Roles of autolysin and pneumolysin in middle ear inflammation caused by a type 3 Streptococcus pneumoniae strain in the chinchilla otitis media model

Preclinical in vitro and in vivo profile of a highly-attenuated, broadly efficacious pneumolysin genetic toxoid

Pneumolysin is a highly conserved, cholesterol-dependent cytolysin that is an important Streptococcus pneumoniae virulence factor and an attractive target for vaccine development. To attenuate pneumolysin toxicity, a genetic toxoid was constructed with two amino acid changes, G293S and L460D, termed PLY-D, that reduced cytolytic activity > 125,000-fold. In mice, PLY-D elicited high anti-PLY IgG antibody titers that neutralized the cytolytic activity of the wild-type toxin in vitro. To evaluate the protective efficacy of PLY-D, mice were immunized intramuscularly and then challenged intranasally with a lethal dose of 28 clinical isolates of S. pneumoniae originating from different geographical locations, disease states (i.e. bacteremia, pneumonia), or body sites (i.e. sputum, blood). PLY-D immunization conferred significant protection from challenge with 17 of 20 serotypes (85%) and 22 of 28 strains (79%). Further, we demonstrated that immunization with PLY-D provided statistically significant improvement in survival against challenge with serotype 4 and 18C strains compared to mice immunized with a pneumococcal conjugate vaccine Prevnar 13® (PCV13). Co-administration of PLY-D and PCV13 conferred greater protection against challenge with a serotype 6B strain than immunization with either vaccine alone. These data indicate that PLY-D is a broadly protective antigen with the potential to serve as a serotype-independent vaccine against invasive pneumococcal disease either alone or in combination with PCVs.

Anatomical site-specific contributions of pneumococcal virulence determinants

Streptococcus pneumoniae is an opportunistic pathogen globally associated with significant morbidity and mortality. It is capable of causing a wide range of diseases including sinusitis, conjunctivitis, otitis media, pneumonia, bacteraemia, sepsis, and meningitis. While its capsular polysaccharide is indispensible for invasive disease, and opsonising antibodies against the capsule are the basis for the current vaccines, a long history of biomedical research indicates that other components of this Gram-positive bacterium are also critical for virulence. Herein we review the contribution of pneumococcal virulence determinants to survival and persistence in the context of distinct anatomical sites. We discuss how these determinants allow the pneumococcus to evade mucociliary clearance during colonisation, establish lower respiratory tract infection, resist complement deposition and opsonophagocytosis in the bloodstream, and invade secondary tissues such as the central nervous system leading to meningitis. We do so in a manner that highlights both the critical role of the capsular polysaccharide and the accompanying and necessary protein determinants. Understanding the complex interplay between host and pathogen is necessary to find new ways to prevent pneumococcal infection. This review is an attempt to do so with consideration for the latest research findings.

Surface Proteins and Pneumolysin of Encapsulated and Nonencapsulated Streptococcus pneumoniae Mediate Virulence in a Chinchilla Model of Otitis Media

Streptococcus pneumoniae infections result in a range of human diseases and are responsible for almost one million deaths annually. Pneumococcal disease is mediated in part through surface structures and an anti-phagocytic capsule. Recent studies have shown that nonencapsulated S. pneumoniae (NESp) make up a significant portion of the pneumococcal population and are able to cause disease. NESp lack some common surface proteins expressed by encapsulated pneumococci, but express surface proteins unique to NESp. A chinchilla model of otitis media (OM) was used to determine the effect various pneumococcal mutations have on pathogenesis in both NESp and encapsulated pneumococci. Epithelial cell adhesion and invasion assays were used to examine the effects in relation to deletion of intrinsic genes or expression of novel genes. A mouse model of colonization was also utilized for comparison of various pneumococcal mutants. It was determined that pneumococcal surface protein K (PspK) and pneumolysin (Ply) affect NESp middle ear pathogenesis, but only PspK affected epithelial cell adhesion. Experiments in an OM model were done with encapsulated strains testing the importance of native virulence factors and treatment of OM. First, a triple deletion of the common virulence factors PspA, PspC, and Ply, (ΔPAC), from an encapsulated background abolished virulence in an OM model while a PspC mutant had detectable, but reduced amounts of recoverable bacteria compared to wildtype. Next, treatment of OM was effective when starting antibiotic treatment within 24 h with resolution by 48 h post-treatment. Expression of NESp-specific virulence factor PspK in an encapsulated strain has not been previously studied, and we showed significantly increased adhesion and invasion of human epithelial cells by pneumococci. Murine colonization was not significantly increased when an encapsulated strain expressed PspK, but colonization was increased when a capsule mutant expressed PspK. The ability of PspK expression to increase colonization in a capsule mutant despite no increase in adhesion can be attributed to other functions of PspK, such as sIgA binding or immune modulation. OM is a substantial economic burden, thus a better understanding of both encapsulated pneumococcal pathogenesis and the emerging pathogen NESp is necessary for effective prevention and treatment.

