Streptococcus pneumoniae induces expression of the antibacterial CXC chemokine MIG/CXCL9 via MyD88-dependent signaling in a murine model of airway infection

MIG/CXCL9 belongs to the CXC family of chemokines and participates in the regulation of leukocyte-trafficking and angiogenesis. Certain chemokines, including human MIG/CXCL9, exert strong antibacterial activity in vitro, although the importance of this property in vivo is unknown. In the present study, we investigated the expression and a possible role for MIG/CXCL9 in host defense during mucosal airway infection caused by Streptococcus pneumoniae in vivo. We found that intranasal challenge of C57BL/6 wild-type mice with pneumococci elicited production of high levels of MIG/CXCL9 in the lungs via the MyD88-dependent signaling pathway. Whereas both human and murine MIG/CXCL9 showed efficient killing of S. pneumoniae in vitro, MIG/CXCL9 knock-out mice were not more susceptible to pneumococcal infection. Our data demonstrate that, in vivo this chemokine probably has a redundant role, acting together with other antibacterial peptides and chemokines, in innate and adaptive host defense mechanisms against pneumococcal infections.     

Novel antibacterial peptides induced by probiotics in Hermetia illucens (Diptera: Stratiomyidae) larvae

There is a need to discover new therapeutic substances due to the emergence of deadly infectious diseases and various antibiotic resistance. We focused on the larvae that are utilized as a medical insect for the treatment of skin damage in Europe and America. This study was to investigate the pharmacological activities of novel antibacterial peptides isolated from Hermetia illucens larvae against the Klebsiella pneumoniae and Shigella dysenteriae. The larvae were immunized by probiotics (Lactobacillus casei) for 24 h. The hemolymph from the immunized larvae was fractionated through reverse‐phase chromatography. Peptides were purified using HPLC and the coomassie blue staining, and identified using Nano‐LC‐ESI‐MS/MS system. Antibacterial activities of the peptides were evaluated by turbidometric assay, liquid broth dilution assay, resazurin assay, and agar disk diffusion method. The minimum inhibitory concentrations (MICs) of the peptides were measured as 150 μg/mL through the turbidometric, liquid broth dilution, and resazurin assays. The peptides effectively inhibited their growth/proliferation as well as the survival rate of the tested bacteria. Furthermore, the immunized larvae exhibited overexpression of the peptides compared to non‐immunized larvae. These results demonstrate that the peptides induced by H. illucens exert strong antibacterial activity against Gram‐negative bacteria. The results suggest that the activation of the humoral immunity induced by immunization functioned to enhance the production of antibacterial peptides from the insect and their antibacterial properties. This study indicates the potential of the peptides produced from larvae as antibacterial peptide substance for the development of novel antibacterial drugs.     

Antibacterial effect of extracts of Hermetia illucens (Diptera: Stratiomyidae) larvae against Gram‐negative bacteria

Larvae of the black soldier fly, Hermetia illucens are well‐known fly larvae that inhabit many countries around the world. Antimicrobial agents derived from the larvae may be among the substances that are produced in the body for their survival. This study was carried out to identify the antimicrobial effects of H. illucens larvae that commonly inhabit animal waste and food waste. To evaluate the pharmacological effects of H. illucens larvae extracts, the larvae were extracted by various organic solvents, and their antibacterial effects were determined by antimicrobial methods, such as agar disk diffusion and turbidometric assays. The methanol extracts (ME) indicated antibacterial effects against the proliferation of Klebsiella pneumoniae, Neisseria gonorrhoeae and Shigella sonnei. However, antibacterial effects were not induced in Gram‐positive bacteria such as Bacillus subtilis, Streptococcus mutans and Sarcina lutea. The bacterial growth treated with ME was strongly inhibited from 20 mg/mL in a dose‐dependent manner compared with other extracts, and antibacterial activity gradually decreased after 24 h. Moreover, the minimal inhibitory concentration (MIC) values of ME against Klebsiella pneumoniae, Neisseria gonorrhoeae and Shigella sonnei for 12 h were measured as 44.74 mg/mL, 43.98 mg/mL and 43.96 mg/mL, respectively. These results demonstrate that ME of H. illucens larvae not only has antibacterial activity which strongly inhibits the growth and proliferation of the bacteria but also unique properties which effectively block the viability of the bacteria.     

