The Streptococcus pneumoniae capsule is required for full virulence in pneumococcal endophthalmitis

Presenting Characteristics, Treatment, and Visual Outcomes in Streptococcal Compared to Non-Streptococcal Endophthalmitis

PURPOSE

Report the clinical findings, risk factors, treatment, and visual outcomes associated with Streptococcus endophthalmitis in comparison to culture-positive endophthalmitis associated with non-Streptococcus species.

METHODS

A retrospective chart review of adults between 18 and 89 years of age diagnosed with exogenous culture-positive endophthalmitis between January 1, 2009, and January 1, 2018, at the Duke Eye Center (Durham, North Carolina) with at least six months of follow-up from time of initial diagnosis was conducted. Clinical data including patient demographics, ocular history, baseline corrected visual acuity (VA) prior to presentation, time to presentation, presenting exam findings, VA at presentation, presumed etiology of endophthalmitis, medical and surgical management, and VA at the six-month follow-up was extracted and statistically analyzed.

RESULTS

Fifty-six eyes from 56 patients with culture-positive endophthalmitis were identified. Eyes with Streptococcus (n=18) had elevated intraocular pressure (IOP) at presentation (p=0.002), worse mean VA (Snellen) at presentation (20/14159 vs. 20/3098, p<0.001), and worse mean VA (Snellen) at six months (20/3475 vs. 20/235, p<0.001) compared to non-Streptococcus cases (n=38). Time to presentation (days) (median, IQR) was longer in eyes that underwent glaucoma surgery for both Streptococcus (2241 (836, 3709) vs. 3 (2, 31), p=0.003) and non-Streptococcus endophthalmitis (1236 (125, 3582) vs. 6 (4, 25), p<0.0001). There was no difference in VA at six months between Streptococcus and non-Streptococcus eyes based on treatment.  Conclusions: Streptococci are rare but important causes of exogenous endophthalmitis, and in our study, they were associated with worse visual outcomes than non-Streptococci. A history of any glaucoma surgery, even procedures performed years earlier, should be elicited when evaluating patients with ocular symptoms.

Bacterial capsules: Occurrence, mechanism, and function

In environments characterized by extended multi-stress conditions, pathogens develop a variety of immune escape mechanisms to enhance their ability to infect the host. The capsules, polymers that bacteria secrete near their cell wall, participates in numerous bacterial life processes and plays a crucial role in resisting host immune attacks and adapting to their niche. Here, we discuss the relationship between capsules and bacterial virulence, summarizing the molecular mechanisms of capsular regulation and pathogenesis to provide new insights into the research on the pathogenesis of pathogenic bacteria.

Serotype 3 Antibody Response and Antibody Functionality Compared to Serotype 19A Following 13-Valent Pneumococcal Conjugate Immunization in Children

BACKGROUND

Prevention of infections in children vaccinated with 13-valent pneumococcal conjugate vaccine (PCV13) may be less effective against serotype 3 than 19A.

OBJECTIVE

The aim of this study was to to determine differences in IgG and functional antibody for serotype 3 versus 19A following PCV13 immunization, in IgG antibody levels induced by PCV13 compared to naturally-induced immunity, and assess effectiveness of PCV13 against serotype 3 and 19A in prevention of acute otitis media (AOM) and colonization among 6-36-month-old children.

METHODS

Samples were from a prospective, longitudinal, observational cohort study conducted in Rochester, NY. Pneumococcal detection was by culture. 713 serum were tested for antibody levels by enzyme-linked immunosorbent assay, 68 for functional antibody by opsonophagocytosis and 47 for antibody avidity by thiocyanate bond disruption. PCV13 effectiveness in preventing AOM and colonization was determined by comparison of pre-PCV13 detection of serotypes 3 and 19A to post-PCV13.

RESULTS

The proportion of children who reached the antibody threshold of ≧0.35 µg/mL after PCV13 was higher for serotype 19A than serotype 3. Only serotype 19A showed significant increase in PCV13-induced opsonophagocytosis assay titers and antibody avidity. Serotype 3 naturally-induced immune children showed a positive trend of increase in antibody level as children got older, but not PCV13-immunized children. PCV13 effectiveness was not identified in preventing AOM or colonization for serotype 3 but effectiveness of 19A was confirmed.

CONCLUSIONS

PCV13 elicits lower antibody levels and lower effectiveness to serotype 3 versus serotype 19A. Post-PCV13-induced antibody levels for serotype 3 are likely insufficient to prevent AOM and colonization in most young children.

Naturally-induced serum antibody levels in children to pneumococcal polysaccharide 15B that correlate with protection from nasopharyngeal colonization but anti-serotype 15B antibody has low functional cross-reactivity with serotype 15C

BACKGROUND

Serotypes 15B and 15C have been added to new different pneumococcal-conjugate vaccines (PCV20 and V116, respectively). We determined a serum anti-15B antibody level that would be a correlate of protection (COP) against nasopharyngeal colonization and assessed functional cross-reactivity against serotype 15B and 15C in children following natural immunization.

