Effects of nicotine on bacterial toxins associated with cot death

The frequency of molecular detection of virulence genes encoding cytolysin A, high-pathogenicity island and cytolethal distending toxin of Escherichia coli in cases of sudden infant death syndrome does not differ from that in other infant deaths and healthy infants

Consistent pathological findings in sudden infant death syndrome (SIDS) are seen which display similarities to the pathogenesis of toxaemic shock and/or sepsis. A key candidate infectious agent that is possibly involved is Escherichia coli, given its universal early colonization of the intestinal tract of infants and an increased frequency of toxigenic and mouse-lethal isolates from SIDS compared with comparison infants. An explanation for these findings has yet to be identified. Using PCR, we screened E. coli isolates from 145 SIDS and 101 dead control and healthy infants for three new candidate pathogenicity-related genes: clyA (cytolysin A), irp2 [high-pathogenicity island (HPI)-specific gene] and cdt (cytolethal distending toxin). The results failed to show a positive correlation with SIDS, instead proving that clyA and irp2 genes were common to the infant intestinal E. coli. Interestingly we observed a high rate of carriage of these two potentially pathogenic genes in E. coli from healthy infants in the absence of diarrhoeal disease, and we report that in a number of cases, the detection of HPI-specific genes was predictable by serotype. Despite the lack of associations defined so far, there remains the likelihood that genetic determinants influence the interactions between E. coli and the host, so these factors may be part of the multi-factorial aspect of SIDS.

Tobacco use increases susceptibility to bacterial infection

Active smokers and those exposed to secondhand smoke are at increased risk of bacterial infection. Tobacco smoke exposure increases susceptibility to respiratory tract infections, including tuberculosis, pneumonia and Legionnaires disease; bacterial vaginosis and sexually transmitted diseases, such as chlamydia and gonorrhoea; Helicobacter pylori infection; periodontitis; meningitis; otitis media; and post-surgical and nosocomial infections. Tobacco smoke compromises the anti-bacterial function of leukocytes, including neutrophils, monocytes, T cells and B cells, providing a mechanistic explanation for increased infection risk. Further epidemiological, clinical and mechanistic research into this important area is warranted.

Environmental tobacco smoke exposure: prevalence and mechanisms of causation of infections in children

BACKGROUND AND OBJECTIVES

Environmental tobacco smoke (ETS) exposure is probably one of the most important public health hazards in our community. Our aim with this article is to (1) review the prevalence of ETS exposure in the United States and how this prevalence is often measured in practice and (2) summarize current thinking concerning the mechanism by which this exposure may cause infections in young children.

METHODS

We conducted a Medline search to obtain data published mainly in peer-reviewed journals.

RESULTS

There is still a very high prevalence of ETS exposure among US children ranging from 35% to 80% depending on the method of measurement used and the population studied. The mechanism by which ETS may be related to these infections is not entirely clear but may be through suppression or modulation of the immune system, enhancement of bacterial adherence factors, or impairment of the mucociliary apparatus of the respiratory tract, or possibly through enhancement of toxicity of low levels of certain toxins that are not easily detected by conventional means.

CONCLUSIONS

The prevalence of ETS exposure in the United States is still very high, and its role in causing infections in children is no longer in doubt even if still poorly understood. Research, therefore, should continue to focus on the various mechanisms of causation of these infections and how to best reduce the exposure levels.

Permissive nicotine regulation as a complement to traditional tobacco control

BACKGROUND

Cigarette smoking takes a staggering toll on human health and attracts considerable public health attention, yet real solutions seem distant. The 2004 Family Smoking Prevention and Tobacco Control Act (US Senate bill S2461) would have given the US Food and Drug Administration limited authority to regulate cigarettes to "protect the public health." However, such legislation is unlikely to substantially reduce smoking or related deaths.

