Factors enhancing adherence of toxigenic Staphylococcus aureus to epithelial cells and their possible role in sudden infant death syndrome

Staphylococcus aureus colonization and non-influenza respiratory viruses: Interactions and synergism mechanisms

Viral infections of the respiratory tract can be complicated by bacterial superinfection, resulting in a significantly longer duration of illness and even a fatal outcome. In this review, we focused on interactions between S. aureus and non-influenza viruses. Clinical data evidenced that rhinovirus infection may increase the S. aureus carriage load in humans and its spread. In children, respiratory syncytial virus infection is associated with S. aureus carriage. The mechanisms by which some non-influenza respiratory viruses predispose host cells to S. aureus superinfection can be summarized in three categories: i) modifying expression levels of cellular patterns involved in S. aureus adhesion and/or internalization, ii) inducing S. aureus invasion of epithelial cells due to the disruption of tight junctions, and iii) decreasing S. aureus clearance by altering the immune response. The comprehension of pathways involved in S. aureus-respiratory virus interactions may help developing new strategies of preventive and curative therapy.

Virus-induced secondary bacterial infection: a concise review

Respiratory diseases are a very common source of morbidity and mortality among children. Health care providers often face a dilemma when encountering a febrile infant or child with respiratory tract infection. The reason expressed by many clinicians is the trouble to confirm whether the fever is caused by a virus or a bacterium. The aim of this review is to update the current evidence on the virus-induced bacterial infection. We present several clinical as well in vitro studies that support the correlation between virus and secondary bacterial infections. In addition, we discuss the pathophysiology and prevention modes of the virus–bacterium coexistence. A search of the PubMed and MEDLINE databases was carried out for published articles covering bacterial infections associated with respiratory viruses. This review should provide clinicians with a comprehensive idea of the range of bacterial and viral coinfections or secondary infections that could present with viral respiratory illness.

Blood Groups in Infection and Host Susceptibility

Blood group antigens represent polymorphic traits inherited among individuals and populations. At present, there are 34 recognized human blood groups and hundreds of individual blood group antigens and alleles. Differences in blood group antigen expression can increase or decrease host susceptibility to many infections. Blood groups can play a direct role in infection by serving as receptors and/or coreceptors for microorganisms, parasites, and viruses. In addition, many blood group antigens facilitate intracellular uptake, signal transduction, or adhesion through the organization of membrane microdomains. Several blood groups can modify the innate immune response to infection. Several distinct phenotypes associated with increased host resistance to malaria are overrepresented in populations living in areas where malaria is endemic, as a result of evolutionary pressures. Microorganisms can also stimulate antibodies against blood group antigens, including ABO, T, and Kell. Finally, there is a symbiotic relationship between blood group expression and maturation of the gastrointestinal microbiome.

Staphylococcus aureus throat carriage is associated with ABO-/secretor status

OBJECTIVES

In 30% of carriers, Staphylococcus aureus colonization affects exclusively the pharynx and occurs independently from its presence in the nares. This additional reservoir has implications for S. aureus transmission, infection, and decolonization. Host factors promoting colonization of the throat, however, are unknown.

METHODS

We determined pharyngeal and persistent nasal carriage of S. aureus, ABO histo-blood group and ABH secretor status phenotypes in 227 individuals.

RESULTS

Compared to group A/non-secretors, group O/non-secretor individuals were at increased risk of carrying S. aureus in their throat (OR 6.50, 95% confidence interval 1.28-33.03, P = 0.02) and group O/secretor individuals were protected (OR 0.24, 0.07-0.77, P = 0.02). Both associations became moderately stronger after adjusting for persistent S. aureus nasal carriage, which was found to be a risk factor for pharyngeal colonization in the univariable analysis (OR 2.41, 1.35-4.33, p = 0.003). Most simultaneous carriers (72%) had identical S. aureus genotypes in their nose and throat.

CONCLUSIONS

These findings are consistent with in vitro studies that proposed a role of histo-blood group antigens as ligands for S. aureus and support their contribution to the observed population variation in nasopharyngeal S. aureus colonization. Based on their tissue specific expression histo-blood group antigens appear to modulate individual S. aureus colonization patterns.

The airway epithelium: soldier in the fight against respiratory viruses

The airway epithelium acts as a frontline defense against respiratory viruses, not only as a physical barrier and through the mucociliary apparatus but also through its immunological functions. It initiates multiple innate and adaptive immune mechanisms which are crucial for efficient antiviral responses. The interaction between respiratory viruses and airway epithelial cells results in production of antiviral substances, including type I and III interferons, lactoferrin, β-defensins, and nitric oxide, and also in production of cytokines and chemokines, which recruit inflammatory cells and influence adaptive immunity. These defense mechanisms usually result in rapid virus clearance. However, respiratory viruses elaborate strategies to evade antiviral mechanisms and immune responses. They may disrupt epithelial integrity through cytotoxic effects, increasing paracellular permeability and damaging epithelial repair mechanisms. In addition, they can interfere with immune responses by blocking interferon pathways and by subverting protective inflammatory responses toward detrimental ones. Finally, by inducing overt mucus secretion and mucostasis and by paving the way for bacterial infections, they favor lung damage and further impair host antiviral mechanisms.

Respiratory syncytial virus and Staphylococcus aureus coinfection in children hospitalized with pneumonia

Respiratory syncytial virus (RSV) infection might facilitate bacterial infection. We describe 5 patients with RSV among 30 children admitted to pediatric hospitals in Atlanta between October 1, 2006 and April 30, 2007 with community-onset Staphylococcus aureus pneumonia. RSV-S. aureus patients were younger and had less medical comorbidity than those without RSV.

Genetics of the sudden infant death syndrome

The sudden infant death syndrome (SIDS) is currently defined as "the sudden unexpected death of an infant less than 1 year of age with onset of the fatal episode apparently occurring during sleep, that remains unexplained after a thorough investigation". SIDS, whose etiology remains rather vague, is still the major cause of death among infants between 1 month and 1 year of age in industrialized countries with varying incidences in different populations. Herein, after touching on definitory approaches and several current hypotheses concerning SIDS etiology, we focus on the triple risk model of SIDS and discuss two large classes of genetic factors potentially contributing to or predisposing for the generation of a vulnerable infant that, when encountering an environmental trigger, may succumb to SIDS. We conclude by acknowledging that for the integration of the vast and complex genetic evidence concerning SIDS, a lot more research will be required and we briefly discuss the potential use of recently presented animal models for functional studies of SIDS pathology.