METHOD

IgG-antibody to serotype 15B polysaccharide was measured by ELISA in 341 sera from 6 to 36 month old children collected before, at the time of, and after pneumococcal colonization caused by serotypes 15B and 15C. 155 age-matched controls who had no detected colonization caused by serotype 15B or 15C strains were used as controls. A two-step method was used for construction of COP models: a generalized estimating equation followed by logistic-regression. Opsonophagocytic (OPA) assays assessed functional cross-reactivity between serotypes 15B and 15C.

RESULTS

The derived COP for prevention of colonization was 1.18 µg/ml for serotype 15B and 0.63 µg/ml for serotype 15C, with a predictive probability of 80 %. Antibody levels did not correlate with OPA titers. 30 % of child samples, with moderate to high amounts of ELISA-measured antibody, showed no OPA titer against either serotype 15B or 15C. For remaining samples, very low or no functional cross-reactivity between serotypes 15B and 15C was measured.

CONCLUSIONS

A COP for prevention of colonization in young children based on naturally-induced antibody levels was derived for serotypes 15B and 15C that differed. Antibody levels correlated poorly with OPA titers and low functional cross-reactivity between serotypes 15B and 15C in child sera was observed.

Ocular Bacterial Infections: A Ten-Year Survey and Review of Causative Organisms Based on the Oklahoma Experience

Ocular infections can be medical emergencies that result in permanent visual impairment or blindness and loss of quality of life. Bacteria are a major cause of ocular infections. Effective treatment of ocular infections requires knowledge of which bacteria are the likely cause of the infection. This survey of ocular bacterial isolates and review of ocular pathogens is based on a survey of a collection of isolates banked over a ten-year span at the Dean McGee Eye Institute in Oklahoma. These findings illustrate the diversity of bacteria isolated from the eye, ranging from common species to rare and unique species. At all sampled sites, staphylococci were the predominant bacteria isolated. Pseudomonads were the most common Gram-negative bacterial isolate, except in vitreous, where Serratia was the most common Gram-negative bacterial isolate. Here, we discuss the range of ocular infections that these species have been documented to cause and treatment options for these infections. Although a highly diverse spectrum of species has been isolated from the eye, the majority of infections are caused by Gram-positive species, and in most infections, empiric treatments are effective.

Update on Current Microbiological Techniques for Pathogen Identification in Infectious Endophthalmitis

Infectious endophthalmitis is a vision-threatening medical emergency that requires prompt clinical diagnosis and the initiation of treatment. However, achieving precision in endophthalmitis management remains challenging. In this review, we provide an updated overview of recent studies that are representative of the current trends in clinical microbiological techniques for infectious endophthalmitis.

Cytokine Expression in Staphylococcal and Streptococcal Endophthalmitis

<b><i>Background:</i></b> Endophthalmitis is an infection of ocular tissues, often with devastating outcomes for vision. Immunomodulation is an emerging avenue for therapeutic intervention in endophthalmitis, with the expression of cytokines central to potential mechanisms. This literature review with a systematic approach characterizes the cytokine expression in both animal and human staphylococcal and streptococcal endophthalmitis. <b><i>Method and Results:</i></b> Four online databases were searched for studies profiling cytokine levels in animal models or human populations with staphylococcal and/or streptococcal endophthalmitis. Of the 1,060 articles identified, 14 studies were included in this review comprising eight animal models and six human populations. Mouse, rat, and rabbit models of <i>Staphylococcus aureus</i>, <i>Staphylococcus epidermidis</i>, and <i>Streptococcus pneumoniae</i> endophthalmitis had elevated levels of IL-1β, IL-6, IFN-γ, TNF-α, and IL-8, with earlier peaks observed in <i>S</i>. <i>epidermidis</i> infection. Human endophthalmitis demonstrated significantly increased mediator levels compared to controls for a range of pro-inflammatory and anti-inflammatory cytokines, chemokines, and growth factors. Several associations were established between cytokine concentrations and both initial visual acuity and visual prognosis, with no consistent correlations across trials. <b><i>Conclusions:</i></b> It may be that virulence factors and the combinations of toll-like receptors activated influence the pathogen-specific visual outcomes observed in endophthalmitis. Furthermore, disease severity and potential therapeutic targets may be dependent on synergistic and compensatory cytokine pathways and the expression of anti-inflammatory mediators. Future research should aim to better characterize the roles of inflammatory mediators and solidify associations between pathogens, inflammation, and endophthalmitis outcomes. This has exciting implications for the prevention and treatment of endophthalmitis in clinical settings.

