The importance of pneumococcal capsule in inate immunity and biofilm formation

Chapter 1 gives an overview about Streptococcus pneumoniae, its role as a human pathogen and its virulence factors. Additionally, biofilm development and its relevance in clinics are introduced, and the innate immune response to pneumococcus as well as bacterial-viral interactions in the upper respiratory tract are also discussed. Chapter 2 emphasizes the three main topics of this thesis: the role of capsule and pneumolysin in the immune response in the respiratory tract, biofilm formation of S. pneumoniae serotypes and commensal streptococci in vitro, and host innate immune responses to RSV and S. pneumoniae during in vitro co-infections. Aims and hypotheses are provided here. Chapter 3 is divided into two parts: First, the release of the pro-inflammatory cytokines CXCL8 and IL-6 from the human pharyngeal epithelial cell line Detroit 562 and from human bronchial epithelial cells (iHBEC) is described in response to S. pneumoniae. Capsule was shown to suppress the release of both cytokines in both cell lines tested, but release was much less from iHBEC cells. During intranasal colonization of mice, suppression of CXCL8 release by the capsule was also observed in vivo, but the effect was only measured in the absence of pneumolysin. Long term, stable nasopharyngeal carriage in a mouse model resulted in the dissemination of nonencapsulated pneumococci into the lungs, whereas encapsulated strains remained in the nasopharynx. The S. pneumoniae capsule thus plays a role in modulation of the pro-inflammatory immune response in the respiratory tract. Second, results on immunological cells and immune regulation in a long term, stable nasopharyngeal carriage mouse model are presented. Mice were infected with encapsulated or nonencapsulated pneumococcal strains, and after 1, 3, 8 and 15 days, were sacrificed to evaluate the numbers of CD45+ cells, neutrophils, macrophages, FoxP3+ regulatory T-cells and CD3+ T-cells in the nasal mucosa as well as the amount of secreted IL-10 in the nasopharynx. Nasopharyngeal colonization which is effectively silent resulted in the stimulation of FoxP3+ regulatory T-cells and IL-10 release associated with immune homeostasis, whereas lung infiltration was required to increase the number of neutrophils and macrophages resulting in a stronger innate immune response in the nasal mucosa. Chapter 4 contains results of mono- and co-stimulation using RSV and pneumococci or pneumococcal virulence factors on the human bronchial epithelial cell line BEAS-2B. An increase in CXCL8 and IL-6 levels was measured for mixed stimulations of RSV and pneumococcus when encapsulated bacteria were used. Increasing pneumolysin concentrations resulted in enhanced CXCL8 levels. Priming of bronchial epithelial cells with RSV opens the door for more severe pneumococcal infections. Chapter 5 is composed of two parts: The first part describes initial biofilm formation of serotypes 6B and 7F in a static model in vitro. Biofilms of both serotypes contained SCVs, but only serotype 6B increased in SCV formation between 16 and 65h of incubation. SCV stability was tested by passaging clones in complex medium, where SCV production is not associated with advantages in growth. Serotype 6B lost the SCV phenotype indicating a fast adaptation to a changing nutritional environment. Limitations of our in vitro model are discussed. The second part is about initial biofilm formation of mixed culture growth of S. pneumoniae with commensal streptococci. Competition dominates this process. S. oralis and pneumococcus compete for nutrients, whereas mixed species growth of S. mitis or S. pseudopneumoniae with S. pneumoniae is mainly influenced by other factors. In Chapter 6 the findings of chapters 3, 4 and 5 are discussed and an outlook for further studies is provided. Chapters 7, 8, 9, 10 and 11 contain the references, the acknowledgements, the curriculum vitae, the appendix and the declaration of originality.

Automated counting of bacterial colony forming units on agar plates.