The pneumococcus: epidemiology, microbiology, and pathogenesis

The pneumococcus is the classic Gram-positive extracellular pathogen. The medical burden of diseases it causes is amongst the greatest in the world. Intense study for more than 100 years has yielded an understanding of fundamental aspects of its physiology, pathogenesis, and immunity. Efforts to control infection have led to the deployment of polysaccharide vaccines and an understanding of antibiotic resistance. The inflammatory response to pneumococci, one of the most potent in medicine, has revealed the double-edged sword of clearance of infection but at a cost of damage to host cells. In virtually every aspect of the infectious process, the pneumococcus has set the rules of the Gram-positive pathogenesis game.

Interaction of phase variation, host and pressure/gas composition: pneumococcal gene expression of PsaA, SpxB, Ply and LytA in simulated middle ear environments

OBJECTIVE

Streptococcus pneumoniae, a leading cause of otitis media (OM), undergoes spontaneous intra-strain variations in colony morphology. Transparent (T) variants are more efficient in colonizing the nasopharynx while opaque (O) variants exhibit greater virulence during systemic infections. This study was intended to delineate the underlying molecular mechanisms by which the predominant S. pneumoniae variant efficiently infects the middle ear (ME) mucosa.

METHODS

Human ME epithelial cells were preconditioned for 24h under one of the three gas/pressure conditions designed to simulate those for (1) normal ME (NME), (2) ME with Eustachian tube obstruction (ETO) and (3) ME with tympanostomy tube placement (TT), and then were incubated with ∼ 10(7)CFU/ml of either T or O variants of S. pneumoniae (6A) for 3h. Relative expression levels of genes encoding virulence factors, PsaA (surface adhesion), SpxB (pyruvate oxidase), Ply (pneumolysin), and LytA (autolysin) were assessed separately in epithelium-attached and supernatant bacteria 3h post infection using real-time PCR.

RESULTS

Basal levels of the virulence molecules in inocula were comparable between two variants. However, relative expression levels of the gene transcripts were significantly induced in epithelium-attached T variants 3h after infection. Comparing with NME and TT conditions, ETO environment produced the largest effect on the differential expression of the virulence genes in the infected ME epithelial cells between T (induced) and O (suppressed) phenotypic pneumococci.

CONCLUSIONS

T variant is a predominant phenotype responsible for the pathogenesis of pneumococcal OM.

Chinchilla as a robust, reproducible and polymicrobial model of otitis media and its prevention

There is compelling evidence that many infectious diseases of humans are caused by more than one microorganism. Multiple diverse in vitro systems have been used to study these complex diseases, and although the data generated have contributed greatly to our understanding of diseases of mixed microbial etiology, having rigorous, reproducible and relevant animal models of human diseases are essential for the development of novel methods to treat or prevent them. All animal models have inherent limitations; however, they also have important advantages over in vitro methods, including the presence of organized organ systems and an intact immune system, which promote our ability to characterize the pathogenesis of, and the immune response to, sequential or coinfecting microorganisms. For the highly prevalent pediatric disease otitis media, or middle-ear infection, the chinchilla (Chinchilla lanigera) has served as a gold-standard rodent host system in which to study this multifactorial and polymicrobial disease.