Capsule Independent Antimicrobial Activity Induced by Nanochitosan against Streptococcus pneumoniae

Background: Streptococcus pneumoniae remains a major cause of community-acquired pneumonia, meningitis, and other diseases, contributing significantly to high morbidity and mortality worldwide. Although it responds to antibiotics, their use is becoming limited due to the rise in antibiotic resistance, which necessitates the development of new therapeutics. Nanotechnology is used to counteract antimicrobial resistance. In this regard, polymeric nanoparticles (NPs) made of natural, biodegradable, biocompatible, and cationic polymers such as Chitosan (CNPs) exhibit wide-spectrum antimicrobial activity. Therefore, this study aimed to prepare CNPs, characterize their physiochemical characteristics: particle size (PZ), polydispersity index (PDI), and zeta potential (ZP), and investigate their antimicrobial activity against Streptococcus pneumoniae TIGR4 (virulent serotype 4) and its capsular mutant (∆cps). Methods: CNPs were prepared at 1, 2.5, and 5 mg/mL concentrations using the ion gelation method. Then, PZ, PDI, and ZP were characterized using a Zetasizer. Transmission electron microscopy (TEM) was used to visualize the CNP’s morphology. Broth and agar dilution methods were used to assess their antimicrobial activity. Cytotoxicity of prepared NPs on A549 cells and their effect on pneumococcal hemolysis were also investigated. Results: Spherical CNPs were produced with PZ ranging from 133.3 nm ± 0.57 to 423 nm ± 12.93 PDI < 0.35, and ZP from 19 ± 0.115 to 27 ± 0.819. The prepared CNPs exhibited antibacterial activity against TIGR4 and its capsule mutant with a minimum inhibitory concentration (MIC90) of 0.5 to 2.5 mg/mL in a non-acidic environment. The hemolysis assay results revealed that CNPs reduced bacterial hemolysis in a concentration-dependent manner. Their mammalian cytotoxicity results indicated that CNPs formed from low concentrations of Chitosan (Cs) were cytocompatible. Conclusion: Nanochitosan particles showed anti-pneumococcal activity regardless of the presence of capsules. They resulted in a concentration-dependent reduction in bacterial hemolysis and were cytocompatible at a lower concentration of Cs. These findings highlight the potential of CNPs in the treatment of pneumococcal diseases.

Intravitreal Injection and Quantitation of Infection Parameters in a Mouse Model of Bacterial Endophthalmitis

Intraocular bacterial infections are a danger to the vision. Researchers use animal models to investigate the host and bacterial factors and immune response pathways associated with infection to identify viable therapeutic targets and to test drugs to prevent blindness. The intravitreal injection technique is used to inject organisms, drugs, or other substances directly into the vitreous cavity in the posterior segment of the eye. Here, we demonstrated this injection technique to initiate infection in the mouse eye and the technique of quantifying intraocular bacteria. Bacillus cereus was grown in brain heart infusion liquid media for 18 hours and resuspended to a concentration 100 colony forming units (CFU)/0.5 µL. A C57BL/6J mouse was anesthetized using a combination of ketamine and xylazine. Using a picoliter microinjector and glass capillary needles, 0.5 µL of the Bacillus suspension was injected into the mid vitreous of the mouse eye. The contralateral control eye was either injected with sterile media (surgical control) or was not injected (absolute control). At 10 hours post infection, mice were euthanized, and eyes were harvested using sterile surgical tweezers and placed into a tube containing 400 µL sterile PBS and 1 mm sterile glass beads. For ELISAs or myeloperoxidase assays, proteinase inhibitor was added to the tubes. For RNA extraction, the appropriate lysis buffer was added. Eyes were homogenized in a tissue homogenizer for 1-2 minutes. Homogenates were serially diluted 10-fold in PBS and track diluted onto agar plates. The remainder of the homogenates were stored at -80 °C for additional assays. Plates were incubated for 24 hours and CFU per eye was quantified. These techniques result in reproducible infections in mouse eyes and facilitate quantitation of viable bacteria, the host immune response, and omics of host and bacterial gene expression.

Opportunities and challenges in managing antibiotic resistance in bacteria using plant secondary metabolites

Development of antibiotic resistance (ABR) in bacteria and its multidimensional spread is an emerging global threat that needs immediate attention. Extensive antibiotics (AB) usage results in development of ABR in bacteria by target modification, production of AB degrading enzymes, porin modifications, efflux pumps overexpression, etc. To counter this, apart from strict regulation of AB use and behavioural changes, research and development (R&D) of newer antimicrobials are in place. One such emerging approach to combat ABR is the use of structurally and functionally diverse plant secondary metabolites (PSMs) in combination with the conventional AB. Either the PSMs are themselves antimicrobial or they potentiate the activity of the AB through a range of mechanisms. However, their use is lagging due to poor knowledge of mode of action, structure-activity relationships, pharmacokinetics, etc. This review paper discussed the opportunities and challenges in managing ABR using PSMs. Mechanisms of ABR development in bacteria and current strategies to counter them were studied and the areas where PSMs can play an important role were highlighted. The use of PSMs, both as an anti-resistance and anti-virulence agent in combination therapy to counter multi-drug resistance along with their mechanisms of action, has been discussed in detail. The difficulties in the commercialisation of PSMs and strategies to overcome them along with future priority areas of research have also been given. Following the given R&D path will definitely help in better understanding and utilising the full potential of PSMs in solving the problem of antimicrobial resistance (AMR).