Manual counting of bacterial colony forming units (CFUs) on agar plates is laborious and error-prone. We therefore implemented a colony counting system with a novel segmentation algorithm to discriminate bacterial colonies from blood and other agar plates.A colony counter hardware was designed and a novel segmentation algorithm was written in MATLAB. In brief, pre-processing with Top-Hat-filtering to obtain a uniform background was followed by the segmentation step, during which the colony images were extracted from the blood agar and individual colonies were separated. A Bayes classifier was then applied to count the final number of bacterial colonies as some of the colonies could still be concatenated to form larger groups. To assess accuracy and performance of the colony counter, we tested automated colony counting of different agar plates with known CFU numbers of S. pneumoniae, P. aeruginosa and M. catarrhalis and showed excellent performance.

Cloning and characterization of an Actinobacillus pleuropneumoniae outer membrane protein belonging to the family of PAL lipoproteins

A 14-kDa outer membrane protein (OMP) was purified from Actinobacillus pleuro-pneumoniae serotype 2. The protein strongly reacts with sera from pigs experimentally or naturally infected with any of the 12 serotypes of A. pleuropneumoniae. The gene encoding this protein was isolated from a gene library of A. pleuropneumoniae serotype 2 reference strain by immunoscreening. Expression of the cloned gene in Escherichia coli revealed that the protein is also located in the outer membrane fraction of the recombinant host. DNA sequence analysis of the gene reveals high similarity of the protein's amino acid sequence to that of the E. coli peptidoglycan-associated lipoprotein PAL, to the Haemophilus influenzae OMP P6 and to related proteins of several other Gram-negative bacteria. We have therefore named the 14-kDa protein PalA, and its corresponding gene, palA. The 20 amino-terminal amino acid residues of PalA constitute a signal sequence characteristic of membrane lipoproteins of prokaryotes with a recognition site for the signal sequence peptidase II and a sorting signal for the final localization of the mature protein in the outer membrane. The DNA sequence upstream of palA contains an open reading frame which is highly similar to the E. coli tolB gene, indicating a gene cluster in A. pleuropneumoniae which is very similar to the E. coli tol locus. The palA gene is conserved and expressed in all A. pleuropneumoniae serotypes and in A. lignieresii. A very similar palA gene is present in A. suis and A. equuli.

Ca2+-dependent repair of pneumolysin pores: A new paradigm for host cellular defense against bacterial pore-forming toxins

Pneumolysin (PLY), a key virulence factor of Streptococcus pneumoniae, permeabilizes eukaryotic cells by forming large trans-membrane pores. PLY imposes a puzzling multitude of diverse, often mutually excluding actions on eukaryotic cells. Whereas cytotoxicity of PLY can be directly attributed to the pore-mediated effects, mechanisms that are responsible for the PLY-induced activation of host cells are poorly understood. We show that PLY pores can be repaired and thereby PLY-induced cell death can be prevented. Pore-induced Ca2+ entry from the extracellular milieu is of paramount importance for the initiation of plasmalemmal repair. Nevertheless, active Ca2+ sequestration that prevents excessive Ca2+ elevation during the execution phase of plasmalemmal repair is of no less importance. The efficacy of plasmalemmal repair does not only define the fate of targeted cells but also intensity, duration and repetitiveness of PLY-induced Ca2+ signals in cells that were able to survive after PLY attack. Intracellular Ca2+ dynamics evoked by the combined action of pore formation and their elimination mimic the pattern of receptor-mediated Ca2+ signaling, which is responsible for the activation of host immune responses. Therefore, we postulate that plasmalemmal repair of PLY pores might provoke cellular responses that are similar to those currently ascribed to the receptor-mediated PLY effects. Our data provide new insights into the understanding of the complexity of cellular non-immune defense responses to a major pneumococcal toxin that plays a critical role in the establishment and the progression of life-threatening diseases. Therapies boosting plasmalemmal repair of host cells and their metabolic fitness might prove beneficial for the treatment of pneumococcal infections.

