Influenza A virus-infected hosts boost an invasive type of Streptococcus pyogenes infection in mice

Respiratory tract barrier dysfunction in viral-bacterial co-infection cases

A preceding viral infection of the respiratory tract predisposes the host to secondary bacterial pneumonia, known as a major cause of morbidity and mortality. However, the underlying mechanism of the viral-bacterial synergy that leads to disease progression has remained elusive, thus hampering the production of effective prophylactic and therapeutic intervention options. In addition to viral-induced airway epithelial damage, which allows dissemination of bacteria to the lower respiratory tract and increases their invasiveness, dysfunction of immune defense following a viral infection has been implicated as a factor for enhanced susceptibility to secondary bacterial infections. Given the proximity of the oral cavity to the respiratory tract, where viruses enter and replicate, it is also well-established that oral health status can significantly influence the initiation, progression, and pathology of respiratory viral infections. This review was conducted to focus on the dysfunction of the respiratory barrier, which plays a crucial role in providing physical and secretory barriers as well as immune defense in the context of viral-bacterial synergy. Greater understanding of barrier response to viral-bacterial co-infections, will ultimately lead to development of effective, broad-spectrum therapeutic approaches for prevention of enhanced susceptibility to these pathogens.

Bovine respiratory syncytial virus enhances the attachment of Trueperella pyogenes to cells

In cattle, bovine respiratory syncytial virus (BRSV) is associated with secondary bacterial infections; however, the mechanisms of the interaction between BRSV and bacteria are unclear. Trueperella pyogenes (T. pyogenes) causes pneumonia in cattle and is involved in secondary infections following viral infections. In this study, we evaluated the effect of BRSV infection on the adhesion of T. pyogenes to BRSV-infected cells. BRSV infection significantly enhanced the adhesion of T. pyogenes to cells in a multiplicity of infection- and time-dependent manner. The BRSV-mediated change in the adhesion of T. pyogenes was widely observed in various cell types and bacterial strains. The results from the gentamicin protection assay showed that BRSV infection did not affect the intracellular invasion ability of T. pyogenes. Furthermore, adhesion assays conducted using BRSV G protein-expressing cells and anti-BRSV G antibodies revealed that the increased adhesion of T. pyogenes to cells was mediated by the G protein of BRSV. In addition, immunofluorescence assay revealed the colocalization of BRSV G protein and T. pyogenes. Thus, BRSV infection can potentially lead to bovine respiratory disease complex by promoting the adhesion of T. pyogenes to the infected cells.

Complicated pneumonia caused by group A Streptococcus in children - 2022/2023 infectious season outbreak and update on clinical characteristics

BACKGROUND

An increased incidence of group A Streptococcus (GAS) infections has been observed in pediatric population post-COVID-19 pandemic. While the majority of reports refer to scarlet fever or invasive GAS disease, detailed data on pulmonary manifestations such as complicated community-acquired pneumonia (CAP) are scarce. The aim of this study was to assess the contribution of GAS to complicated CAP in children during the 2022/2023 infectious season.

METHODS

We retrospectively analyzed the etiology and clinical presentation of complicated CAP patients hospitalized in our tertiary care center in Warsaw, Poland, between August 2022 and May 2023.

RESULTS

Among 91 patients with complicated CAP, GAS was the dominant cause constituting 24.2% (22/91; 95% CI 15.8-34.3%) of the study group. 68.2% of GAS pneumonia patients presented symptoms of scarlet fever, and 27.3% had preceding or concurrent viral infection. GAS complicated CAP was associated with longer hospitalization, higher incidence of chest tube insertion, but shorter duration of chest tube drainage than complicated CAP of other etiology. Children with GAS complicated CAP had higher procalcitonin concentration (28.1 vs. 1.5 ng/dL; p<0.0001) and a lower platelets level (254.5 vs. 422 × 103/μL; p = 0.0031) than those with non-GAS infection.

CONCLUSIONS

GAS is currently the predominant pathogen of complicated CAP in children. Clinicians should be aware of the current epidemiological situation and a more severe course of GAS pneumonia in this age group, and should monitor patients presenting with symptoms of scarlet fever and preceding viral infection closely.

Clinical and molecular epidemiological features of critically ill patients with invasive group A Streptococcus infections: a Belgian multicenter case-series

BACKGROUND

Recent alerts have highlighted an increase in group A streptococcal (GAS) infections since 2022 in Europe and the United States. Streptococcus pyogenes can cause limited skin or mucosal disease, but can also present as severe invasive disease necessitating critical care. We performed a multicenter retrospective study of patients with GAS infections recently admitted to Belgian intensive care units (ICUs) since January 2022. We describe patient characteristics and investigate the molecular epidemiology of the S. pyogenes strains involved.

RESULTS

Between January 2022 and May 2023, a total of 86 cases (56 adults, 30 children) with GAS disease were admitted to critical care in the university hospitals of Leuven, Antwerp and Liège. We noted a strikingly high incidence of severe community-acquired pneumonia (sCAP) (45% of adults, 77% of children) complicated with empyema in 45% and 83% of adult and pediatric cases, respectively. Two-thirds of patients with S. pyogenes pneumonia had viral co-infection, with influenza (13 adults, 5 children) predominating. Other disease presentations included necrotizing fasciitis (23% of adults), other severe skin/soft tissue infections (16% of adults, 13% of children) and ear/nose/throat infections (13% of adults, 13% of children). Cardiogenic shock was frequent (36% of adults, 20% of children). Fifty-six patients (65%) had toxic shock syndrome. Organ support requirements were high and included invasive mechanical ventilation (77% of adults, 50% of children), renal replacement therapy (29% of adults, 3% of children) and extracorporeal membrane oxygenation (20% of adults, 7% of children). Mortality was 21% in adults and 3% in children. Genomic analysis of S. pyogenes strains from 55 out of 86 patients showed a predominance of emm1 strains (73%), with a replacement of the M1global lineage by the toxigenic M1UK lineage (83% of emm1 strains were M1UK).

CONCLUSIONS

The recent rise of severe GAS infections (2022-23) is associated with introduction of the M1UK lineage in Belgium, but other factors may be at play-including intense circulation of respiratory viruses and potentially an immune debt after the COVID pandemic. Importantly, critical care physicians should include S. pyogenes as causative pathogen in the differential diagnosis of sCAP.

Streptococcus pyogenes Colonization in Children Aged 24-59 Months in the Gambia: Impact of Live Attenuated Influenza Vaccine and Associated Serological Responses

BACKGROUND

Immunity to Streptococcus pyogenes in high burden settings is poorly understood. We explored S. pyogenes nasopharyngeal colonization after intranasal live attenuated influenza vaccine (LAIV) among Gambian children aged 24-59 months, and resulting serological response to 7 antigens.

METHODS

A post hoc analysis was performed in 320 children randomized to receive LAIV at baseline (LAIV group) or not (control). S. pyogenes colonization was determined by quantitative polymerase chain reaction (qPCR) on nasopharyngeal swabs from baseline (day 0), day 7, and day 21. Anti-streptococcal IgG was quantified, including a subset with paired serum before/after S. pyogenes acquisition.

RESULTS

The point prevalence of S. pyogenes colonization was 7%-13%. In children negative at day 0, S. pyogenes was detected at day 7 or 21 in 18% of LAIV group and 11% of control group participants (P = .12). The odds ratio (OR) for colonization over time was significantly increased in the LAIV group (day 21 vs day 0 OR, 3.18; P = .003) but not in the control group (OR, 0.86; P = .79). The highest IgG increases following asymptomatic colonization were seen for M1 and SpyCEP proteins.

