Emerging invasive liver abscess caused by K1 serotype Klebsiella pneumoniae in Korea

<italic>Klebsiella pneumoniae</italic>-induced Liver Abscess Complicated with Septic Pulmonary Embolism in a Non-diabetic Adult

<p>A 72-year-old non-diabetic man was admitted to the intensive care unit because of liver abscess, cholecystitis, and septic shock. He underwent percutaneous catheter drainage and received intravenous antibiotics. Shock was improved, and the patient’s fever subsided. Klebsiella pneumoniae was isolated in blood and bile cultures. However, he suddenly developed dyspnea and oxygen desaturation. Chest computed tomography scan revealed multifocal ground-glass opacities with consolidation with peripheral preponderance. Appropriate antibiotic therapy was provided for 2 weeks. The patient recovered fully, and cholecystectomy was then performed. Herein, we report a case of K. pneumoniae-induced liver abscess complicated with septic pulmonary embolism in a non-diabetic patient.

Clinical and computed tomography features of extended-spectrum β-lactamase-producing Klebsiella pneumoniae liver abscess

Background

Klebsiella pneumoniae (KP) is the primary pathogen associated with pyogenic liver abscesses (PLAs). Moreover, there has been an increase in the proportion of extended-spectrum beta-lactamase (ESBL)-producing KP. However, the clinical and computed tomography (CT) features of liver abscesses caused by ESBL-producing KP have not been separately described. We aimed to compare the clinical and CT features present in patients with ESBL-producing and non-ESBL-producing KP as well as to determine the risk factors for ESBL-producing KP liver abscesses (KPLAs).

Methods

We performed a retrospective analysis of data obtained from the medical records of patients with a first episode of KPLA admitted to Shengjing Hospital of China Medical University between May 2015 and May 2019. We compared the clinical and CT features between patients with ESBL-producing and non-ESBL-producing KPLA.

Results

We enrolled 100 patients with KPLA (14 and 86 in the ESBL-producing and non-ESBL-producing groups, respectively). There was no significant between-group difference in the proportion of patients with comorbid diabetes (71.43% vs. 66.2%, p = 0.086). The ESBL-producing KPLA group had a greater proportion of patients with a history of biliary disease (78.57% vs. 26.74%, p < 0.001) and gastrointestinal malignancy (50% vs. 6.98%, p < 0.001). Multivariate regression analysis showed that a history of biliary disease was an independent risk factor for ESBL-producing KPLA. Compared with the non-ESBL-producing KPLA group, the ESBL-producing KPLA group had a significantly higher intensive care unit (ICU) admission rate (28.57% vs. 2.33%, p < 0.001). All ESBL-producing KP isolates were susceptible to carbapenems and amikacin. Only the presence of multiloculation on CT was found to be significantly different between the groups (50% vs. 82.56%, p = 0.012).

Conclusions

The presence of biliary disease was an independent risk factor for ESBL-producing KPLA. Patients with ESBL-producing KPLA had a higher ICU admission rate, with only half of patients having evidence of multiloculation on CT.

Identification of hypervirulent Klebsiella pneumoniae isolates using the string test in combination with Galleria mellonella infectivity

Distinguishing between hypervirulent Klebsiella pneumoniae (hvKp) and classical Klebsiella pneumoniae (cKp) is a challenge to clinical laboratories. The aim of this study was to determine the practicability of combining the G. mellonella killing assay with a string test to differentiate hvKp from cKp. One hundred and three clinical K. pneumoniae isolates were collected. PCR amplification and wzi sequencing were used to determine the capsular serotype. Virulence genes allS, iro, iuc, and rmpA2, used frequently to identify hvKp, were detected by PCR. The virulence of K. pneumoniae isolates was evaluated using the following assays in parallel: molecular markers detection, G. mellonella killing assay alone, G. mellonella killing assay combined with the string test, and mouse infection. The results showed that the sensitivity, specificity, positive predictive value, and negative predictive value of combining the G. mellonella killing assay with a string test were 95.56%, 94.83%, 93.48%, and 96.49%, respectively, compared with mouse infection used as a positive reference. These values were significantly greater than those obtained using the G. mellonella killing assay only. The sensitivity, specificity, positive predictive value, and negative predictive value of allS, iro, iuc, and rmpA2 were greater than 77.78%, but less than combining the G. mellonella killing assay and string test. G. mellonella killing assay used in conjugation with the string test is a relatively simple and accurate method to assess K. pneumoniae virulence and differentiate between hvKp and cKp.

Clinical and Pathologic Features of Spontaneous Klebsiella pneumoniae Infection in 9 Rhesus Macaques (Macaca mulatta)

Klebsiella pneumoniae is a gram-negative bacterium found in the environment and as a commensal in humans and animals. In humans, K. pneumoniae is one of the most serious nosocomial infections encountered currently and is characterized by liver abscesses, pneumonia, and bacteremia resulting in meningoencephalitis and endophthalmitis. K. pneumoniae in veterinary medicine is rarely reported in NHP, and recent literature describing this disease is sparse. In our colony of predominantly outdoor-housed rhesus macaques (Macaca mulatta), K. pneumoniae is cultured infrequently from healthy animals during routine screening and is even rarer in sick animals. This report summarizes the clinical and postmortem findings associated with this pathogen in 9 rhesus macaques and compares these results with the disease outcomes reported for humans. In these cases, K. pneumoniae infection was confirmed through culture or PCR testing or both. In our experience, when this bacterium does cause clinical signs, the disease is rapidly progressive and severe. At necropsy of NHP, the findings are strikingly similar to opportunistic Klebsiella-associated syndromes described in humans and include liver abscesses, meningoencephalitis, and endophthalmitis. In addition, many of the affected macaques had similar risk factors to humans that succumb to disease, thus perhaps indicating that rhesus macaques could be a viable model for investigating these syndromes.

Characteristics of Klebsiella pneumoniae Isolates from Stool Samples of Patients with Liver Abscess Caused by Hypervirulent K. pneumoniae

BACKGROUND

Hypervirulent Klebsiella pneumoniae (hvKP) has been the most significant pathogen for liver abscesses in East Asia including the Republic of Korea (ROK). Although gastrointestinal colonization of K. pneumoniae may cross the intestinal barrier to invade the liver, characteristics of gastrointestinal carriage K. pneumoniae of hvKP liver abscess patients in the ROK are not well known.

METHODS

Characteristics of K. pneumoniae isolated from stool samples and liver aspirate samples of patients with hvKP liver abscess at a tertiary care hospital in the ROK between 2017 and 2018 were evaluated.

RESULTS

Out of 37 patients with hvKP liver abscess, 11 patients were noted to have K. pneumoniae isolated from stool samples and were enrolled for analysis. The median age was 71 years. For hvKP isolates from the liver aspirate samples, the most common serotype was K1 (72.7%) followed by K2 (27.3%). For K. pneumoniae isolates from the stool sample, the majority was non-K1/K2 serotype (72.7%). Among non-K1/K2 serotype isolates, high variability of sequence type (ST; ST15, ST307, ST37, ST273, ST2622, and ST42) with high rate of presence of extended-spectrum beta-lactamase (100.0%) was noted. The concordance rate of the K. pneumoniae isolates between the liver aspirate samples and the stool samples from the primary hvKP liver abscess was low (27.3%).