Application of S-thanatin,an antimicrobial peptide derived from thanatin,in mouse model of Klebsiella pneumoniae infection

Thanatin was first discovered from the hemipteran insect Podisus maculiventris and showed a promising antimicrobial activity. Multidrug-resistant (MDR) clinical isolates of Klebsiella pneumoniae have developed resistance to current therapies. As an attempt to resolve this problem, the efficacy of thanatin and its analogues against clinical isolates of K. pneumoniae was studied in vitro and in vivo. S-thanatin showed an improved antimicrobial activity with the tested MIC values was 2–8-fold lower than those of other thanatin analogs. Antimicrobial assay indicated a high activity of S-thanatin against K. pneumoniae in vitro with MIC between 4 and 8 μg/ml. Its in vivo activity was evaluated using a K. pneumoniae-infected mice model. Adult male ICR mice were randomly grouped and given an intraperitoneal (i.p.) administration of 2 × 10¹⁰ colony-forming units of K. pneumoniae (CI 120204205). Afterwards, mouse groups were subjected to i.p. administration of saline or S-thanatin (5, 10, or 15 mg/kg). After an inspection of 72 h, the mice were finally sacrificed for analysis of in vivo bacterial growth and plasma endotoxin level. The results showed that S-thanatin administration apparently improved the survival rate and reduced the bacterial CFU from intra-abdominal fluid in mice. The plasma endotoxin level was improved as well. All above implied that S-thanatin, as an alternative, may provide a novel strategy for treating K. pneumoniae infection and other infections due to multidrug-resistant bacteria.     

Antimicrobial activity of bitespiramycin,a new genetically engineered macrolide

The antimicrobial activity of bitespiramycin (BT) against Chlamydia trachomatis (Ct), Chlamydia pneumoniae (Cp), Ureaplasma urealyticum (Uu), and Mycoplasma pneumoniae (Mp), was compared with those of azithromycin (AZM) and acetylspiramycin (AT-SP) in vitro. Furthermore, the anti-Mp activities of BT and AZM were evaluated in a hamster model. The activities of BT in vitro were similar to those of AZM but were more effective than those of AT-SP. BT effectively inhibited Mp infection at a dose of 200 mg/kg in a hamster model.     

Otitis Media: A Review, with a Focus on Alternative Treatments

Otitis media (OM) is the accumulation of fluids in the middle ear, with or without symptoms of inflammation. The infection is caused by dysfunction or obstruction of the eustachian tube and is most commonly diagnosed in children under the age of two. The microbiology of OM differs, with Streptococcus pneumoniae, non-typeable Haemophilus influenzae and Moraxella catarrhalis the most commonly isolated pathogens. The emergence of penicillin-resistant Strep. pneumoniae, β-lactamase-producing strains, Haem. influenzae and Mor. catarrhalis is a major concern and health care costs associated with treatment are substantial, especially in cases of unresponsive treatment as a result of incorrect diagnosis. Alternative treatments such as vaccines and a nasal spray containing α-haemolytic streptococci with antimicrobial activity against OM pathogens, have been developed. The rationale behind such treatments is to induce an appropriate immune response against the pathogens and decrease bacterial colonisation in the nasopharynx. Another approach may be treatment with bacteriocins (natural antimicrobial peptides) or bacteriocin-like inhibitory substances (BLIS) produced by lactic acid bacteria. We have recently described an antibacterial peptide produced by Enterococcus mundtii ST4SA and have published on bacteriocins (enterocins) with antibacterial and antiviral activity. This review discusses the condition OM, summarises current methods used to treat the infection, and suggests alternative safe and natural treatments that need to be explored.     

Structure-activity relationship studies on the inhibition of the bacterial translation of novel Odilorhabdins analogues

A structure–activity relationship (SAR) study of NOSO-95179, a nonapeptide from the Odilorhabdin class of antibacterials, was performed by systematic variations of amino acids in positions 2 and 5 of the peptide. A series of non-proteinogenic amino acids was synthesized in high enantiomeric purity from Williams’ chiral diphenyloxazinone by highly diastereoselective alkylation or by aldol-type reaction. NOSO-95179 analogues for SAR studies were prepared using solid-phase peptide synthesis. Inhibition of bacterial translation by each of the synthesized Odilorhabdin analogues was measured using an in vitro test. For the most efficient analogues, antibacterial efficacy was measured against two wild-type Enterobacteriaceae (Escherichia coli and Klebsiella pneumoniae) and against an efflux defective E. coli strain (ΔtolC) to evaluate the impact of efflux on the antibacterial activity.     