DISCUSSION

The past 500 years of tobacco control efforts demonstrate that nicotine prohibition is a practical impossibility for numerous reasons, state revenue being one of the most ominous. The FDA already has regulatory authority over pharmaceutical grade nicotine products, and requires pharmacists to dispense the most addictive of these only with prescriptions. Meanwhile, every corner store can sell far more addictive and dangerous cigarettes to any adult. The FDA could immediately increase competition between cigarettes and clean nicotine products by approving available nicotine products for over-the-counter sales to adults. Similarly permissive regulation of cigarettes and addictive nicotine products will reduce tobacco use and improve smokers' health, but increase nicotine use in the population. Fortunately, restricted youth access and accurate labeling of nicotine's absolute risks will dissuade many non-smokers from experimenting with it, while accurate depiction of its risks relative to cigarette smoking will encourage many smokers to switch. The FDA could take a series of small steps that might ultimately replace a large proportion of cigarette smoking with equally addictive nicotine products, without risking serious public health setbacks. Vaccine, methadone, and injury prevention policies establish relevant public health precedents.

SUMMARY

Cigarettes, or an equally addictive alternative, will be a permanent and common product in most societies. Regulations restricting only the safest addictive nicotine products are hard to justify. Addictive nicotine compliments other tobacco control strategies. Modern tobacco control policies are applicable to addictive nicotine. Controlled trials and test market studies are urgently needed to evaluate addictive nicotine as an alternative to smoking. Meanwhile, legislators should preserve the Food and Drug Administration's option to permit non-prescription sales of addictive nicotine.

Animal models of sudden unexplained death

The etiology of sudden infant death syndrome (SIDS) is unknown but thought to be multifactorial. Several animal models have been developed that induce death without pre-existing symptoms and with pathology similar to that seen in SIDS infants; however, the relevance of these animal models to the events leading to SIDS remains elusive, in part because animal models are as varied as the potential causes of SIDS. In addition, it is difficult to find an animal model that can accurately reflect the genetic, developmental and environmental risk factors for SIDS. Comparisons between species can prove difficult but animal models provide a useful tool for evaluating potential mechanisms related to sudden unexplained death. This review focuses on models developed to examine the association of infection and inflammation with mechanisms proposed to explain sudden unexplained death.

Common bacterial toxins and physiological vulnerability to sudden infant death: the role of deleterious genetic mutations

The common bacterial toxin hypothesis of sudden infant death syndrome (SIDS) is consistent with the epidemiological features of the condition including the age distribution, seasonal incidence, association with prone sleeping and with exposure to tobacco smoke. The hypothesis is supported by experimental evidence but there are two barriers to its acceptance: the speed of onset does not fit with conventional concepts of an infective process; furthermore, the hypothesis appears to offer a single explanation for what is regarded as a multifactorial disease. Concepts from information theory are used to explore these objections. Complex physiological systems process information and need a high level of redundancy to minimise error. Models show that deleterious mutations in such a system will interact synergistically. Environmental perturbations are most likely to cause failure (sudden death) in systems with several mutations. Models also indicate that mutation rates will pose a limit to the size of the functioning genome and, therefore, increased complexity in evolution depends on using old genes in new combinations rather than the chance appearance of new genes. The idea that we share our genes with the rest of creation (same genes but different combinations) leads to the following conjecture: for every receptor controlling the flow of information across a cell membrane there will be a bacterially coded molecule that can switch it off or on. Based on this premise, bacterial toxaemia could cause sudden death, merely the time it takes for a molecule to associate with or dissociate from its receptor. Regardless of the number of physiological systems involved in SIDS, the age distribution will have a unimodal peak corresponding to the age range during which infant serum IgG reaches its nadir. In this way, the two barriers to the common bacterial toxin hypothesis can be overcome: one explanation but multiple bacteria and toxins acting with variable speed on multiple target systems.

SIDS pathogenesis: pathological findings indicate infection and inflammatory responses are involved

This article explores the pathological evidence that supports the hypothesis that infection and inflammation are underlying mechanisms in SIDS. It reviews the pathological findings in relation to the risk factors reported for SIDS and compares these findings with other hypotheses suggested as causes of these unexplained deaths in infants. The roles of environmental factors and bacterial products such as soluble curlin detectable in SIDS sera in triggering cytokine cascades and aberrant inflammatory responses resulting in a toxic shock-like event are also explored. Areas for future research are outlined.