Plant-Based Phytochemicals as Possible Alternative to Antibiotics in Combating Bacterial Drug Resistance

The unprecedented use of antibiotics that led to development of resistance affect human health worldwide. Prescription of antibiotics imprudently and irrationally in different diseases progressed with the acquisition and as such development of antibiotic resistant microbes that led to the resurgence of pathogenic strains harboring enhanced armors against existing therapeutics. Compromised the treatment regime of a broad range of antibiotics, rise in resistance has threatened human health and increased the treatment cost of diseases. Diverse on metabolic, genetic and physiological fronts, rapid progression of resistant microbes and the lack of a strategic management plan have led researchers to consider plant-derived substances (PDS) as alternative or in complementing antibiotics against the diseases. Considering the quantitative characteristics of plant constituents that attribute health beneficial effects, analytical procedures for their isolation, characterization and phytochemical testing for elucidating ethnopharmacological effects has being worked out for employment in the treatment of different diseases. With an immense potential to combat bacterial infections, PDSs such as polyphenols, alkaloids and tannins, present a great potential for use, either as antimicrobials or as antibiotic resistance modifiers. The present study focuses on the mechanisms by which PDSs help overcome the surge in resistance, approaches for screening different phytochemicals, methods employed in the identification of bioactive components and their testing and strategies that could be adopted for counteracting the lethal consequences of multidrug resistance.

The cereus matter of Bacillus endophthalmitis

Bacillus cereus (B. cereus) endophthalmitis is a devastating intraocular infection primarily associated with post-traumatic injuries. The majority of these infections result in substantial vision loss, if not loss of the eye itself, within 12-48 h. Multifactorial mechanisms that lead to the innate intraocular inflammatory response during this disease include the combination of robust bacterial replication, migration of the organism throughout the eye, and toxin production by the organism. Therefore, the window of therapeutic intervention in B. cereus endophthalmitis is quite narrow compared to that of other pathogens which cause this disease. Understanding the interaction of bacterial and host factors is critical in understanding the disease and formulating more rational therapeutics for salvaging vision. In this review, we will discuss clinical and research findings related to B. cereus endophthalmitis in terms of the organism's virulence and inflammogenic potential, and strategies for improving of current therapeutic regimens for this blinding disease.

A Pyrrhic Victory: The PMN Response to Ocular Bacterial Infections

Some tissues of the eye are susceptible to damage due to their exposure to the outside environment and inability to regenerate. Immune privilege, although beneficial to the eye in terms of homeostasis and protection, can be harmful when breached or when an aberrant response occurs in the face of challenge. In this review, we highlight the role of the PMN (polymorphonuclear leukocyte) in different bacterial ocular infections that invade the immune privileged eye at the anterior and posterior segments: keratitis, conjunctivitis, uveitis, and endophthalmitis. Interestingly, the PMN response from the host seems to be necessary for pathogen clearance in ocular disease, but the inflammatory response can also be detrimental to vision retention. This "Pyrrhic Victory" scenario is explored in each type of ocular infection, with details on PMN recruitment and response at the site of ocular infection. In addition, we emphasize the differences in PMN responses between each ocular disease and its most common corresponding bacterial pathogen. The in vitro and animal models used to identify PMN responses, such as recruitment, phagocytosis, degranulation, and NETosis, are also outlined in each ocular infection. This detailed study of the ocular acute immune response to infection could provide novel therapeutic strategies for blinding diseases, provide more general information on ocular PMN responses, and reveal areas of bacterial ocular infection research that lack PMN response studies.

A Transcriptional Activator of Ascorbic Acid Transport in Streptococcus pneumoniae Is Required for Optimal Growth in Endophthalmitis in a Strain-Dependent Manner

Streptococcus pneumoniae is among the top causes of bacterial endophthalmitis, an infectious disease of the intraocular fluids. The mechanisms by which S. pneumoniae grows and thrives in the intraocular cavity are not well understood. We used a bacterial genome-wide assessment tool (transposon insertion site sequencing) to determine genes essential for S. pneumoniae growth in vitreous humor. The results indicated that an ascorbic acid (AA) transport system subunit was important for growth. We created an isogenic gene deletion mutant of the AA transcriptional activator, ulaR2, in 2 strains of S. pneumoniae. Growth curve analysis indicated that ulaR2 deletion caused attenuated growth in vitro for both strains. However, in vivo vitreous humor infection in rabbits with either strain determined that ulaR2 was necessary for growth in one strain but not the other. These results demonstrate that ulaR2 may be important for fitness during S. pneumoniae endophthalmitis depending on the background of the strain.

