathogenesis of Infection Due to Multidrug-Resistant Bacteria in the Intensive Care Unit.

The diverse responses of critically ill patients to infection with multi-drug resistant (MDR) bacteria are determined by many complex factors. These include the nature of the immune response activated by specific organisms. Properties unique to each organism such as adherence proteins, microvesicle formation, toxin production and the propensity to form biofilms are important factors in pathogenesis. Equally important is the variability in the host immune response, whether due to genetic or iatrogenic factors, including the presence of major comorbidities, treatment with immunomodulatory therapy and disruption of the microbiome. Future approaches in treating infections caused by MDR bacteria will be heavily influenced by a precision medicine approach, with rapid diagnostic techniques of both bacterial and host factors and high throughput screening of novel therapeutics becoming the mainstay of treatment.

Toxin-induced necroptosis is a major mechanism of Staphylococcus aureus lung damage.

Staphylococcus aureus USA300 strains cause a highly inflammatory necrotizing pneumonia. The virulence of this strain has been attributed to its expression of multiple toxins that have diverse targets including ADAM10, NLRP3 and CD11b. We demonstrate that induction of necroptosis through RIP1/RIP3/MLKL signaling is a major consequence of S. aureus toxin production. Cytotoxicity could be prevented by inhibiting either RIP1 or MLKL signaling and S. aureus mutants lacking agr, hla or Hla pore formation, lukAB or psms were deficient in inducing cell death in human and murine immune cells. Toxin-associated pore formation was essential, as cell death was blocked by exogenous K+ or dextran. MLKL inhibition also blocked caspase-1 and IL-1ß production, suggesting a link to the inflammasome. Rip3(-/-) mice exhibited significantly improved staphylococcal clearance and retained an alveolar macrophage population with CD200R and CD206 markers in the setting of acute infection, suggesting increased susceptibility of these leukocytes to necroptosis. The importance of this anti-inflammatory signaling was indicated by the correlation between improved outcome and significantly decreased expression of KC, IL-6, TNF, IL-1α and IL-1ß in infected mice. These findings indicate that toxin-induced necroptosis is a major cause of lung pathology in S. aureus pneumonia and suggest the possibility of targeting components of this signaling pathway as a therapeutic strategy.

Ketogenesis promotes tolerance to Pseudomonas aeruginosa pulmonary infection.

Pseudomonas aeruginosa is a common cause of pulmonary infection. As a Gram-negative pathogen, it can initiate a brisk and highly destructive inflammatory response; however, most hosts become tolerant to the bacterial burden, developing chronic infection. Using a murine model of pneumonia, we demonstrate that this shift from inflammation to disease tolerance is promoted by ketogenesis. In response to pulmonary infection, ketone bodies are generated in the liver and circulate to the lungs where they impose selection for P. aeruginosa strains unable to display surface lipopolysaccharide (LPS). Such keto-adapted LPS strains fail to activate glycolysis and tissue-damaging cytokines and, instead, facilitate mitochondrial catabolism of fats and oxidative phosphorylation (OXPHOS), which maintains airway homeostasis. Within the lung, P. aeruginosa exploits the host immunometabolite itaconate to further stimulate ketogenesis. This environment enables host-P. aeruginosa coexistence, supporting both pathoadaptive changes in the bacteria and the maintenance of respiratory integrity via OXPHOS.

Staphylococcus aureus protein A mediates invasion across airway epithelial cells through activation of RhoA GTPase signaling and proteolytic activity.

Staphyococcus aureus and especially the epidemic methicillin-resistant S. aureus strains cause severe necrotizing pneumonia. The mechanisms whereby these organisms invade across the mucosal epithelial barrier to initiate invasive infection are not well understood. Protein A (SpA), a highly conserved and abundant surface protein of S. aureus, activates TNF receptor 1 and EGF receptor (EGFR) signaling cascades that can perturb the cytoskeleton. We demonstrate that wild-type S. aureus, but not spa mutants, invade across polarized airway epithelial cell monolayers via the paracellular junctions. SpA stimulated a RhoA/ROCK/MLC cascade, resulting in the contraction of the cytoskeleton. SpA(+) but not SpA(-) mutants stimulated activation of EGFR and along with subsequent calpain activity cleaved the membrane-spanning junctional proteins occludin and E-cadherin, facilitating staphylococcal transmigration through the cell-cell junctions. Treatment of polarized human airway epithelial monolayers with inhibitors of ROCK, EGFR, MAPKs, or calpain prevented staphylococcal penetration through the monolayers. In vivo, blocking calpain activity impeded bacterial invasion into the lung parenchyma. Thus, S. aureus exploits multiple receptors available on the airway mucosal surface to facilitate invasion across epithelial barriers.