CONCLUSION

This study suggests that significant heterogeneity of K. pneumoniae colonizing intestinal tract of the hvKP liver abscess patients. Further studies involving a larger number of hvKP liver abscess patients with continuing surveillance are needed to define the changing epidemiology and the role of gastrointestinal K. pneumoniae in the hvKP liver abscess patients in the ROK.

A Novel Role for the Klebsiella pneumoniae Sap (Sensitivity to Antimicrobial Peptides) Transporter in Intestinal Cell Interactions, Innate Immune Responses, Liver Abscess, and Virulence

Klebsiella pneumoniae is an important human pathogen causing hospital-acquired and community-acquired infections. Systemic K. pneumoniae infections may be preceded by gastrointestinal colonization, but the basis of this bacterium’s interaction with the intestinal epithelium remains unclear. Here, we report that the K. pneumoniae Sap (sensitivity to antimicrobial peptides) transporter contributes to bacterial–host cell interactions and in vivo virulence. Gene deletion showed that sapA is required for the adherence of a K. pneumoniae blood isolate to intestinal epithelial, lung epithelial, urinary bladder epithelial, and liver cells. The ΔsapA mutant was deficient for translocation across intestinal epithelial monolayers, macrophage interactions, and induction of proinflammatory cytokines. In a mouse gastrointestinal infection model, ΔsapA yielded significantly decreased bacterial loads in liver, spleen and intestine, reduced liver abscess generation, and decreased mortality. These findings offer new insights into the pathogenic interaction of K. pneumoniae with the host gastrointestinal tract to cause systemic infection.

Concomitant Liver and Brain Abscesses Caused by Parvimonas Micra

Anaerobic infections have been reported to be responsible for 3-10% of pyogenic liver abscesses in Korea, and reported anaerobes include Fusobacterium, Bacillus fragilis, and Bacteroides melaninogenicus. Parvimonas micra is an anaerobic, Gram-positive, non-spore-forming bacterial species and a constituent of normal flora on skin, vagina, gastrointestinal tract, and oral cavity that can cause opportunistic infections. However, it has only rarely been reported to be a cause of liver abscess; only one such case has been reported in Korea. We experienced a case of concomitant liver and brain abscesses caused by Parvimonas micra in a non-immunodeficient 65-year-old female patient without diabetes or periodontal disease. Parvimonas micra infection was confirmed by blood culture using VITEK^® 2 cards and by bacterial 16s ribosomal RNA gene sequencing. We conclude that we should not overlook anaerobes as a cause of liver abscess.

Liver abscess: diagnostic and management issues found in the low resource setting

INTRODUCTION

Liver abscesses are mainly caused by parasitic or bacterial infection and are an important cause of hospitalization in low-middle income countries (LMIC). The pathophysiology of abscesses is different depending on the etiology and requires different strategies for diagnosis and management. This paper discusses pathophysiology and epidemiology, the current diagnostic approach and its limitations and management of liver abscess in low resource settings.

SOURCES OF DATA

We searched PubMed for relevant reviews by typing the following keywords: 'amoebic liver abscess' and 'pyogenic liver abscess'.

AREAS OF AGREEMENT

Amoebic liver abscess can be treated medically while pyogenic liver abscess usually needs to be percutaneously drained and treated with effective antibiotics.

AREAS OF CONTROVERSY

In an LMIC setting, where misuse of antibiotics is a recognized issue, liver abscesses are a therapeutic conundrum, leaving little choices for treatment for physicians in low capacity settings.

GROWING POINTS

As antimicrobial resistance awareness and antibiotic stewardship programs are put into place, liver abscess management will likely improve in LMICs provided that systematic adapted guidelines are established and practiced.

AREAS TIMELY FOR DEVELOPING RESEARCH

The lack of a quick and reliable diagnostic strategy in the majority of LMIC makes selection of appropriate treatment challenging.

Klebsiella pneumoniae Type VI Secretion System Contributes to Bacterial Competition, Cell Invasion, Type-1 Fimbriae Expression, and In Vivo Colonization

Background

We previously isolated a Klebsiella pneumoniae strain, NTUH-K2044, from a community-acquired pyogenic liver abscess (PLA) patient. Analysis of the NTUH-K2044 genome revealed that this strain harbors 2 putative type VI secretion system (T6SS)-encoding gene clusters.

Methods

The distribution of T6SS genes in the PLA and intestinal-colonizing K pneumoniae clinical isolates was examined. icmF1-, icmF2-, icmF1/icmF2-, and hcp-deficient K pneumoniae strains were constructed using an unmarked deletion method. The roles of T6SSs in antibacterial activity, type-1 fimbriae expression, cell adhesion, and invasion and intestinal colonization were determined.

Results

The prevalence of T6SSs is higher in the PLA strains than in the intestinal-colonizing strains (37 of 42 vs 54 of 130). Deletion of icmF1/icmF2 and hcp genes significantly reduced interbacterial and intrabacterial killing. Strain deleted for icmF1 and icmF2 exhibited decreased transcriptional expression of type-1 fimbriae and reduced adherence to and invasion of human colorectal epithelial cells and was attenuated for in vivo competition to enable colonization of the host gut. Finally, Hcp expression in K pneumoniae was silenced by the histone-like nucleoid structuring protein via direct binding.

Conclusions

These results provide new insights into T6SS-mediated bacterial competition and attachment in K pneumoniae and could facilitate the prevention of K pneumoniae infection.

Metastatic Klebsiella pneumoniae Invasive Liver Abscess Syndrome in Denver, Colorado

BACKGROUND

Klebsiella pneumoniae has gained recognition for its association with invasive liver abscess syndrome (ILAS). ILAS is associated with a hypervirulent strain of K pneumoniae and can impact immunocompetent as well as immunocompromised patients.

CASE REPORT

A 42-year-old Hispanic male with no significant past medical history was admitted with complaints of subjective fevers and worsening fatigue. The patient was found to have multiple septic pulmonary emboli, a prostate abscess, a seminal vesicle abscess, bilateral frontoparietal and left temporal infarcts thought to be due to septic emboli, pyelonephritis, endophthalmitis, and hepatic abscesses. Cultures grew K pneumoniae that was determined to be the hypervirulent strain associated with ILAS. The patient was treated for a total of 71 days, including ceftriaxone and multiple intravitreal injections with ceftazidime.

CONCLUSION

Notably, this case report details a disease state new to Colorado. Pharmacists are able to assist in the care of ILAS with antibiotic selection, considering sites of infection and encouraging appropriate consultation of specialized care teams.

Endogenous Endophthalmitis Associated with Pyogenic Liver Abscess Caused by Klebsiella pneumoniae

We report 2 cases of endogenous endophthalmitis associated with pyogenic liver abscess caused by Klebsiella pneumoniae. Case 1 involved a 70-year-old woman and case 2 involved a 50-year-old man who were admitted to our hospital with diagnoses of liver abscess and endogenous endophthalmitis, respectively. The liver abscess resolved with antibiotics and percutaneous transhepatic drainage in case 1 and with antibiotics alone in case 2. Even though both cases underwent ophthalmic surgery, they were discharged from our hospital without the recovery of their eyesight. An earlier diagnosis and treatment are needed to improve the prognosis of endophthalmitis.