Targets of immunomodulation in bacterial endophthalmitis

Bacterial infection of the posterior segment of the eye (endophthalmitis) leads to a robust host response that often results in irreversible damage to the layers of the retina, significant vision loss, and in some patients, enucleation of the globe. While a great deal of effort has gone into understanding the role of bacterial virulence factors in disease initiation and propagation, it is becoming increasingly clear that the host response to infection plays a major role in causing the damage associated with endophthalmitis. Researchers have identified the host receptors which detect infecting organisms and initiate the cascade of events that result in inflammation. This inflammation may damage nonregenerative tissues of the eye while attempting to clear the infection. Both Gram-positive and Gram-negative bacteria can cause endophthalmitis. These organisms initiate an immune response by activating toll-like receptor (TLR) pathways. Once an inflammatory response is initiated, the expression of immunomodulators, such as proinflammatory chemokines and cytokines, affect the recruitment of PMNs and other inflammatory cells into the eye. We and others have reported that knockout mice that do not express specific inflammatory pathways and molecules have an attenuated response to infection and retain significant retinal function. These findings suggest that host immune mediators are important components of the response to infections in the posterior segment of the eye, and the timing and level of their production may be related to the severity of the damage and the ultimate visual outcome. If that is the case, a better understanding of the complex and often redundant role of these pathways and inflammatory mediators may identify host molecules as potential anti-inflammatory therapeutic targets. This review highlights potential anti-inflammatory targets during acute inflammation in endophthalmitis, compares and contrasts those with findings in other models of ocular inflammation, and translates current immunomodulatory strategies for other types of infection and inflammation to this blinding disease. Given the poor visual outcomes seen in patients treated with antibiotics alone or in combination with corticosteroids, immunomodulation in addition to antibiotic therapy might be more effective in preserving vision than current regimens.

Culture-Proven Endophthalmitis After Intravitreal Injection: A 10-Year Analysis

BACKGROUND AND OBJECTIVE

To report on the microbiology, management, and visual outcomes of intravitreal injection (IVI)-associated, culture-proven endophthalmitis.

PATIENTS AND METHODS

All patients seen at a tertiary referral center with culture-proven endophthalmitis associated with an IVI between June 2007 and July 2017 were included in this retrospective analysis.

RESULTS

Thirty-five patients with culture-positive endophthalmitis following IVI were identified. All gram-positive organisms (34 of 35) were susceptible to vancomycin. Cases due to pathogens associated with oral or respiratory flora were common (31.4%, n = 11), presented earlier (2.0 days vs. 4.6 days, P < .001), were more likely to undergo pars plana vitrectomy (81.8% vs. 25.0%, P = .002) and had worse visual acuity outcomes.

CONCLUSION

IVI-associated endophthalmitis pathogens and anti-microbial susceptibilities in the Pacific Northwest are similar to those reported from other geographic locations. Bacteria associated with the oral and respiratory flora are common isolates that result in a more aggressive course and worse visual outcomes. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:33-38.].

The Role of Pneumococcal Virulence Factors in Ocular Infectious Diseases

Streptococcus pneumoniae is a gram-positive, facultatively anaerobic pathogen that can cause severe infections such as pneumonia, meningitis, septicemia, and middle ear infections. It is also one of the top pathogens contributing to bacterial keratitis and conjunctivitis. Though two pneumococcal vaccines exist for the prevention of nonocular diseases, they do little to fully prevent ocular infections. This pathogen has several virulence factors that wreak havoc on the conjunctiva, cornea, and intraocular system. Polysaccharide capsule aids in the evasion of host complement system. Pneumolysin (PLY) is a cholesterol-dependent cytolysin that acts as pore-forming toxin. Neuraminidases assist in adherence and colonization by exposing cell surface receptors to the pneumococcus. Zinc metalloproteinases contribute to evasion of the immune system and disease severity. The main purpose of this review is to consolidate the multiple studies that have been conducted on several pneumococcal virulence factors and the role each plays in conjunctivitis, keratitis, and endophthalmitis.