SitA contributes to the virulence of Klebsiella pneumoniae in a mouse infection model

Klebsiella pneumoniae is an opportunistic pathogen, which causes a wide range of nosocomial infections. Recently, antibiotic resistance makes K. pneumoniae infection difficult to deal with. Investigation on virulence determinants of K. pneumoniae can provide more information about pathogenesis and unveil new targets for treatment or vaccine development. In this study, SitA, a Fur-regulated divalent cation transporter, was found significantly increased when K. pneumoniae was cultured in a nutrient-limited condition. A sitA-deletion strain (ΔsitA) was created to characterize the importance of SitA in virulence. ΔsitA showed higher sensitivity toward hydroperoxide than its parental strain. In a mouse intraperitoneal infection model, the survival rate of mice infected with ΔsitA strain increased greatly when compared with that of mice infected with the parental strain, suggesting that sitA deletion attenuates the bacterial virulence in vivo. To test whether ΔsitA strain is a potential vaccine candidate, mice were immunized with inactivated bacteria and then challenged with the wild-type strain. The results showed that using ΔsitA mutant protected mice better than using the wild-type strain or the capsule-negative congenic bacteria. In summary, SitA was found being important for the growth of K. pneumoniae in vivo and deleting sitA might be a potential approach to generate vaccines against K. pneumoniae.     

Investigation of the antibacterial activity of a short cationic peptide against multidrug-resistant Klebsiella pneumoniae and Salmonella typhimurium strains and its cytotoxicity on eukaryotic cells

With the growing microbial resistance to conventional antimicrobial agents, the development of novel and alternative therapeutic strategies are vital. During recent years novel peptide antibiotics with broad spectrum activity against many Gram-positive and Gram-negative bacteria have been developed. In this study, antibacterial activity of CM11 peptide (WKLFKKILKVL-NH2), a short cecropin–melittin hybrid peptide, is evaluated against antibiotic-resistant strains of Klebsiella pneumoniae and Salmonella typhimurium as two important pathogenic bacteria. To appraise the antibacterial activity, minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC) and bactericidal killing assay were utilized with different concentrations (2–128 mg/L) of peptide. To evaluate cytotoxic effect of peptide, viability of RAJI, Hela, SP2/0, CHO, LNCAP cell lines and primary murine macrophage cells were also investigated with MTT assay in different concentrations (3–24 and 0.5–16 mg/L, respectively). MICs of K. pneumoniae and S. typhimurium isolates were in range of 8–16 and 4–16 mg/L, respectively. In bactericidal killing assay no colonies were observed at 2X MIC for K. pneumoniae and S. typhimurium isolates after 80–90 min, respectively. Despite the fact that CM11 reveals no significant cytotoxicity on RAJI, Hela, SP2/0, and CHO cell lines beneath 6 mg/L at first 24 and 48 h, the viability of LNCAP cells are about 50 % at 3 mg/L, which indicates strong cytotoxicity of the peptide. In addition, macrophage toxicity by MTT assay showed that LD₅₀ of CM11 peptide is 12 μM (16 mg/L) after 48 h while in this concentration after 24 h macrophage viability was about 70 %.     

Antimicrobial and antibiofilm activity of cathelicidins and short, synthetic peptides against Francisella

Francisella infects the lungs causing pneumonic tularemia. Focusing on the lung’s host defense, we have examined antimicrobial peptides as part of the innate immune response to Francisella infection. Interest in antimicrobial peptides, such as the cathelicidins, has grown due their potential therapeutic applications and the increasing problem of bacterial resistance to commonly used antibiotics. Only one human cathelicidin, LL-37, has been characterized. Helical cathelicidins have also been discovered in snakes including the Chinese King Cobra, Naja atra (NA-CATH). Four synthetic 11-residue peptides (ATRA-1, -2, -1A and -1P) containing variations of a repeated motif within NA-CATH were designed. We hypothesized that these smaller synthetic peptides could have excellent antimicrobial effectiveness with shorter length (and less cost), making them strong potential candidates for development into broad-spectrum antimicrobial compounds. We tested the susceptibility of F. novicida to four ATRA peptides, LL-37, and NA-CATH. Two of the ATRA peptides had high antimicrobial activity (μM), while the two proline-containing ATRA peptides had low activity. The ATRA peptides did not show significant hemolytic activity even at high peptide concentration, indicating low cytotoxicity against host cells. NA-CATH killed Francisella bacteria more quickly than LL-37. However, LL-37 was the most effective peptide against F. novicida (EC50 = 50 nM). LL-37 mRNA was induced in A549 cells by Francisella infection. We recently demonstrated that F. novicida forms in vitro biofilms. LL-37 inhibited F. novicida biofilm formation at sub-antimicrobial concentrations. Understanding the properties of these peptides, and their endogenous expression in the lung could lead to potential future therapeutic interventions for this lung infection.     