Engineered liposomes sequester bacterial exotoxins and protect from severe invasive infections in mice

Gram-positive bacterial pathogens that secrete cytotoxic pore-forming toxins, such as Staphylococcus aureus and Streptococcus pneumoniae, cause a substantial burden of disease. Inspired by the principles that govern natural toxin-host interactions, we have engineered artificial liposomes that are tailored to effectively compete with host cells for toxin binding. Liposome-bound toxins are unable to lyse mammalian cells in vitro. We use these artificial liposomes as decoy targets to sequester bacterial toxins that are produced during active infection in vivo. Administration of artificial liposomes within 10 h after infection rescues mice from septicemia caused by S. aureus and S. pneumoniae, whereas untreated mice die within 24-33 h. Furthermore, liposomes protect mice against invasive pneumococcal pneumonia. Composed exclusively of naturally occurring lipids, tailored liposomes are not bactericidal and could be used therapeutically either alone or in conjunction with antibiotics to combat bacterial infections and to minimize toxin-induced tissue damage that occurs during bacterial clearance

The mood-stabilizer lithium prevents hippocampal apoptosis and improves spatial memory in experimental meningitis.

Pneumococcal meningitis is associated with high morbidity and mortality rates. Brain damage caused by this disease is characterized by apoptosis in the hippocampal dentate gyrus, a morphological correlate of learning deficits in experimental paradigms. The mood stabilizer lithium has previously been found to attenuate brain damage in ischemic and inflammatory diseases of the brain. An infant rat model of pneumococcal meningitis was used to investigate the neuroprotective and neuroregenerative potential of lithium. To assess an effect on the acute disease, LiCl was administered starting five days prior to intracisternal infection with live Streptococcus pneumoniae. Clinical parameters were recorded, cerebrospinal fluid (CSF) was sampled, and the animals were sacrificed 42 hours after infection to harvest the brain and serum. Cryosections of the brains were stained for Nissl substance to quantify brain injury. Hippocampal gene expression of Bcl-2, Bax, p53, and BDNF was analyzed. Lithium concentrations were measured in serum and CSF. The effect of chronic lithium treatment on spatial memory function and cell survival in the dentate gyrus was evaluated in a Morris water maze and by quantification of BrdU incorporation after LiCl treatment during 3 weeks following infection. In the hippocampus, LiCl significantly reduced apoptosis and gene expression of Bax and p53 while it increased expression of Bcl-2. IL-10, MCP-1, and TNF were significantly increased in animals treated with LiCl compared to NaCl. Chronic LiCl treatment improved spatial memory in infected animals. The mood stabilizer lithium may thus be a therapeutic alternative to attenuate neurofunctional deficits as a result of pneumococcal meningitis.

Designer aminoglycosides prevent cochlear hair cell loss and hearing loss.

Bacterial infections represent a rapidly growing challenge to human health. Aminoglycosides are widely used broad-spectrum antibiotics, but they inflict permanent hearing loss in up to ~50% of patients by causing selective sensory hair cell loss. Here, we hypothesized that reducing aminoglycoside entry into hair cells via mechanotransducer channels would reduce ototoxicity, and therefore we synthesized 9 aminoglycosides with modifications based on biophysical properties of the hair cell mechanotransducer channel and interactions between aminoglycosides and the bacterial ribosome. Compared with the parent aminoglycoside sisomicin, all 9 derivatives displayed no or reduced ototoxicity, with the lead compound N1MS 17 times less ototoxic and with reduced penetration of hair cell mechanotransducer channels in rat cochlear cultures. Both N1MS and sisomicin suppressed growth of E. coli and K. pneumoniae, with N1MS exhibiting superior activity against extended spectrum β lactamase producers, despite diminished activity against P. aeruginosa and S. aureus. Moreover, systemic sisomicin treatment of mice resulted in 75% to 85% hair cell loss and profound hearing loss, whereas N1MS treatment preserved both hair cells and hearing. Finally, in mice with E. coli-infected bladders, systemic N1MS treatment eliminated bacteria from urinary tract tissues and serially collected urine samples, without compromising auditory and kidney functions. Together, our findings establish N1MS as a nonototoxic aminoglycoside and support targeted modification as a promising approach to generating nonototoxic antibiotics.

The antidepressant fluoxetine protects the hippocampus from brain damage in experimental pneumococcal meningitis.