Role of pneumococcal proteins in sensorineural hearing loss due to otitis media

HYPOTHESIS

Two Streptococcus pneumoniae proteins, pneumococcal surface protein A (PspA) and pneumolysin (Ply), have functional and histopathologic effects on the inner ear.

BACKGROUND

Temporary or permanent sensorineural hearing loss is known to be a sequela of pneumococcal otitis media. Several pneumococcal proteins such as PspA and Ply have been shown to contribute to the pathogenesis of the middle ear; however, effects of these proteins on the inner ear and hearing loss are unknown.

METHODS

Middle ears of chinchillas were inoculated with either wild-type S. pneumoniae or its mutants, deficient in PspA or Ply proteins. After 28 days, auditory brainstem response of animals was tested, and their bullae were processed for histopathologic analysis by light microscopy.

RESULTS

Twenty-eight days after instillation of 20 colony-forming units of wild-type pneumococci, auditory brainstem response test showed threshold changes of 10 to 15 dB for 4 to 32 kHz and more than 20 dB for 1 to 2 kHz. No significant hearing loss was observed after instillation of the same or even higher doses of isogenic S. pneumoniae mutants of PspA or Ply proteins, or saline injection, after the same period. Histologic analysis showed no fluid, inflammatory cells, or bacteria in the middle ear, indicating that hearing loss was sensorineural. Inner ear morphology showed pathologic changes in the stria vascularis, suggesting it as the target of otitis media-induced damage, which may lead to sensorineural hearing loss.

CONCLUSION

The virulence PspA and Ply proteins of S. pneumoniae affect the inner ear and auditory function.

Animal models of Streptococcus pneumoniae disease

SUMMARY

Streptococcus pneumoniae is a colonizer of human nasopharynx, but it is also an important pathogen responsible for high morbidity, high mortality, numerous disabilities, and high health costs throughout the world. Major diseases caused by S. pneumoniae are otitis media, pneumonia, sepsis, and meningitis. Despite the availability of antibiotics and vaccines, pneumococcal infections still have high mortality rates, especially in risk groups. For this reason, there is an exceptionally extensive research effort worldwide to better understand the diseases caused by the pneumococcus, with the aim of developing improved therapeutics and vaccines. Animal experimentation is an essential tool to study the pathogenesis of infectious diseases and test novel drugs and vaccines. This article reviews both historical and innovative laboratory pneumococcal animal models that have vastly added to knowledge of (i) mechanisms of infection, pathogenesis, and immunity; (ii) efficacies of antimicrobials; and (iii) screening of vaccine candidates. A comprehensive description of the techniques applied to induce disease is provided, the advantages and limitations of mouse, rat, and rabbit models used to mimic pneumonia, sepsis, and meningitis are discussed, and a section on otitis media models is also included. The choice of appropriate animal models for in vivo studies is a key element for improved understanding of pneumococcal disease.

Up-regulation of macrophage migration inhibitory factor induced by endotoxin in experimental otitis media with effusion in mice

CONCLUSION

Injection of endotoxin into the middle ear causes production of macrophage migration inhibitory factor (MIF) in an experimental mouse model of otitis media with effusion (OME). Down-regulation of MIF may become a new approach for the management of OME.

OBJECTIVE

To determine the role of MIF in OME.

MATERIALS AND METHODS

Mice were divided into two groups and their middle ears were injected with either endotoxin or phosphate-buffered saline (PBS). Mice were sacrificed at 6 h, 12 h, or 1, 3, 7, or 14 days after injection and concentrations of MIF, interleukin-1 beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) in middle ear effusions were measured by enzyme-linked immunosorbent assay.

RESULTS

Concentrations of MIF in the endotoxin group at 1 day and 3 days were significantly higher than in the PBS control group. Concentrations of IL-1beta in the endotoxin group at 6 h, 12 h, 1 day, and 3 days were significantly higher than in controls. Concentrations of TNF-alpha in the endotoxin group at 1 day and 3 days were significantly higher than in controls. Concentration of MIF in the endotoxin group was positively correlated with that of IL-1beta and TNF-alpha.