Blood group O and vWf expression may be involved in development of peptic ulcer disease secondary to Helicobacter pylori infection

Helicobacter pylori is a gram negative organism involved in peptic ulcer disease and has been linked to a number of extra-intestinal diseases. There is a large body of evidence describing the link between blood group O/non-secretor phenotypes with H. pylori infection and the risk of peptic ulcer disease. Blood group O individuals also have a higher risk of bleeding disorders due to low levels of the circulating plasma protein von Willebrand factor (vWf). vWf is one of the main proteins that binds platelets during platelet activation and aggregation. The mechanisms of how ulcers develop during H. pylori infection are not fully understood. There is however recent evidence of vWf involvement in platelet aggregation in H. pylori infection. Our new hypothesis states that H. pylori bacteria present in blood group O/non-secretor individuals are binding the available vWf to promote adhesion and subsequent platelet aggregation within the microvasculature. This in turn may deplete any available vWf for wound repair to take place leading to an increased risk of peptic ulceration and bleeding and eventually leading to an ulcer.

Seasonal invasive pneumococcal disease in children: role of preceding respiratory viral infection

OBJECTIVE

Our objective was to demonstrate correlations between invasive pneumococcal disease in children and circulating respiratory viruses.

METHODS

This retrospective study included 6 winter respiratory viral seasons (2001-2007) in Intermountain Healthcare, an integrated health system in the Intermountain West, including Primary Children's Medical Center in Salt Lake City, Utah. Children <18 years of age who were hospitalized with either invasive pneumococcal disease in any Intermountain Healthcare facility or culture-confirmed invasive pneumococcal disease at Primary Children's Medical Center were included. We analyzed the correlation between invasive pneumococcal disease and circulating respiratory viruses.

RESULTS

A total of 435 children with invasive pneumococcal disease and 203 with culture-confirmed invasive pneumococcal disease were hospitalized in an Intermountain Healthcare facility or Primary Children's Medical Center during the study period. During the same period, 6963 children with respiratory syncytial virus, 1860 with influenza virus, 1459 with parainfluenza virus, and 818 with adenoviruses were evaluated at Primary Children's Medical Center. A total of 253 children with human metapneumovirus were identified during the last 5 months of the study. There were correlations between invasive pneumococcal disease and seasonal respiratory syncytial virus, influenza virus, and human metapneumovirus activity. The correlation with invasive pneumococcal disease was strong up to 4 weeks after respiratory syncytial virus activity. For influenza virus and human metapneumovirus, the correlations were strong at 2 weeks after activity of these viruses. Pneumonia was the most common clinical disease associated with culture-confirmed invasive pneumococcal disease, mostly attributable to serotypes 1, 19A, 3, and 7F.

CONCLUSIONS

In the post-pneumococcal conjugate vaccine era, seasonal increases in respiratory syncytial virus, influenza virus, and human metapneumovirus infections in children were associated with increased pediatric admissions with invasive pneumococcal disease, especially pneumonia caused by nonvaccine serotypes.

RSV mediates Pseudomonas aeruginosa binding to cystic fibrosis and normal epithelial cells

Cystic fibrosis lung disease typically has a course of exacerbations and remissions, suggesting that external factors like viral infections can influence this course. Clinical data suggest synergism between respiratory syncytial virus (RSV) infections and Pseudomonas aeruginosa in cystic fibrosis (CF) lung disease. We studied the influence of RSV infection on adherence of P. aeruginosa to IB3-1, HEp-2, and A549 epithelial cell monolayers in vitro. RSV infection of epithelial cells as well as simultaneous addition of RSV and P. aeruginosa to noninfected cells both strongly enhanced the pseudomonal adherence to epithelial cells. The increased adherence varied from 1.2- to 8.2-fold in case of previous RSV infection, and from 1.7- to 16.1-fold in case of simultaneous addition. We observed direct binding of RSV to P. aeruginosa, and blocking of RSV with heparin eliminated the effect on increased adherence. This suggests that RSV possibly acts as a coupling agent between P. aeruginosa and epithelial cells. In conclusion, RSV enhances P. aeruginosa infection of respiratory epithelial cells. It suggests a role of specific viral-bacterial interactions in exacerbations of CF lung disease, which could have important implications on prevention and treatment.

Ethnicity, infection and sudden infant death syndrome

Epidemiological studies found the incidence of SIDS among Indigenous groups such as Aboriginal Australians, New Zealand Maoris and Native Americans were significantly higher than those for non-Indigenous groups within the same countries. Among other groups such as Asian families in Britain, the incidence of SIDS has been lower than among groups of European origin. Cultural and childrearing practices as well as socio-economic factors have been proposed to explain the greater risk of SIDS among Indigenous peoples; however, there are no definitive data to account for the differences observed. We addressed the differences among ethnic groups in relation to susceptibility to infection because there is evidence from studies of populations of European origin that infectious agents, particularly toxigenic bacteria might trigger the events leading to SIDS. The risk factors for SIDS parallel those for susceptibility to infections in infants, particularly respiratory tract infections which are also major health problems among Indigenous groups. Many of the risk factors identified in epidemiological studies of SIDS could affect three stages in the infectious process: (1) frequency or density of colonisation by the toxigenic species implicated in SIDS; (2) induction of temperature-sensitive toxins; (3) modulation of the inflammatory responses to infection or toxins. In this review we compare genetic, developmental and environmental risk factors for SIDS in ethnic groups with different incidences of SIDS: low (Asians in Britain); moderate (European/Caucasian); high (Aboriginal Australian). Our findings indicate: (1) the major difference was high levels of exposure to cigarette smoke among infants in the high risk groups; (2) cigarette smoke significantly reduced the anti-inflammatory cytokine interleukin-10 responses which control pro-inflammatory responses implicated in SIDS; (3) the most significant effect of cigarette smoke on reduction of IL-10 responses was observed for donors with a single nucleotide polymorphism for the IL-10 gene that is predominant among both Asian and Aboriginal populations. If genetic makeup were a major factor for susceptibility to SIDS, the incidence of these deaths should be similar for both populations. They are, however, significantly different and most likely reflect differences in maternal smoking which could affect frequency and density of colonisation of infants by potentially pathogenic bacteria and induction and control of inflammatory responses.