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.

Detection of specific antibodies in cord blood, infant and maternal saliva and breast milk to staphylococcal toxins implicated in sudden infant death syndrome (SIDS)

The common bacterial toxins hypothesis of sudden infant death syndrome (SIDS) is that nasopharyngeal bacterial toxins can trigger events leading to death in infants with absent/low levels of antibody that can neutralise the toxins. The aim of this study was to investigate nasopharyngeal carriage of Staphylococcus aureus and determine levels of immunity in the first year of life to toxic shock syndrome toxin (TSST-1) and staphylococcal enterotoxin C (SEC). Both toxins have been implicated in SIDS cases. Seventy-three mothers and their infants (39 males and 34 females) were enrolled onto the study. The infants had birth dates spread evenly throughout the year. In infants, S. aureus carriage decreased significantly with age (P<0.001). Between 40% and 50% of infants were colonised with S. aureus in the first three months of life and 49% of the isolates produced one or both of the staphylococcal toxins. There was a significant correlation between nasopharyngeal carriage of S. aureus in mothers and infants in the three months following the birth (P<0.001). Carriage of S. aureus in infants and their mothers was not significantly associated with levels of antibody to TSST-1 or SEC in cord blood, adult saliva or breast milk. Infants colonised by S. aureus had higher levels of salivary IgA to TSST-1 than infants who were culture negative. Analysis of cord blood samples by a quantitative ELISA detected IgG bound to TSST-1 and SEC in 95.5% and 91.8% of cases respectively. There was a marked variation in levels of maternal IgG to both TSST-1 and SEC among cord blood samples. Maternal age, birth weight, and seasonality significantly affected the levels of IgG binding to TSST-1 or SEC. Analysis of infant saliva samples detected IgA to TSST-1 and SEC in the first month after birth; 11% of samples tested positive for salivary IgA to TSST-1 and 5% for salivary IgA to SEC. By the age of two months these proportions had increased to 36% and 33% respectively. More infants who used a dummy tested positive for salivary IgA to TSST-1 compared to infants who did not use a dummy. Levels of IgA to TSST-1 and SEC detected in the breast-milk samples varied greatly among mothers. There was a trend for infants receiving breast milk with low levels of antibody to TSST-1 or SEC to have higher levels of salivary antibody to the toxins. In conclusion, passive immunity to toxins implicated in SIDS cases varies greatly among infants. Infants are able to mount an active mucosal immune response to TSST-1 and SEC in the first month of life.

Cot mattresses as reservoirs of potentially harmful bacteria and the sudden infant death syndrome

Cot mattress materials were investigated as potential reservoirs of bacteria in relation to the sudden infant death syndrome (SIDS). The sleeping position of the infant significantly influenced bacterial population density of cot mattress polyurethane foams (p<0.0000001) and their covers (p<0.004). Staphylococcus aureus was isolated at significantly higher frequency (p<0.03) from the infant's head region of cot mattress materials. Significantly higher bacterial population densities (p<0.001) were associated with polyurethane foams from non-integral mattresses (exposed polyurethane foam), when compared to those from mattresses completely covered by polyvinyl chloride (integral type mattress). The frequency of isolation of S. aureus from polyurethane foams from non-integral mattresses was also significantly higher (p=0.03) than from foams from the integral type. The following factors were significantly associated with increased frequency of isolation of S. aureus: from the polyurethane foam, previous use of non-integral mattresses by another child (p=0.03 for all sample sites, p=0.01 for torso region); from the covers, sleeping in the prone position (p=0.003 head region, p=0.001 torso region). Prone sleeping was also significantly associated with increased bacterial population levels (p=0.01) and increased frequency of isolation of Escherichia coli (p=0.02) from the torso region of cot mattress covers. These findings could explain some recently identified risk factors for SIDS associated with type and previous use of cot mattresses. Clostridium perfringens was isolated at very low frequency and Streptococcus pyogenes was not isolated from any cot mattress materials tested.