Klebsiella pneumoniae induces host metabolic stress that promotes tolerance to pulmonary infection.

K. pneumoniae sequence type 258 (Kp ST258) is a major cause of healthcare-associated pneumonia. However, it remains unclear how it causes protracted courses of infection in spite of its expression of immunostimulatory lipopolysaccharide, which should activate a brisk inflammatory response and bacterial clearance. We predicted that the metabolic stress induced by the bacteria in the host cells shapes an immune response that tolerates infection. We combined in situ metabolic imaging and transcriptional analyses to demonstrate that Kp ST258 activates host glutaminolysis and fatty acid oxidation. This response creates an oxidant-rich microenvironment conducive to the accumulation of anti-inflammatory myeloid cells. In this setting, metabolically active Kp ST258 elicits a disease-tolerant immune response. The bacteria, in turn, adapt to airway oxidants by upregulating the type VI secretion system, which is highly conserved across ST258 strains worldwide. Thus, much of the global success of Kp ST258 in hospital settings can be explained by the metabolic activity provoked in the host that promotes disease tolerance.

An acquired acyltransferase promotes Klebsiella pneumoniae ST258 respiratory infection.

Klebsiella pneumoniae ST258 is a human pathogen associated with poor outcomes worldwide. We identify a member of the acyltransferase superfamily 3 (atf3), enriched within the ST258 clade, that provides a major competitive advantage for the proliferation of these organisms in vivo. Comparison of a wild-type ST258 strain (KP35) and a Δatf3 isogenic mutant generated by CRISPR-Cas9 targeting reveals greater NADH:ubiquinone oxidoreductase transcription and ATP generation, fueled by increased glycolysis. The acquisition of atf3 induces changes in the bacterial acetylome, promoting lysine acetylation of multiple proteins involved in central metabolism, specifically Zwf (glucose-6 phosphate dehydrogenase). The atf3-mediated metabolic boost leads to greater consumption of glucose in the host airway and increased bacterial burden in the lung, independent of cytokine levels and immune cell recruitment. Acquisition of this acyltransferase enhances fitness of a K. pneumoniae ST258 isolate and may contribute to the success of this clonal complex as a healthcare-associated pathogen.

Participation of the IL-10RB Related Cytokines, IL-22 and IFN-λ in Defense of the Airway Mucosal Barrier.

The airway epithelial barrier is a major barrier protecting against clinically significant infections of the lung. Its integrity is often compromised due to mechanical, chemical, or infectious causes. Opportunistic bacterial pathogens are poised to cause parenchymal infection and become difficult to eradicate due to adaptive metabolic changes, biofilm formation, and the acquisition of antimicrobial resistance and fitness genes. Enhancing mucosal defenses by modulating the cytokines that regulate barrier functions, such as interleukin-22 (IL-22) and interferon-λ (IFN-λ), members of the IL-10 family of cytokines, is an attractive approach to prevent these infections that are associated with high morbidity and mortality. These cytokines both signal through the cognate receptor IL-10RB, have related protein structures and common downstream signaling suggesting shared roles in host respiratory defense. They are typically co-expressed in multiple models of infections, but with differing kinetics. IL-22 has an important role in the producing antimicrobial peptides, upregulating expression of junctional proteins in the airway epithelium and working in concert with other inflammatory cytokines such as IL-17. Conversely, IFN-λ, a potent antiviral in influenza infection with pro-inflammatory properties, appears to decrease junctional integrity allowing for bacterial and immune cell translocation. The effects of these cytokines are pleotropic, with pathogen and tissue specific consequences. Understanding how these cytokines work in the mucosal defenses of the respiratory system may suggest potential targets to prevent invasive infections of the damaged lung.

L-Arginine Enhances Intracellular Killing of Carbapenem-Resistant Klebsiella pneumoniae ST258 by Murine Neutrophils.