Enhanced adherence of Streptococcus pneumoniae to human epithelial cells infected with respiratory syncytial virus

In the present study, we analyzed the effect of a preceding respiratory syncytial virus (RSV) infection of human respiratory epithelial cells on the adherence of Streptococcus pneumoniae tested by means of a cytometric fluorescence assay. Adherence of clinically relevant pneumococcal serotypes 3, 9, 14, 18, 19, and 23 was studied using uninfected and RSV-infected monolayers. To this end, monolayers of both human nasopharyngeal cells (HEp-2) and pneumocyte type II cells (A549) were infected with RSV serotype A. Adherence to uninfected epithelial cells varied between pneumococcal serotypes. After RSV infection of the monolayers, all serotypes showed a strongly (2- to 10- fold) and significantly increased adherence when compared with adherence to uninfected monolayers. Enhanced adherence was observed with both cell lines. By fluorescence and scanning electron microscopy, we observed redistribution of pneumococcal adherence over the epithelial surface due to RSV infection, with dense bacterial accumulations near to epithelial syncytia.

Respiratory viruses predisposing to bacterial infections: role of neuraminidase

BACKGROUND AND METHODS

Viral-bacterial coinfections in humans are well-documented. Viral infections often lead to bacterial superinfections. In vitro and animal models for influenza, as well as molecular microbiology study of viruses and bacteria, provide an understanding of the mechanisms that explain how respiratory viruses and bacteria combine to cause disease. This article focuses on viral and bacterial combinations, particularly synergism between influenza and Streptococcus pneumoniae.

RESULTS

Potential mechanisms for synergism between viruses and bacteria include: virus destruction of respiratory epithelium may increase bacterial adhesion; virus-induced immunosuppression may cause bacterial superinfections; and inflammatory response to viral infection may up-regulate expression of molecules that bacteria utilize as receptors. Influenza and parainfluenza viruses possess neuraminidase (NA) activity, which appears to increase bacterial adherence after viral preincubation. Experimental studies demonstrate that viral NA exposes pneumococcal receptors on host cells by removing terminal sialic acids. Other studies show that inhibition of viral NA activity reduces adherence and invasion of S. pneumoniae, independently of effects on viral replication. Clinical studies reveal that influenza vaccination reduces the incidence of secondary bacterial respiratory tract infections.

CONCLUSIONS

Detection of viral factors (e.g. high NA activity) that increase the likely potential of epidemic/pandemic influenza strains for causing morbidity and mortality from secondary bacterial infections provides new possibilities for intervention. Additional study is needed to identify the mechanisms for the development of bacterial complications after infections with respiratory syncytial virus and other important respiratory viruses that lack NA activity. Prevention of bacterial superinfection is likely to depend on effective antiviral measures.

Comparison of Moraxella catarrhalis isolates from children and adults for growth on modified New York City medium and potential virulence factors

Initial studies found that Moraxella catarrhalis isolates from adults that grew on modified New York City medium (MNYC(+)) that contained antibiotics selective for pathogenic neisseriae differed from strains that did not grow on this medium (MNYC(-)) in their potential virulence properties. It was predicted that higher usage of antibiotics to treat respiratory illness in children might result in higher proportions of MNYC(+) isolates if antibiotics were an important selective pressure for this phenotype. Two of 100 adult isolates (2 %) were MNYC(+), compared to 88 of 88 isolates (100 %) from children (P = 0.000). MNYC(+) strains were serum-resistant and bound in higher numbers to HEp-2 cells that were infected with respiratory syncytial virus (RSV). Endotoxin from an MNYC(+) isolate induced significantly higher pro-inflammatory response levels than endotoxin from an MNYC(-) strain. MNYC(-) adult isolates expressed haemagglutinins and bound in lower numbers to RSV-infected cells, but serum resistance was variable. All isolates from children were MNYC(+), serum-resistant and bound in greater numbers to RSV-infected cells. These results indicate that both RSV infection and antibiotic usage select for the MNYC(+) phenotype.

The role of bacterial toxins in sudden infant death syndrome (SIDS)

There is increasing evidence for the involvement of bacterial toxins in some cases of sudden infant death syndrome (SIDS), particularly the pyrogenic toxins of Staphylococcus aureus. This had led to the hypothesis that some SIDS deaths are due to induction of inflammatory mediators by infectious agents or their products during a period in which the infant is unable to control these normally protective responses. The genetic, developmental and environmental risk factors identified for SIDS are assessed in relation to frequency or density of mucosal colonisation by toxigenic bacteria and their effects on induction and control of inflammatory responses to the toxins.

What determines nasal carriage of Staphylococcus aureus?

Nasal carriage of Staphylococcus aureus is an important risk factor for infection by this organism in both community and hospital settings; this article reviews the role of host and bacterial factors in carriage. A host genetic influence appears likely but the phenotypic determinants are unknown. Possibilities include variability in host adhesins, immune response or secretion of antimicrobial molecules. Colonization resistance by S. aureus, together with the observation that persistent carriers often carry a single strain whereas intermittent carriers can be colonized with unrelated strains over time, suggests that bacterial factors could also be involved.

Relationship of blood group determinants on Helicobacter pylori lipopolysaccharide with host lewis phenotype and inflammatory response

As Lewis a (Le(a)) and Lewis b (Le(b)) blood group antigens are isoforms of Lewis x (Le(x)) and Lewis y (Le(y)) and are expressed in the gastric mucosa, we evaluated whether the patterns of expression of Le(x) and Le(y) on Helicobacter pylori lipopolysaccharides reflected those of host expression of Le(a) and Le(b). When 79 patients (secretors and nonsecretors) were examined for concordance between bacterial and host Le expression, no association was found (chi(2) = 5.734, 3 df, P = 0.125), nor was there a significant difference between the amount of Le(x) or Le(y) expressed on isolates from ulcer and chronic gastritis patients (P > 0.05). Also, the effect of host and bacterial expression of Le antigens on bacterial colonization and the observed inflammatory response was assessed. In ulcer patients, Le(x) expression was significantly related to neutrophil infiltration (r(s) = 0.481, P = 0.024), whereas in chronic gastritis patients significant relationships were found between Le(x) expression and H. pylori colonization density (r(s) = 0.296, P = 0.03), neutrophil infiltrate (r(s) = 0.409, P = 0. 001), and lymphocyte infiltrate (r(s) = 0.389, P = 0.002). Furthermore, bacterial Le(y) expression was related to neutrophil (r(s) = 0.271, P = 0.033) and lymphocyte (r(s) = 0.277, P = 0.029) infiltrates. Thus, although no evidence of concordance was found between bacterial and host expression of Le determinants, these antigens may be crucial for bacterial colonization, and the ensuing inflammatory response appears, at least in part, to be influenced by Le antigens.