Sudden infant death syndrome: a critical review of approaches to research

This review explores the various research approaches taken attempting to solve the problem of SIDS. It would appear that major clues provided by pathological findings have been largely overlooked and as a consequence much effort, time, and money has been wasted on projects that satisfy only sub-specialty and political needs. Close examination of the pathological clues would provide better insights into the mechanisms underlying this enigmatic and heartbreaking problem.

Estimating the health consequences of replacing cigarettes with nicotine inhalers

BACKGROUND

A fast acting, clean nicotine delivery system might substantially displace cigarettes. Public health consequences would depend on the subsequent prevalence of nicotine use, hazards of delivery systems, and intrinsic hazards of nicotine.

METHODS

A spreadsheet program, DEMANDS, estimates differences in expected mortality, adjusted for nicotine delivery system features and prevalence of nicotine use, by extending the data and methods of the SAMMEC 3 software from the US Centers for Disease Control and Prevention. The user estimates disease risks attributable to nicotine, other smoke components, and risk factors that coexist with smoking. The public health consequences of a widely used clean nicotine inhaler replacing cigarettes were compared to historical observations and public health goals, using four different risk attribution scenarios and nicotine use prevalence from 0-100%.

MAIN OUTCOME MEASURES

Changes in years of potential life before age 85 (YPL85).

RESULTS

If nicotine accounts for less than a third of smokers' excess risk of SAMMEC diseases, as it most likely does, then even with very widespread use of clean nicotine DEMANDS predicts public health gains, relative to current tobacco use. Public health benefits accruing from a widely used clean nicotine inhaler probably equal or exceed the benefits of achieving Healthy People 2010 goals.

CONCLUSIONS

Clean nicotine inhalers might improve public health as much as any feasible tobacco control effort. Although the relevant risk estimates are somewhat uncertain, partial nicotine deregulation deserves consideration as part of a broad tobacco control policy.

Myocarditis and sudden infant death syndrome

This is a retrospective survey of findings of myocarditis in 437 infants under the age of 1 year who died suddenly and unexpectedly between 1982 and 1999, and were investigated at the Department of Forensic Medicine in Stockholm, Sweden. Myocarditis was diagnosed in 69/410 infants who died naturally (16.8%) and in 2/27 violent deaths (7.4%). In 43/410 natural deaths (10.5%) the myocarditis was an isolated finding and the only explanation for cause of death and in 26 (6.3%) there were additional possible causes of death. The myocarditis was acute in 45/69 and chronic in 24/69 natural deaths, and was found to occur as early as at a few weeks of age. No specific risk factors were found when reviewing critical time of year, age, gender, previous symptoms, sleeping position, aspiration of gastric contents and environmental factors in infant deaths with finding of myocarditis compared to 313 deaths due to sudden infant death syndrome. Myocarditis was found in 13 of 37 deaths where cultures for cytomegalovirus were positive. More than 50% of the foci of the isolated myocarditis were located in the upper part of the interventricular septum and the adjacent part of the right atrium, areas including parts of the conduction system. This localisation is significant for the cause of death when comparing deaths with myocarditis as an isolated finding to deaths with other possible causes.

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.

Review of risk factors for sudden infant death syndrome

Sudden infant death syndrome (SIDS) accounts for the largest number of deaths during the first year of life in developed countries. The possible causes of SIDS are numerous and, to date, there is no adequate unifying pathological explanation for SIDS. Epidemiological studies have played a key role in identifying risk factors, knowledge of which has underpinned successful preventive programmes. This review critically assesses information on the main risk factors and causal hypotheses put forward for SIDS, focusing on research published since 1994. The overall picture that emerges from this review is that affected infants are not completely normal in development, but possess some inherent weakness, which may only become obvious when the infant is subjected to stress. Initially there may be some minor impairment or delay in development of respiratory, cardiovascular or neuromuscular function. None of these is likely to be sufficient, in isolation, to cause death and, provided the infant survives the first year of life, may no longer be of any significance. However, when a compromised infant is confronted with one or more stressful situations, several of which are now clearly identified as risk factors, and from which the majority of infants would normally escape, the combination may prove fatal.