Differential uptake and processing of a Haemophilus influenzae P5-derived immunogen by chinchilla dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells involved in the initiation and modulation of immune responses after immunization via their ability to process and present antigen to naive T cells. We wanted to examine the role of DCs in the development of protective immunity against nontypeable Haemophilus influenzae (NTHI)-induced experimental otitis media (OM) after intranasal immunization of chinchillas with an NTHI P5-derived synthetic peptide immunogen called LB1. As chinchilla DCs have not been described, we adapted well-established protocols to induce the differentiation of chinchilla bone marrow precursor cells into DCs, which resulted in cells that were morphologically and phenotypically similar to DCs of other species. In vitro, chinchilla DCs readily internalized LB1, upregulated expression of the maturation markers CD80 and major histocompatibility complex class II, and presented processed LB1 to primed CD3+ T cells, which resulted in antigen-specific T-cell proliferation. In vivo, LB1-activated DCs trafficked from the chinchilla nasal cavity primarily to the nasal-associated lymphoid tissues and were detected in close proximity to CD3+ T cells within this lymphoid aggregate. These data are the first to characterize chinchilla DCs and their functional properties. Furthermore, they suggest an important role for chinchilla DCs in the development of protective immunity against experimental NTHI-induced OM after intranasal immunization.

Eustachian tube gland tissue changes are related to bacterial species in acute otitis media

BACKGROUND AND OBJECTIVE

Prior investigations have shown that the number of mucus producing goblet cells in the middle ear and Eustachian tube (ET) mucosa is highly increased during and up to at least six months after experimental acute otitis media (AOM) caused by Streptococcus pneumoniae (SP). Further, the volume of the mucus producing paratubal gland components is increased up to 3 months after the acute infection. These changes may in conjunction with a deteriorated ET function predispose a subsequent development of secretory otitis media. The present investigation compares changes in goblet cell density and gland structures of the ET during and after AOM caused by various bacteria typically encountered in this disease, with emphasis on potential differences due to bacterial species.

METHODS

Rat models of AOM caused by SP, non-typeable or type b Haemophilus influenzae (NTHI/HIB) or Moraxella catarrhalis (MC) were studied longitudinally up to 6 months after bacterial challenge. The ET was dissected and decalcified, paraffin embedded and serially sectioned, followed by PAS/alcian blue staining. The goblet cell density and the paratubal gland composition and volume were determined morphometrically in every 20th section, using a light microscope.

RESULTS

Regardless of bacterial species, the ET goblet cell density was increased from day 8 and peaked day 16, followed by some degree of normalisation, although not reaching normal numbers within the 6 month period, except for MC. The highest increase was seen in AOM caused by the non-typeable Haemophilus strain, followed by HIB, SP and MC. Except with MC, pathological intra-epithelial glands formed and goblet cells were found in mucosal areas normally devoid of these. In all species but MC, the volume of the paratubal glands progressed to peak 16 days post-inoculation, followed by a gradual normalisation. The volume was still increased 3 months after the acute infection, but completely normalised after 6 months. The increase was primarily due to hypertrophy of the mucous gland components and highest in AOM caused by the Haemophilus species, followed by SP.

CONCLUSION

The Eustachian tube goblet cell density is increased during and up to at least six months after AOM regardless of bacterial species, except when employing MC, by which the density was increased for a few weeks only. Except in AOM caused by MC, the volume of the ET glands increases during and up to at least 3 months after infection, primarily due to hypertrophy of the mucous gland components. The non-typeable Haemophilus strain induced the highest increase of both goblet cell density and mucous gland volume. The increased secretory capacity of the ET following AOM may by excessive mucus secretion contribute to the deteriorated ET function found after AOM and thus predispose, sustain or aggravate middle ear disease.