Respiratory viral infection predisposing for bacterial disease: a concise review

Although bacterial superinfection in viral respiratory disease is a clinically well documented phenomenon, the pathogenic mechanisms are still poorly understood. Recent studies have revealed some of the mechanisms involved. Physical damage to respiratory cells as a result of viral infection may lead to opportunistic adherence of bacteria. Enhanced bacterial adherence by specific mechanisms has been documented for respiratory cells infected with influenza A virus, respiratory syncytial virus and adenovirus in both in vitro and in vivo models. To date, results of various experimental studies indicate that different mechanisms for increased bacterial adherence induced by viruses are operating for specific viral-bacterial combinations. In the present review, a number of key findings obtained during the past two decades is presented and discussed.

Toxigenic bacteria and sudden infant death syndrome (SIDS): nasopharyngeal flora during the first year of life

Many developmental and environmental risk factors for sudden infant death syndrome (SIDS) are similar to those for susceptibility to respiratory tract infection, and toxigenic bacteria have been implicated in some SIDS cases. We assessed nasopharyngeal flora of healthy infants in relation to risk factors to determine which species best lit the mathematical model proposed for the common bacterial toxin hypothesis and if these findings complemented results obtained from SIDS cases which occurred during the period of the survey. Longitudinal studies were carried out between April 1993 and March 1996 on 253 healthy infants and their mothers. 150 from a multiply deprived area, 103 from an affluent area. Concurrent SIDS infants (37) were screened for nasopharyngeal flora. Among healthy infants < or = 3 months of age, the predominant isolate was Staphylococcus aureus 57% compared with 86% for SIDS infants in that age range (P< 0.02). There were significant associations between isolation of different species from both mother and baby but no association between isolation of any species with: area of residence: parental smoking habits; breast or bottle feeding; symptoms of viral infection: seasonality. We conclude that S. aureus fits the mathematical model for SIDS. Both staphylococci and/or their toxins were identified in a significant proportion of SIDS cases. Isolation of staphylococci from healthy infants was associated with the 2-4-month age range, a risk factor consistently found in all epidemiological studies of SIDS. This might reflect the developmental stage in which 80-90% of infants express the Lewis(a) antigen which we have shown to be one of the receptors for S. aureus.

Immune and inflammatory responses in sudden infant death syndrome

Infancy is a time of unparalleled infection exposure. Coming from the privilege of the uterus, the newborn infant must make appropriate immune responses following infection that eliminates the infection but protects the host. There is evidence that in sudden infant death syndrome (SIDS) subjects there is a background of recent 'trivial' infection and immunological/inflammatory reactivity. This immunological/inflammatory reactivity is seen in enhanced pulmonary immunoglobulins and T-cell activation. It may be that in certain SIDS cases a trivial infection triggers an exaggerated inflammatory response, inducing cytokine cascades and eventual demise of the infant.

The protective effect of breast feeding in relation to sudden infant death syndrome (SIDS): I. The effect of human milk and infant formula preparations on binding of toxigenic Staphylococcus aureus to epithelial cells

Epidemiological studies indicate that breast-fed infants are at a decreased risk of sudden infant death syndrome (SIDS) compared to formula-fed infants. Increasing evidence suggests that infectious agents might be involved in some of these deaths, in particular bacteria which colonise mucosal surfaces and produce superantigenic toxins. One species implicated in recent studies of SIDS infants is Staphylococcus aureus. We tested the hypothesis that in comparison to infant formula, human milk might be a better inhibitor of binding of S. aureus to epithelial cells. In this study, two protocols were used for the binding assays which were assessed by flow cytometry: the in vitro method in which bacteria were treated with milk or formula, washed and added to epithelial cells; and a method more closely reflecting the competitive interactions in vivo in which cells, bacteria, and milk or infant formula were added at the same time. With the in vivo method, breast milk caused enhancement of bacterial binding to cells whilst infant formula caused inhibition; however, for the in vitro method, both human milk and infant formula caused consistent enhancement of binding. Flow cytometry and light microscopy studies indicated that the enhancement was due to the formation of bacterial aggregates. Human milk and infant formula preparations were also compared for components (antibodies or oligosaccharides) that could inhibit binding of S. aureus using the in vitro method. Human milk contained both IgA and IgG. Neither human milk nor infant formula contained oligosaccharides reactive with the Ulex europaeus lectin but both contained components that bound monoclonal antibodies to Lewis(a) and Lewis(b) antigens which can act as receptors for S. aureus. With both methods, synthetic Lewis(a) and Lewis(b) inhibited S. aureus binding in a dose-dependent manner. With human milk, however, the only component which showed a significant correlation with inhibition of binding was the IgA specific for the staphylococcal surface component that binds Lewis(a). Both human milk and infant formula contain components which could potentially inhibit bacterial binding but only breast milk contains the IgA specific for the bacterial adhesin that binds Lewis(a). Studies using the in vivo method suggest that protection associated with breast feeding in relation to SIDS could be due mainly to the formation of bacterial aggregates. The studies have implications for further research into constituents of infant formula.

Sudden infant death syndrome, virus infections and cytokines

Many epidemiological risk factors identified for sudden infant death syndrome (SIDS) suggest a viral aetiology, e.g. exposure to cigarette smoke and winter peak, mild respiratory symptoms. Virus infections and bacterial toxins induce cytokine activity and it has been suggested that uncontrolled inflammatory mediators could be involved in some cases of SIDS. The aim of this review was to assess the evidence for virus infection in SIDS and to examine those findings in relation to individual variations in cytokine responses and various pathophysiological mechanisms proposed for SIDS such as sleep derangement, hypoxia, cardiac arrhythmia, vascular hypotonicity and hypoglycaemia.