BACKGROUND High mortality and morbidity rates are observed in patients with bacterial meningitis (BM) and urge for new adjuvant treatments in addition to standard antibiotic therapies. In BM the hippocampal dentate gyrus is injured by apoptosis while in cortical areas ischemic necrosis occurs. Experimental therapies aimed at reducing the inflammatory response and brain damage have successfully been evaluated in animal models of BM. Fluoxetine (FLX) is an anti-depressant of the selective serotonin reuptake inhibitors (SSRI) and was previously shown to be neuroprotective in vitro and in vivo. We therefore assessed the neuroprotective effect of FLX in experimental pneumococcal meningitis. METHODS Infant rats were infected intracisternally with live Streptococcus pneumoniae. Intraperitoneal treatment with FLX (10mgkg(-1)d(-1)) or an equal volume of NaCl was initiated 15min later. 18, 27, and 42h after infection, the animals were clinically (weight, clinical score, mortality) evaluated and subject to a cisternal puncture and inflammatory parameters (i.e., cyto-/chemokines, myeloperoxidase activity, matrix metalloproteinase concentrations) were measured in cerebrospinal fluid (CSF) samples. At 42h after infection, animals were sacrificed and the brains collected for histomorphometrical analysis of brain damage. RESULTS A significant lower number of animals treated with FLX showed relevant hippocampal apoptosis when compared to littermates (9/19 animals vs 18/23, P=0.038). A trend for less damage in cortical areas was observed in FLX-treated animals compared to controls (13/19 vs 13/23, P=ns). Clinical and inflammatory parameters were not affected by FLX treatment. CONCLUSION A significant neuroprotective effect of FLX on the hippocampus was observed in acute pneumococcal meningitis in infant rats.

The matrix metalloproteinase inhibitor RS-130830 attenuates brain injury in experimental pneumococcal meningitis.

BACKGROUND Pneumococcal meningitis (PM) is characterized by high mortality and morbidity including long-term neurofunctional deficits. Neuropathological correlates of these sequelae are apoptosis in the hippocampal dentate gyrus and necrosis in the cortex. Matrix metalloproteinases (MMPs) play a critical role in the pathophysiology of PM. RS-130830 (Ro-1130830, CTS-1027) is a potent partially selective inhibitor of MMPs of a second generation and has been evaluated in clinical trials as an anti-arthritis drug. It inhibits MMPs involved in acute inflammation but has low activity against MMP-1 (interstitial collagenase), MMP-7 (matrilysin) and tumour necrosis factor α converting enzyme (TACE). METHODS A well-established infant rat model of PM was used where live Streptococcus pneumoniae were injected intracisternally and antibiotic treatment with ceftriaxone was initiated 18 h post infection (hpi). Treatment with RS-130830 (75 mg/kg bis in die (bid) i.p., n = 40) was started at 3 hpi while control littermates received the vehicle (succinylated gelatine, n = 42). RESULTS Cortical necrosis was significantly attenuated in animals treated with RS-130830, while the extent of hippocampal apoptosis was not influenced. At 18 hpi, concentrations of interleukin (IL)-1β and IL-10 were significantly lower in the cerebrospinal fluid of treated animals compared to controls. RS-130830 significantly reduced weight loss and leukocyte counts in the cerebrospinal fluid of survivors of PM. CONCLUSION This study identifies MMP inhibition, specifically with RS-130830, as an efficient strategy to attenuate disease severity and cortical brain injury in PM.

Patients with community acquired pneumonia admitted to European intensive care units: an epidemiological survey of the GenOSept cohort.