A promising bioconjugate vaccine against hypervirulent Klebsiella pneumoniae

Klebsiella pneumoniae is considered a nosocomial pathogen, usually infecting immunocompromised patients. However, a pathotype of K. pneumoniae, termed hypervirulent K. pneumoniae (hvKp), has emerged and is spreading throughout the community, causing severe, often fatal, disease in healthy individuals. Moreover, reports on multidrug-resistant hvKp isolates are increasing in frequency. It is imperative that strategies to combat hvKp begin immediately to prevent further dissemination of this new class of “superbugs.” Here, we show that bioconjugate vaccines targeting the capsule of hvKp can provide immunity and protection against extremely lethal hvKp strains. Further, we demonstrate that bioconjugation is a promising technology for rapid development of efficacious vaccines against emerging bacterial threats.

Hypervirulent Klebsiella pneumoniae (hvKp) is globally disseminating as a community-acquired pathogen causing life-threatening infections in healthy individuals. The fact that a dose as little as 50 bacteria is lethal to mice illustrates the dramatic increase of virulence associated with hvKp strains compared with classical K. pneumoniae (cKp) strains, which require lethal doses greater than 10⁷ bacteria. Until recently, these virulent strains were mostly antibiotic-susceptible. However, multidrug-resistant (MDR) hvKp strains have been emerging, spawning a new generation of hypervirulent “superbugs.” The mechanisms of hypervirulence are not fully defined, but overproduction of capsular polysaccharide significantly impedes host clearance, resulting in increased pathogenicity of hvKp strains. While there are more than 80 serotypes of K. pneumoniae, the K1 and K2 serotypes cause the vast majority of hypervirulent infections. Therefore, a glycoconjugate vaccine targeting these 2 serotypes could significantly reduce hvKp infection. Conventionally, glycoconjugate vaccines are manufactured using intricate chemical methodologies to covalently attach purified polysaccharides to carrier proteins, which is widely considered to be technically challenging. Here we report on the recombinant production and analytical characterization of bioconjugate vaccines, enzymatically produced in glycoengineered Escherichia coli cells, against the 2 predominant hypervirulent K. pneumoniae serotypes, K1 and K2. The K. pneumoniae bioconjugates are immunogenic and efficacious, protecting mice against lethal infection from 2 hvKp strains, NTUH K-2044 and ATCC 43816. This preclinical study constitutes a key step toward preventing further global dissemination of hypervirulent MDR hvKp strains.

Early predictors for the diagnosis of liver abscess in the emergency department

Diagnosing pyogenic liver abscess (PLA) in the emergency department (ED) is challenging due to its non-specific clinical presentation. We aim to identify predictors that aid in diagnosis of PLA in ED patients. This retrospective chart review included patients diagnosed with PLA in a tertiary hospital between January 2008 and December 2012. We compared the demographics, clinical characteristics, investigations and outcomes between patients with PLA diagnosed and missed in the ED. During the study period, 155 patients were admitted via the ED with a cause of death or discharge diagnosis of PLA. Mean age was 58.1 (standard deviation [SD] 15.8) years, with male predominance of 69.7%. There were 79.4% of patients with diagnosis of PLA missed in the ED. Fulfillment of SIRS criteria was associated with increased odds of diagnosing PLA in the ED (adjusted OR 3.20, 95% CI 1.03-9.92), while a higher SpO₂/FiO₂ ratio was associated with decreased odds of a timely ED diagnosis (adjusted OR 0.993, 95% CI 0.988-0.998). Missed ED diagnosis of PLA did not result in significant differences in mortality or treatment failure (p = 0.939), and median length of stay (11 days [IQR 8-16] vs. 11 days [IQR 7-17], p = 0.48). Non-fulfillment of the SIRS criteria and a higher SpO₂/FiO₂ ratio at ED presentation were associated with higher likelihood of missed diagnosis. Despite that, a missed diagnosis of PLA in the ED did not appear to affect outcomes.

Hypervirulence and carbapenem resistance: two distinct evolutionary directions that led high-risk Klebsiella pneumoniae clones to epidemic success

Introduction: Over the past few decades, Klebsiella pneumoniae has become a significant threat to public health and is now listed as an ESKAPE pathogen. Evolving with versatile capabilities, K. pneumoniae is a population composed of genetically and phenotypically diverse bacteria. However, epidemic K. pneumoniae are restricted to specific clonal lineages. The clonal group CG23 comprises hypervirulent K. pneumoniae displaying limited resistance to antimicrobials and is frequently associated with the community-acquired invasive syndrome. On the other hand, CG258 is another clonal group of K. pneumoniae that has evolved resistance to carbapenems, primarily by acquiring the carbapenemase-encoding genes through nosocomial carriage. Areas covered: With a focus on the high-risk K. pneumoniae clonal lineages CG23 and CG258, we review recent advances including the newly discovered lineage-specific genomic features, and the molecular basis of K. pneumoniae-associated epidemiology, antimicrobial resistance, and hypervirulence. Expert opinion: Both CG23 and CG258 can establish reservoirs in susceptible individuals. Empirical antimicrobial regimens that are prescribed for immediate treatments frequently create selective pressures that favor the high-risk lineages to develop into prominent colonizers. This dilemma reinforces the need for effective therapies that require rapid and accurate diagnosis of epidemic K. pneumoniae.

Hypervirulent Klebsiella pneumoniae

Hypervirulent K. pneumoniae (hvKp) is an evolving pathotype that is more virulent than classical K. pneumoniae (cKp). hvKp usually infects individuals from the community, who are often healthy. Infections are more common in the Asian Pacific Rim but are occurring globally. hvKp infection frequently presents at multiple sites or subsequently metastatically spreads, often requiring source control. hvKp has an increased ability to cause central nervous system infection and endophthalmitis, which require rapid recognition and site-specific treatment. The genetic factors that confer hvKp's hypervirulent phenotype are present on a large virulence plasmid and perhaps integrative conjugal elements. Increased capsule production and aerobactin production are established hvKp-specific virulence factors. Similar to cKp, hvKp strains are becoming increasingly resistant to antimicrobials via acquisition of mobile elements carrying resistance determinants, and new hvKp strains emerge when extensively drug-resistant cKp strains acquire hvKp-specific virulence determinants, resulting in nosocomial infection. Presently, clinical laboratories are unable to differentiate cKp from hvKp, but recently, several biomarkers and quantitative siderophore production have been shown to accurately predict hvKp strains, which could lead to the development of a diagnostic test for use by clinical laboratories for optimal patient care and for use in epidemiologic surveillance and research studies.

Variation in the formation of persister cells against meropenem in Klebsiella pneumoniae bacteremia and analysis of its clinical features

We investigated variations in the rate of persister cell formation against meropenem in 68 Klebsiella pneumoniae isolates from blood. The persister cell formation rates varied markedly but were not significantly different between the patient survival group and death group at 30 days. In addition, they were not associated with the patients' underlying diseases. However, the isolates of CC15 and CC23 showed higher survival rates against 10× MIC of meropenem than CC11. The survival rate of persister cells was less for amikacin and colistin than that for ciprofloxacin. When combinations of meropenem and other antibiotics were administered, persister formation rates decreased compared with those against only meropenem. However, no synergistic effect to remove persister cells was observed. Further investigation is needed to understand persister cell formation in K. pneumoniae with respect to the mechanism involved and clinical implications and that diverse strategies should be explored to remove persister cells.