Immunological evidence for a bacterial toxin aetiology in sudden infant death syndrome

Toxin-specific antibodies to clostridial, enterobacterial and staphylococcal toxins implicated in sudden infant death syndrome were studied in sera from sudden infant death syndrome infants and a comparison group of infants (babies with phenylketonuria). The results indicated a higher proportion of sera from sudden infant death syndrome infants contained IgA that bound to clostridial and enterobacterial toxins but a higher proportion of sera from the phenylketonuria comparison group contained IgA that bound staphylococcal toxins. The higher proportion of serum samples with IgG and IgM in the healthy comparison babies serum probably indicated immunity in this group of babies to these toxins. The effect of gender and age had a minimal effect on the incidence of these antibodies. The presence of toxin-specific antibodies in sudden infant death syndrome and the of comparison infants suggests that all infants are exposed to these toxins and most babies successfully overcome the toxic challenge. Some infants with predisposing risk factors (temperature change, smoking, infection, immune development, sleeping position, etc.) that could affect the baby's immune competency could succumb to these and possibly other toxins. This immunological evidence further strengthens the view that bacterial toxins are a significant cause of sudden infant death syndrome.

The nasopharyngeal bacterial flora in infancy: effects of age, gender, season, viral upper respiratory tract infection and sleeping position

The aim of the investigation was to determine the effect of age, gender, viral upper respiratory tract infection (URTI), season and sleeping position on the composition of the nasopharyngeal bacterial flora in infancy. Seventy-two babies, 38 male and 34 female, whose birthdates were evenly spread throughout the year were followed from birth to 18 months of age. From 0 to 6 months nasopharyngeal swabs were obtained once a month in periods without URTI and daily for 3 days during episodes of URTI. From 12 to 18 months of age nasopharyngeal swabs were obtained in the early morning alter an overnight sleep and later in the day after the baby had been up for over 2 h. Swabs were obtained in prone and supine sleepers with and without infection. In infants aged 0-6 months URTI had little effect on the nasopharyngeal bacterial flora, but there was a marked effect of age and less marked effect of season and gender. In particular Staphylococcus aureus carriage decreased with age, was most common in the winter months and the density of colonisation was greater in males than females. In infants aged 12-18 months the combination of prone sleeping with URTI and an early morning swab led to increased carriage of staphylococci, streptococci. Haemophilus influenzae and Gram-negative bacilli which are not normally part of the nasopharyngeal flora. These results are relevant to sudden infant death syndrome (SIDS). The combination of prone sleeping and URTI reproduces the nasopharyngeal flora seen in SIDS. Gram-negative bacilli isolated from SIDS cases should not be dismissed as post-mortem contaminants. The features of S. aureus make it a prime candidate for a pathogenic role in SIDS.

The protective effect of breast feeding in relation to sudden infant death syndrome (SIDS): II. The effect of human milk and infant formula preparations on binding of Clostridium perfringens to epithelial cells

Breast feeding is known to protect an infant against gastrointestinal pathogens and epidemiological studies indicate that compared to breast fed infants, formula fed infants are at a greater risk of dying from sudden infant death syndrome (SIDS). Many SIDS infants have symptoms of gastrointestinal infections prior to death and one gastrointestinal pathogen associated with SIDS is Clostridium perfringens. Studies have found that a significantly higher number of formula fed SIDS infants have C perfringens and its enterotoxin in their faeces compared to breast fed infants. The aim of the study was to compare the effects of human milk and infant formula on binding of C perfringens to epithelial cells. Two protocols were used to assess the effect of human milk and infant formula to inhibit binding of C perfringens to epithelial cells. Binding was assessed by flow cytometry. For the in vivo protocol which more closely represents interactions on the mucosal surface, breast milk enhanced bacterial binding but infant formula caused inhibition of binding; however for the in vitro method, both human milk and infant formula resulted in consistent enhancement of binding. Flow cytometry studies indicated that enhancement of binding was due to the formation of bacterial aggregates. Lewis(a) and Lewis(b) antigens, found in both breast milk and infant formula, inhibited C. perfringens binding in a dose dependent manner. The Lewis(a) and Lewis(b) antigens in human milk and infant formula can inhibit C. perfringens binding to epithelial cells. While infant formula reduced binding of C. perfringens to epithelial cells in the experiments carried out with the in vivo protocol, the protective effects of breast feeding in relation to colonisation with C. perfringens are more likely to be due to formation of bacterial aggregates. These findings have implications for improving infant formula preparations.

Infection, inflammation and sleep: more pieces to the puzzle of sudden infant death syndrome (SIDS)

Risk factors for sudden infant death syndrome (SIDS) parallel those for respiratory tract infections; however, infectious agents suggested to be involved in SIDS do not fulfil Koch's postulates. No single agent has been identified in all cases and there is no suitable animal model for SIDS which could be used to test the candidate organisms. Based on epidemiological and experimental work by our group and others, we suggested some SIDS deaths are due to pathophysiological responses elicited by combinations of microbial products and/or cigarette smoke during a developmental stage when infants' endocrine responses are less able to "damp down" the effects of inflammatory mediators. Here we review evidence from studies on interactions between developmental and environmental risk factors that could affect 1) mucosal colonization of infants by potentially pathogenic bacteria, and 2) induction and control of infants', inflammatory responses to infectious agents. New evidence suggests that there are genetic factors involved in the induction of inflammatory responses to some bacterial antigens implicated in SIDS. Further investigation of the role of infection, exposure to cigarette smoke and inflammation in infants, particularly differences in ethnic groups at increased risk of SIDS, could lead to new insights into the events leading to a fatal outcome and perhaps to new intervention schemes to reduce further the incidence of these deaths.