Contribution of pneumolysin and autolysin to the pathogenesis of experimental pneumococcal endophthalmitis

PURPOSE

To determine the contribution of pneumolysin and autolysin, two putative pneumococcal virulence proteins, to the pathogenesis of Streptococcus pneumoniae endophthalmitis.

METHODS

Endophthalmitis was established in Lewis rats by intravitreal injection of pneumococcal strains at an inoculum of 10 organisms. The virulence of three closely related type 2 S. pneumoniae strains were compared: a pneumolysin-deficient derivative (PLN-A), an autolysin-deficient derivative (AL-6), and their isogenic wild-type parent (D 39). Clinical and histologic inflammation scores were compared 24 hours and 48 hours after inoculation.

RESULTS

Eyes infected with PLN-A and AL-6 strains showed less anterior segment inflammation clinically at 24 hours than did eyes infected with the wild-type strain. Histologic examination at 24 hours showed significantly less corneal infiltration and vitritis and more relative preservation of retinal tissue in eyes infected with PLN-A and AL-6 strains than in eyes infected with the wild-type strain. At 48 hours, no observable differences between PLN-A and wild-type strains were present clinically or histologically. Histologically, however, the AL-6 strain caused less retinal damage than did the wild-type strain.

CONCLUSIONS

Intraocular infection with pneumolysin-deficient S. pneumoniae results in less severe tissue damage in the first 24 hours of disease compared with infection with pneumolysin-producing S. pneumoniae. Autolysin-deficient S. pneumoniae shows a similar degree of attenuated virulence. Pneumolysin and autolysin may contribute to the early pathogenesis of pneumococcal endophthalmitis.

Histopathologic differences due to bacterial species in acute otitis media

OBJECTIVE

To compare selected features of histopathology in acute otitis media caused by various bacteria and examine potential differences due to bacterial species, as well as possible correlation to experimental and human clinical findings.

METHODS

Rat models of acute otitis media caused by Streptococcus pneumoniae (MC), non-typeable or type b Haemophilus influenzae (NTHI/HIB) or Moraxella catarrhalis (MC) were studied longitudinally up to 6 months after bacterial challenge. Findings related to dynamics of goblet cell density, modeling and remodeling of bone tissue structures and polyp, as well as fibrous adhesion formation and persistence are presented.

RESULTS

Middle ear goblet cell density progressed to peak 2 weeks after bacterial inoculation, thereafter gradually normalizing. However, density and accordingly middle ear secretory capacity was still significantly increased after 6 months in all bacteria, except MC. The HI species induced the highest increase. Initial osteoresorption was followed by massive osteoneogenesis, progressing to a peak after 2-3 months, followed by some degree of normalization, concurrently classic remodeling. Primarily SP, but also the HI species induced more new bone formation than MC. Mucosal polyp and fibrous adhesion formation occurred regardless of bacterial species. Most polyps appeared in the early phases and the HI species induced formation of more polyps and adhesions than the other bacteria.

CONCLUSION

Acute middle ear infection with the Haemophilus species induce the highest increase of mucosal secretory capacity, lasting for at least 6 months after the acute incident. Thus, a subsequent development of secretory otitis media seems more likely following infection with these bacteria. Equivalently, mucosal scarring observed as polyp and fibrous adhesion formation was more severe following Haemophilus infection. S. pneumoniae induced the most marked changes of bone tissue structures, seen as initial osteoresorption and subsequent osteoneogenesis. Overall, infection with M. catarrhalis induced the mildest changes.