Treatment of Bacillus cereus endophthalmitis with endoscopy-assisted vitrectomy

To evaluate the use of endoscopy-assisted vitrectomy in patients with sight-threatening Bacillus cereus endophthalmitis.A retrospective analysis was conducted in 15 eyes with Bacillus cereus endophthalmitis. Patients were divided into 2 groups: endoscopy-assisted vitrectomy (5 eyes) and conventional vitrectomy (10 eyes). The following clinical data were recorded and analyzed: sex, age, latent period, symptom duration, follow-up time, visual acuity pre- and postsurgery, recurrence of endophthalmitis, incidence of phithisis bulbi, and incidence of enucleation.In the conventional vitrectomy group, postoperative visual acuity ranged from no light perception in 5 patients (50%), light perception in 3 patients (30%), 20/1000 in 1 patient (10%), and 20/50 in 1 patient (10%). In the endoscopy-assisted vitrectomy group, postoperative visual acuity ranged from no light perception in 2 patients (40%), light perception in 1 patient (20%), and hand movements in 2 patients (40%). There was no statistically significant difference between the 2 groups in terms of the final postoperative visual acuity (F = 0.006, P = .937). There is no difference between the 2 groups in terms of the incidence of enucleation. The median symptom duration was 4 hours (range: 2-6 hours) in the conventional group and 9 hours (range: 7-11 hours) in the endoscopy-assisted vitrectomy group. The difference in the symptom duration between the 2 groups was statistically significant (P = .002).There is no statistical significant difference between the 2 groups in terms of visual acuity and incidence of enucleation. Therefore, endoscopy-assisted vitrectomy can be considered as an alternative treatment for treatment of B cereus endophthalmitis particularly for cases when symptom duration was more than 6 hours.

Bacterial and Fungal Endophthalmitis

Endophthalmitis is a severe eye infection that may result in permanent loss of useful vision in the affected eye. Most cases are exogenous and occur as a complication of cataract surgery, an intravitreal injection, or penetrating ocular trauma. Endogenous endophthalmitis results from hematogenous seeding of the eye by bacteria or fungi, but bacteremia or fungemia may be transient and patients may present without symptoms of systemic infection. Nearly all endophthalmitis patients present with decreased vision, and some also have eye pain. Eye examination usually reveals a hypopyon and intraocular inflammation. Diagnosis is clinical, supported by cultures of the vitreous and/or aqueous or by blood cultures in some endogenous cases. Molecular diagnostic techniques have been used in research laboratories for pathogen identification in endophthalmitis and offer the possibility of rapid diagnosis, including in culture-negative cases. Intravitreal injection of antibiotics is the most important component of treatment; some cases also benefit from surgical debridement of the vitreous by a vitrectomy. The visual outcome depends partly on the pathogen: coagulase-negative staphylococcal endophthalmitis has a better prognosis than does streptococcal endophthalmitis, for example. Endophthalmitis is a medical emergency, and prompt diagnosis and treatment are essential for saving vision.

Exogenous Streptococcus pneumoniae Endophthalmitis in Diabetic Rabbits

Diabetics are at increased risk for eye infections including bacterial endophthalmitis. It is unclear whether the severity of endophthalmitis is greater in these patients due to confounding factors such as pre-existing ocular diseases in some but not others. Therefore, we tested the hypothesis that disease severity and/or bacterial loads would be significantly higher in a Type I diabetic rabbit model of Streptococcus pneumoniae endophthalmitis. Rabbits were treated with alloxan to destroy pancreatic islet cells, or mock-treated with vehicle, and maintained for 10 days before intravitreal infection with S. pneumoniae E353. Clinical scoring of the eyes was performed 24 and 48 hours after infection, followed by euthanasia and vitreous harvest to quantitate bacterial loads. There were no significant differences in clinical scores (P ≥ 0.440) or bacterial loads (P = 0.736), however, 4/12 (33%) of the diabetic rabbits became bacteremic. This finding not only indicates a breakdown in the blood-ocular barrier, but also prompts further investigation into the exploitation of the diabetic eye by the streptococci.

Modeling intraocular bacterial infections

Bacterial endophthalmitis is an infection and inflammation of the posterior segment of the eye which can result in significant loss of visual acuity. Even with prompt antibiotic, anti-inflammatory and surgical intervention, vision and even the eye itself may be lost. For the past century, experimental animal models have been used to examine various aspects of the pathogenesis and pathophysiology of bacterial endophthalmitis, to further the development of anti-inflammatory treatment strategies, and to evaluate the pharmacokinetics and efficacies of antibiotics. Experimental models allow independent control of many parameters of infection and facilitate systematic examination of infection outcomes. While no single animal model perfectly reproduces the human pathology of bacterial endophthalmitis, investigators have successfully used these models to understand the infectious process and the host response, and have provided new information regarding therapeutic options for the treatment of bacterial endophthalmitis. This review highlights experimental animal models of endophthalmitis and correlates this information with the clinical setting. The goal is to identify knowledge gaps that may be addressed in future experimental and clinical studies focused on improvements in the therapeutic preservation of vision during and after this disease.