CONCLUSIONS

Asymptomatic S. pyogenes colonization appears modestly increased by LAIV, and may be immunologically significant. LAIV could be used to study influenza-S. pyogenes interactions. Clinical Trials Registration. NCT02972957.

Influenza A Virus Exacerbates Group A Streptococcus Infection and Thwarts Anti-Bacterial Inflammatory Responses in Murine Macrophages

Seasonal influenza epidemics pose a considerable hazard for global health. In the past decades, accumulating evidence revealed that influenza A virus (IAV) renders the host vulnerable to bacterial superinfections which in turn are a major cause for morbidity and mortality. However, whether the impact of influenza on anti-bacterial innate immunity is restricted to the vicinity of the lung or systemically extends to remote sites is underexplored. We therefore sought to investigate intranasal infection of adult C57BL/6J mice with IAV H1N1 in combination with bacteremia elicited by intravenous application of Group A Streptococcus (GAS). Co-infection in vivo was supplemented in vitro by challenging murine bone marrow derived macrophages and exploring gene expression and cytokine secretion. Our results show that viral infection of mice caused mild disease and induced the depletion of CCL2 in the periphery. Influenza preceding GAS infection promoted the occurrence of paw edemas and was accompanied by exacerbated disease scores. In vitro co-infection of macrophages led to significantly elevated expression of TLR2 and CD80 compared to bacterial mono-infection, whereas CD163 and CD206 were downregulated. The GAS-inducible upregulation of inflammatory genes, such as Nos2, as well as the secretion of TNFα and IL-1β were notably reduced or even abrogated following co-infection. Our results indicate that IAV primes an innate immune layout that is inadequately equipped for bacterial clearance.

Oral mitis group streptococci reduce infectivity of influenza A virus via acidification and H2O2 production

Members of the mitis group streptococci are the most abundant inhabitants of the oral cavity and dental plaque. Influenza A virus (IAV), the causative agent of influenza, infects the upper respiratory tract, and co-infection with Streptococcus pneumoniae is a major cause of morbidity during influenza epidemics. S. pneumoniae is a member of mitis group streptococci and shares many features with oral mitis group streptococci. In this study, we investigated the effect of viable Streptococcus oralis, a representative member of oral mitis group, on the infectivity of H1N1 IAV. The infectivity of IAV was measured by a plaque assay using Madin-Darby canine kidney cells. When IAV was incubated in growing culture of S. oralis, the IAV titer decreased in a time- and dose-dependent manner and became less than 100-fold, whereas heat-inactivated S. oralis had no effect. Other oral streptococci such as Streptococcus mutans and Streptococcus salivarius also reduced the viral infectivity to a lesser extent compared to S. oralis and Streptococcus gordonii, another member of the oral mitis group. S. oralis produces hydrogen peroxide (H2O2) at a concentration of 1–2 mM, and its mutant deficient in H2O2 production showed a weaker effect on the inactivation of IAV, suggesting that H2O2 contributes to viral inactivation. The contribution of H2O2 was confirmed by an inhibition assay using catalase, an H2O2-decomposing enzyme. These oral streptococci produce short chain fatty acids (SCFA) such as acetic acid as a by-product of sugar metabolism, and we also found that the inactivation of IAV was dependent on the mildly acidic pH (around pH 5.0) of these streptococcal cultures. Although inactivation of IAV in buffers of pH 5.0 was limited, incubation in the same buffer containing 2 mM H2O2 resulted in marked inactivation of IAV, which was similar to the effect of growing S. oralis culture. Taken together, these results reveal that viable S. oralis can inactivate IAV via the production of SCFAs and H2O2. This finding also suggests that the combination of mildly acidic pH and H2O2 at low concentrations could be an effective method to inactivate IAV.

Decreased Antibiotic Consumption Coincided with Reduction in Bacteremia Caused by Bacterial Species with Respiratory Transmission Potential during the COVID-19 Pandemic

Nonpharmaceutical interventions implemented during the COVID-19 pandemic (2020−2021) have provided a unique opportunity to understand their impact on the wholesale supply of antibiotics and incidences of infections represented by bacteremia due to common bacterial species in Hong Kong. The wholesale antibiotic supply data (surrogate indicator of antibiotic consumption) and notifications of scarlet fever, chickenpox, and tuberculosis collected by the Centre for Health Protection, and the data of blood cultures of patients admitted to public hospitals in Hong Kong collected by the Hospital Authority for the last 10 years, were tabulated and analyzed. A reduction in the wholesale supply of antibiotics was observed. This decrease coincided with a significant reduction in the incidence of community-onset bacteremia due to Streptococcus pyogenes, Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis, which are encapsulated bacteria with respiratory transmission potential. This reduction was sustained during two pandemic years (period 2: 2020−2021), compared with eight pre-pandemic years (period 1: 2012−2019). Although the mean number of patient admissions per year (1,704,079 vs. 1,702,484, p = 0.985) and blood culture requests per 1000 patient admissions (149.0 vs. 158.3, p = 0.132) were not significantly different between periods 1 and 2, a significant reduction in community-onset bacteremia due to encapsulated bacteria was observed in terms of the mean number of episodes per year (257 vs. 58, p < 0.001), episodes per 100,000 admissions (15.1 vs. 3.4, p < 0.001), and per 10,000 blood culture requests (10.1 vs. 2.1, p < 0.001), out of 17,037,598 episodes of patient admissions with 2,570,164 blood culture requests. Consistent with the findings of bacteremia, a reduction in case notification of scarlet fever and airborne infections, including tuberculosis and chickenpox, was also observed; however, there was no reduction in the incidence of hospital-onset bacteremia due to Staphylococcus aureus or Escherichia coli. Sustained implementation of non-pharmaceutical interventions against respiratory microbes may reduce the overall consumption of antibiotics, which may have a consequential impact on antimicrobial resistance. Rebound of conventional respiratory microbial infections is likely with the relaxation of these interventions.

The Contribution of Viral Proteins to the Synergy of Influenza and Bacterial Co-Infection

A severe course of acute respiratory disease caused by influenza A virus (IAV) infection is often linked with subsequent bacterial superinfection, which is difficult to cure. Thus, synergistic influenza-bacterial co-infection represents a serious medical problem. The pathogenic changes in the infected host are accelerated as a consequence of IAV infection, reflecting its impact on the host immune response. IAV infection triggers a complex process linked with the blocking of innate and adaptive immune mechanisms required for effective antiviral defense. Such disbalance of the immune system allows for easier initiation of bacterial superinfection. Therefore, many new studies have emerged that aim to explain why viral-bacterial co-infection can lead to severe respiratory disease with possible fatal outcomes. In this review, we discuss the key role of several IAV proteins-namely, PB1-F2, hemagglutinin (HA), neuraminidase (NA), and NS1-known to play a role in modulating the immune defense of the host, which consequently escalates the development of secondary bacterial infection, most often caused by Streptococcus pneumoniae. Understanding the mechanisms leading to pathological disorders caused by bacterial superinfection after the previous viral infection is important for the development of more effective means of prevention; for example, by vaccination or through therapy using antiviral drugs targeted at critical viral proteins.

