Panel 6: Vaccines

Reprioritization of biofilm metabolism is associated with nutrient adaptation and long-term survival of Haemophilus influenzae

Nontypeable Haemophilus influenzae (NTHI) is a human-restricted pathogen with an essential requirement for heme-iron acquisition. We previously demonstrated that microevolution of NTHI promotes stationary phase survival in response to transient heme-iron restriction. In this study, we examine the metabolic contributions to biofilm formation using this evolved NTHI strain, RM33. Quantitative analyses identified 29 proteins, 55 transcripts, and 31 metabolites that significantly changed within in vitro biofilms formed by RM33. The synthesis of all enzymes within the tryptophan and glycogen pathways was significantly increased in biofilms formed by RM33 compared with the parental strain. In addition, increases were observed in metabolite transport, adhesin production, and DNA metabolism. Furthermore, we observed pyruvate as a pivotal point in the metabolic pathways associated with changes in cAMP phosphodiesterase activity during biofilm formation. Taken together, changes in central metabolism combined with increased stores of nutrients may serve to counterbalance nutrient sequestration.

Otitis Media in Fully Vaccinated Preschool Children in the Pneumococcal Conjugate Vaccine Era

Objectives. To evaluate the effect of pneumococcal conjugate vaccine (PCV13) on the burden of acute otitis media (AOM) and to evaluate the characteristics of AOM versus otitis media with effusion (OME) in the 2 PCV periods. Methods. A cohort of fully vaccinated children aged 18 to 60 months diagnosed with AOM from 2006 to 2015 was identified. Patients with otorrhea/bulging tympanic membrane were considered as true AOM, while those without bulging/otorrhea were considered to have OME. Burden of true AOM in the PCV7 and PCV13 periods and clinical features of true AOM versus OME were compared. Results. Of 393 episodes in our cohort, 50.8% occurred in PCV7 period. Burden of true AOM in the 2 PCV groups was similar: 26% in PCV7 versus 26.4% in PCV13 (odds ratio [OR] = 1.02, 95% confidence interval [CI] = 0.65-1.60). Factors significantly associated with OME were cold season (OR = 1.54, 95% CI = 1.04-2.4), fever (OR = 2.05, 95% CI = 1.29-3.3), and recurrence (OR = 2.24, 95% CI = 1.22-4.09). No complications of AOM were identified. Majority episodes were treated with antibiotics. Conclusion. Unlike the role of PCV13 in reducing invasive pneumococcal disease, its effect on reducing the burden of AOM is minimal as compared with PCV7. With regard to characteristics of AOM versus OME, findings of tympanic membrane should be used to suggest a diagnosis of AOM, instead of occurrence of fever or recurrence of AOM episodes. Using this approach would help in guiding the use of antibiotics appropriately.

Immunogenicity of Nontypeable Haemophilus influenzae Outer Membrane Vesicles and Protective Ability in the Chinchilla Model of Otitis Media

Outer membrane vesicles (OMVs) produced by Gram-negative bacteria are enriched in several outer membrane components, including major and minor outer membrane proteins and lipooligosaccharide. We assessed the functional activity of nontypeable Haemophilus influenzae (NTHi) OMV-specific antisera and the protective ability of NTHi OMVs as vaccine antigens in the chinchilla otitis media model. OMVs were purified from three HMW1/HMW2-expressing NTHi strains, two of which were also engineered to overexpress Hia proteins. OMV-specific antisera raised in guinea pigs were assessed for their ability to mediate killing of representative NTHi in an opsonophagocytic assay. The three OMV-specific antisera mediated killing of 18 of 65, 24 of 65, and 30 of 65 unrelated HMW1/HMW2-expressing NTHi strains. Overall, they mediated killing of 39 of 65 HMW1/HMW2-expressing strains. The two Hia-expressing OMV-specific antisera mediated killing of 17 of 25 and 14 of 25 unrelated Hia-expressing NTHi strains. Overall, they mediated killing of 20 of 25 Hia-expressing strains. OMVs from prototype NTHi strain 12 were used to immunize chinchillas and the course of middle ear infection was monitored following intrabullar challenge with the homologous strain. All control animals developed culture-positive otitis media, as did two of three HMW1/HMW2-immunized animals. All OMV-immunized animals, with or without supplemental HMW1/HMW2 immunization, were completely protected against otitis media. NTHi OMVs are the first immunogens examined in this model that provided complete protection with sterile immunity after NTHi strain 12 challenge. These data suggest that NTHi OMVs hold significant potential as components of protective NTHi vaccines, possibly in combination with HMW1/HMW2 proteins.