INTRODUCTION Community acquired pneumonia (CAP) is the most common infectious reason for admission to the Intensive Care Unit (ICU). The GenOSept study was designed to determine genetic influences on sepsis outcome. Phenotypic data was recorded using a robust clinical database allowing a contemporary analysis of the clinical characteristics, microbiology, outcomes and independent risk factors in patients with severe CAP admitted to ICUs across Europe. METHODS Kaplan-Meier analysis was used to determine mortality rates. A Cox Proportional Hazards (PH) model was used to identify variables independently associated with 28-day and six-month mortality. RESULTS Data from 1166 patients admitted to 102 centres across 17 countries was extracted. Median age was 64 years, 62% were male. Mortality rate at 28 days was 17%, rising to 27% at six months. Streptococcus pneumoniae was the commonest organism isolated (28% of cases) with no organism identified in 36%. Independent risk factors associated with an increased risk of death at six months included APACHE II score (hazard ratio, HR, 1.03; confidence interval, CI, 1.01-1.05), bilateral pulmonary infiltrates (HR1.44; CI 1.11-1.87) and ventilator support (HR 3.04; CI 1.64-5.62). Haematocrit, pH and urine volume on day one were all associated with a worse outcome. CONCLUSIONS The mortality rate in patients with severe CAP admitted to European ICUs was 27% at six months. Streptococcus pneumoniae was the commonest organism isolated. In many cases the infecting organism was not identified. Ventilator support, the presence of diffuse pulmonary infiltrates, lower haematocrit, urine volume and pH on admission were independent predictors of a worse outcome.

Colonization with resistant microorganisms in patients transferred from abroad: who needs to be screened?

BACKGROUND While multi-drug resistant organisms (MDRO) are a global phenomenon, there are significant regional differences in terms of prevalence. Traveling to countries with a high MDRO prevalence increases the risk of acquiring such an organism. In this study we determined risk factors for MDRO colonization among patients who returned from a healthcare system in a high-prevalence area (so-called transfer patients). Factors predicting colonization could serve as screening criteria to better target those at highest risk. METHODS This screening study included adult patients who had been exposed to a healthcare system abroad or in a high-prevalence region in Switzerland over the past six months and presented to our 950-bed tertiary care hospital between January 1, 2012 and December 31, 2013, a 24-month period. Laboratory screening tests focused on Gram-negative MDROs and methicillin-resistant Staphylococcus aureus (MRSA). RESULTS A total of 235 transfer patients were screened and analyzed, of which 43 (18 %) were positive for an MDRO. Most of them yielded Gram-negative bacteria (42; 98 %), with only a single screening revealing MRSA (2 %); three screenings showed a combination of Gram-negative bacteria and MRSA. For the risk factor analysis we focused on the 42 Gram-negative MDROs. Most of them were ESBL-producing Escherichia coli and Klebsiella pneumoniae while only two were carbapenemase producers. In univariate analysis, factors associated with screening positivity were hospitalization outside of Europe (p < 0.001), surgical procedure in a hospital abroad (p = 0.007), and - on admission to our hospital - active infection (p = 0.002), antibiotic treatment (p = 0.014) and presence of skin lesions (p = 0.001). Only hospitalization outside of Europe (Odds Ratio, OR 3.2 (95 % CI 1.5- 6.8)) and active infection on admission (OR 2.7 (95 % CI 1.07- 6.6)) remained as independent predictors of Gram-negative MDRO colonization. CONCLUSION Our data suggest that a large proportion of patients (i.e., 82 %) transferred to Switzerland from hospitals in high MDRO prevalence areas are unnecessarily screened for MDRO colonization. Basing our screening strategy on certain criteria (such as presence of skin lesions, active infection, antibiotic treatment, history of a surgical procedure abroad and hospitalization outside of Europe) promises to be a better targeted and more cost-effective strategy.

Synthesis, spectral, and anti-microbial studies of thioiminium iodides and amine hydrochlorides

To avoid the undesired deprotonation during the addition of organolithium and organomagnesium reagents to ketones, the thioiminium salts, easily prepared from lactams and amides are converted into 2,2-disubstituted and 2-monosubstituted amines by reaction with simple nucleophiles such as organocerium and organocopper reagents. The reaction of thioiminium iodides with organocerium reagents derived by transmetalation of corresponding lithium reagents with anhydrous cerium(III) chloride has been investigated. These thioiminium iodides act as good electrophiles and accept alkylceriums towards bisaddition. The newly synthesized amines have been characterized by 1H and 13C NMR, IR and mass spectra. The amines have been converted into their hydrochlorides and characterized by COSY. These hydrochlorides have been subjected to antimicrobial screening with clinically isolated microorganisms, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi and Candida albicans. The hydrochlorides show quite good activity against these bacteria and fungus.