Secondary streptococcal infection following influenza

Secondary bacterial infection following influenza A virus (IAV) infection is a major cause of morbidity and mortality during influenza epidemics. Streptococcus pneumoniae has been identified as a predominant pathogen in secondary pneumonia cases that develop following influenza. Although IAV has been shown to enhance susceptibility to the secondary bacterial infection, the underlying mechanism of the viral-bacterial synergy leading to disease progression is complex and remains elusive. In this review, cooperative interactions of viruses and streptococci during co- or secondary infection with IAV are described. IAV infects the upper respiratory tract, therefore, streptococci that inhabit or infect the respiratory tract are of special interest. Since many excellent reviews on the co-infection of IAV and S. pneumoniae have already been published, this review is intended to describe the unique interactions between other streptococci and IAV. Both streptococcal and IAV infections modulate the host epithelial barrier of the respiratory tract in various ways. IAV infection directly disrupts epithelial barriers, though at the same time the virus modifies the properties of infected cells to enhance streptococcal adherence and invasion. Mitis group streptococci produce neuraminidases, which promote IAV infection in a unique manner. The studies reviewed here have revealed intriguing mechanisms underlying secondary streptococcal infection following influenza. This article is protected by copyright. All rights reserved.

The global proteome and ubiquitinome of bacterial and viral co-infected bronchial epithelial cells

Viral infections facilitate bacterial trafficking to the lower respiratory tract resulting in bacterial-viral co-infections. Bacterial dissemination to the lower respiratory tract is enhanced by influenza A virus induced epithelial cell damage and dysregulation of immune responses. Epithelial cells act as a line of defense and detect pathogens by a high variety of pattern recognition receptors. The post-translational modification ubiquitin is involved in almost every cellular process. Moreover, ubiquitination contributes to the regulation of host immune responses, influenza A virus uncoating and transport within host cells. We applied proteomics with a special focus on ubiquitination to assess the impact of single bacterial and viral as well as bacterial-viral co-infections on bronchial epithelial cells. We used Tandem Ubiquitin Binding Entities to enrich polyubiquitinated proteins and assess changes in the ubiquitinome. Infecting 16HBE cells with Streptococcus pyogenes led to an increased abundance of proteins related to mitochondrial translation and energy metabolism in proteome and ubiquitinome. In contrast, influenza A virus infection mainly altered the ubiquitinome. Co-infections had no additional impact on protein abundances or affected pathways. Changes in protein abundance and enriched pathways were assigned to imprints of both infecting pathogens. SIGNIFICANCE: Viral and bacterial co-infections of the lower respiratory tract are a burden for health systems worldwide. Therefore, it is necessary to elucidate the complex interplay between the host and the infecting pathogens. Thus, we analyzed the proteome and the ubiquitinome of co-infected bronchial epithelial cells to elaborate a potential synergism of the two infecting organisms. The results presented in this work can be used as a starting point for further analyses.

Induction of cyclophilin A by influenza A virus infection facilitates group A Streptococcus coinfection

During influenza A epidemics, bacterial coinfection is a major cause of increased morbidity and mortality. However, the roles of host factors in regulating influenza A virus (IAV)-triggered bacterial coinfection remain elusive. Cyclophilin A (CypA) is an important regulator of infection and immunity. Here, we show that IAV-induced CypA expression facilitates group A Streptococcus (GAS) coinfection both in vitro and in vivo. Upon IAV infection, CypA interacts with focal adhesion kinase (FAK) and inhibited E3 ligase cCbl-mediated, K48-linked ubiquitination of FAK, which positively regulates integrin α5 expression and actin rearrangement via the FAK/Akt signaling pathway to facilitate GAS colonization and invasion. Notably, CypA deficiency or inhibition by cyclosporine A significantly inhibits IAV-triggered GAS coinfection in mice. Collectively, these findings reveal that CypA is critical for GAS infection, and induction of CypA expression is another way for IAV to promote bacterial coinfection, suggesting that CypA is a promising therapeutic target for the secondary bacterial infection.

Cytomegalovirus infection: friend or foe in rheumatoid arthritis?

Human cytomegalovirus (HCMV) is a β-herpesvirus that causes inflammation and remains for life in a latent state in their host. HCMV has been at the center of many hypotheses regarding RA.

We have recently shown that HCMV infection impairs bone erosion through the induction of the mRNA-binding protein QKI5. Latently infected RA patients display a slower progression of bone erosion in patients from a national cohort. Our observations question the possible association between HCMV and the pathophysiology of RA. In this review, we examine the possibility that HCMV may be an aggravating factor of inflammation in RA while protecting from bone erosion. We also assess its relationship with other pathogens such as bacteria causing periodontitis and responsible for ACPA production.

This review thus considers whether HCMV can be regarded as a friend or a foe in the pathogenesis and the course of RA.

Molecular pathogenesis of secondary bacterial infection associated to viral infections including SARS-CoV-2

Secondary bacterial infections are commonly associated with prior or concomitant respiratory viral infections. Viral infections damage respiratory airways and simultaneously defects both innate and acquired immune response that provides a favorable environment for bacterial growth, adherence, and facilitates invasion into healthy sites of the respiratory tract. Understanding the molecular mechanism of viral-induced secondary bacterial infections will provide us a chance to develop novel and effective therapeutic approaches for disease prevention. The present study describes details about the secondary bacterial infection during viral infections and their immunological changes.The outcome of discussion avails an opportunity to understand possible secondary bacterial infections associated with novel SARS-CoV-2, presently causing pandemic outbreak COVID-19.

Immunotherapy targeting the Streptococcus pyogenes M protein or streptolysin O to treat or prevent influenza A superinfection

Viral infections complicated by a bacterial infection are typically referred to as coinfections or superinfections. Streptococcus pyogenes, the group A streptococcus (GAS), is not the most common bacteria associated with influenza A virus (IAV) superinfections but did cause significant mortality during the 2009 influenza pandemic even though all isolates are susceptible to penicillin. One approach to improve the outcome of these infections is to use passive immunization targeting GAS. To test this idea, we assessed the efficacy of passive immunotherapy using antisera against either the streptococcal M protein or streptolysin O (SLO) in a murine model of IAV-GAS superinfection. Prophylactic treatment of mice with antiserum to either SLO or the M protein decreased morbidity compared to mice treated with non-immune sera; however, neither significantly decreased mortality. Therapeutic use of antisera to SLO decreased morbidity compared to mice treated with non-immune sera but neither antisera significantly reduced mortality. Overall, the results suggest that further development of antibodies targeting the M protein or SLO may be a useful adjunct in the treatment of invasive GAS diseases, including IAV-GAS superinfections, which may be particularly important during influenza pandemics.

Clinical Description and Outcomes of Australian Children With Invasive Group A Streptococcal Disease

BACKGROUND

Invasive group A streptococcal disease is a severe infection with a high case fatality rate, estimated to cause more than 150,000 deaths per year worldwide. The clinical presentation of this infection is variable, and early diagnosis can be challenging. There are few data on its short- and longer-term outcomes, especially in children. The aim of this study was to assess the clinical presentation, management and short- and longer-term outcomes of invasive group A streptococcal disease in children in Australia.

METHODS

We undertook a prospective surveillance study of children with laboratory-confirmed invasive group A streptococcus disease admitted to 7 sentinel tertiary and quaternary pediatric hospitals in Australia between July 2016 and June 2018. We collected demographic and clinical data and contacted patients 6 months after discharge to assess longer-term outcomes.

RESULTS

We enrolled 181 children, 7 days to 16 years of age. The principal site of invasive infection was blood (126 children, 69.6%), and the most frequent clinical presentation was pneumonia in 46 children (25.4%). Twenty-six children developed streptococcal toxic shock syndrome (14.4%), and 74 had severe disease (40.9%), including 71 admitted to the intensive care unit. Five children died (2.8%). At discharge and 6 months, 29.3% and 15.2% of the children had persisting health problems, respectively.