Antibiotic Resistance and Clinical Presentation of Health Care-Associated Hypervirulent Klebsiella pneumoniae Infection in Korea

Hypervirulent Klebsiella pneumoniae typically presents as a community-acquired infection causing a liver abscess. It is often associated with rmpA and magA genes and confers a mucoid phenotype. Our aim was to evaluate the clinical presentation and antibiotic resistance of hypervirulent K. pneumoniae (hvKP) of health care-associated origin. The study was performed on 414 K. pneumoniae isolates recovered from patients that visited our hospital from December 2013 through November 2015. Hypervirulence was determined by the presence of a hypermucoviscous phenotype, in 155 isolates (37.4%). We compared health care-associated hvKP infections with community-acquired infections. The hypermucoviscous phenotype was 60 isolates (24.2%) in health care-associated infection and 90 isolates (53.8%) in community-acquired infection. Respiratory infection was the most common source of health care-associated K. pneumoniae. Antibiotic resistance was higher in health care-associated hvKP infections, which were more frequently associated with non-K1/K2 serotypes and less frequently associated with rmpA gene. In our study, 38% of hvKP was health care associated. Pneumonia is the most common infection, besides intraabdominal infection, in community-originating strains. These results suggest that health care-associated hvKP may have different microbiological characteristics from classical community-associated infections. Further investigation is needed for other virulent factors associated with health care-associated hvKP.

Klebsiella pneumoniae Liver Abscess

Since the mid 1980s, the prevalence of liver abscess caused by hypervirulent Klebsiella pneumoniae strain has increased in Asia, particularly in Taiwan and Korea. This strain is mostly K1 or K2 serotype, and has hypercapsular and hypermucoid phenotypes. Most infections are community acquired, and patients rarely have a hepatobiliary disease prior to infection. Clinical manifestations are characterized by fever and high C-reactive protein, and metastatic infections, such as septic emboli in the lung and endophthalmitis and meningitis are frequently observed. Antibiotic resistance is rare. Antibiotic treatment and abscess drainage are needed, and early diagnosis and treatment of endophthalmitis is also important.

Rapidly Fatal Emphysematous Osteomyelitis with Multiple Septic Emboli and Liver Abscess Caused by Klebsiella pneumoniae

Emphysematous osteomyelitis, characterized by intraosseous gas, is a rare but potentially fatal condition that requires prompt diagnosis and aggressive therapy. Causative organisms are members of the bacterial family Enterobacteriaceae or anaerobes in most cases and significant comorbidities such as diabetes mellitus and malignancy, may predispose an individual to the development of emphysematous osteomyelitis. We report a case of extensive emphysematous osteomyelitis via hematogenous spread from Klebsiella pneumoniae liver abscess, complicated by gas-containing abscesses in adjacent soft tissues and epidural space, and multiple systemic septic emboli in a diabetic patient.

Cryptogenic and non-cryptogenic liver abscess: A retrospective analysis of 178 cases revealed distinct characteristics

Objective

To enhance theoretical support of pyogenic liver abscess (PLA) treatment by comparing characteristics of patients with either PLA with an identified infectious origin (non-cryptogenic) or PLA with no obvious underlying cause (cryptogenic).

Methods

This retrospective study included all first episodes of PLA in adults admitted to a tertiary hospital between 2009 and 2016. Relevant clinical data were collected for patients with cryptogenic or non-cryptogenic PLA and compared across a number of characteristics.

Results

In all, 178 patients were included: 111 cases (62.4%) of cryptogenic PLA, and 67 cases (37.6%) of non-cryptogenic PLA. Diabetes mellitus was significantly more prevalent in patients with cryptogenic PLA than those with non-cryptogenic PLA. The proportion of multidrug resistance/poly-microbial infection was significantly lower and Klebsiella pneumoniae infection was significantly higher in the cryptogenic versus non-cryptogenic PLA group. Metastatic infection occurred in four patients with cryptogenic PLA only, and all had diabetes and K. pneumoniae infection. Multivariate logistic regression analysis revealed that male sex, diabetes and K. pneumoniae were independent predictors for cryptogenic PLA.

Conclusions

Cryptogenic and non-cryptogenic PLA have distinctly different characteristics, suggesting a potential need for different treatment approaches.

Hypervirulent Klebsiella pneumoniae K1 liver abscess and endogenous endophthalmitis in a Caucasian man

Invasive Liver Abscess Syndrome is the most frequent of a number of infectious syndromes caused by hypervirulent Klebsiella pneumoniae clones. While incidences peak in Southeast Asia, travels to Asia and Asian ethnicity are independent risk factors for infection in the western countries, although non-Asians are infected as well. Although challenging, a prompt diagnosis is of utmost importance to ensure adequate treatment and improve overall survival and visual outcome in cases with ocular involvement.

Changing trends in clinical characteristics and antibiotic susceptibility of Klebsiella pneumoniae bacteremia

BACKGROUND/AIMS

Klebsiella pneumoniae is second most common organism of gram-negative bacteremia in Korea and one of the most common cause of urinary tract infection, and intra-abdominal infection.

METHODS

We compared clinical and microbiological characteristics about K. pneumoniae bacteremia in a tertiary hospital between 10 years. Group A is who had K. pneumoniae bacteremia at least one time from January 2004 to December 2005. Group B is from January 2012 to December 2013. We also analyzed antibiotic resistance, clinical manifestation of the K. pneumoniae bacteremia divided into community-acquired infections, healthcare associated infections, and nosocomial infections.

RESULTS

The resistance for ampicillin, aztreonam, cefazolin, and cefotaxime significantly increased compared to 10 years ago. Extended spectrum β-lactamase positivity surged from 4.3% to 19.6%. Ten years ago, 1st, 2nd cephalosporin, and aminoglycoside were used more as empirical antibiotics. But these days, empirical antibiotics were broad spectrum such as 3rd and 4th cephalosporin. In treatment outcome, acute kidney injury decreased from 47.5% to 28.7%, and mortality decreased from 48.9% to 33.2%. In community-acquired infections, there was similar in antimicrobial resistance and mortality. In healthcare-associated and nosocomial infections, there was significantly increasing in antibiotic resistance, decreasing in mortality, and acute kidney injury.

CONCLUSIONS

In community-acquired infections, broader antibiotics were more used than 10 years ago despite of similar antimicrobial resistance. When K. pneumoniae bacteremia is suspected, we recommend to use the narrow spectrum antibiotics as initial therapy if there are no healthcare-associated risk factors, because the antibiotic resistance is similar to 10 years ago in community-acquired infections.

The NFκB signaling pathway serves an important regulatory role in Klebsiella pneumoniae liver abscesses

The incidence of Klebsiella pneumoniae liver abscess (KPLA) has increased in a number of Asian countries over the past 30 years. Diabetes mellitus (DM) is a risk factor for KPLA. The prevalence and clinical features of KPLA in patients with and without DM have been well described; however, the underlying molecular mechanism responsible for the increased incidence of KPLA in patients with DM remains unclear. In the present study, a mouse model of DM was constructed and mice were infected with K. pneumoniae. Tissues were harvested for immunohistochemical and inflammatory factor expression analyses. The results revealed that the number of liver abscesses in mice with DM was greater than that observed in normal mice. The expression of interleukin (IL)-1β, IL-2, IL-6, macrophage inflammatory protein-1α and tumor necrosis factor-α in the liver tissues of mice with DM was significantly higher compared with normal mice. Western blotting results revealed that the expression of phosphorylated (p)-inhibitor of nuclear factor κB (NFκB) kinase subunit β, p-NFκB and p-inhibitor of NFκB was significantly increased in the liver tissue of mice with DM compared with that of normal mice. These results suggest that activation of the NFκB signaling pathways has a regulatory effect on the pathogenesis of K. pneumoniae bacteria liver abscesses and that high glucose conditions may promote the activation of NFκB signaling.