SIDS: more facts and controversies

A more robust theory of the causation of sudden infant death syndrome (SIDS) is needed. The asphyxial theory of SIDS, which encompasses the prone sleeping position, relies on contradictory pathological evidence and fails to explain infants with SIDS who are found in the supine or lateral position. Many of the risk factors for SIDS point to an infective cause. The relative risks of these infection-related factors differ from study to study, as does the relative risk of prone sleeping position. I present the case for an infection model for SIDS causation, which has largely been neglected by mainstream SIDS researchers.

A prospective study of smoking during pregnancy and SIDS

AIMS

To study the association between smoking during pregnancy and sudden infant death syndrome (SIDS) using prospectively collected data, making it possible to account for a number of potential confounders.

DESIGN

Prospective follow up study (n = 24 986).

RESULTS

The overall rate of SIDS was 0.80 per 1000 live births (n = 20). Children of smokers had more than three times the risk of SIDS compared with children of non-smokers (OR = 3.5; 95% CI 1.4-8.7), and the risk of SIDS increased with the number of cigarettes smoked per day (p < 0.05). Adjustment for parity, alcohol, and caffeine intake during pregnancy, maternal height and weight before pregnancy, years of school, occupational status, marital status, and number of antenatal care visits did not change the results. Adjustment for mother's age marginally reduced the risk of SIDS associated with smoking (OR = 3.0; 95% CI 1.2-7.3).

CONCLUSIONS

Given the prospective nature of the study, the number of deaths is small; however, if our results reflect a true association between smoking during pregnancy and SIDS, approximately 30-40% of all cases of SIDS could be avoided if all pregnant women stopped smoking in a population with 30% pregnant smokers. Our study adds to earlier evidence for an association between smoking during pregnancy and SIDS. The strengths of the study are the possibility to adjust for a number of potential confounders and the fact that information about smoking habits during pregnancy was prospectively collected.

Perinatal complications associated with maternal tobacco use

The use of tobacco products by pregnant women is associated with placenta previa, abruptio placentae, premature rupture of the membranes, preterm birth, intrauterine growth restriction and sudden infant death syndrome. Approximately 15-20% of women smoke during pregnancy. It has been suggested that smoking is responsible for 15% of all preterm births, 20-30% of all infants of low birthweight, and a 150% increase in overall perinatal mortality. Cigarette smoking is one of the most important and modifiable risk factors associated with adverse perinatal outcomes.

Sudden infant death syndrome: a toxic response

Causes of sudden infant death syndrome (SIDS) remain elusive. Much of the current literature points to an infectious cause with a role for proinflammatory cytokines and septic shock in stimulating an overwhelming response in an infant. This article reviews the literature and possible causes of this devastating condition.

Possible potentiation of toxins from Prevotella intermedia, Prevotella nigrescens, and Porphyromonas gingivalis by cotinine

BACKGROUND

Smoking is a recognized risk factor for the initiation and progression of periodontitis. However, the mechanism by which smoking induces its negative effects on the periodontium is not clear. This study aimed to test the hypothesis that synergy may occur between cotinine and bacterial products isolated from 3 putative periodontopathogens.

METHODS

A chick embryo toxin assay was used to investigate bacterial toxins (cell-free extracellular toxins and cell-free cell lysates) from 5 species with and without cotinine. A total of 9 putative periodontopathogens (3 species) and 2 non-oral controls (2 species) were studied. The periodontal species were: Prevotella intermedia (n = 4), Prevotella nigrescens (n = 4), and Porphyromonas gingivalis (n = 1). The control species tested were: Staphylococcus aureus (n = 1) and Escherichia coli (n = 1).

RESULTS

The toxicity kill was significantly greater than expected by simple addition alone (P <0.05, Fisher's exact test) between cotinine (800 ng/ml) and 1) the cell-free extracellular toxins of P. nigrescens MH1 and 2) the cell-free cell lysates of P. intermedia MH2. Synergy occurred with cotinine plus the cell-free extracellular toxins in all but 3 periodontal isolates, and the cell-free cell lysates in all but 2 periodontal isolates. Cotinine significantly (P <0.05, Fisher's exact test) enhanced the effects of cell-free extracellular toxins and cell lysates from one control species (E. coli), but not the other (S. aureus).