CONCLUSIONS

Invasive group A streptococcal infection in Australian children is frequently severe and has a high long-term morbidity burden, highlighting the need for strengthened clinical care pathways, epidemiologic surveillance and prevention strategies.

Volatile scents of influenza A and S. pyogenes (co-)infected cells

Influenza A is a serious pathogen itself, but often leads to dangerous co-infections in combination with bacterial species such as Streptococcus pyogenes. In comparison to classical biochemical methods, analysis of volatile organic compounds (VOCs) in headspace above cultures can enable destruction free monitoring of metabolic processes in vitro. Thus, volatile biomarkers emitted from biological cell cultures and pathogens could serve for monitoring of infection processes in vitro. In this study we analysed VOCs from headspace above (co)-infected human cells by using a customized sampling system. For investigating the influenza A mono-infection and the viral-bacterial co-infection in vitro, we analysed VOCs from Detroit cells inoculated with influenza A virus and S. pyogenes by means of needle-trap micro-extraction (NTME) and gas chromatography mass spectrometry (GC-MS). Besides the determination of microbiological data such as cell count, cytokines, virus load and bacterial load, emissions from cell medium, uninfected cells and bacteria mono-infected cells were analysed. Significant differences in emitted VOC concentrations were identified between non-infected and infected cells. After inoculation with S. pyogenes, bacterial infection was mirrored by increased emissions of acetaldehyde and propanal. N-propyl acetate was linked to viral infection. Non-destructive monitoring of infections by means of VOC analysis may open a new window for infection research and clinical applications. VOC analysis could enable early recognition of pathogen presence and in-depth understanding of their etiopathology.

TIV Vaccination Modulates Host Responses to Influenza Virus Infection that Correlate with Protection against Bacterial Superinfection

Background: Influenza virus infection predisposes to secondary bacterial pneumonia. Currently licensed influenza vaccines aim at the induction of neutralizing antibodies and are less effective if the induction of neutralizing antibodies is low and/or the influenza virus changes its antigenic surface. We investigated the effect of suboptimal vaccination on the outcome of post-influenza bacterial superinfection. Methods: We established a mouse vaccination model that allows control of disease severity after influenza virus infection despite inefficient induction of virus-neutralizing antibody titers by vaccination. We investigated the effect of vaccination on virus-induced host immune responses and on the outcome of superinfection with Staphylococcus aureus. Results: Vaccination with trivalent inactivated virus vaccine (TIV) reduced morbidity after influenza A virus infection but did not prevent virus replication completely. Despite the poor induction of influenza-specific antibodies, TIV protected from mortality after bacterial superinfection. Vaccination limited loss of alveolar macrophages and reduced levels of infiltrating pulmonary monocytes after influenza virus infection. Interestingly, TIV vaccination resulted in enhanced levels of eosinophils after influenza virus infection and recruitment of neutrophils in both lungs and mediastinal lymph nodes after bacterial superinfection. Conclusion: These observations highlight the importance of disease modulation by influenza vaccination, even when suboptimal, and suggest that influenza vaccination is still beneficial to protect during bacterial superinfection in the absence of complete virus neutralization.

Associations between common respiratory viruses and invasive group A streptococcal infection: A time-series analysis

Background

Invasive infections by group A Streptococcus (iGAS, Streptococcus pyogenes) have a winter seasonality which largely coincides with the season for influenza and other respiratory viruses. Influenza superinfections with GAS have been described to occur regularly and to show a severe clinical picture with high mortality. We aimed to study the extent to which influenza A and B viruses (IAV and IBV), respiratory syncytial virus (RSV) and rhinovirus circulation contribute to iGAS incidence and severity.

Methods

Time‐series regression models were built to explore the temporal associations between weekly laboratory counts of IAV, IBV, RSV and rhinovirus as independent variables and weekly counts of GAS disease notifications or laboratory GAS cultures as dependent variables.

Results

The weekly number of IAV detections showed a significant temporal association with the number of notifications of streptococcal toxic shock syndrome (STSS), a severe complication of iGAS. Depending on the season, up to 40% of all notified STSS cases was attributable to IAV circulation. Besides STSS, none of the other iGAS manifestations were associated with a respiratory virus.

Conclusions

Our study found an ecological temporal association between IAV and STSS, the most severe complication of iGAS. Future studies are needed to confirm this association and assess the possible preventability of STSS by influenza vaccination, especially in the age group 60 years and older.

Characterization of Host and Bacterial Contributions to Lung Barrier Dysfunction Following Co-infection with 2009 Pandemic Influenza and Methicillin Resistant Staphylococcus aureus

Influenza viruses are a threat to global public health resulting in ~500,000 deaths each year. Despite an intensive vaccination program, influenza infections remain a recurrent, yet unsolved public health problem. Secondary bacterial infections frequently complicate influenza infections during seasonal outbreaks and pandemics, resulting in increased morbidity and mortality. Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), is frequently associated with these co-infections, including the 2009 influenza pandemic. Damage to alveolar epithelium is a major contributor to severe influenza-bacterial co-infections and can result in gas exchange abnormalities, fluid leakage, and respiratory insufficiency. These deleterious manifestations likely involve both pathogen- and host-mediated mechanisms. However, there is a paucity of information regarding the mechanisms (pathogen- and/or host-mediated) underlying influenza-bacterial co-infection pathogenesis. To address this, we characterized the contributions of viral-, bacterial-, and host-mediated factors to the altered structure and function of alveolar epithelial cells during co-infection with a focus on the 2009 pandemic influenza (pdm2009) and MRSA. Here, we characterized pdm2009 and MRSA replication kinetics, temporal host kinome responses, modulation of MRSA virulence factors, and disruption of alveolar barrier integrity in response to pdm2009-MRSA co-infection. Our results suggest that alveolar barrier disruption during co-infection is mediated primarily through host response dysregulation, resulting in loss of alveolar barrier integrity.

Coinfection With Influenza A Virus and Klebsiella oxytoca: An Underrecognized Impact on Host Resistance and Tolerance to Pulmonary Infections

Pneumonia is a world health problem and a leading cause of death, particularly affecting children and the elderly (1, 2). Bacterial pneumonia following infection with influenza A virus (IAV) is associated with increased morbidity and mortality but the mechanisms behind this phenomenon are not yet well-defined (3). Host resistance and tolerance are two processes essential for host survival during infection. Resistance is the host's ability to clear a pathogen while tolerance is the host's ability to overcome the impact of the pathogen as well as the host response to infection (4-8). Some studies have shown that IAV infection suppresses the immune response, leading to overwhelming bacterial loads (9-13). Other studies have shown that some IAV/bacterial coinfections cause alterations in tolerance mechanisms such as tissue resilience (14-16). In a recent analysis of nasopharyngeal swabs from patients hospitalized during the 2013-2014 influenza season, we have found that a significant proportion of IAV-infected patients were also colonized with Klebsiella oxytoca, a gram-negative bacteria known to be an opportunistic pathogen in a variety of diseases (17). Mice that were infected with K. oxytoca following IAV infection demonstrated decreased survival and significant weight loss when compared to mice infected with either single pathogen. Using this model, we found that IAV/K. oxytoca coinfection of the lung is characterized by an exaggerated inflammatory immune response. We observed early inflammatory cytokine and chemokine production, which in turn resulted in massive infiltration of neutrophils and inflammatory monocytes. Despite this swift response, the pulmonary pathogen burden in coinfected mice was similar to singly-infected animals, albeit with a slight delay in bacterial clearance. In addition, during coinfection we observed a shift in pulmonary macrophages toward an inflammatory and away from a tissue reparative phenotype. Interestingly, there was only a small increase in tissue damage in coinfected lungs as compared to either single infection. Our results indicate that during pulmonary coinfection a combination of seemingly modest defects in both host resistance and tolerance may act synergistically to cause worsened outcomes for the host. Given the prevalence of K. oxytoca detected in human IAV patients, these dysfunctional tolerance and resistance mechanisms may play an important role in the response of patients to IAV.