Clinical, microbial, and biochemical aspects of the exfoliative toxins causing staphylococcal scalded-skin syndrome

The exfoliative (epidermolytic) toxins of Staphylococcus aureus are the causative agents of the staphylococcal scalded-skin syndrome (SSSS), a blistering skin disorder that predominantly affects children. Clinical features of SSSS vary along a spectrum, ranging from a few localized blisters to generalized exfoliation covering almost the entire body. The toxins act specifically at the zona granulosa of the epidermis to produce the characteristic exfoliation, although the mechanism by which this is achieved is still poorly understood. Despite the availability of antibiotics, SSSS carries a significant mortality rate, particularly among neonates with secondary complications of epidermal loss and among adults with underlying diseases. The aim of this article is to provide a comprehensive review of the literature spanning more than a century and to cover all aspects of the disease. The epidemiology, clinical features, potential complications, risk factors, susceptibility, diagnosis, differential diagnoses, investigations currently available, treatment options, and preventive measures are all discussed in detail. Recent crystallographic data on the toxins has provided us with a clearer and more defined approach to studying the disease. Understanding their mode of action has important implications in future treatment and prevention of SSSS and other diseases, and knowledge of their specific site of action may provide a useful tool for physiologists, dermatologists, and pharmacologists.

Binding of bacteria to HEp-2 cells infected with influenza A virus

Epidemiological studies indicate influenza virus infection increases susceptibility to bacterial respiratory pathogens and to meningococcal disease. Because density of colonisation is an important factor in the development of bacterial disease, the objectives of the study were to use flow cytometry methods for assessment of bacterial binding and detection of cell surface antigens to determine: (1) if HEp-2 cells infected with human influenza A virus bind greater numbers of bacteria than uninfected cells; (2) if influenza infection alters expression of cell surface antigens which act as receptors for bacterial binding; (3) if neuraminidase affects binding of bacteria to HEp-2 cells. There was significantly increased binding of all isolates tested regardless of surface antigen characteristics. There were no significant differences between virus-infected and -uninfected Hep-2 cells in binding of monoclonal antibodies to Lewisb, Lewisx or H type 2. There were significant increases in binding of monoclonal antibodies to CD14 (P < 0.05) and CD18 (P < 0.01). Treatment of cells with monoclonal antibodies significantly reduced binding of Neisseria meningitidis strain C:2b:P1.2, CD14 (P < 0.001) and CD18 (P < 0.001). No reduction in binding of a strain of Streptococcus pneumoniae (12F) was observed in these experiments. Neuraminidase treatment of HEp-2 cells increased binding of monoclonal antibodies to CD14 (P < 0.01) and CD18 (P < 0.01). In three experiments, the increase in binding of meningococcal strain C:2b:P1.2 to neuraminidase-treated cells was not significant, but binding of Staphylococcus aureus strain NCTC 10655 was significant (P < 0.05).

Infection with respiratory syncytial virus enhances expression of native receptors for non-pilate Neisseria meningitidis on HEp-2 cells

Respiratory virus infections have been suggested to be predisposing factors for meningococcal disease. Respiratory syncytial virus (RSV) affects young children in the age range at greatest risk of disease caused by Neisseria meningitidis. It has been previously shown that glycoprotein G expressed on the surface of RSV-infected HEp-2 cells (a human epithelial cell line) contributed to higher levels of binding of meningococci compared with uninfected cells. The aim of the present study was to examine the effect of RSV infection on expression of surface molecules native to HEp-2 cells and their role in bacterial binding. Flow cytometry and fluorescence microscopy were used to assess bacterial binding and expression of host cell antigens. Some molecules analysed in this study have not been reported previously on epithelial cells. RSV infection significantly enhanced the expression of CD15 (P < 0.05), CD14 (P < 0.001) and CD18 (P < 0.01), and the latter two contributed to increased binding of meningococci to cells but not the Gram-positive Streptococcus pneumoniae.

The effect of cigarette smoke on adherence of respiratory pathogens to buccal epithelial cells

Smoking is associated with an increased risk of respiratory tract infection in adults. In children, exposure to cigarette smoke is a risk factor for respiratory tract infection and bacterial meningitis: Active smoking and passive exposure to cigarette smoke is also associated with carriage of some potentially pathogenic species of bacteria in both adults and children. The aims of the study were to determine the effect of active smoking on: (1) bacterial binding to epithelial cells; (2) expression of host cell antigens that act as receptors for some species; and (3) the effects of passive exposure to water-soluble components of cigarette smoke on bacterial binding. Flow cytometry was used to assess binding to buccal epithelial cells of the following species labelled with fluorescein isothiocyanate: Neisseria meningitidis, Neisseria lactamica, Streptococcus pneumoniae, Bordetella pertussis, Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus. Flow cytometry was also used to assess expression of host cell antigens which have been identified as bacterial receptors. For each species, binding to cells of smokers was significantly higher than to cells of non-smokers; however, expression of host cell antigens was similar on epithelial cells of both groups. Non-dilute cigarette smoke extract reduced binding of bacteria to epithelial cells, but dilutions between 1 in 10 and 1 in 320 enhanced binding. We conclude that smokers might be more densely colonised by a variety of potentially pathogenic bacteria. The enhanced bacterial binding to epithelial cells of smokers is not related to enhanced expression of host cell antigens that can act as receptors for some species, but possibly to components in the smoke that alter charge or other properties of the epithelial cell surface. Passive coating of mucosal surfaces with components of cigarette smoke might enhance binding of potentially pathogenic bacteria.

Enzyme-linked immunoassay for respiratory syncytial virus is not predictive of bronchiolitis in sudden infant death syndrome

Although respiratory syncytial virus (RSV)-infected infants may present with apnea, the role that RSV plays in sudden infant death syndrome (SIDS) is speculative. To determine whether RSV is associated with bronchiolitis in these patients, we examined histologic sections of lungs from 41 apparent SIDS cases and compared the results with those of enzyme-linked immunofluorescent assay (EIA) from nasal washings. Bronchiolitis was defined by a bronchiolar inflammatory cell infiltrate plus epithelial necrosis. A positive EIA was associated with bronchiolitis in 8 instances, compared with 6 having a positive EIA and negative histology, 14 having a negative EIA and positive histology, and 13 having EIA and histology both negative. These results yield a predictive value of a positive test of 57% and a predictive value of a negative test of 48% (P > .9 by chi square analysis). Although RSV of the upper respiratory tract may be related to SIDS, our results indicate that EIA of nasal washings is not predictive of bronchiolitis, and we recommend other means of verification of histologic results.