CONCLUSIONS

These findings indicate that synergy in an in vitro assay can occur between cotinine and toxins from putative periodontopathogens. This may be one important mechanism by which smoking increases the severity of periodontitis.

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.

Exposure to cigarette smoke, a major risk factor for sudden infant death syndrome: effects of cigarette smoke on inflammatory responses to viral infection and bacterial toxins

Exposure to cigarette smoke is a major risk factor for sudden infant death syndrome and also for respiratory infections in children. It has been suggested that toxigenic bacteria colonizing the respiratory tract might play a role in some cases of sudden infant death syndrome and nicotine has been demonstrated to enhance the lethality of bacterial toxins in a model system. Pyrogenic toxins of Staphylococcus aureus have been identified in tissues of infants who died of sudden infant death syndrome. It has been suggested that some of these deaths were due to induction of inflammatory mediators by infectious agents during a period when infants are less able to control these responses. The aim of this study was to assess the effects of a water-soluble cigarette smoke extract on the production of tumor necrosis factor alpha and nitric oxide from human monocytes in response to staphylococcal toxic shock syndrome toxin 1 or infection of the monocytes with respiratory syncytial virus. Cell culture supernatants were examined by a bioassay using mouse fibroblasts (L-929 cell line) for tumor necrosis factor alpha activity and by a spectrophotometric method for nitrite. Compared with monocytes incubated with medium only, monocytes incubated with any of the factors or their combinations tested in the study released higher levels of tumor necrosis factor alpha and lower levels of nitric oxide. Incubation with cigarette smoke extract increased tumor necrosis factor alpha from respiratory syncytial virus-infected cells while it decreased tumor necrosis factor alpha from cells incubated with toxic shock syndrome toxin. Incubation with cigarette smoke extract decreased the nitric oxide production from respiratory syncytial virus-infected cells while it increased the nitric oxide production from cells incubated with toxic shock syndrome toxin. Monocytes from a minority of individuals demonstrated extreme tumor necrosis factor alpha responses and/or very high or very low nitric oxide. The proportion of samples in which extreme responses with a very high tumor necrosis factor alpha and very low nitric oxide were detected was increased in the presence of the three agents to 20% compared with 0% observed with toxic shock syndrome toxin 1 or 4% observed with cigarette smoke extract or respiratory syncytial virus.

Preliminary investigation of lethally toxic sera of sudden infant death syndrome victims and neutralisation by commercially available immunoglobulins and adult sera

The aim of the study was to test the hypotheses (i) that sudden infant death syndrome sera are toxic to 11-day old chick embryos and (ii) that such a toxicity can be counteracted by immunoglobulin or adult sera. Serum samples from 11 SIDS victims and five controls were tested for lethal toxicity in the chick embryo bioassay. Five serum samples were used to challenge chick embryos injected with the following: sudden infant death syndrome serum plus Hank's balanced salt solution; Hank's balanced salt solution alone; sudden infant death syndrome serum plus 3% w/v commercial immunoglobulin; sudden infant death syndrome serum plus 6% w/v immunoglobulin; sudden infant death syndrome serum plus pooled sera of 40 healthy adults. Results obtained revealed that Hank's balanced salt solution, the pooled adult serum and the commercial immunoglobulin were all non-lethal, in the chick embryo test system. By contrast. 10 sudden infant death syndrome victims yielded sera containing lethal levels of toxin(s) compared to 2/5 controls which was statistically significant (P < 0.05, Fischer's exact test). In the tests of sudden infant death syndrome serum plus immunoglobulin or pooled adult serum, the lethality of sudden infant death syndrome serum was abolished in all cases. The reduction in toxicity of individual sudden infant death syndrome serum plus immunoglobulin or pooled adult serum was often statistically significant (P<0.05-P<0.00005, Fischer's exact test). We conclude that lethal levels of toxin are present in sudden infant death syndrome sera and that they can be neutralised by normal immune serum. These results indicate that passive immunisation is a potential treatment to protect babies considered at risk from sudden infant death syndrome.