Role of the Mycoplasma pneumoniae/Interleukin-8/Neutrophil Axis in the Pathogenesis of Pneumonia

Neutrophil infiltration is the characteristic pathological feature of M. pneumoniae pneumonia (MPP). This study aimed to explore the associations among neutrophil activity, clinical presentation, and role of the M. pneumoniae/interleukin-8 (IL-8)/neutrophil axis in the pathogenesis of MPP. A total of 42 patients with MPP were prospectively enrolled in the study. Neutrophil activity, including matrix metalloproteinase-9 (MMP-9), myeloperoxidase (MPO), and neutrophil elastase (NE), were measured. Clinical information was collected for all patients and control group. In vitro, IL-8 production was measured at different time points after M. pneumoniae infection of bronchial epithelial cells, and neutrophil activity was analyzed after IL-8 stimulation. The percentage of neutrophil in the bronchoalveolar lavage fluid was higher in the group of patients with high levels of M. pneumoniae DNA than in those with low levels of M. pneumoniae DNA (P < 0.05). IL-8, MMP-9, and NE in patients with MPP significantly increased compared with controls and decreased after treatment (P < 0.05). MPO and MMP-9 were associated with duration of fever (r = 0.332, P < 0.05) and length of stay (r = 0.342, P < 0.05), respectively. In vitro, M. pneumoniae induced IL-8 production by bronchial epithelial cells in a time dependent manner. MPO, MMP-9 and NE production by neutrophils significantly increased compared with medium controls after IL-8 stimulation. In summary, the M. pneumoniae/IL-8/neutrophil axis likely plays a vital role in the pathogenesis of MPP.     

Rational Design of Berberine-Based FtsZ Inhibitors with Broad-Spectrum Antibacterial Activity

Inhibition of the functional activity of Filamenting temperature-sensitive mutant Z (FtsZ) protein, an essential and highly conserved bacterial cytokinesis protein, is a promising approach for the development of a new class of antibacterial agents. Berberine, a benzylisoquinoline alkaloid widely used in traditional Chinese and native American medicines for its antimicrobial properties, has been recently reported to inhibit FtsZ. Using a combination of in silico structure-based design and in vitro biological assays, 9-phenoxyalkyl berberine derivatives were identified as potent FtsZ inhibitors. Compared to the parent compound berberine, the derivatives showed a significant enhancement of antibacterial activity against clinically relevant bacteria, and an improved potency against the GTPase activity and polymerization of FtsZ. The most potent compound 2 strongly inhibited the proliferation of Gram-positive bacteria, including methicillin-resistant S. aureus and vancomycin-resistant E. faecium, with MIC values between 2 and 4 µg/mL, and was active against the Gram-negative E. coli and K. pneumoniae, with MIC values of 32 and 64 µg/mL respectively. The compound perturbed the formation of cytokinetic Z-ring in E. coli. Also, the compound interfered with in vitro polymerization of S. aureus FtsZ. Taken together, the chemical modification of berberine with 9-phenoxyalkyl substituent groups greatly improved the antibacterial activity via targeting FtsZ.     

Preparative HPLC fraction of Hibiscus rosa-sinensis essential oil against biofilm forming Klebsiella pneumoniae

Recent years Klebsiella pneumoniae (K. pneumoniae) biofilm formation (BF) is emerging thread worldwide. For tackling this problem, we have chosen Hibiscus rosa-. pneumoniae. The HPLC purified essential oils (EOs sinensis (H. rosa-sinensis) (HRS) to inhibit the BF K) of H. rosa-sinensis was performed against BF K. pneumoniae and showed concentration dependent biofilm inhibition. At the MBIC of EOs (90 µg/ml), the biofilm inhibition was showed at 92% against selected BF K. Pneumoniae. The biofilm metabolic assay, exopolysaccharide quantification and hydrophobicity index variation results exhibited with 88%, 92% and 89% reduction at 90 μg/mL was observed respectively. In addition, the morphological modification of MBIC treated K. pneumoniae was clearly viewed by scanning electron microscope (SEM). Overall, all the invitro experiments result were confirmed that the MBIC of H. rosa-sinensis EOs was very effective against BF K. pneumonia.     