Effect of host Lewis and ABO blood group antigen expression on Helicobacter pylori colonisation density and the consequent inflammatory response

The Lewis(b) blood group antigen has been implicated as a putative receptor for Helicobacter pylori in the gastric mucosa. Furthermore, an increased prevalence of duodenal ulcer was found in non-secretors and it has been suggested that secretor status may influence bacterial colonisation density. Other investigators have hypothesised that severity of antral gastritis may be related to colonisation density of the bacterium alone, and that a critical bacterial load is necessary for the development of duodenal ulcer. Our objectives were to investigate whether a relationship existed between host Lewis and ABO blood group phenotype and prevalence of H. pylori infection. In addition we investigated whether bacterial colonisation density and the ensuing inflammatory response was influenced by secretor status and ABO blood group phenotype. The Lewis and ABO blood group phenotype of 207 patients undergoing upper endoscopy was determined. Of these, 136 were secretors and 62 were nonsecretors. Forty-five percent of patients were infected with H. pylori. No significant association was found between H. pylori infection and expression of Lewis(a) or Lewis(b) blood group antigen. The mean histological density of H. pylori was 1.8 +/- 0.2 among non-secretors and 1.51 +/- 0.13 among secretors (P = 0.209), with a mean grade of lymphocytic infiltration significantly greater in H. pylori-infected non-secretors (2.23 +/- 0.123 vs 1.8 +/- 0.074; P = 0.003). In addition, blood group O non-secretors had a significantly higher grade of lymphocyte infiltration of their gastric mucosa compared to non-O non-secretors (2.53 +/- 0.133 vs 1.93 +/- 0.181, P = 0.027). These results suggest that although no in vivo relationship exists between H. pylori and preferential adhesion to the putative Lewis(b) receptor, bacterial colonisation and the ensuing inflammatory response may be influenced at least in part by host expression of ABO and Lewisa blood group antigens.

Bacterial toxins and sudden unexpected death in a young child

The sudden unexpected death of a six year old child following an upper respiratory tract infection is reported. Laboratory investigations revealed the presence of staphylococcal toxic shock syndrome toxin-1 (TSST-1) in samples of brain tissue. The significance of this finding is discussed.

Studies of bronchoalveolar lavage in sudden infant death syndrome: a clinical-pathological study

The incidence of sudden infant death syndrome (SIDS) in Hungary was 0.3 per 1000 live births in 1992. We investigated bronchoalveolar lavage (BAL) of eight infants with SIDS, using bacteriological, light and electron microscopic methods to collect data about the role of respiratory inflammations in SIDS children and to determine the usefulness of the BAL technique. Findings are discussed.

Is the nasopharynx warmer in children than in adults?

Recent studies on the aetiology of the Sudden Infant Death Syndrome (SIDS) have suggested that some of these deaths are the consequence of an overwhelming inflammatory response to the production of pyrogenic toxins from bacteria colonizing the upper respiratory tract, particularly the nasopharynx. The pyrogenic toxins of Staphlococcus aureus, one of the likelier bacterial candidates, are only produced in temperatures of over 37 degrees C. This study examined nasopharyngeal temperatures in children. It is a preliminary study to develop an accurate means to measure how close to 37 degrees C the nasopharyngeal temperature lies in infants at the age when SIDS deaths occur. Following a pilot study and power calculation, measurements of nasopharyngeal temperature were made on 30 apyrexial children aged 4-10 years and 30 adults with no nasal pathology, undergoing surgery under general anaesthesia, using an accurately sited thermocouple probe. The mean temperature in children (35.64 degrees C) was significantly higher than in adults (34.01 degrees C). Comparable measurements attempted with the same subjects awake gave similar results.

Developmental and environmental factors that enhance binding of Bordetella pertussis to human epithelial cells in relation to sudden infant death syndrome (SIDS)

Asymptomatic infection due to Bordetella pertussis has been suggested to be one cause of sudden infant death syndrome (SIDS). We examined developmental and environmental factors previously found to affect binding of another toxigenic species, Staphylococcus aureus, to human epithelial cells: expression of the Lewis(a) antigen; infection with respiratory syncytial virus (RSV); exposure to cigarette smoke; and the inhibitory effect of breast milk on bacterial binding. Binding of two strains of B. pertussis (8002 and 250825) to buccal epithelial cells was significantly reduced by treating the cells with monoclonal antibodies to Lewis(a) (P < 0.05) and Lewis(x) (P < 0.01) antigens. Both strains bound in significantly greater numbers to cells from smokers compared with cells from non-smokers (P < 0.05). HEp-2 cells infected with RSV subtypes A or B had higher binding indices for both 8002 (P < 0.001) and 250825 (P < 0.01). On RSV-infected cells, there was significantly enhanced binding of monoclonal antibodies to Lewis(x) (P < 0.05), CD14 (P < 0.001) and CD18 (P < 0.01); and pre-treatment of cells with anti-CD14 or CD18 also significantly reduced binding of both strains of B. pertussis. Pre-treatment of the bacteria with human milk significantly reduced their binding to epithelial cells. The results are discussed in relation to our three-year survey of bacterial carriage among 253 healthy infants, their mothers and local SIDS cases between 1993-1995 and in relation to the change to an earlier immunisation schedule for infants and the recent decline in SIDS in Britain.

Clostridium perfringens type A enterotoxin (CPE): more than just explosive diarrhea

The bacterial pathogen Clostridium perfringens is the most prolific toxin-producing species within the clostridial group. The toxins are responsible for a wide variety of human and veterinary diseases, many of which are lethal. C. perfringens type A strains are also associated with one of the most common forms of food-borne illness (FBI). The toxicosis results from the production and gastrointestinal absorption of a protein-enterotoxin known as CPE. The regulation, expression, and mechanism of action of CPE has been of considerable interest as the protein is unique. CPE expression is sporulation associated, although the mechanism of cpe-gene regulation is not fully elucidated. Cloning studies suggest the involvement of global regulators, but these have not been identified. Although very few type A strains are naturally enterotoxigenic, the cpe gene appears highly conserved. In FBI strains, cpe is chromosomally encoded; whereas in veterinary strains, cpe may be plasmid-encoded. Variation in cpe location suggests the involvement of transposable genetic element(s). CPE-like proteins are produced by some C. perfringens types C and D; and silent remnants of the cpe gene can be found in C. perfringens type E strains associated with the iota toxin gene. CPE has received attention for its biomedical importance. The toxin has been implicated in sudden infant death syndrome (SIDS) because of its superantigenic nature. CPE can destroy a wide variety of cell types both in vitro and in vivo, suggesting that it could have potential in the construction of immunotoxins to neoplastic cells. It is obvious that CPE is an interesting protein that deserves continued attention.