Pneumococcal virulence factors: structure and function

The overall goal for this review is to summarize the current body of knowledge about the structure and function of major known antigens of Streptococcus pneumoniae, a major gram-positive bacterial pathogen of humans. This information is then related to the role of these proteins in pneumococcal pathogenesis and in the development of new vaccines and/or other antimicrobial agents. S. pneumoniae is the most common cause of fatal community-acquired pneumonia in the elderly and is also one of the most common causes of middle ear infections and meningitis in children. The present vaccine for the pneumococcus consists of a mixture of 23 different capsular polysaccharides. While this vaccine is very effective in young adults, who are normally at low risk of serious disease, it is only about 60% effective in the elderly. In children younger than 2 years the vaccine is ineffective and is not recommended due to the inability of this age group to mount an antibody response to the pneumococcal polysaccharides. Antimicrobial drugs such as penicillin have diminished the risk from pneumococcal disease. Several pneumococcal proteins including pneumococcal surface proteins A and C, hyaluronate lyase, pneumolysin, autolysin, pneumococcal surface antigen A, choline binding protein A, and two neuraminidase enzymes are being investigated as potential vaccine or drug targets. Essentially all of these antigens have been or are being investigated on a structural level in addition to being characterized biochemically. Recently, three-dimensional structures for hyaluronate lyase and pneumococcal surface antigen A became available from X-ray crystallography determinations. Also, modeling studies based on biophysical measurements provided more information about the structures of pneumolysin and pneumococcal surface protein A. Structural and biochemical studies of these pneumococcal virulence factors have facilitated the development of novel antibiotics or protein antigen-based vaccines as an alternative to polysaccharide-based vaccines for the treatment of pneumococcal disease.

Peritoneal culture alters Streptococcus pneumoniae protein profiles and virulence properties

We have examined the properties of Streptococcus pneumoniae cultured in the murine peritoneal cavity and compared its virulence-associated characteristics to those of cultures grown in vitro. Analysis of mRNA levels for specific virulence factors demonstrated a 2.8-fold increase in ply expression and a 2.2-fold increase in capA3 expression during murine peritoneal culture (MPC). Two-dimensional gels and immunoblots using convalescent-phase patient sera and murine sera revealed distinct differences in protein production in vivo (MPC). MPC-grown pneumococci adhered to A549 epithelial cell lines at levels 10-fold greater than those cultured in vitro.

Virulence factors and the pathogenesis of disease caused by Streptococcus pneumoniae

Streptococcus pneumoniae is a major pathogen of man causing diseases such as pneumonia, meningitis and otitis media. The mechanisms by which this organism causes these diseases are still largely unknown. The use of molecular approaches to identifying and studying putative virulence factors in combination with the application of animal models has allowed some of the mechanisms of the disease process to be defined.

Biological properties of pneumolysin

Pneumolysin is a thiol-activated membrane-damaging toxin produced by Streptococcus pneumoniae. The toxin plays a role in virulence of the pneumococcus in animal models of infection. Pneumolysin has a range of biological activity including the ability to lyse eukaryotic cells and to interfere with the function of cells and soluble molecules of the immune system. The use of purified native and mutant toxin and of isogenic mutants of the pneumococcus expressing altered versions of the toxin has allowed the contribution of the various activities of this multifunctional toxin to virulence to be defined.

Molecular analysis of putative pneumococcal virulence proteins

Although the polysaccharide capsule has been recognized as a sine qua non of virulence, recent attention has focused on the role of pneumococcal proteins in pathogenesis, particularly in view of their potential as vaccine antigens. The contribution of pneumolysin, two distinct neuraminidases, autolysin, hyaluronidase, and the 37 kDa pneumococcal surface adhesin A has been examined by specifically mutagenizing the respective genes in the pneumococcal chromosome and examining the impact on virulence in animal models. The vaccine potential of these proteins has also been assessed by immunization of mice with purified antigens, followed by challenge with virulent pneumococci.