A Cation-Binding Surface Protein as a Vaccine Antigen To Prevent Moraxella catarrhalis Otitis Media and Infections in Chronic Obstructive Pulmonary Disease

Moraxella catarrhalis is an exclusively human respiratory tract pathogen that is a common cause of otitis media in children and respiratory tract infections in adults with chronic obstructive pulmonary disease. A vaccine to prevent these infections would have a major impact on reducing the substantial global morbidity and mortality in these populations. Through a genome mining approach, we identified AfeA, an ∼32-kDa substrate binding protein of an ABC transport system, as an excellent candidate vaccine antigen. Recombinant AfeA was expressed and purified and binds ferric, ferrous, manganese, and zinc ions, as demonstrated by thermal shift assays. It is a highly conserved protein that is present in all strains of M. catarrhalis Immunization with recombinant purified AfeA induces high-titer antibodies that recognize the native M. catarrhalis protein. AfeA expresses abundant epitopes on the bacterial surface and induces protective responses in the mouse pulmonary clearance model following aerosol challenge with M. catarrhalis Finally, AfeA is expressed during human respiratory tract infection of adults with chronic obstructive pulmonary disease (COPD). Based on these observations, AfeA is an excellent vaccine antigen to be included in a vaccine to prevent infections caused by M. catarrhalis.

Panel 6: Vaccines

Objective To review the literature on progress regarding (1) effectiveness of vaccines for prevention of otitis media (OM) and (2) development of vaccine antigens for OM bacterial and viral pathogens. Data Sources PubMed database of the National Library of Science. Review Methods We performed literature searches in PubMed for OM pathogens and candidate vaccine antigens, and we restricted the searches to articles in English that were published between July 2011 and June 2015. Panel members reviewed literature in their area of expertise. Conclusions Pneumococcal conjugate vaccines (PCVs) are somewhat effective for the prevention of pneumococcal OM, recurrent OM, OM visits, and tympanostomy tube insertions. Widespread use of PCVs has been associated with shifts in pneumococcal serotypes and bacterial pathogens associated with OM, diminishing PCV effectiveness against AOM. The 10-valent pneumococcal vaccine containing Haemophilus influenzae protein D (PHiD-CV) is effective for pneumococcal OM, but results from studies describing the potential impact on OM due to H influenzae have been inconsistent. Progress in vaccine development for H influenzae, Moraxella catarrhalis, and OM-associated respiratory viruses has been limited. Additional research is needed to extend vaccine protection to additional pneumococcal serotypes and other otopathogens. There are likely to be licensure challenges for protein-based vaccines, and data on correlates of protection for OM vaccine antigens are urgently needed. Implications for Practice OM continues to be a significant health care burden globally. Prevention is preferable to treatment, and vaccine development remains an important goal. As a polymicrobial disease, OM poses significant but not insurmountable challenges for vaccine development.

Sulfate-binding protein, CysP, is a candidate vaccine antigen of Moraxella catarrhalis

Moraxella catarrhalis causes otitis media in children and respiratory tract infections in adults with chronic obstructive pulmonary disease (COPD). A vaccine to prevent M. catarrhalis infections would have an enormous impact globally in preventing morbidity caused by M. catarrhalis in these populations. Using a genome mining approach we have identified a sulfate binding protein, CysP, of an ATP binding cassette (ABC) transporter system as a novel candidate vaccine antigen. CysP expresses epitopes on the bacterial surface and is highly conserved among strains. Immunization with CysP induces potentially protective immune responses in a murine pulmonary clearance model. In view of these features that indicate CysP is a promising vaccine antigen, we conducted further studies to elucidate its function. These studies demonstrated that CysP binds sulfate and thiosulfate ions, plays a nutritional role for the organism and functions in intracellular survival of M. catarrhalis in human respiratory epithelial cells. The observations that CysP has features of a vaccine antigen and also plays an important role in growth and survival of the organism indicate that CysP is an excellent candidate vaccine antigen to prevent M. catarrhalis otitis media and infections in adults with COPD.