Infectious agents, the inflammatory responses of infants and sudden infant death syndrome (SIDS)

There is no convincing epidemiological or pathological evidence that particular infectious agents cause sudden infant death syndrome (SIDS); therefore, we have explored the concept that synergy between bacterial endotoxins, exotoxins or viruses might elicit inflammatory responses during a period when the infant's endocrine system is less able to 'damp down' the effects of powerful mediators such as tumour necrosis factor or to maintain glucose homoeostasis which is affected by these mediators. This hypothesis is discussed with reference to the recent decline in the number of cot deaths.

Inhibitory effect of saliva from secretors and non-secretors on binding of meningococci to epithelial cells

Carriage of Neisseria meningitidis B:4:P1.15 was higher among non-secretors during a school outbreak of meningitis; non-secretors had lower levels of anti-meningococcal salivary IgM. Flow cytometry was used to assess effects of secretor and non-secretor saliva on binding of B:4:P1.15 to buccal epithelial cells: (1) to assess inhibition by IgA and IgM; and (2) to assess contributions of salivary antibodies to inhibitory activities. Greater inhibition was obtained with secretor saliva: pooled (P = 0.049); fresh (P = 0.0001). Purified IgA (P = 0.02) and IgM (P = 0.03) were equally inhibitory. After absorption of anti-meningococcal antibodies, there was still significant inhibitory activity in the pools: secretors (P = 0.018); non-secretors (P = 0.005). These results indicate that both secretory immunoglobulins and other factors contribute to protection against colonisation by meningococci and might explain the increased carriage of B:4:1.15 in this population.

The role of infectious agents in sudden infant death syndrome

Epidemiological factors associated with susceptibility to respiratory infections are similar to those associated with Sudden Infant Death Syndrome. Here we review the evidence that respiratory pathogens might be involved in some cases of Sudden Infant Death Syndrome in the context of factors identified in epidemiological studies of cot deaths: the age range affected; mother' smoking; respiratory viral infections; immunisation status. Both laboratory and epidemiological evidence suggests that vulnerability of infants to infectious agents depends on interactions between genetic, developmental and environmental factors that contribute to colonisation by microorganisms, the inflammatory and specific immune responses and the infants' physiological responses to inflammatory mediators. A model is proposed to explain how microorganisms might trigger a series of events resulting in some of these unexpected deaths and discusses how the the present recommendations regarding child care practices might help reduce the numbers of Sudden Infant Death Syndrome cases associated with infectious agents.

Can superantigens trigger sudden infant death?

A majority of sudden infant death syndrome (SIDS) victims have respiratory or gastrointestinal infections prior to death. This has led to an investigation of the role of pathogenic bacteria and the potentially lethal toxins they produce as triggers for sudden infant death. A small group of bacteria have been consistently identified in SIDS victims as compared to controls, and remarkably, three of these produce superantigenic toxins. Superantigens exert a powerful effect on the immune system, stimulating T-cells, which subsequently induces the formation of large amounts of cytokines. Generation of an overwhelming inflammatory response may lead to death by shock, or other, as yet unrecognized effects of the toxin on the respiratory or cardiac systems. A SIDS/superantigen model is proposed which may explain many of the pathological characteristics of SIDS and establish quantifiable markers for SIDS.

Sudden unexpected nocturnal deaths among Thai immigrant workers in Singapore. The possible role of toxigenic bacteria

Sudden Unexpected Nocturnal Deaths (SUND) occur in young, apparently healthy immigrant workers from Thailand, the Philippines and Bangladesh living among ex-patriot labour forces in countries such as Singapore and Saudi Arabia. Several factors associated with these deaths are similar to those observed for Sudden Infant Death Syndrome (SIDS): sleep related and mainly nocturnal occurrence; no prodromal illnesses other than mild respiratory tract infection; exposure to cigarette smoke; absence of invasive microorganisms at autopsy. The hypotheses proposed to explain these deaths in adults are examined. Based on our studies of the role toxigenic bacteria might play in some cases of SIDS, we suggest a new approach to the investigation of SUND.

Detection of microbial surface antigens that bind Lewis(a) antigen

There is evidence that the Lewis(a) blood group antigen is one of the receptors for a number of potentially pathogenic microorganisms. To determine how widely distributed the microbial adhesins are that bind this antigen, anti-idiotypic antibodies produced against monoclonal anti-Lewis(a) were used in coagglutination assays to screen a variety of species. The following were agglutinated: 7/7 strains of Staphylococcus aureus; 10/19 (53%) strains of Neisseria meningitidis; 8/13 (62%) strains of Haemophilus influenzae; 1/3 strains of Helicobacter pylori; 1/2 strains of Neisseria gonorrhoeae; 1/2 strains of Candida albicans. The application of the anti-idiotypic antibodies to studies of host cell receptors, isolation of adhesins and development of new epidemiological typing reagents is discussed.

Isolation of an adhesin from Staphylococcus aureus that binds Lewis a blood group antigen and its relevance to sudden infant death syndrome

A 67 kDa protein was isolated from cell membrane preparations of Staphylococcus aureus (NCTC 10655) by affinity adsorption with synthetic Lewis a antigen conjugated to Synsorb beads. Pre-treatment of buccal epithelial cells expressing Lewis a with the purified protein reduced binding of the staphylococcal strain to a greater extent than the material not bound to the Synsorb beads. The significance of this work is discussed with reference to expression of Lewis a antigen in infants and the proposed role of toxigenic strains of staphylococci in some cases of sudden infant death syndrome.

Lewis antigen expression on human monocytes and binding of pyrogenic toxins

Toxigenic bacteria such as Bordetella pertussis and Staphylococcus aureus have been implicated in some cases of sudden infant death syndrome (SIDS). We have previously demonstrated that the Lewis(a) antigen is an epithelial cell receptor for S. aureus, and this study demonstrated that Lewis(a) on human monocytes is also a receptor for staphylococcal enterotoxin B (SEB). Values obtained in assays for production of TNF-alpha and nitric oxide were greater for monocytes treated with SEB compared with those treated with lipopolysaccharide (LPS). Exposure to LPS increased the expression of Lewis(a) on monocytes. These results are discussed with reference to the reported enhancement of endotoxic shock by pyrogenic toxins.