Carbapenem-resistant Klebsiella pneumoniae ST258 (CRKP-ST258) are a global concern due to their rapid dissemination, high lethality, antibiotic resistance and resistance to components of the immune response, such as neutrophils. Neutrophils are major host mediators, able to kill well-studied and antibiotic-sensitive laboratory reference strains of K. pneumoniae. However, CRKP-ST258 are able to evade neutrophil phagocytic killing, persisting longer in the host despite robust neutrophil recruitment. Here, we show that neutrophils are unable to clear a CRKP-ST258 isolate (KP35). Compared to the response elicited by a prototypic K. pneumoniae ATCC 43816 (KPPR1), the neutrophil intracellular response against KP35 is characterized by equivalent production of reactive oxygen species (ROS) and myeloperoxidase content, but impaired phagosomal acidification. Our results ruled out that this phenomenon is due to a phagocytosis defect, as we observed similar efficiency of phagocytosis by neutrophils infected with KP35 or KPPR1. Genomic analysis of the cps loci of KPPR1 and KP35 suggest that the capsule composition of KP35 explain the high phagocytosis efficiency by neutrophils. Consistent with other reports, we show that KP35 did not induce DNA release by neutrophils and KPPR1 only induced it at 3 h, when most of the bacteria have already been cleared. l-arginine metabolism has been identified as an important modulator of the host immune response and positively regulate T cells, macrophages and neutrophils in response to microbes. Our data show that l-arginine supplementation improved phagosome acidification, increased ROS production and enhanced nitric oxide consumption by neutrophils in response to KP35. The enhanced intracellular response observed after l-arginine supplementation ultimately improved KP35 clearance in vitro. KP35 was able to dysregulate the intracellular microbicidal machinery of neutrophils to survive in the intracellular environment. This process, however, can be reversed after l-arginine supplementation.

A Clinical Pathway for Hospitalized Pediatric Patients With Initial SARS-CoV-2 Infection.

The novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread quickly across the globe, creating unique and pressing challenges for today's physicians. Although this virus disproportionately affects adults, initial SARS-CoV-2 infection can present a significant disease burden for the pediatric population. A review of the literature yields descriptive studies in pediatric patients; however, no evidence-based or evidence-informed guidelines for the diagnosis and treatment of the hospitalized pediatric patient have been published in peer-reviewed journals. The authors, working at a quaternary care children's hospital in the national epicenter of the SARS-CoV-2 pandemic, found an urgent need to create a unified, multidisciplinary, evidence-informed set of guidelines for the diagnosis and management of coronavirus disease 2019 in children. In this article, the authors describe our institutional practices for the hospitalized pediatric patient with confirmed or suspected initial SARS-CoV-2 infection. The authors anticipate that developing evidence-informed and institution-specific guidelines will lead to improvements in care quality, efficiency, and consistency; minimization of staff risk of exposure to SARS-CoV-2; and increased provider comfort in caring for pediatric patients with SARS-CoV-2 infection.

CrrB Positively Regulates High-Level Polymyxin Resistance and Virulence in Klebsiella pneumoniae.

Polymyxin resistance (PR) threatens the treatment of carbapenem-resistant Klebsiella pneumoniae (CRKP) infections. PR frequently arises through chemical modification of the lipid A portion of lipopolysaccharide. Various mutations are implicated in PR, including in three two-component systems-CrrA/B, PmrA/B, and PhoP/Q-and the negative regulator MgrB. Few have been functionally validated. Therefore, here we adapt a CRISPR-Cas9 system to CRKP to elucidate how mutations in clinical CRKP isolates induce PR. We demonstrate that CrrB is a positive regulator of PR, and common clinical mutations lead to the addition of both 4-amino-4-deoxy-L-arabinose (L-Ara4N) and phosophethanolamine (pEtN) to lipid A, inducing notably higher polymyxin minimum inhibitory concentrations than mgrB disruption. Additionally, crrB mutations cause a significant virulence increase at a fitness cost, partially from activation of the pentose phosphate pathway. Our data demonstrate the importance of CrrB in high-level PR and establish important differences across crrB alleles in balancing resistance with fitness and virulence.

Pseudomonas aeruginosa Utilizes Host-Derived Itaconate to Redirect Its Metabolism to Promote Biofilm Formation.