Antimicrobial Activity of Novel Synthetic Peptides Derived from Indolicidin and Ranalexin against Streptococcus pneumoniae

Antimicrobial peptides (AMPs) represent promising alternatives to conventional antibiotics in order to defeat multidrug-resistant bacteria such as Streptococcus pneumoniae. In this study, thirteen antimicrobial peptides were designed based on two natural peptides indolicidin and ranalexin. Our results revealed that four hybrid peptides RN7-IN10, RN7-IN9, RN7-IN8, and RN7-IN6 possess potent antibacterial activity against 30 pneumococcal clinical isolates (MIC 7.81-15.62µg/ml). These four hybrid peptides also showed broad spectrum antibacterial activity (7.81µg/ml) against S. aureus, methicillin resistant S. aureus (MRSA), and E. coli. Furthermore, the time killing assay results showed that the hybrid peptides were able to eliminate S. pneumoniae within less than one hour which is faster than the standard drugs erythromycin and ceftriaxone. The cytotoxic effects of peptides were tested against human erythrocytes, WRL-68 normal liver cell line, and NL-20 normal lung cell line. The results revealed that none of the thirteen peptides have cytotoxic or hemolytic effects at their MIC values. The in silico molecular docking study was carried out to investigate the binding properties of peptides with three pneumococcal virulent targets by Autodock Vina. RN7IN6 showed a strong affinity to target proteins; autolysin, pneumolysin, and pneumococcal surface protein A (PspA) based on rigid docking studies. Our results suggest that the hybrid peptides could be suitable candidates for antibacterial drug development.     

Sex differences in the impact of ozone on survival and alveolar macrophage function of mice after Klebsiella pneumoniae infection

Background

Sex differences have been described in a number of pulmonary diseases. However, the impact of ozone exposure followed by pneumonia infection on sex-related survival and macrophage function have not been reported. The purpose of this study was to determine whether ozone exposure differentially affects: 1) survival of male and female mice infected with Klebsiella pneumoniae, and 2) the phagocytic ability of macrophages from these mice.

Methods

Male and female C57BL/6 mice were exposed to O₃ or to filtered air (FA) (control) and then infected intratracheally with K. pneumoniae bacteria. Survival was monitored over a 14-day period, and the ability of alveolar macrophages to phagocytize the pathogen in vivo was investigated after 1 h.

Results

1) Both male and female mice exposed to O₃ are significantly more susceptible to K. pneumoniae infection than mice treated with FA; 2) although females appeared to be more resistant to K. pneumoniae than males, O₃ exposure significantly increased the susceptibility of females to K. pneumoniae infection to a greater degree than males; 3) alveolar macrophages from O₃-exposed male and female mice have impaired phagocytic ability compared to macrophages from FA-exposed mice; and 4) the O₃-dependent reduction in phagocytic ability is greater in female mice.

Conclusion

O₃ exposure reduces the ability of mice to survive K. pneumoniae infection and the reduced phagocytic ability of alveolar macrophages may be one of the contributing factors. Both events are significantly more pronounced in female mice following exposure to the environmental pollutant, ozone.     

A Technology for Developing Synbodies with Antibacterial Activity

The rise in antibiotic resistance has led to an increased research focus on discovery of new antibacterial candidates. While broad-spectrum antibiotics are widely pursued, there is evidence that resistance arises in part from the wide spread use of these antibiotics. Our group has developed a system to produce protein affinity agents, called synbodies, which have high affinity and specificity for their target. In this report, we describe the adaptation of this system to produce new antibacterial candidates towards a target bacterium. The system functions by screening target bacteria against an array of 10,000 random sequence peptides and, using a combination of membrane labeling and intracellular dyes, we identified peptides with target specific binding or killing functions. Binding and lytic peptides were identified in this manner and in vitro tests confirmed the activity of the lead peptides. A peptide with antibacterial activity was linked to a peptide specifically binding Staphylococcus aureus to create a synbody with increased antibacterial activity. Subsequent tests showed that this peptide could block S. aureus induced killing of HEK293 cells in a co-culture experiment. These results demonstrate the feasibility of using the synbody system to discover new antibacterial candidate agents.     