Contributions of Influenza Virus Hemagglutinin and Host Immune Responses Toward the Severity of Influenza Virus: Streptococcus pyogenes Superinfections

Influenza virus infections can be complicated by bacterial superinfections, which are medically relevant because of a complex interaction between the host, the virus, and the bacteria. Studies to date have implicated several influenza virus genes, varied host immune responses, and bacterial virulence factors, however, the host-pathogen interactions that predict survival versus lethal outcomes remain undefined. Previous work by our group showed that certain influenza viruses could yield a survival phenotype (A/swine/Texas/4199-2/98-H3N2, TX98), whereas others were associated with a lethal phenotype (A/Puerto Rico/8/34-H1N1, PR8). Based on this observation, we developed the hypothesis that individual influenza virus genes could contribute to a superinfection, and that the host response after influenza virus infection could influence superinfection severity. The present study analyzes individual influenza virus gene contributions to superinfection severity using reassortant viruses created using TX98 and PR8 viral genes. Host and pathogen interactions, relevant to survival and lethal phenotypes, were studied with a focus on pathogen clearance, host cellular infiltrates, and cytokine levels after infection. Specifically, we found that the hemagglutinin gene expressed by an influenza virus can contribute to the severity of a secondary bacterial infection, likely through modulation of host proinflammatory responses. Altogether, these results advance our understanding of molecular mechanisms underlying influenza virus-bacteria superinfections and identify viral and corresponding host factors that may contribute to morbidity and mortality.

Influenza interaction with cocirculating pathogens and its impact on surveillance, pathogenesis, and epidemic profile: A key role for mathematical modelling

Evidence is mounting that influenza virus interacts with other pathogens colonising or infecting the human respiratory tract. Taking into account interactions with other pathogens may be critical to determining the real influenza burden and the full impact of public health policies targeting influenza. This is particularly true for mathematical modelling studies, which have become critical in public health decision-making. Yet models usually focus on influenza virus acquisition and infection alone, thereby making broad oversimplifications of pathogen ecology. Herein, we report evidence of influenza virus interactions with bacteria and viruses and systematically review the modelling studies that have incorporated interactions. Despite the many studies examining possible associations between influenza and Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, Neisseria meningitidis, respiratory syncytial virus (RSV), human rhinoviruses, human parainfluenza viruses, etc., very few mathematical models have integrated other pathogens alongside influenza. The notable exception is the pneumococcus-influenza interaction, for which several recent modelling studies demonstrate the power of dynamic modelling as an approach to test biological hypotheses on interaction mechanisms and estimate the strength of those interactions. We explore how different interference mechanisms may lead to unexpected incidence trends and possible misinterpretation, and we illustrate the impact of interactions on public health surveillance using simple transmission models. We demonstrate that the development of multipathogen models is essential to assessing the true public health burden of influenza and that it is needed to help improve planning and evaluation of control measures. Finally, we identify the public health, surveillance, modelling, and biological challenges and propose avenues of research for the coming years.

Secondary Bacterial Infections Associated with Influenza Pandemics

Lower and upper respiratory infections are the fourth highest cause of global mortality (Lozano et al., 2012). Epidemic and pandemic outbreaks of respiratory infection are a major medical concern, often causing considerable disease and a high death toll, typically over a relatively short period of time. Influenza is a major cause of epidemic and pandemic infection. Bacterial co/secondary infection further increases morbidity and mortality of influenza infection, with Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus reported as the most common causes. With increased antibiotic resistance and vaccine evasion it is important to monitor the epidemiology of pathogens in circulation to inform clinical treatment and development, particularly in the setting of an influenza epidemic/pandemic.

Viral-bacterial interactions in the respiratory tract

In the respiratory tract, viruses and bacteria can interact on multiple levels. It is well known that respiratory viruses, particularly influenza viruses, increase the susceptibility to secondary bacterial infections. Numerous mechanisms, including compromised physical and immunological barriers, and changes in the microenvironment have hereby been shown to contribute to the development of secondary bacterial infections. In contrast, our understanding of how bacteria shape a response to subsequent viral infection is still limited. There is emerging evidence that persistent infection (or colonization) of the lower respiratory tract (LRT) with potential pathogenic bacteria, as observed in diseases like chronic obstructive pulmonary disease or cystic fibrosis, modulates subsequent viral infections by increasing viral entry receptors and modulating the inflammatory response. Moreover, recent studies suggest that even healthy lungs are not, as had long been assumed, sterile. The composition of the lung microbiome may thus modulate responses to viral infections. Here we summarize the current knowledge on the co-pathogenesis between viruses and bacteria in LRT infections.

IL-2 Expression and T lymphocyte Phenotyping in Young Children Suffering from Upper Respiratory Tract Infection with Streptococcus Pyogenes

T cells are components of adaptive immunity and are involved in the resolution of respiratory infections, which are a major cause of morbidity and mortality in young children worldwide. Activation and differentiation of T cells is given mostly by the cytokine IL-2. This study aimed to determine the phenotype of T cells and IL-2 expression in children suffering from upper respiratory tract infection with Streptococcus pyogenes (S. pyogenes). For this purpose, IL-2 expression at its gene and protein levels and quantitation of CD4(+) and CD8(+) T lymphocytes were assessed in children aged 0-5 years old suffering from upper respiratory tract infection with S. pyogenes and healthy children of the same age. Children with S. pyogenes infection had a higher expression of IL-2 gene and a lower level of this cytokine expression at protein level than healthy children. The numbers of CD4(+) T lymphocytes were similar among the groups. In contrast, difference in the numbers of CD8(+) T lymphocytes among the groups was found. We conclude that infections by S. pyogenes in young children lead to an increased expression of IL-2 mRNA.

The Association between Invasive Group A Streptococcal Diseases and Viral Respiratory Tract Infections

Viral infections of the upper respiratory tract are associated with a variety of invasive diseases caused by Streptococcus pyogenes, the group A streptococcus, including pneumonia, necrotizing fasciitis, toxic shock syndrome, and bacteremia. While these polymicrobial infections, or superinfections, are complex, progress has been made in understanding the molecular basis of disease. Areas of investigation have included the characterization of virus-induced changes in innate immunity, differences in bacterial adherence and internalization following viral infection, and the efficacy of vaccines in mitigating the morbidity and mortality of superinfections. Here, we briefly summarize viral-S. pyogenes superinfections with an emphasis on those affiliated with influenza viruses.