Altered Profiles of Gut Microbiota in Klebsiella pneumoniae-Induced Pyogenic Liver Abscess

Intestinal microbiota plays a crucial role in preventing the colonization and invasion by pathogens, and disruption of microbiota may cause opportunistic infections and diseases. Pathogens often have strategies to escape from the colonization resistance mediated by microbiota, but whether they also modulate the microbiota composition is still a topic of investigation. In the present study, we addressed this question using an opportunistic pathogen, Klebsiella pneumoniae serotype K1, which is known to cause pyogenic liver abscess (KLA) in about 30% of mice. We examined the effect of K. pneumoniae infection on cecal microbiota composition by performing high-throughput 454 pyrosequencing of the hypervariable V3-V4 regions of bacterial 16S rRNA gene. Our data revealed that K. pneumoniae inoculation substantially changed the cecal microbiota composition when analyzed at the phylum, order, and family levels. Most strikingly, the KLA-infected mice had significantly increased abundance of Bacteroidales and Enterobacteriales and decreased abundance of Lactobacillales and Eggerthellales. Furthermore, by comparing the infected mice with or without KLA disease symptoms, we identified specific microbiota changes associated with the KLA disease induction. Especially, the KLA group had dramatically decreased sequence identical to Lactobacillus compared with non-KLA mice. These findings suggest that the pathogenic process of KLA infection may involve alteration of microbiota compositions, particularly reduction in Lactobacillus.

Molecular epidemiology of Klebsiella pneumoniae K1 and K2 isolates in Japan

Although severe infections caused by hypervirulent Klebsiella pneumoniae isolates, such as K1 isolates belonging to sequence type (ST) 23, have been a significant problem in Asian countries, epidemiology of these isolates in Japan remains unclear. We performed a nationwide molecular epidemiological study of K. pneumoniae K1 and K2 isolates in Japan. Of the 259K. pneumoniae isolates collected, 14 and 16 isolates were identified as capsular genotypes K1 and K2, respectively. All K1 isolates were ST23 or its closely related clones and showed high genetic similarity by pulsed-field gel electrophoresis (PFGE) and the DiversiLab system (DL). K2 isolates, belonging to ST14, ST25, ST65, ST86, and ST110, were more genetically diverse than K1 isolates. Isolates belonging to a specific ST showed identical virulence gene profiles with a few exceptions. PFGE and DL results using K1 and K2 isolates were generally in agreement.

Colonization, Infection, and the Accessory Genome of Klebsiella pneumoniae

Klebsiella pneumoniae is a Gram-negative pathogen that has a large accessory genome of plasmids and chromosomal gene loci. This accessory genome divides K. pneumoniae strains into opportunistic, hypervirulent, and multidrug-resistant groups and separates K. pneumoniae from two closely related species, Klebsiella variicola and Klebsiella quasipneumoniae. Some strains of K. pneumoniae act as opportunistic pathogens, infecting critically ill and immunocompromised patients. These K. pneumoniae are a common cause of health-care associated infections including pneumonia, urinary tract infections (UTIs), and bloodstream infections. K. variicola and K. quasipneumoniae are often clinically indistinguishable from opportunistic K. pneumoniae. Other strains of K. pneumoniae are hypervirulent, infecting healthy people in community settings and causing severe infections including pyogenic liver abscess, endophthalmitis, and meningitis. A third group of K. pneumoniae encode carbapenemases, making them highly antibiotic-resistant. These strains act as opportunists but are exceedingly difficult to treat. All of these groups of K. pneumoniae and related species can colonize the gastrointestinal tract, and the accessory genome may determine if a colonizing strain remains asymptomatic or progresses to cause disease. This review will explore the associations between colonization and infection with opportunistic, antibiotic-resistant, and hypervirulent K. pneumoniae strains and the role of the accessory genome in distinguishing these groups and related species. As K. pneumoniae infections become progressively more difficult to treat in the face of antibiotic resistance and hypervirulent strains, an increased understanding of the epidemiology and pathogenesis of these bacteria is vital.

Antimicrobial Resistance of Hypervirulent Klebsiella pneumoniae: Epidemiology, Hypervirulence-Associated Determinants, and Resistance Mechanisms

Klebsiella pneumoniae is one of the most clinically relevant species in immunocompromised individuals responsible for community-acquired and nosocomial infections, including pneumonias, urinary tract infections, bacteremias, and liver abscesses. Since the mid-1980s, hypervirulent K. pneumoniae, generally associated with the hypermucoviscosity phenotype, has emerged as a clinically significant pathogen responsible for serious disseminated infections, such as pyogenic liver abscesses, osteomyelitis, and endophthalmitis, in a generally younger and healthier population. Hypervirulent K. pneumoniae infections were primarily found in East Asia and now are increasingly being reported worldwide. Although most hypervirulent K. pneumoniae isolates are antibiotic-susceptible, some isolates with combined virulence and resistance, such as the carbapenem-resistant hypervirulent K. pneumoniae isolates, are increasingly being detected. The combination of multidrug resistance and enhanced virulence has the potential to cause the next clinical crisis. To better understand the basic biology of hypervirulent K. pneumoniae, this review will provide a summarization and discussion focused on epidemiology, hypervirulence-associated factors, and antibiotic resistance mechanisms of such hypervirulent strains. Epidemiological analysis of recent clinical isolates in China warns the global dissemination of hypervirulent K. pneumoniae strains with extensive antibiotic resistance in the near future. Therefore, an immediate response to recognize the global dissemination of this hypervirulent strain with resistance determinants is an urgent priority.

Klebsiella Pneumoniae Liver Abscess: A Case Series of Six Asian Patients

BACKGROUND Liver abscesses represent a serious infection of hepatic parenchyma and are associated with significant morbidity and mortality. The emergence of a new hypervirulent variant of Klebsiella pneumoniae, which can cause serious infections in the Asian population, is under investigation. We report a case series of six Asian patients hospitalized at our institution from January 2013 to November 2015 for liver abscess due to Klebsiella pneumoniae. CASE REPORT Charts of six Asian patients were retrospectively reviewed. Four patients were male and two were female. The mean age was 53 years (range: 35-64 years). All patients had no known past medical history of immunodeficiency. Three patients had multiple liver abscesses at the time of initial presentation. In five patients, the source of entry of the pathogenic microorganism was unknown and in one patient the suspected source of entry was the gastrointestinal tract. In three patients there was also concomitant Klebsiella pneumoniae bacteremia. The mean duration of antibiotic treatment was seven weeks and the mean duration of hospital stay was 13.5 days. CONCLUSIONS Liver abscess should always be included in the differential diagnosis in cases of sepsis without obvious source and/or in the clinical scenarios of fever, abdominal pain, and liver lesions.