Endotoxin in blood and tissue in the sudden infant death syndrome

Although the explanation for sudden infant death syndrome (SIDS) remains unknown, an increasing body of evidence now exists to suggest a possible role for bacterial toxins in the aetiology, and a number of investigators have considered that endotoxaemia could explain some of the associated features. Following the development of an animal model which confirmed that endotoxaemia could be detected after death, we studied endotoxin levels in blood and tissue samples taken at autopsy from SIDS infants, child controls and adult controls. There were significant correlations between endotoxin levels in blood and the various organs sampled particularly in SIDS cases and child controls, and blood endotoxin levels in SIDS cases were higher in those infants where there was histological evidence of mild to moderate inflammation. However, overall no significant differences were found between endotoxin levels in blood or tissue in the three study groups. Further studies into possible actions or interactions of endotoxin in SIDS are required.

Effect of time post mortem on the concentration of endotoxin in rat organs: implications for sudden infant death syndrome (SIDS)

The aim of the study was to test the following hypotheses: (i) that endotoxin injected 40 min prior to death can be detected in rat organs post mortem and (ii) that endotoxin levels do not change with increasing time post mortem. Rats were injected with or without endotoxin in buffered saline, 40 min prior to being killed. Endotoxin levels in rat organs were assessed using a Limulus amoebocyte assay. The effect of storage time post mortem was assessed by following various storage regimes at 25 degrees C and 8 degrees C. Significant differences (P = < 0.001) in endotoxin levels of all samples tested were found between rats injected with and without endotoxin. A significant increase in detectable endotoxin was observed between 0 h and 6 h post mortem in rats injected with or without endotoxin. No difference in detectable endotoxin levels in the kidney, liver and spleen was observed from 30 h to 102 h post mortem in rats injected with or without endotoxin. In rats injected with endotoxin, detectable endotoxin levels in the heart were raised between 0 h and 6 h, 6 h and 54 h, and 30 h and 78 h. Endotoxin injected into rats 40 min prior to death can be detected post mortem. For rats injected with saline or endotoxin prior to death levels in the kidney, liver and spleen were not affected by storage at 8 degrees C for 30-102 h, after initial storage at room temperature for 6 h. Levels of endotoxin detected in the hearts of rats injected with saline were not affected by storage up to 102 h. In rats injected with endotoxin prior to death, detectable levels in the heart were significantly affected by increasing time in storage.

The common bacterial toxins hypothesis of sudden infant death syndrome

The background to the common bacterial toxin hypothesis of sudden infant death syndrome is presented. The idea is that some cases of sudden infant death syndrome are due to the lethal effects of nasopharyngeal bacterial toxins which can act synergistically to trigger the events leading to death. The concept is consistent with the age distribution of sudden infant death syndrome, the winter excess of cases and the role of prone sleeping and passive exposure to cigarette smoke. A number of laboratory-based investigations are described. There is an increased isolation of staphylococci and Gram-negative bacilli from sudden infant death syndrome infants compared with age- and season-matched healthy infants. Bacteria from sudden infant death syndrome infants interact synergistically to cause sudden death in gnotobiotic weanling rats. Bacterial toxins implicated in sudden infant death syndrome interact synergistically to cause death in chick embryos. Nicotine in very low doses potentiates the lethal effect of toxin combinations in chick embryos. Staphylococcal toxins and endotoxins have been demonstrated in sudden infant death syndrome tissues, antibodies to endotoxins are low in sudden infant death syndrome cases and the prone sleeping position leads to pooling of secretions in the upper airways, increasing the risk of bacterial growth and toxin production. If the hypothesis is correct, then there is the possibility of a further reduction in the incidence of sudden infant death syndrome based on immunisation against the toxins involved.

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.