The Role of Virus Infection in Deregulating the Cytokine Response to Secondary Bacterial Infection

Proinflammatory cytokines are produced by macrophages and dendritic cells (DCs) after infection to stimulate T helper (Th) cells, linking innate and adaptive immunity. Virus infections can deregulate the proinflammatory cytokine response like tumor necrosis factor-α and interleukin (IL)-2, making the host more susceptible to secondary bacterial infections. Studies using various viruses such as lymphocytic choriomeningitis virus, influenza A virus, and human immunodeficiency virus have revealed several intriguing mechanisms that account for the increased susceptibility to several prevalent bacterial infections. In particular, type I interferons induced during a virus infection have been observed to play a role in suppressing the production of some key antibacterial proinflammatory cytokines such as IL-23 and IL-17. Other suppressive mechanisms as a result of cytokine deregulation by viral infections include reduced function of immune cells such as DC, macrophage, natural killer, CD4(+), and CD8(+) T cells leading to impaired clearance of secondary bacterial infections. In this study, we highlight some of the immune mechanisms that become deregulated by viral infections, and can thus become defective during secondary bacterial infections.

Reducing the impact of influenza-associated secondary pneumococcal infections

When administered prophylactically, we show that the Toll-like receptor-2 (TLR-2) agonist PEG-Pam2Cys (pegylated-S-(2,3-bis(palmitoyloxy)propyl)cysteine) not only mediates potent anti-viral activity against influenza virus but also reduces the impact of secondary infections with Streptococcus pneumoniae (the pneumococcus) by reducing (i) pulmonary viral and bacterial burdens, (ii) the levels of proinflammatory cytokines that normally accompany influenza and S. pneumoniae secondary infections and (iii) the vascular permeability of the pulmonary tract that can allow bacterial invasion of the blood in mice. We also show that an inactivated detergent-disrupted influenza virus vaccine formulated with the Pam2Cys-based adjuvant R4-Pam2Cys provides the host with both immediate and long-term protection against secondary pneumococcal infections following influenza virus infection through innate and specific immune mechanisms, respectively. Vaccinated animals generated influenza virus-specific immune responses that provided the host with long-term protection against influenza virus and its sequelae. This vaccine, which generates an immediate response, provides an additional countermeasure, which is ideal for use even in the midst of an influenza outbreak.

Molecular and genomic characterization of pathogenic traits of group A Streptococcus pyogenes

Group A streptococcus (GAS) or Streptococcus pyogenes causes various diseases ranging from self-limiting sore throat to deadly invasive diseases. The genome size of GAS is 1.85-1.9 Mb, and genomic rearrangement has been demonstrated. GAS possesses various surface-associated substances such as hyaluronic capsule, M proteins, and fibronectin/laminin/immunoglobulin-binding proteins. These are related to the virulence and play multifaceted and mutually reflected roles in the pathogenesis of GAS infections. Invasion of GAS into epithelial cells and deeper tissues provokes immune and non-immune defense or inflammatory responses including the recruitment of neutrophils, macrophages, and dendritic cells in hosts. GAS frequently evades host defense mechanisms by using its virulence factors. Extracellular products of GAS may perturb cellular and subcellular functions and degrade tissues enzymatically, which leads to the aggravation of local and/or systemic disorders in the host. In this review, we summarize some important cellular and extracellular substances that may affect pathogenic processes during GAS infections, and the host responses to these.

Vaccination against the M protein of Streptococcus pyogenes prevents death after influenza virus: S. pyogenes super-infection

Influenza virus infections are associated with a significant number of illnesses and deaths on an annual basis. Many of the deaths are due to complications from secondary bacterial invaders, including Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, and Streptococcus pyogenes. The β-hemolytic bacteria S. pyogenes colonizes both skin and respiratory surfaces, and frequently presents clinically as strep throat or impetigo. However, when these bacteria gain access to normally sterile sites, they can cause deadly diseases including sepsis, necrotizing fasciitis, and pneumonia. We previously developed a model of influenza virus:S. pyogenes super-infection, which we used to demonstrate that vaccination against influenza virus can limit deaths associated with a secondary bacterial infection, but this protection was not complete. In the current study, we evaluated the efficacy of a vaccine that targets the M protein of S. pyogenes to determine whether immunity toward the bacteria alone would allow the host to survive an influenza virus:S. pyogenes super-infection. Our data demonstrate that vaccination against the M protein induces IgG antibodies, in particular those of the IgG1 and IgG2a isotypes, and that these antibodies can interact with macrophages. Ultimately, this vaccine-induced immunity eliminated death within our influenza virus:S. pyogenes super-infection model, despite the fact that all M protein-vaccinated mice showed signs of illness following influenza virus inoculation. These findings identify immunity against bacteria as an important component of protection against influenza virus:bacteria super-infection.

Secondary bacterial infections in influenza virus infection pathogenesis

Influenza is often complicated by bacterial pathogens that colonize the nasopharynx and invade the middle ear and/or lung epithelium. Incidence and pathogenicity of influenza-bacterial coinfections are multifactorial processes that involve various pathogenic virulence factors and host responses with distinct site- and strain-specific differences. Animal models and kinetic models have improved our understanding of how influenza viruses interact with their bacterial co-pathogens and the accompanying immune responses. Data from these models indicate that considerable alterations in epithelial surfaces and aberrant immune responses lead to severe inflammation, a key driver of bacterial acquisition and infection severity following influenza. However, further experimental and analytical studies are essential to determining the full mechanistic spectrum of different viral and bacterial strains and species and to finding new ways to prevent and treat influenza-associated bacterial coinfections. Here, we review recent advances regarding transmission and disease potential of influenza-associated bacterial infections and discuss the current gaps in knowledge.

Engagement of NKG2D on bystander memory CD8 T cells promotes increased immunopathology following Leishmania major infection

One of the hallmarks of adaptive immunity is the development of a long-term pathogen specific memory response. While persistent memory T cells certainly impact the immune response during a secondary challenge, their role in unrelated infections is less clear. To address this issue, we utilized lymphocytic choriomeningitis virus (LCMV) and Listeria monocytogenes immune mice to investigate whether bystander memory T cells influence Leishmania major infection. Despite similar parasite burdens, LCMV and Listeria immune mice exhibited a significant increase in leishmanial lesion size compared to mice infected with L. major alone. This increased lesion size was due to a severe inflammatory response, consisting not only of monocytes and neutrophils, but also significantly more CD8 T cells. Many of the CD8 T cells were LCMV specific and expressed gzmB and NKG2D, but unexpectedly expressed very little IFN-γ. Moreover, if CD8 T cells were depleted in LCMV immune mice prior to challenge with L. major, the increase in lesion size was lost. Strikingly, treating with NKG2D blocking antibodies abrogated the increased immunopathology observed in LCMV immune mice, showing that NKG2D engagement on LCMV specific memory CD8 T cells was required for the observed phenotype. These results indicate that bystander memory CD8 T cells can participate in an unrelated immune response and induce immunopathology through an NKG2D dependent mechanism without providing increased protection.

Cutaneous leishmaniasis has a wide spectrum of clinical presentations, from mild self-healing lesions to severe chronic infections. Differences in each individual's response are related to pathogen dose and the genetic and physiological status of the host, but exactly what causes the broad spectrum of disease is not well understood. Here we show that previous infection with a viral or bacterial pathogen led to increased immunopathology associated with L. major infection. This increase in immunopathology was not associated with any changes in parasite control and was characterized by an exaggerated inflammatory infiltrate into the site of infection. Ultimately, this increase in immunopathology was dependent on the presence of memory CD8 T cells from the previous infection and their expression of the NK cell receptor NKG2D, as depletion of these cells prior to infection with L. major or blockade of this receptor during infection ameliorated the disease. Our work suggests that the immunological history of a patient may be playing an underlying role in the pathology associated with leishmania infection and could be an important consideration for the understanding and treatment of this and other human diseases. This work also identifies the NKG2D pathway as a potential new target for therapeutic intervention.