Differential bacterial gene expression during experimental pneumococcal endophthalmitis

Streptococcus pneumoniae (pneumococcus) is a potential cause of bacterial endophthalmitis in humans that can result in ocular morbidity. We sought to identify pneumococcal genes that are differentially expressed during growth in the vitreous humor of the eye in an experimental endophthalmitis model. Microarray analysis was used to identify genes that were differentially expressed when pneumococci replicated in the vitreous of rabbit eyes as compared with bacteria grown in vitro in Todd Hewitt medium. Array results were verified by quantitative real-time PCR analysis of representative genes. Select genes potentially playing a role in virulence during endophthalmitis were deleted, and mutants were tested for reduced eye pathogenesis and altered adhesion to host cells. Array analysis identified 134 genes that were differentially expressed during endophthalmitis; 112 genes demonstrated increased expression during growth in the eye whereas 22 were downregulated. Real-time analysis verified increased expression of neuraminidase A (NanA; SP1693), neuraminidase B (NanB; SP1687) and serine protease (SP1954), and decreased expression of RlrA (SP0461) and choline transporter (SP1861). Mutation of NanA and NanB had no major effect on pathogenesis. Loss of SP1954 led to increased adherence to host cells. S. pneumoniae enhances and represses the expression of a variety of genes during endophthalmitis. While some of these genes reflect changes in metabolic requirements, some appear to play a role in immune evasion and pathogenesis in the eye.

Silver polyvinyl pyrrolidone nanoparticles exhibit a capsular polysaccharide influenced bactericidal effect against Streptococcus pneumoniae

Streptococcus pneumoniae remains a leading cause of morbidity and mortality worldwide. The highly adaptive nature of S. pneumoniae exemplifies the need for next generation antimicrobials designed to avoid high level resistance. Metal based nanomaterials fit this criterion. Our study examined the antimicrobial activity of gold nanospheres, silver coated polyvinyl pyrrolidone (AgPVP), and titanium dioxide (TiO₂) against various serotypes of S. pneumoniae. Twenty nanometer spherical AgPVP demonstrated the highest level of killing among the tested materials. AgPVP (0.6 mg/mL) was able to kill pneumococcal serotypes 2, 3, 4, and 19F within 4 h of exposure. Detailed analysis of cultures during exposure to AgPVP showed that both the metal ions and the solid nanoparticles participate in the killing of the pneumococcus. The bactericidal effect of AgPVP was lessened in the absence of the pneumococcal capsular polysaccharide. Capsule negative strains, JD908 and RX1, were only susceptible to AgPVP at concentrations at least 33% higher than their respective capsule expressing counterparts. These findings suggest that mechanisms of killing used by nanomaterials are not serotype dependent and that the capsular polysaccharide participates in the inhibition. In the near future these mechanisms will be examined as targets for novel antimicrobials.

Combating pathogenic microorganisms using plant-derived antimicrobials: a minireview of the mechanistic basis

The emergence of antibiotic resistance in pathogenic bacteria has led to renewed interest in exploring the potential of plant-derived antimicrobials (PDAs) as an alternative therapeutic strategy to combat microbial infections. Historically, plant extracts have been used as a safe, effective, and natural remedy for ailments and diseases in traditional medicine. Extensive research in the last two decades has identified a plethora of PDAs with a wide spectrum of activity against a variety of fungal and bacterial pathogens causing infections in humans and animals. Active components of many plant extracts have been characterized and are commercially available; however, research delineating the mechanistic basis of their antimicrobial action is scanty. This review highlights the potential of various plant-derived compounds to control pathogenic bacteria, especially the diverse effects exerted by plant compounds on various virulence factors that are critical for pathogenicity inside the host. In addition, the potential effect of PDAs on gut microbiota is discussed.

Role of TLR5 and flagella in bacillus intraocular infection

B. cereus possesses flagella which allow the organism to migrate within the eye during a blinding form of intraocular infection called endophthalmitis. Because flagella is a ligand for Toll-like receptor 5 (TLR5), we hypothesized that TLR5 contributed to endophthalmitis pathogenesis. Endophthalmitis was induced in C57BL/6J and TLR5−/− mice by injecting 100 CFU of B. cereus into the mid-vitreous. Eyes were analyzed for intraocular bacterial growth, retinal function, and inflammation by published methods. Purified B. cereus flagellin was also injected into the mid-vitreous of wild type C57BL/6J mice and inflammation was analyzed. TLR5 activation by B. cereus flagellin was also analyzed in vitro. B. cereus grew rapidly and at similar rates in infected eyes of C57BL/6J and TLR5−/− mice. A significant loss in retinal function in both groups of mice was observed at 8 and 12 hours postinfection. Retinal architecture disruption and acute inflammation (neutrophil infiltration and proinflammatory cytokine concentrations) increased and were significant at 8 and 12 hours postinfection. Acute inflammation was comparable in TLR5−/− and C57BL/6J mice. Physiological concentrations of purified B. cereus flagellin caused significant inflammation in C57BL/6J mouse eyes, but not to the extent of that observed during active infection. Purified B. cereus flagellin was a weak agonist for TLR5 in vitro. These results demonstrated that the absence of TLR5 did not have a significant effect on the evolution of B. cereus endophthalmitis. This disparity may be due to sequence differences in important TLR5 binding domains in B. cereus flagellin or the lack of flagellin monomers in the eye to activate TLR5 during infection. Taken together, these results suggest a limited role for flagellin/TLR5 interactions in B. cereus endophthalmitis. Based on this and previous data, the importance of flagella in this disease lies in its contribution to the motility of the organism within the eye during infection.