Animal models used to test the interactions between infectious agents and products of cigarette smoked implicated in sudden infant death syndrome

Animal test systems are reviewed that have relevance to sudden infant death syndrome (SIDS) are reviewed. These test interactions between infectious agents (or their toxins) and products of cigarette smoke. Infectious agents implicated in SIDS include members of the enterobacteria and clostridia, Staphylococcus aureus and Streptococcus pyogenes. Smoking is thought to be the single most preventable cause of SIDS. Tobacco smoke contains many extremely toxic products including cyanide and nicotine. Many animal test systems are available to examine the potency of bacterial toxins and smoke-derived components. These include mice, hamsters, rats and chick embryos. Such systems reveal synergy between bacterial toxins, especially endotoxin and superantigens. They have also demonstrated potentiation of low levels of bacterial toxin by low levels of both nicotine and its primary metabolite, cotinine. These findings suggest a possible causal explanation for the fact that passive exposure to cigarette smoke is a risk factor in sudden infant death syndrome.

Extraintestinal Escherichia coli isolations from SIDS cases and other cases of sudden death in Victoria, Australia

This investigation is an extension of previous studies on the possible role of intestinal Escherichia coli in sudden infant death syndrome (SIDS) to include the isolation of extraintestinal E. coli. The lungs of 52 and the blood of 144 SIDS infants were cultured and isolates were investigated. E. coli was isolated from about a quarter of post-mortem lung samples and about 15% of blood samples from SIDS infants. The isolates were subjected to microbiological studies, including serotyping and haemolysin assays. The majority were found to belong to serogroups commonly associated with bacteraemia. These results may indicate that extraintestinal E. coli plays a role in SIDS.

Maternal cigarette smoking and pregnancy outcome

Maternal smoking rates in pregnancy have declined, particularly in the non-manual social classes, and perinatal mortality rates have fallen over the last 20 years. We have therefore re-evaluated the relationship between maternal cigarette smoking and pregnancy outcome against this background. A total of 608 stillbirths and 634 infant deaths were identified using the All Wales Perinatal Survey. The cause of death was classified using the clinicopathological system. Maternal smoking rates and social class groupings were compared with those in a cohort of 16047 survivors born to women resident in South Glamorgan. The smoking rate was 37.8% in mothers of babies who died compared with 27.2% in mothers of survivors, an odds ratio (OR) of 1.63 [95% CI 1.44, 1.84]. The OR for unexplained stillbirth was 1.72 [95% CI 1.38, 2.13], placental abruption 2.07 [95% CI 1.29, 3.31], infection 3.70 [95% CI 2.23, 6.13] and sudden infant death syndrome 4.84 [95% CI 3.05, 7.69]. Maternal smoking was not associated with death due to prematurity or a congenital anomaly. Despite changes in smoking habits and the causes of perinatal death, smoking during pregnancy continues to be strongly associated with fetal and infant mortality. It is important that health promotion activities are effective in reducing smoking during pregnancy.

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.

Possible lethal enhancement of toxins from putative periodontopathogens by nicotine: implications for periodontal disease

AIM

To test the hypothesis that lethal synergy in the chick embryo model may occur between nicotine and bacterial products (cell-free extracellular toxins and cell lysates) of five putative periodontopathogens.

METHODS

The lethality of cell-free extracellular toxins and cell lysates of five periodontal species was assessed with or without nicotine in the chick embryo assay system. Ten putative periodontopathogens (five species) were studied: Prevotella intermedia (n = 5), Porphyromonas gingivalis (n = 1), Porphyromonas asaccharolytica (n = 1), Fusobacterium nucleatum (n = 2), and Fusobacterium necrophorum (n = 1).

RESULTS

Simultaneous testing of cell-free extracellular toxins from isolates W50, PS2, PS3, PS4, and PS5 and nicotine resulted in a percentage kill significantly greater than expected (Fisher's Exact test). Simultaneous testing of cell lysates from isolates W50, PS2, and PS5 and nicotine resulted in a percentage kill significantly greater than expected (Fisher's Exact test).

CONCLUSIONS

Lethal synergy in the chick embryo model may occur between nicotine and toxins from putative periodontopathogens (both cell-free extracellular toxins and cell lysates). This may be an important mechanism by which smoking increases the severity of periodontal disease.