Antibacterial and antibiofilm efficacy of Ag NPs,Ni NPs and Al2O3 NPs singly and in combination against multidrug-resistant Klebsiella pneumoniae isolates

BackgroundAlthough traditional antibiotic therapy provided an effective approach to combat pathogenic bacteria, the long-term and widespread use of antibiotic results in the evolution of multidrug-resistant bacteria. Recent progress in nanotechnology offers an alternative opportunity to discover and develop novel antibacterial agents.MethodsA total of 51 K. pneumoniae strains were collected from several specimens of hospitalized patients and identified by two parallel methods (biochemical tests and Vitek-2 system). The antibiotic sensitivity of isolates was evaluated by disk diffusion antibiogram and Vitek-2 system. The biofilms formation ability of antibiotic-resistant strains was examined by microtiter plate and tube methods based on crystal violet staining. The molecular technique was used to determine key genes responsible for biofilms formation of clinical isolates. The antibacterial and antibiofilm activities of Ag NPs, Ni NPs, Al₂O₃ NPs singly (NPs) and in combination (cNPs) were investigated against selected strains using standard methods. Moreover, the cytotoxicity of NPs was evaluated on mouse neural crest-derived (Neuro-2A) cell line.ResultsThe results of bacterial studies revealed that more than 80 % of the isolates were resistant to commonly used antibiotics and about 95 % of them were able to form biofilms. Moreover, the presence of fimA and mrkA genes were determined in all biofilm-producing strains. The results of antibacterial and antibiofilm activities of NPs and cNPs demonstrated the lower MIC and MBEC values for Al₂O₃ NPs singly as well as for Ag/Ni cNPs and Ag/Al₂O₃ cNPs in combination, respectively. Overall, the inhibitory effects of cNPs were superior to NPs against all strains. Furthermore, the results of the checkerboard assays showed that Ag NPs act synergistically with two other NPs against multidrug-resistant Klebsiella pneumoniae (MDR-K. pneumoniae) isolates. The in vitro cytotoxicity assay revealed no significant toxicity of NPs against Neuro-2A cells.ConclusionIn the present study, the combination of Ag NPs, Ni NPs, and Al₂O₃ NPs were used against MDR-K. pneumoniae strains and antibacterial and antibiofilm activities were observed for Ag/Ni cNPs and Ag/Al₂O₃ cNPs.     

N-terminal phosphorylation of HP1α increases its nucleosome-binding specificity

Heterochromatin protein 1 (HP1) is an evolutionarily conserved chromosomal protein that binds to lysine 9-methylated histone H3 (H3K9me), a hallmark of heterochromatin. Although HP1 phosphorylation has been described in several organisms, the biological implications of this modification remain largely elusive. Here we show that HP1''s phosphorylation has a critical effect on its nucleosome binding properties. By in vitro phosphorylation assays and conventional chromatography, we demonstrated that casein kinase II (CK2) is the kinase primarily responsible for phosphorylating the N-terminus of human HP1α. Pull-down assays using in vitro-reconstituted nucleosomes showed that unmodified HP1α bound H3K9-methylated and H3K9-unmethylated nucleosomes with comparable affinity, whereas CK2-phosphorylated HP1α showed a high specificity for H3K9me3-modified nucleosomes. Electrophoretic mobility shift assays showed that CK2-mediated phosphorylation diminished HP1α''s intrinsic DNA binding, which contributed to its H3K9me-independent nucleosome binding. CK2-mediated phosphorylation had a similar effect on the nucleosome-binding specificity of fly HP1a and S. pombe Swi6. These results suggested that HP1 phosphorylation has an evolutionarily conserved role in HP1''s recognition of H3K9me-marked nucleosomes.     

Complement mediated Klebsiella pneumoniae capsule changes

The Gram-negative bacterium Klebsiella pneumoniae is an opportunistic pathogen, which can cause life-threatening infections such as sepsis. Worldwide, emerging multidrug resistant K. pneumoniae infections are challenging to treat, hence leading to increased mortality. Therefore, understanding the interactions between K. pneumoniae and the immune system is important to develop new treatment options.We characterized ten clinical K. pneumoniae isolates obtained from blood of bacteremia patients. The interaction of the isolates with human serum was investigated to elucidate how K. pneumoniae escapes the host immune system, and how complement activation by K. pneumoniae changed the capsule structure. All K. pneumoniae isolates activated the alternative complement pathway despite serum resistance of seven isolates. One serum sensitive isolate activated two or all three pathways, and this isolate was lysed and had numerous membrane attack complexes in the outer membrane. However, we also found deposition of complement components in the capsule of serum resistant isolates resulting in morphological capsule changes and capsule shedding. These bacteria did not lyse, and no membrane attack complex was observed despite deposition of C5b-9 within the capsule, indicating that the capsule of serum resistant K. pneumoniae isolates is a defense mechanism against complement-mediated lysis.