The bacterium Pseudomonas aeruginosa is especially pathogenic, often being associated with intractable pneumonia and high mortality. How P. aeruginosa avoids immune clearance and persists in the inflamed human airway remains poorly understood. In this study, we show that P. aeruginosa can exploit the host immune response to maintain infection. Notably, unlike other opportunistic bacteria, we found that P. aeruginosa alters its metabolic and immunostimulatory properties in response to itaconate, an abundant host-derived immunometabolite in the infected lung. Itaconate induces bacterial membrane stress, resulting in downregulation of lipopolysaccharides (LPS) and upregulation of extracellular polysaccharides (EPS). These itaconate-adapted P. aeruginosa accumulate lptD mutations, which favor itaconate assimilation and biofilm formation. EPS, in turn, induces itaconate production by myeloid cells, both in the airway and systemically, skewing the host immune response to one permissive of chronic infection. Thus, the metabolic versatility of P. aeruginosa needs to be taken into account when designing therapies.

Epidemiology, Clinical Features, and Disease Severity in Patients With Coronavirus Disease 2019 (COVID-19) in a Children's Hospital in New York City, New York.

Importance: Descriptions of the coronavirus disease 2019 (COVID-19) experience in pediatrics will help inform clinical practices and infection prevention and control for pediatric facilities. Objective: To describe the epidemiology, clinical, and laboratory features of patients with COVID-19 hospitalized at a children's hospital and to compare these parameters between patients hospitalized with and without severe disease. Design, Setting, and Participants: This retrospective review of electronic medical records from a tertiary care academically affiliated children's hospital in New York City, New York, included hospitalized children and adolescents (≤21 years) who were tested based on suspicion for COVID-19 between March 1 to April 15, 2020, and had positive results for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Exposures: Detection of SARS-CoV-2 from a nasopharyngeal specimen using a reverse transcription-polymerase chain reaction assay. Main Outcomes and Measures: Severe disease as defined by the requirement for mechanical ventilation. Results: Among 50 patients, 27 (54%) were boys and 25 (50%) were Hispanic. The median days from onset of symptoms to admission was 2 days (interquartile range, 1-5 days). Most patients (40 [80%]) had fever or respiratory symptoms (32 [64%]), but 3 patients (6%) with only gastrointestinal tract presentations were identified. Obesity (11 [22%]) was the most prevalent comorbidity. Respiratory support was required for 16 patients (32%), including 9 patients (18%) who required mechanical ventilation. One patient (2%) died. None of 14 infants and 1 of 8 immunocompromised patients had severe disease. Obesity was significantly associated with mechanical ventilation in children 2 years or older (6 of 9 [67%] vs 5 of 25 [20%]; P = .03). Lymphopenia was commonly observed at admission (36 [72%]) but did not differ significantly between those with and without severe disease. Those with severe disease had significantly higher C-reactive protein (median, 8.978 mg/dL [to convert to milligrams per liter, multiply by 10] vs 0.64 mg/dL) and procalcitonin levels (median, 0.31 ng/mL vs 0.17 ng/mL) at admission (P < .001), as well as elevated peak interleukin 6, ferritin, and D-dimer levels during hospitalization. Hydroxychloroquine was administered to 15 patients (30%) but could not be completed for 3. Prolonged test positivity (maximum of 27 days) was observed in 4 patients (8%). Conclusions and Relevance: In this case series study of children and adolescents hospitalized with COVID-19, the disease had diverse manifestations. Infants and immunocompromised patients were not at increased risk of severe disease. Obesity was significantly associated with disease severity. Elevated inflammatory markers were seen in those with severe disease.

Pseudomonas aeruginosa and Klebsiella pneumoniae Adaptation to Innate Immune Clearance Mechanisms in the Lung.

Many different species of gram-negative bacteria are associated with infection in the lung, causing exacerbations of chronic obstructive pulmonary disease, cystic fibrosis (CF), and ventilator-associated pneumonias. These airway pathogens must adapt to common host clearance mechanisms that include killing by antimicrobial peptides, antibiotics, oxidative stress, and phagocytosis by leukocytes. Bacterial adaptation to the host is often evident phenotypically, with increased extracellular polysaccharide production characteristic of some biofilm-associated organisms. Given the relatively limited repertoire of bacterial strategies to elude airway defenses, it seems likely that organisms sharing the same ecological niche might also share common strategies to persistently infect the lung. In this review, we will highlight some of the major factors responsible for the adaptation of Pseudomonas aeruginosa to the lung, addressing how growth in biofilms enables persistent infection, relevant to, but not limited to, the pathogenesis of infection in CF. In contrast, we will discuss how carbapenem-resistant Klebsiella pneumoniae evade immune clearance, an organism often associated with ventilator-associated pneumonia and health-care-acquired pneumonias, but not a typical pathogen in CF.