The Vaccine Candidate Substrate Binding Protein SBP2 Plays a Key Role in Arginine Uptake, Which Is Required for Growth of Moraxella catarrhalis

Moraxella catarrhalis is an exclusively human pathogen that is an important cause of otitis media in children and lower respiratory tract infections in adults with chronic obstructive pulmonary disease. A vaccine to prevent M. catarrhalis infections would have an enormous global impact in reducing morbidity resulting from these infections. Substrate binding protein 2 (SBP2) of an ABC transporter system has recently been identified as a promising vaccine candidate antigen on the bacterial surface of M. catarrhalis. In this study, we showed that SBP1, -2, and -3 individually bind different basic amino acids with exquisite specificity. We engineered mutants that each expressed a single SBP from this gene cluster and showed in growth experiments that SBP1, -2, and -3 serve a nutritional function through acquisition of amino acids for the bacterium. SBP2 mediates uptake of arginine, a strict growth requirement of M. catarrhalis. Adherence and invasion assays demonstrated that SBP1 and SBP3 play a role in invasion of human respiratory epithelial cells, consistent with a nutritional role in intracellular survival in the human respiratory tract. This work demonstrates that the SBPs of an ABC transporter system function in the uptake of basic amino acids to support growth of M. catarrhalis. The critical role of SBP2 in arginine uptake may contribute to its potential as a vaccine antigen.

A biphasic epigenetic switch controls immunoevasion, virulence and niche adaptation in non-typeable Haemophilus influenzae

Non-typeable Haemophilus influenzae contains an N⁶-adenine DNA-methyltransferase (ModA) that is subject to phase-variable expression (random ON/OFF switching). Five modA alleles, modA2, modA4, modA5, modA9 and modA10, account for over two-thirds of clinical otitis media isolates surveyed. Here, we use single molecule, real-time (SMRT) methylome analysis to identify the DNA-recognition motifs for all five of these modA alleles. Phase variation of these alleles regulates multiple proteins including vaccine candidates, and key virulence phenotypes such as antibiotic resistance (modA2, modA5, modA10), biofilm formation (modA2) and immunoevasion (modA4). Analyses of a modA2 strain in the chinchilla model of otitis media show a clear selection for ON switching of modA2 in the middle ear. Our results indicate that a biphasic epigenetic switch can control bacterial virulence, immunoevasion and niche adaptation in an animal model system.

Non-typeable Haemophilus influenzae, which causes ear and lung infections, has a DNA methyltransferase encoded by alternative alleles that are subject to random ON/OFF switching. Here, Atack et al. show that this epigenetic switch controls the expression of key proteins involved in virulence.

Acute otitis media in children-current treatment and prevention

Acute otitis media (AOM) is the most common bacterial infection in children and has a very varied clinical spectrum, ranging from spontaneous resolutions to serious complications. The effect of antibiotics in AOM depends on the chosen outcome, but has been shown to reduce pain somewhat, and have a greater beneficial effect in severe cases of AOM. Today, not all episodes of AOM are treated with antibiotics, but most countries have issued guidelines that include an option of watchful waiting in many cases. Prevention of AOM reaches from modification of environmental risk factors to vaccinations and surgery. Conjugate pneumococcal vaccines and influenza vaccines have been shown to somewhat reduce the number of AOM episodes in different groups of children. Grommets, with or without adenoidectomy, are effective at least during the first 6 months after surgery.

Vaccines for Nontypeable Haemophilus influenzae: the Future Is Now

Infections due to nontypeable Haemophilus influenzae result in enormous global morbidity in two clinical settings: otitis media in children and respiratory tract infections in adults with chronic obstructive pulmonary disease (COPD). Recurrent otitis media affects up to 20% of children and results in hearing loss, delays in speech and language development and, in developing countries, chronic suppurative otitis media. Infections in people with COPD result in clinic and emergency room visits, hospital admissions, and respiratory failure. An effective vaccine would prevent morbidity, help control health care costs, and reduce antibiotic use, a major contributor to the global crisis in bacterial antibiotic resistance. The widespread use of the pneumococcal conjugate vaccines is causing a relative increase in H. influenzae otitis media. The partial protection against H. influenzae otitis media induced by the pneumococcal H. influenzae protein D conjugate vaccine represents a proof of principle of the feasibility of a vaccine for nontypeable H. influenzae. An ideal vaccine antigen should be conserved among strains, have abundant epitopes on the bacterial surface, be immunogenic, and induce protective immune responses. Several surface proteins of H. influenzae have been identified as potential vaccine candidates and are in various stages of development. With continued research, progress toward a broadly effective vaccine to prevent infections caused by nontypeable H. influenzae is expected over the next several years.