Cigarette Smoke Exposure Increases Myeloid Cell Production and Lung Bacterial Clearance in Mice

Pneumonia is a leading cause of hospitalization in patients with chronic obstructive pulmonary disease (COPD). Although most COPD patients are smokers, the effects of cigarette smoke exposure on clearance of lung bacterial pathogens and on immune and inflammatory responses are incompletely defined. Here, clearance of Streptococcus pneumoniae and Pseudomonas aeruginosa and associated immune responses were examined in mice exposed to cigarette smoke or following smoking cessation. Mice exposed to cigarette smoke for 6 weeks or 4 months demonstrated decreased lung bacterial burden compared to air-exposed mice when infected 16-24 hours post-exposure. When infection was performed after smoke cessation, bacterial clearance kinetics of mice previously exposed to smoke reversed to comparable levels as those of control mice suggesting that the observed defects were not dependent on adaptive immunological memory to bacterial determinants found in smoke. Comparing cytokine levels and myeloid cell production prior to infection in mice exposed to cigarette smoke relative to mice never exposed or following smoke cessation revealed that reduced bacterial burden was most strongly associated with higher levels of IL-1β and GM-CSF in the lungs and with increased neutrophil reserve and monocyte turnover in the bone marrow. Using serpinb1a-deficient mice with reduced neutrophil numbers and treatment with G-CSF showed that increased neutrophil numbers contribute only in part to the effect of smoke on infection. Our findings indicate that cigarette smoke induces a temporary and reversible increase in clearance of lung pathogens, which correlates with local inflammation and increased myeloid cell output from the bone marrow.

High quality draft genomes of the Mycoplasma mycoides subsp. mycoides challenge strains Afadé and B237.

Members of the Mycoplasma mycoides cluster' represent important livestock pathogens worldwide. Mycoplasma mycoides subsp. mycoides is the etiologic agent of contagious bovine pleuropneumonia (CBPP), which is still endemic in many parts of Africa. We report the genome sequences and annotation of two frequently used challenge strains of Mycoplasma mycoides subsp. mycoides, Afadé and B237. The information provided will enable downstream 'omics' applications such as proteomics, transcriptomics and reverse vaccinology approaches. Despite the absence of Mycoplasma pneumoniae like cyto-adhesion encoding genes, the two strains showed the presence of protrusions. This phenotype is likely encoded by another set of genes.

Mycoplasma-induced minimally conscious state

Mycoplasma pneumoniae (M. pneumoniae) frequently causes community-acquired respiratory tract infection and often presents as atypical pneumonia. Following airborne infection and a long incubation period, affected patients mostly suffer from mild or even asymptomatic and self-limiting disease. In particular in school-aged children, M. pneumoniae is associated with a wide range of extrapulmonary manifestations including central nervous system (CNS) disease. In contrast to children, severe CNS manifestations are rarely observed in adults. We report a case of a 37 year-old previously healthy immunocompetent adult with fulminant M. pneumoniae-induced progressive encephalomyelitis who was initially able to walk to the emergency department. A few hours later, she required controlled mechanical ventilation for ascending transverse spinal cord syndrome, including complete lower extremity paraplegia. Severe M. pneumoniae-induced encephalomyelitis was postulated, and antimicrobial, anti-inflammatory and immunosuppressive therapy was applied on the intensive care unit. Despite early and targeted therapy using four different immunosuppressive strategies, clinical success was limited. In our patient, locked-in syndrome developed followed by persistent minimally conscious state. The neurological status was unchanged until day 230 of follow-up. Our case underlines that severe M. pneumoniae- related encephalomyelitis must not only be considered in children, but also in adults. Moreover, it can be fulminant and fatal in adults. Our case enhances the debate for an optimal antimicrobial agent with activity beyond the blood-brain barrier. Furthermore, it may underline the difficulty in clinical decision making regarding early antimicrobial treatment in M. pneumoniae disease, which is commonly self-limited.