Otitis media: the chinchilla model

Streptococcus pneumoniae infection and disease have been modeled in several animal species including infant and adult mice, infant and adult rats, infant Rhesus monkeys, and adolescent and adult chinchillas. Most are models of sepsis arising from intravenous or intraperitoneal inoculation of bacteria, and a few were designed to study disease arising from intranasal infection. Chinchillas provide the only animal model of middle ear pneumococcal infection in which the disease can be produced by very small inocula injected into the middle ear (ME) or intranasally, and in which the disease remains localized to the ME in most cases. This model, developed at the University of Minnesota in 1975, has been used to study pneumococcal pathogenesis at a mucosal site, immunogenicity and efficacy of pneumococcal capsular polysaccharide (PS) vaccine antigens, and the kinetics and efficacy of antimicrobial drugs. Pathogenesis experiments in the chinchilla model have revealed variation in ME virulence among different pneumococcal serotypes, enhancement of ME infection during concurrent intranasal influenza A virus infections, and natural resolution of pneumococcal otitis media (OM) without intervention. Research has explored the relative contribution of pneumococcal and host products to ME inflammation. Pneumococcal cell wall components and pneumolysin have been studied in the model. Host inflammatory responses studied in the chinchilla ME include polymorphonuclear leukocyte oxidative products, hydrolytic enzymes, cytokine and eicosanoid metabolites, and ME epithelial cell adhesion and mucous glycoprotein production. Both clinical (tympanic membrane appearance) and histopathology (ME, Eustachian tube, inner ear) endpoints can be quantified. Immunologic and inflammatory studies have been facilitated by the production of affinity-purified antichinchilla immunoglobulin G (IgG), IgM, and secretory IgA polyclonal antibody reagents, and the identification of cross-reactivity between human and chinchilla cytokines, and between guinea pig and chinchilla C3. Alteration of ME mucosa by pneumococcal neuraminidase and alteration of ME epithelial cell (MEEC) surface carbohydrates during intranasal pneumococcal infection have been demonstrated. Pathogenesis studies have been aided by cultured chinchilla MEEC systems, in which the ability of platelet activating factor and interleukin (IL)-1 beta to stimulate epithelial mucous glycoprotein synthesis has recently been demonstrated. Because chronic OM with effusion is characterized by presence of large amounts of mucous glycoprotein in the ME, pneumococcus may have an important role in both acute and chronic ME disease. Both unconjugated PS and PS-protein-conjugated vaccines are immunogenic after intramuscular administration without adjuvant in chinchillas. Passive protection studies with human hyperimmune immunoglobulin demonstrated that anti-PS IgG alone is capable of protecting the chinchilla ME from direct ME challenge with pneumococci. Active PS immunization studies demonstrated protection following direct ME and intranasal pneumococcal challenge with and without concurrent influenza A virus infection. An attenuated influenza A virus vaccine also showed protection for pneumococcal OM. Antimicrobial treatment of acute OM has been based almost exclusively on empirical drug use and clinical trials without a foundation of ME pharmacokinetics. Studies in the chinchilla model have started to bring a rational basis to drug selection and dosing. Microassays have been developed using high-pressure liquid chromatography for many relevant drugs. Studies have explored the in vivo ME response in pneumococcal OM to antimicrobial drugs at supra- and sub-minimum inhibitory concentration (MIC), the effect of concurrent influenza A virus infection on ME drug penetration, and the effect of treatment on sensorineural hearing loss produced by pneumococcal OM.

The autolysin-encoding gene (lytA) of Streptococcus pneumoniae displays restricted allelic variation despite localized recombination events with genes of pneumococcal bacteriophage encoding cell wall lytic enzymes

The lytA-encoded autolysin (N-acetylmuramoyl-L-alanine amidase) of Streptococcus pneumoniae is believed to play an important role in the pathogenesis of pneumococcal infection and has been identified as a putative vaccine target. Allelic diversity of lytA in an extensive collection of clinical isolates was assessed by restriction fragment length polymorphism and confirmatory sequencing studies. Genetic diversity within lytA is limited, especially compared to the high levels of diversity seen in other pneumococcal virulence factor genes, although small blocks generating mosaic structure were identified. Sequence comparisons with genes encoding cell wall lytic enzymes of pneumococcal bacteriophage suggest that localized recombination events have occurred between host lytA and these bacteriophage genes. These results confirm earlier suggestions that recombination between DNA encoding bacteriophage autolytic enzymes and chromosomally encoded lytA might be important in the evolution of lytA. The implications of these findings for understanding the evolution of lytA and the potential utility of LytA as a vaccine target are discussed.