Capsule ofStreptococcus pyogenesIs Essential for Delayed Death of Mice in a Model of Streptococcal Toxic Shock Syndrome

We have previously reported a mouse model of severe group A streptococcal infection (Microbiol. Immunol. 45: 777-786, 2001). When we injected Streptococcus pyogenes strains intramuscularly, the mice suffered from acute phase of infection for a few days but recovered from the illness and gained body weight. These mice, however, began to die after 3 weeks of infection, which we called 'delayed death.' Bacterial strains isolated from organs of the dead mice showed thick capsules. We, therefore, constructed a hyaluronic acid capsule gene, hasA, knockout mutant by homologous recombination and the effect of capsule on the death was observed. hasA knockout strain did not cause delayed death, though it caused acute death at high doses of infection. According to this result, the capsule is a critical pathogenic factor for causing the delayed death in our mouse model.

[Study of next generation influenza vaccine focused on "cross-protection by mucosal immunization" and "seed virus strains"]

Endemic infection by seasonal influenza virus usually occurs every winter season. Inside the host, human influenza viruses frequently undergo various point mutations at antigenic regions, in response to antibody pressure. Furthermore, the influenza virus has undergone frequent antigenic shifts for at least 100 years, some of which have caused influenza pandemics. In Japan, intramuscular immunization with influenza split-virion vaccines has been used to prevent seasonal influenza virus infections. Unfortunately, the efficacy of the current influenza vaccine immunization method is limited, even against viruses belonging to the same clade. Furthermore, the current vaccines are not expected to be protective against antigenically shifted viruses. Therefore, new approaches to vaccine development are needed to protect human populations against a potential pandemic virus. We are studying novel influenza vaccine designs to resolve the above weaknesses of the current influenza vaccines. I will describe our vaccine studies, "Cross-protection by mucosal immunization," and, "Preparation of seed virus strains to produce vaccines for possible pandemic influenza," in this symposium.

Bacterial coinfection in influenza: a grand rounds review

Bacterial coinfection complicated nearly all influenza deaths in the 1918 influenza pandemic and up to 34% of 2009 pandemic influenza A(H1N1) infections managed in intensive care units worldwide. More than 65,000 deaths attributable to influenza and pneumonia occur annually in the United States. Data from 683 critically ill patients with 2009 pandemic influenza A(H1N1) infection admitted to 35 intensive care units in the United States reveal that bacterial coinfection commonly occurs within the first 6 days of influenza infection, presents similarly to influenza infection occurring alone, and is associated with an increased risk of death. Pathogens that colonize the nasopharynx, including Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes, are most commonly isolated. Complex viral, bacterial, and host factors contribute to the pathogenesis of coinfection. Reductions in morbidity and mortality are dependent on prevention with available vaccines as well as early diagnosis and treatment.

Modulation of potential respiratory pathogens by pH1N1 viral infection

While much effort has been made to characterize influenza A pdm09 virus (pH1N1), the flu that was responsible for the fourth influenza pandemic, there is a lack of study on the composition of bacteria that lead to secondary infection. In this study, we recruited pneumonia patients with and without pH1N1 infection and characterized their oropharyngeal microbiota by the unbiased high-throughput sequencing method. While there were no significant differences in common bacterial pneumonia-causative agents (Acinetobacter and Streptococcus species), previously unreported Pseudomonas species equipped with chemotaxis and flagellar assembly genes significantly increased (>20-fold) in the pH1N1-infected group. Bacillus and Ralstonia species that also increased significantly (5-10-fold) were also found to possess similar signaling and motility genes. In contrast, no such genes were found in oral commensal Prevotella, Veillonella and Neisseria species, which decreased significantly, or in either Acinetobacter or 10 out of 21 Streptococcus species, including Streptococcus pneumoniae. Our results support the notion that pH1N1 infection provides a niche for previously unnoticed potential respiratory pathogens that were able to access the lower respiratory tract with weakened immunity.

Influenza virus neuraminidase contributes to the dextran sulfate-dependent suppressive replication of some influenza A virus strains

Dextran sulfate (DS), a negatively charged, sulfated polysaccharide, suppresses the replication of an influenza A virus strain, and this suppression is associated with inhibition of the hemagglutinin (HA)-dependent fusion activity. However, it remains unknown whether the replication of all or just some influenza A virus strains is suppressed by DS, or whether HA is the only target for the replication suppression. In the present study, we found that DS inhibited the replication of some, but not all influenza A virus strains. The suppression in the DS-sensitive strains was dose-dependent and neutralized by diethylaminoethyl-dextran (DD), which has a positive charge. The suppression by DS was observed not only at the initial stage of viral infection, which includes viral attachment and entry, but also at the late stage, which includes virus assembly and release from infected cells. Electron microscopy revealed that the DS induced viral aggregation at the cell surface. The neuraminidase (NA) activity of the strains whose viral replication was inhibited at the late stage was also more suppressed by DS than that of the strains whose replication was not inhibited, and this inhibition of NA activity was also neutralized by adding positively charged DD. Furthermore, we found that replacing the NA gene of a strain in which viral replication was inhibited by DS at the late stage with the NA gene from a strain in which viral replication was not inhibited, eliminated the DS-dependent suppression. These results suggest that the influenza virus NA contributes to the DS-suppressible virus release from infected cells at the late stage, and the suppression may involve the inhibition of NA activity by DS's negative charge.

Streptococcus pyogenes and re-emergence of scarlet fever as a public health problem

Explosive outbreaks of infectious diseases occasionally occur without immediately obvious epidemiological or microbiological explanations. Plague, cholera and Streptococcus pyogenes infection are some of the epidemic-prone bacterial infections. Besides epidemiological and conventional microbiological methods, the next-generation gene sequencing technology permits prompt detection of genomic and transcriptomic profiles associated with invasive phenotypes. Horizontal gene transfer due to mobile genetic elements carrying virulence factors and antimicrobial resistance, or mutations associated with the two component CovRS operon are important bacterial factors conferring survival advantage or invasiveness. The high incidence of scarlet fever in children less than 10 years old suggests that the lack of protective immunity is an important host factor. A high population density, overcrowded living environment and a low yearly rainfall are environmental factors contributing to outbreak development. Inappropriate antibiotic use is not only ineffective for treatment, but may actually drive an epidemic caused by drug-resistant strains and worsen patient outcomes by increasing the bacterial density at the site of infection and inducing toxin production. Surveillance of severe S. pyogenes infection is important because it can complicate concurrent chickenpox and influenza. Concomitant outbreaks of these two latter infections with a highly virulent and drug-resistant S. pyogenes strain can be disastrous.

Invasive bacterial infections following influenza: a time-series analysis in Montréal, Canada, 1996-2008

BACKGROUND

Shared seasonal patterns, such as between influenza and some respiratory bacterial infections, can create associations between phenomena not causally related.

OBJECTIVES

To estimate the association of influenza with subsequent bacterial infections after full adjustment for confounding by seasonal and long-term trends.

METHODS

Time series of weekly counts of notified cases of invasive infections with Haemophilus influenzae, Neisseria meningitidis, Streptococcus pneumoniae and Streptococcus pyogenes, in Montréal, Canada, 1996-2008, were modelled by negative binomial regression, with terms representing seasonal and long-term trends and terms for numbers of positive laboratory tests for influenza A and B.