Comparison of Diabetic and Non-diabetic Human Leukocytic Responses to Different Capsule Types of Klebsiella pneumoniae Responsible for Causing Pyogenic Liver Abscess

The major risk factor for Klebsiella liver abscess (KLA) is type 2 diabetes mellitus (DM), but the immunological mechanisms involved in the increased susceptibility are poorly defined. We investigated the responses of neutrophils and peripheral blood mononuclear cells (PBMCs) to hypervirulent Klebsiella pneumoniae (hvKP), the causative agent of KLA. DNA and myeloperoxidase levels were elevated in the plasma of KLA patients compared to uninfected individuals indicating neutrophil activation, but diabetic status had no effect on these neutrophil extracellular trap (NET) biomarkers in both subject groups. Clinical hvKP isolates universally stimulated KLA patient neutrophils to produce NETs ex vivo, regardless of host diabetic status. Ability of representative capsule types (K1, K2, and non-K1/K2 strains) to survive intra- and extra-cellular killing by type 2 DM and healthy neutrophils was subsequently examined. Key findings were: (1) type 2 DM and healthy neutrophils exhibited comparable total, phagocytic, and NETs killing against hvKP, (2) phagocytic and NETs killing were equally effective against hvKP, and (3) hypermucoviscous K1 and K2 strains were more resistant to total, phagocytic, and NETs killing compared to the non-mucoviscous, non-K1/K2 strain. The cytokine response and intracellular killing ability of type 2 DM as well as healthy PBMCs upon encounter with the different capsule types was also examined. Notably, the IL-12–IFNγ axis and its downstream chemokines MIG, IP-10, and RANTES were produced at slightly lower levels by type 2 DM PBMCs than healthy PBMCs in response to representative K1 and non-K1/K2 strains. Furthermore, type 2 DM PBMCs have a mild defect in its ability to control hvKP replication relative to healthy PBMCs. In summary, our work demonstrates that type 2 DM does not overtly impact neutrophil intra- and extra-cellular killing of hvKP, but may influence cytokine/chemokine production and intracellular killing by PBMCs.

Novel complication of an emerging disease: Invasive Klebsiella pneumoniae liver abscess syndrome as a cause of acute respiratory distress syndrome

Klebsiella pneumoniae is an increasingly recognized cause of a unique invasive syndrome manifesting as pyogenic liver abscess and hematogenous extrahepatic dissemination to a variety of sites, including the lung. Originally described only in Asia, this entity has now been reported across continents and ethnicities. Intrathoracic complications of invasive Klebsiella pneumoniae liver abscess syndrome (IKPLAS) have been characterized sporadically but have not been the subject of an all-encompassing investigation. Review of the English-language literature yields no reports of the acute respiratory distress syndrome as a consequence of IKPLAS. Herein we report what, to our knowledge, is the first such description.

Two T7-like Bacteriophages, K5-2 and K5-4, Each Encodes Two Capsule Depolymerases: Isolation and Functional Characterization

Two Klebsiella bacteriophages K5-2 and K5-4, which are able to infect and grow on either capsular types K30/K69 and K5 or K8 and K5 of Klebsiella strains, were isolated and characterized. Each phage contained two open reading frames (ORFs), which encoded two putative capsule depolymerases, respectively. The first ORF encoded tail fiber proteins, which have K30/K69 depolymerase and K8 depolymerase activities. The second ORF encoded hypothetical proteins, which are almost identical in amino acid sequences, and have K5 depolymerase activity. Alcian blue staining of enzyme-treated capsular polysaccharides (CPS) showed that purified depolymerases can cleave purified Klebsiella CPS in vitro and liberate monosaccharaides. Capsule K5 deletion mutants were not lysed by either phage, suggesting that the capsule was essential for phage infection. Bacterial killing was observed when incubated Klebsiella strains with phages but not with purified depolymerases. Treatment with the K5-4 phage significantly increased the survival of mice infected with a K. pneumoniae K5 strain. In conclusion, two dual host-specific Klebsiella phages and their tailspikes exhibit capsule depolymerase activity were characterized. Each phage and phage-encoded depolymerase has specificity for capsular type K30/K69, K8 or K5, and could be used for the typing and treatment of K. pneumoniae infection.

Metastatic endophthalmitis and thyroid abscess complicating Klebsiella pneumoniae liver abscess

The thyroid is resistant to infection due to its anatomical and physiological characteristics. We present a rare case of invasive liver abscess with metastatic thyroid abscess and endogenous endophthalmitis in a previously healthy 55-year-old female patient without diabetes or other medical illness. This report raises an important question of the virulence of Klebsiella pneumoniae as an increasingly common causative agent of liver abscess.

Bacteremia and other body site infection caused by hypervirulent and classic Klebsiella pneumoniae

OBJECTIVES

To investigate bacteremia and other body site infection caused by hypervirulent Klebsiella pneumoniae (hvKP), a recently recognized pathogen of invasive infection, and classic Klebsiella pneumoniae (cKP), a very common organism associated with many kinds of nosocomial infection.

METHODS

Clinical information obtained from patients with both bacteremia and other body site infections caused by hvKP and/or cKP was retrospectively reviewed. Homo-hvKP (or homo-cKP) was defined as homologous hvKP (or cKP) strains from different body sites in each individual patient according to string test, virulence gene amplification and PFGE pattern. MLST was carried on to understand the correlation of sequence type with capsular polysaccharide type for Klebsiella pneumoniae from blood.

RESULTS

Sixty-four hvKP and 101 cKP strains were isolated from blood and other body sites of 76 patients who had bacteremia accompanied by other site infection. Among these patients, 27 were infected with homo-hvKP, 32 were with homo-cKP, 12 were with heterogeneous cKP, and five were with both hvKP and cKP. Patients with bacteremia and liver abscesses caused by homo-hvKP accounted for 51.9%, and 92.6% of homo-hvKP infected patients did not receive any invasive procedures before bacteremia. However, patients with bacteremia and biliary tract infection caused by homo-cKP accounted for 34.4%, and 78.1% of homo-cKP infected patients had history of invasive procedures before bacteremia. More homo-hvKP strains (59.3%) than homo-cKP strains (34.4%) were isolated from blood earlier than other sites. HvKP strains were statistically more susceptible to the tested antimicrobials than cKP strains. An outbreak of carbapenem-resistant cKP infection and possible gene transfer of KPC-2 from cKP to hvKP were brought to notice.

CONCLUSIONS

Both hvKP and cKP could cause bacteremia and other body site infection. But patients with hvKP bacteremia usually suffered from liver abscess without previous invasive procedures, most patients with cKP bacteremia had history of invasive medical procedures.

Antibody-Based Immunotherapy To Treat and Prevent Infection with Hypervirulent Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae (hvKp) strains are predicted to become a major threat in Asia if antibiotic resistance continues to spread. Anticapsular antibodies (Abs) were developed because disseminated infections caused by hvKp are associated with significant morbidity and mortality, even with antibiotic-sensitive strains. K1-serotype polysaccharide capsules (K1-CPS) are expressed by the majority of hvKp strains. In this study, K1-CPS-specific IgG Abs were generated by conjugation of K1-CPS to immunogenic anthrax protective antigen (PA) protein. Opsonophagocytic efficacy was measured in vitro and in vivo by intravital microscopy in murine livers. In vivo protection was tested in murine models, including a novel model for dissemination in hvKp-colonized mice. Protective efficacy of monoclonal antibodies (MAbs) 4C5 (IgG1) and 19A10 (IgG3) was demonstrated both in murine sepsis and pulmonary infection. In hvKp-colonized mice, MAb treatment significantly decreased dissemination of hvKp from the gut to mesenteric lymph nodes and organs. Intravital microscopy confirmed efficient opsonophagocytosis and clearance of bacteria from the liver. In vitro studies demonstrate that MAbs work predominantly by promoting FcR-mediated phagocytosis but also indicate that MAbs enhance the release of neutrophil extracellular traps (NETs). In anticipation of increasing antibiotic resistance, we propose further development of these and other Klebsiella-specific MAbs for therapeutic use.