Course of IL-1beta, IL-6, IL-8, and TNF-alpha in the middle ear fluid of the guinea pig otitis media model induced by nonviable Haemophilus influenzae

To characterize the local response in acute otitis media, courses of interleukin (IL)-1beta, IL-6, IL-8, and tumor necrosis factor (TNF)alpha in middle ear fluid (MEF) of the guinea pig otitis media model induced by nonviable Haemophilus influenzae were investigated with enzyme-linked immunosorbent assay (ELISA) kits. The IL-1beta concentration in H. influenzae-inoculated ears peaked 24 hours after inoculation. The IL-8 concentration was significantly higher in H. influenzae-inoculated ears than in controls 48 and 96 hours after inoculation. The TNF-alpha concentration in H. influenzae-inoculated ears had an initial peak 6 hours after inoculation and had significant late increases 48 and 96 hours after inoculation. The results suggest that IL-1beta and TNF-alpha were produced by middle ear mucosa in the early stage of the experiment by stimulation of bacterial inoculation, which caused subsequent inflammatory cell accumulation, and that IL-8 and TNF-alpha were produced in the late stage by accumulating inflammatory cells.

Middle ear fluid cytokine and inflammatory cell kinetics in the chinchilla otitis media model

Streptococcus pneumoniae is the most frequent microbe causing middle ear infection. The pathophysiology of pneumococcal otitis media has been characterized by measurement of local inflammatory mediators such as inflammatory cells, lysozyme, oxidative metabolic products, and inflammatory cytokines. The role of cytokines in bacterial infection has been elucidated with animal models, and interleukin (IL)-1beta, IL-6, and IL-8 and tumor necrosis factor alpha (TNF-alpha) are recognized as being important local mediators in acute inflammation. We characterized middle ear inflammatory responses in the chinchilla otitis media model after injecting a very small number of viable pneumococci into the middle ear, similar to the natural course of infection. Middle ear fluid (MEF) concentrations of IL-1beta, IL-6, IL-8, and TNF-alpha were measured by using anti-human cytokine enzyme-linked immunosorbent assay reagents. IL-1beta showed the earliest peak, at 6 h after inoculation, whereas IL-6, IL-8, and TNF-alpha concentrations were increasing 72 h after pneumococcal inoculation. IL-6, IL-8, and TNF-alpha but not IL-1beta concentrations correlated significantly with total inflammatory cell numbers in MEF, and all four cytokines correlated significantly with MEF neutrophil concentration. Several intercytokine correlations were significant. Cytokines, therefore, participate in the early middle ear inflammatory response to S. pneumoniae.

Vaccination against middle-ear bacterial and viral pathogens

Considerable evidence suggests that otitis media (OM) can be prevented by systemic immunization. Building on the highly effective H. influenzae type b (Hib) conjugate vaccine technology, pneumococcal conjugate vaccines are being developed to circumvent T-independence of these antigens and provide durable immunity at a very young age. Several pneumococcal conjugate vaccines are currently in clinical testing. Potential vaccine antigens of nontypable H. influenzae (NTHi) include OMP, HMW, pili, and fimbriae. Several OMPs show extensive homology among strains, but surface, determinants of others are highly variable so that antibodies to surface epitopes of one strain will not bind to surface epitopes of another. Several M. catarrhalis OMP and HMW antigens have vaccine potential, but no functional correlates of protection have been identified, and there is no clear evidence that antibody to M. catarrhalis is associated with OM protection. Attenuated viral vaccines also hold promise of preventing childhood OM. Two clinical trials with killed influenza vaccines have shown a significant reduction in OM among vaccine recipients compared to control children during periods of high influenza disease activity in the community. Passive immunoprophylaxis also has potential for preventing OM. Human bacterial polysaccharide immune globulin was protective for pneumococcal OM in children and in the chinchilla OM model. High-dose respiratory syncytial virus-enriched immunoglobulin reduced the incidence and severity of RSV lower respiratory tract infection in high-risk children. Passive immunoprophylaxis may also be effective in children with specific immune deficiencies, such as IgG2 deficiency, and patients who fail to respond to vaccines.