Streptococcus pneumoniae ocular infections, prominent role of unencapsulated isolates in conjunctivitis

The aim of this study was to determine the characteristics and shifts in serotype distribution of pneumococcal isolates causing ocular infections in a region of northern Spain in two periods: 1999-2010 for episodes of conjunctivitis (n = 612) and 1980-2010 for uncommon and more severe non-conjunctival ocular infections (n = 36). All isolates were serotyped and non-typeable isolates were confirmed as unencapsulated by multiplex-PCR of the lytA, ply and cpsA genes. Genotyping was done by pulsed-field gel electrophoresis and multi-locus sequence typing. Most conjunctivitis cases occurred in children under 5 years old (89.5%), and more severe non-conjunctival ocular infections occurred in patients older than 25 years (86.1%). Unencapsulated isolates were detected in 213 conjunctivitis episodes (34.8%) and one non-conjunctival infection (2.8%). Rates of unencapsulated isolates were similar throughout the study. Among 399 conjunctival encapsulated isolates, the most prevalent were serotypes 19A (n = 53), 15B (n = 30), 6A (n = 27), 19F (n = 25), 23F (n = 21) and 6B (n = 17). The most prevalent serotypes in non-conjunctival infections were serotype 3 (n = 4), 23F (n = 4), 6B (n = 3) and 19A (n = 3). Conjunctivitis caused by serotypes included in the hepta-valent pneumococcal conjugate vaccine steadily decreased, accounting for 34.9% (22/63) in 1999-2001, 19.7% (23/117) in 2002-04, 13.6% (33/242) in 2005-07 and 3.2% (6/190) in 2008-10. Among the 213 unencapsulated isolates, 31 different pulsed-field gel electrophoresis patterns were identified. The main clonal complexes (CC) were CC941 (ST941, ST942), CC448 (ST448) and CC344 (ST344, ST3097). CC941 was the predominant CC in 1999-2001, 2002-04 and 2005-07, being replaced by CC448 in 2008-10. The multidrug-resistant CC344 was present throughout the study.

Passive immunization with Pneumovax® 23 and pneumolysin in combination with vancomycin for pneumococcal endophthalmitis

Background

Capsule and pneumolysin (PLY) are two major virulence factors of Streptococcus pneumoniae. S. pneumoniae is one of the leading causes of bacterial endophthalmitis. The aim of this study is to determine whether passive immunization with the 23-valent pneumococcal polysaccharide vaccine (Pneumovax^® 23; PPSV23) or PLY protects against pneumococcal endophthalmitis.

Methods

New Zealand white rabbits were passively immunized with antiserum to PLY, PPSV23, a mixture of PPSV23/PLY, or PBS (mock). Vitreous was infected with a clinical strain of S. pneumoniae. In a separate group of experiments, vancomycin was injected 4 hours post-infection (PI) for each passively immunized group. Severity of infection, bacterial recovery, myeloperoxidase (MPO) activity and percent loss of retinal function were determined.

Results

Passive immunization with each antiserum significantly lowered clinical severity compared to mock immunization (PPSV23 = 9.19, PPSV23/PLY = 10.45, PLY = 8.71, Mock = 16.83; P = 0.0467). A significantly higher bacterial load was recovered from the vitreous of PLY passively immunized rabbits 24 hours PI (7.87 log₁₀ CFU) compared to controls (7.10 log₁₀ CFU; P = 0.0134). Retinas from immunized rabbits were more intact. Vitreous of PLY (2.88 MPO untis/mL) and PPSV23/PLY (2.17) passively immunized rabbits had less MPO activity compared to controls (5.64; P = 0.0480), and both passive immunizations (PLY = 31.34% loss of retinal function, PPSV23/PLY = 27.44%) helped to significantly preserve retinal function compared to controls (64.58%; P = 0.0323). When vancomycin was administered 4 hours PI, all eyes were sterile at 24 hours PI. A significantly lower clinical severity was observed for rabbits administered the combination immunization (5.29) or PPSV23 (5.29) with vancomycin treatment compared to controls (17.68; P = 0.0469).

Conclusions

Passive immunization with antisera to these antigens is effective in reducing clinical severity of pneumococcal endophthalmitis in rabbits. Addition of vancomycin to immunization is effective at eliminating the bacteria.

16S rRNA gene-based identification of bacteria in postoperative endophthalmitis by PCR-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) fingerprinting

Conventional microbiological culture techniques are frequently insufficient to confirm endophthalmitis clinical cases which could require urgent medical attention because it could lead to permanent vision loss. We are proposing PCR-DGGE and 16S rRNA gene libraries as an alternative to improve the detection and identification rate of bacterial species from endophthalmitis cases.