Emergence of an extended-spectrum β-lactamase-producing serotype K1 Klebsiella pneumoniae ST23 strain from Asian countries

Extended-spectrum β-lactamase (ESBL) production has been very rare in serotype K1 Klebsiella pneumoniae ST23 strains, which are well-known invasive community strains. Among 92 ESBL-producing strains identified in 218 isolates from nine Asian countries, serotype K1 K. pneumoniae strains were screened. Two ESBL-producing K. pneumoniae isolates from Singapore and Indonesia were determined to be serotype K1 and ST23. Their plasmids, which contain CTX-M-15 genes, are transferable rendering the effective transfer of ESBL resistance plasmids to other organisms.

A retrospective study of pyogenic liver abscess focusing on Klebsiella pneumoniae as a primary pathogen in China from 1994 to 2015

Pyogenic liver abscess (PLA) is a common intra-abdominal infection in adults. In this study, we aim to explore demographic and clinical characteristics of PLA focusing on Klebsiella pneumoniae (K. pneumoniae) induced PLA (KP-PLA) in mainland China. A retrospective review of medical records from all patients with KP-PLA admitted to a tertiary teaching hospital over a 21-year period (1994–2015) was performed. Among 296 PLA cases with confirmed culture-positive data, K. pneumoniae was revealed as the predominant pathogen (n = 189, 63.9%), followed by Escherichia coli (n = 39, 13.2%). Strikingly, KP-PLA patients had a higher incidence of metabolic disorders, such as diabetes mellitus (49.7% vs. 36.4%, P = 0.027; odds ratio (OR): 1.725; 95% confidence interval (CI): 1.061–2.805), hypertension (38.1% vs. 19.6%, P = 0.001; OR: 2.520; 95% CI: 1.439–4.413), and fatty liver (32.3% vs. 14.0%, P = 0.001; OR: 2.923; 95% CI: 1.564–5.462) than those with non-K. pneumoniae induced PLA (non-KP-PLA). Moreover, patients with KP-PLA had higher susceptibility to septic metastatic infection at distant sites compared to those with non-KP-PLA (10.6% vs. 3.7%, p = 0.038). Our results indicate that K. pneumoniae is the predominant pathogen of PLA in mainland China. KP-PLA is frequently diagnosed in patients with metabolic diseases and has a higher risk for septic metastatic infection.

Emergence of serotype K1 Klebsiella pneumoniae ST23 strains co-producing the plasmid-mediated AmpC beta-lactamase DHA-1 and an extended-spectrum beta-lactamase in Korea

BACKGROUND

Serotype K1 Klebsiella pneumoniae has emerged as an important community pathogen causing various infections, including liver abscesses. Although serotype K1 K. pneumoniae community isolates have been reported as susceptible to most classes of antimicrobial agents, a few cases of infection caused by extended-spectrum beta-lactamase (ESBL)-producing serotype K1 K. pneumoniae have recently been reported in Asian countries. We identified three ESBL-producing strains of serotype K1 K. pneumoniae and conducted a molecular characterization of their drug resistance.

METHODS

Three ESBL-producing serotype K1 K. pneumoniae ST23 strains were identified from strains in the Asian Bacterial Bank. Antimicrobial susceptibility testing was performed using the broth microdilution method, and ESBL production was tested by the double-disk synergy test and a confirmatory test. PCR was performed to detect the genes for plasmid-mediated ESBL and AmpC beta-lactamases.

RESULTS

All three strains were resistant to cefotaxime, ceftazidime, and piperacillin/tazobactam, and all were determined to be ESBL-producers. No known ESBL genes, including bla_SHV, bla_TEM, bla_CTX-M, bla_GES, bla_PER, and bla_VEB, were detected among the three strains. Of all plasmid-mediated AmpC beta-lactamase (PAB) genes, including bla_DHA-1, bla_CMY, bla_FOX, and bla_MOX, the bla_DHA-1 gene was detected in two of the strains. The PFGE patterns revealed that the two isolates carrying bla_DHA-1 were closely related (84% similarity).

CONCLUSIONS

No ESBL genes were detected among three ESBL-producing serotype K1 K. pneumoniae ST23 strains. Two strains contained the PAB gene bla_DHA-1. The emergence of resistant strains of community-origin serotype K1 K. pneumoniae has important implications for effective treatment and infection control practices.

Klebsiella pneumonia liver abscess syndrome: Case presentation to a college student health clinic

The authors describe a case of Klebsiella pneumoniae liver abscess (KPLA) in a student presenting to a university student health center. The authors also provide a review of KPLA and invasive Klebsiella pneumoniae liver abscess syndrome (IKPLAS), including epidemiology, common clinical manifestations, standard diagnostic work-up, management options, and potential complications.

Geme JW. Kingella kingae Expresses Four Structurally Distinct Polysaccharide Capsules That Differ in Their Correlation with Invasive Disease

Kingella kingae is an encapsulated gram-negative organism that is a common cause of osteoarticular infections in young children. In earlier work, we identified a glycosyltransferase gene called csaA that is necessary for synthesis of the [3)-β-GalpNAc-(1→5)-β-Kdop-(2→] polysaccharide capsule (type a) in K. kingae strain 269-492. In the current study, we analyzed a large collection of invasive and carrier isolates from Israel and found that csaA was present in only 47% of the isolates. Further examination of this collection using primers based on the sequence that flanks csaA revealed three additional gene clusters (designated the csb, csc, and csd loci), all encoding predicted glycosyltransferases. The csb locus contains the csbA, csbB, and csbC genes and is associated with a capsule that is a polymer of [6)-α-GlcpNAc-(1→5)-β-(8-OAc)Kdop-(2→] (type b). The csc locus contains the cscA, cscB, and cscC genes and is associated with a capsule that is a polymer of [3)-β-Ribf-(1→2)-β-Ribf-(1→2)-β-Ribf-(1→4)-β-Kdop-(2→] (type c). The csd locus contains the csdA, csdB, and csdC genes and is associated with a capsule that is a polymer of [P-(O→3)[β-Galp-(1→4)]-β-GlcpNAc-(1→3)-α-GlcpNAc-1-] (type d). Introduction of the csa, csb, csc, and csd loci into strain KK01Δcsa, a strain 269-492 derivative that lacks the native csaA gene, was sufficient to produce the type a capsule, type b capsule, type c capsule, and type d capsule, respectively, indicating that these loci are solely responsible for determining capsule type in K. kingae. Further analysis demonstrated that 96% of the invasive isolates express either the type a or type b capsule and that a disproportionate percentage of carrier isolates express the type c or type d capsule. These results establish that there are at least four structurally distinct K. kingae capsule types and suggest that capsule type plays an important role in promoting K. kingae invasive disease.

The emergence of Klebsiella pneumoniae liver abscess in non-diabetic patients and the distribution of capsular types

Background

Klebsiella pneumoniae is the most common pathogen of community-acquired pyogenic liver abscess in East Asia. Diabetes mellitus (DM) is a well-established risk factor for K. pneumoniae liver abscess (KPLA). However, reports regarding the emergence of KPLA in non-diabetic patients are limited.

Results

A total 230 patients with KPLA from a medical center in Taiwan were identified retrospectively. The rate of DM in patients with KPLA was 44.4 % in 2011, 57.9 % in 2012, 44.9 % in 2013, 35.0 % in 2014, and 53.5 % in 2015. Diabetic patients had higher rate of gas-forming abscesses than non-diabetic patients, but the clinical outcomes were not different. The six virulent capsular types (K1, K2, K5, K20, K54, and K57) accounted for 90.2 % of all K. pneumoniae isolates, and were more prevalent in non-diabetic than diabetic patients (93.9 vs 85.9 %, P = 0.048). The six virulent capsular types were also more prevalent in the group with optimal glycemic levels (Non-DM and DM with HbA1c level <7 %) than the DM group with HbA1c level ≥7 % (93.9 vs 84.3 %, P = 0.022).