RESULTS

The associations of S. pneumoniae, H. influenzae and N. meningitidis with influenza disappeared after seasonal terms were added to the model. However, the influenza B count remained associated with the S. pyogenes counts for the same week and the following week: S. pyogenes incidence rate ratios were 1.0376 (95% CI: 1.0009-1.0757) and 1.0354 (0.9958-1.0766), respectively, for each increase of 1 in the influenza count.

CONCLUSIONS

Influenza B accounts for about 8 percnt; of the incidence of invasive S. pyogenes infections, over and above any effect associated with modellable seasonal and long-term trends. This association of influenza B with S. pyogenes infections can be attributed largely to the years 1997, 2001, 2007 and 2008, when late peaks in influenza B counts were followed by peaks in S. pyogenes notifications. This finding reinforces the case for universal immunization against influenza, as partial protection against the 'flesh eating disease'.

Oral administration of milk fermented with Lactococcus lactis subsp. cremoris FC protects mice against influenza virus infection

AIMS

To evaluate the protective effects of oral administration of milk fermented with a Lactococcus strain against influenza virus (IFV) infection in a mouse model.

METHODS AND RESULTS

Milk fermented with exopolysaccharide-producing Lactococcus lactis subsp. cremoris (L. cremoris) FC was orally administered to BALB/c mice for 12 days. Mice were intranasally infected with IFV A/New Caledonia/20/99 (H1N1) on day 8, and survival was determined for 14 days after IFV infection. Survival rate and body weight loss after IFV infection in the L. cremoris FC fermented milk-administered group were significantly improved compared with those in the control group. In the unfermented milk-administered group, survival rate was not improved, whereas body weight loss was slightly improved compared with that in the control group. The mean virus titre in the lung of the L. cremoris FC fermented milk-administered group 3 days after infection was significantly decreased compared with that in the control group.

CONCLUSIONS

These results suggest that oral administration of milk fermented with L. cremoris FC protects mice against IFV infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results demonstrate that oral administration of milk fermented with exopolysaccharide-producing Lactococcus strains might protect host animals against IFV infection.

Morphology and infectivity of virus that persistently caused infection in an AGS cell line

A recent report has indicated that proteins and genes of simian virus 5 (SV5) are detected in a human gastric adenocarcinoma (AGS) cell line, which is widely provided for oncology, immunology, and microbiology research. However, the production of infective virions has not been determined in this cell line. In this study, the morphology and infectivity of the virus particles of the AGS cell line were studied by light and electron microscopy and virus transmission assay. The virus particles were approximately 176.0 ± 41.1 nm in diameter. The particles possessed projections 8-12 nm long on the surface and contained a nucleocapsid determined to be 13-18 nm in width and less than 1,000 nm in length. The virus was transmissible to the Vero cell line, induced multinuclear giant cell formation, and reproduced the same shape of antigenic virions. In this study, the persistently infected virus in the AGS cell line was determined to be infective and form reproducible virions, and a new morphological feature of SV5 was determined.

Augmented adherence and internalization of group A Streptococcus pyogenes to influenza A virus infected MDCK cells

Respiratory tract infections are one of the leading causes of morbidity and mortality. There is considerable epidemiologic evidence that infection with respiratory viruses increases the incidence and severity of secondary bacterial complications. However, very limited number of studies were concerned with the mechanism behind such synergy. In this context, our study aimed to explore the interaction between Group A Streptococcus pyogenes (GAS) and Influenza A virus (IAV). Our results revealed that the GAS adherence and internalization into Madin-Darby canine kidney (MDCK) cells markedly increased after IAV infection. When M6 protein defective mutant of GAS was used, the virus enhanced adherence and internalization was nearly abolished indicating the involvement of M protein binding sites on the MDCK cell surface. Interestingly, the modulation of some O-linked glycolproteins as well as sialic acid, mucin and fibrinogen-like residues on the surface of MDCK cells contributed to augmented bacterial adherence and/or internalization. In the same way, qRT-PCR experiments showed an overexpression of the membrane associated mucin (MUC1) on the surface of the MDCK cells after IAV infection. Altogether, the present study revealed that IAV infection augments the adherence and internalization of GAS to MDCK cells via modulation of membrane associated O-linked glycoproteins, fibrinogen, sialic acid residues and the mucin, MUC1 on the surface of MDCK cell.

Inactivated and live, attenuated influenza vaccines protect mice against influenza: Streptococcus pyogenes super-infections

Mortality associated with influenza virus super-infections is frequently due to secondary bacterial complications. To date, super-infections with Streptococcus pyogenes have been studied less extensively than those associated with Streptococcus pneumoniae. This is significant because a vaccine for S. pyogenes is not clinically available, leaving vaccination against influenza virus as our only means for preventing these super-infections. In this study, we directly compared immunity induced by two types of influenza vaccine, either inactivated influenza virus (IIV) or live, attenuated influenza virus (LAIV), for the ability to prevent super-infections. Our data demonstrate that both IIV and LAIV vaccines induce similar levels of serum antibodies, and that LAIV alone induces IgA expression at mucosal surfaces. Upon super-infection, both vaccines have the ability to limit the induction of pro-inflammatory cytokines within the lung, including IFN-γ which has been shown to contribute to mortality in previous models of super-infection. Limiting expression of these pro-inflammatory cytokines within the lungs subsequently limits recruitment of macrophages and neutrophils to pulmonary surfaces, and ultimately protects both IIV- and LAIV-vaccinated mice from mortality. Despite their overall survival, both IIV- and LAIV-vaccinated mice demonstrated levels of bacteria within the lung tissue that are similar to those seen in unvaccinated mice. Thus, influenza virus:bacteria super-infections can be limited by vaccine-induced immunity against influenza virus, but the ability to prevent morbidity is not complete.

Systemic cytokine response in moribund mice of streptococcal toxic shock syndrome model

Streptococcus pyogenes causes severe invasive disease in humans, including streptococcal toxic shock syndrome (STSS). We previously reported a mouse model that is similar to human STSS. When mice were infected intramuscularly with 10(7) CFU of S. pyogenes, all of them survived acute phase of infection. After 20 or more days of infection, a number of them died suddenly accompanied by S. pyogenes bacteremia. We call this phenomenon "delayed death". We analyzed the serum cytokine levels of mice with delayed death, and compared them with those of mice who died in the acute phase of intravenous S. pyogenes infection. The serum levels of TNF-α and IFN-γ in mice of delayed death were more than 100 times higher than those in acute death mice. IL-10 and IL-12, which were not detected in acute death, were also significantly higher in mice of delayed death. IL-6 and MCP-1 (CCL-2) were elevated in both groups of mice. It was noteworthy that not only pro-inflammatory cytokines but also anti-inflammatory cytokines were elevated in delayed death. We also found that intravenous TNF-α injection accelerated delayed death, suggesting that an increase of serum TNF-α induced S. pyogenes bacteremia in our mouse model.

Mixed community-acquired lower respiratory tract infections

Although mixed infections are known to be clinically relevant in conditions such as nosocomial pneumonia and ventilator-related pneumonia, it is increasingly recognized that a substantial number of community-acquired lower respiratory tract infections may also be attributed to more than one pathogenic organism. A better definition of the true incidence of mixed infections in community-acquired lower respiratory tract infections is partly derived from recent advances in available diagnostic methods (eg, molecular biology). Two points still must be determined: whether the presence of a mixed infection is associated with altered outcomes and whether empirical antibiotic selection should be modified to account for potential polymicrobial infections.