Medical prevention of recurrent acute otitis media: an updated overview

Acute otitis media (AOM) is one of the most common pediatric diseases; almost all children experience at least one episode, and a third have two or more episodes in the first three years of life. The disease burden of AOM has important medical, social and economic effects. AOM requires considerable financial assistance due to needing at least one doctor visit and a prescription for antipyretics and/or antibiotics. AOM is also associated with high indirect costs, which are mostly related to lost days of work for one parent. Moreover, due to its acute symptoms and frequent recurrences, AOM considerably impacts both the child and family's quality of life. AOM prevention, particularly recurrent AOM (rAOM), is a primary goal of pediatric practice. In this paper, we review current evidence regarding the efficacy of medical treatments and vaccines for preventing rAOM and suggest the best approaches for AOM-prone children.

Update on otitis media - prevention and treatment

Acute otitis media and otitis media with effusion are common childhood disorders, a source of significant morbidity, and a leading cause of antibiotic prescription in primary health care. Although effective treatments are available, some shortcomings remain, and thus better treatments would be welcome. Recent discoveries within the field of otitis media research relating to its etiology and pathogenesis have led to further investigation aimed at developing novel treatments. This article provides a review of the latest evidence relating to the understanding of acute otitis media and otitis media with effusion, current treatment strategies, their limitations, new areas of research, and novel strategies for treatment.

Trends in otitis media-related health care use in the United States, 2001-2011

IMPORTANCE

Otitis media (OM) is a leading cause of pediatric health care visits and the most frequent reason children consume antibiotics or undergo surgery. During recent years, several interventions have been introduced aiming to decrease OM burden.

OBJECTIVE

To study the trend in OM-related health care use in the United States during the pneumococcal conjugate vaccine (PCV) era (2001-2011).

DESIGN, SETTING, AND PARTICIPANTS

An analysis of an insurance claims database of a large, nationwide managed health care plan was conducted. Enrolled children aged 6 years or younger with OM visits were identified.

MAIN OUTCOMES AND MEASURES

Annual OM visit rates, OM-related complications, and surgical interventions were analyzed.

RESULTS

Overall, 7.82 million unique children (5.51 million child-years) contributed 6.21 million primary OM visits; 52% were boys and 48% were younger than 2 years. There was a downward trend in OM visit rates from 2004 to 2011, with a significant drop that coincided with the advent of the 13-valent vaccine (PCV-13) in 2010. The observed OM visit rates in 2010 (1.00/child-year) and 2011 (0.81/child-year) were lower than the projected rates based on the 2005-2009 trend had there been no intervention (P < .001). Recurrent OM (≥3 OM visits within 6-month look-back) rates decreased at 0.003/child-year (95% CI, 0.002-0.004/child-year) in 2001-2009 and at 0.018/child-year (95% CI, 0.008-0.028/child-year) in 2010-2011. In the PCV-13 premarket years, there was a stable rate ratio (RR) between OM visit rates in children younger than 2 years and in those aged 2 to 6 years (RR, 1.38; 95% CI, 1.38-1.39); the RR decreased significantly (P < .001) during the transition year 2010 (RR 1.32; 95% CI, 1.31-1.33) and the postmarket year 2011 (RR 1.01; 95% CI, 1.00-1.02). Tympanic membrane perforation/otorrhea rates gradually increased (from 3721 per 100,000 OM child-years in 2001 to 4542 per 100,000 OM child-years in 2011; P < .001); the increase was significant only in the older children group. Mastoiditis rates substantially decreased (from 61 per 100,000 child-years in 2008 to 37 per 100,000 child-years in 2011; P < .001). Ventilating tube insertion rate decreased by 19% from 2010 to 2011 (P = .03).

CONCLUSIONS AND RELEVANCE

There was an overall downward trend in OM-related health care use from 2001 to 2011. The significant reduction in OM visit rates in 2010-2011 in children younger than 2 years coincided with the advent of PCV-13. Although tympanic membrane perforation/otorrhea rates steadily increased during that period, mastoiditis and ventilating tube insertion rates decreased in the last years of the study.