Conclusion

Klebsiella pneumoniae liver abscess has emerged in non-diabetic patients in Taiwan. Diabetic patients were at higher risk of acquiring gas-forming abscesses. Non diabetic patients and diabetic patients with optimal glycemic levels are more susceptible to the virulent capsular types of K. pneumoniae.

CD36 Provides Host Protection Against Klebsiella pneumoniae Intrapulmonary Infection by Enhancing Lipopolysaccharide Responsiveness and Macrophage Phagocytosis

Klebsiella pneumoniae remains an important cause of intrapulmonary infection and invasive disease worldwide. K. pneumoniae can evade serum killing and phagocytosis primarily through the expression of a polysaccharide capsule, but its pathogenicity is also influenced by host factors. We examined whether CD36, a scavenger receptor that recognizes pathogen and modified self ligands, is a host determinant of K. pneumoniae pathogenicity. Despite differences in serum sensitivity and virulence of 3 distinct K. pneumoniae (hypermucoviscous K1, research K2, and carbapenemase-producing ST258) strains, the absence of CD36 significantly increased host susceptibility to acute intrapulmonary infection by K. pneumoniae, regardless of strain. We demonstrate that CD36 enhances LPS responsiveness to K. pneumoniae to increase downstream cytokine production and macrophage phagocytosis that is independent of polysaccharide capsular antigen. Our study provides new insights into host determinants of K. pneumoniae pathogenicity and raises the possibility that functional mutations in CD36 may predispose individuals to K. pneumoniae syndromes.

Identification of a capsular variant and characterization of capsular acetylation in Klebsiella pneumoniae PLA-associated type K57

Klebsiella pneumoniae can cause community-acquired pyogenic liver abscess (PLA). Capsular polysaccharide (CPS) is important for its virulence. Among 79 capsular (K) types discovered thus far, K57 is often associated with PLA. Here, we report the identification of a K57 variant. Cps gene locus sequencing revealed differences between the K57 reference strain 4425/51 (Ref-K57) and a variant, the PLA isolate A1142. While Ref-K57 cps contained orf13 encoding a putative acetyltransferase, the insertion of a putative transposase-encoding gene at this position was detected in A1142. This variation was detected in other K57 clinical strains. Biochemical analyses indicated that A1142 was deficient in CPS acetylation. Genetic replacement and complementation verified that orf13 was responsible for CPS acetylation. Acetylation increased CPS immunoreactivity to antiserum and enhanced K. pneumoniae induction of pro-inflammatory cytokines through JNK and MAPK signaling. While acetylation diminished the serum resistance of bacteria, it promoted adhesion to intestinal epithelial cells possibly via increasing production of type I fimbriae. In conclusion, acetylation-mediated capsular variation in K57 was observed. Capsular acetylation contributed to the variety and antigenic diversity of CPS, influenced its biological activities, and was involved in K. pneumoniae-host interactions. These findings have implications for vaccine design and pathogenicity of K. pneumoniae.

Influence of cAMP receptor protein (CRP) on bacterial virulence and transcriptional regulation of allS by CRP in Klebsiella pneumoniae

cAMP receptor protein (CRP) is one of the most important transcriptional regulators, which can regulate large quantities of operons in different bacteria. The gene allS was well-known as allantoin-utilizing capability and involving in bacterial virulence in Klebsiella pneumoniae (K. pneumoniae). The specific DNA recognition motif of transcription regulator CRP was found in allS promoter region. Therefore, this study is aimed to investigate the function of CRP on virulence and its transcriptional regulation mechanism to gene allS in K. pneumoniae. The wild-type (WT) K. pneumoniae NTUH-2044, crp knockout (Kp-Δcrp) and the complemented knockout (KpC-Δcrp) strains were used to determine the function of crp gene. The lacZ fusion, qRT-PCR, electrophoretic mobility shift and DNase I footprinting assays were performed to study the transcriptional regulation of CRP on allS. The result showed a decreased virulence in crp knockout strain. Complement through supplementing crp fragment in expression plasmid partially restore virulence of knockout bacteria. The CRP could bind to the allS promoter-proximal region and the binding site was further refined to be located from 60bp to 94bp upstream of the allS promoter. Based on these results, we proposed that CRP is an essential virulence regulator and knock out of crp gene will result in reduced virulence in K. pneumoniae. In the meantime, the transcription of gene allS is positively regulated by CRP via directly binding to upstream of allS promoter.

Toll-like receptor 4-related immunostimulatory polysaccharides: Primary structure, activity relationships, and possible interaction models

Toll-like receptor (TLR) 4 is an important polysaccharide receptor; however, the relationships between the structures and biological activities of TLR4 and polysaccharides remain unknown. Many recent findings have revealed the primary structure of TLR4/MD-2-related polysaccharides, and several three-dimensional structure models of polysaccharide-binding proteins have been reported; and these models provide insights into the mechanisms through which polysaccharides interact with TLR4. In this review, we first discuss the origins of polysaccharides related to TLR4, including polysaccharides from higher plants, fungi, bacteria, algae, and animals. We then briefly describe the glucosidic bond types of TLR4-related heteroglycans and homoglycans and describe the typical molecular weights of TLR4-related polysaccharides. The primary structures and activity relationships of polysaccharides with TLR4/MD-2 are also discussed. Finally, based on the existing interaction models of LPS with TLR4/MD-2 and linear polysaccharides with proteins, we provide insights into the possible interaction models of polysaccharide ligands with TLR4/MD-2. To our knowledge, this review is the first to summarize the primary structures and activity relationships of TLR4-related polysaccharides and the possible mechanisms of interaction for TLR4 and TLR4-related polysaccharides.

The Klebsiella pneumoniae YfgL (BamB) lipoprotein contributes to outer membrane protein biogenesis, type-1 fimbriae expression, anti-phagocytosis, and in vivo virulence

Klebsiella pneumoniae is an opportunistic pathogen that causes several kinds of infections, including pneumonia, bacteremia, urinary tract infection and community-acquired pyogenic liver abscess (PLA). Adhesion is the critical first step in the infection process. Our previous work demonstrated that the transcellular translocation is exploited by K. pneumoniae strains to migrate from the gut flora into other tissues, resulting in systemic infections. However, the initial stages of K. pneumoniae infection remain unclear. In this study, we demonstrated that a K. pneumoniae strain deleted for yfgL (bamB) exhibited reduced adherence to and invasion of host cells; changed biogenesis of major β-barrel outer membrane proteins; decreased transcriptional expression of type-1 fimbriae; and increased susceptibility to vancomycin and erythromycin. The yfgL deletion mutant also had reduced ability to against neutrophil phagocytosis; exhibited decreased induction of host IL-6 production; and was profoundly attenuated for virulence in a K. pneumoniae model of bacteremia. Thus, the K. pneumoniae YfgL lipoprotein mediates in outer membrane proteins biogenesis and is crucial for anti-phagocytosis and survival in vivo. These data provide a new insight for K. pneumoniae attachment and such knowledge could facilitate preventive therapies or alternative therapies against K. pneumoniae.