Transient bacteraemia: A possible cause of sudden life threatening events

Enhanced Bacteremia in Dextran Sulfate-Induced Colitis in Splenectomy Mice Correlates with Gut Dysbiosis and LPS Tolerance

Because both endotoxemia and gut dysbiosis post-splenectomy might be associated with systemic infection, the susceptibility against infection was tested by dextran sulfate solution (DSS)-induced colitis and lipopolysaccharide (LPS) injection models in splenectomy mice with macrophage experiments. Here, splenectomy induced a gut barrier defect (FITC-dextran assay, endotoxemia, bacteria in mesenteric lymph nodes, and the loss of enterocyte tight junction) and gut dysbiosis (increased Proteobacteria by fecal microbiome analysis) without systemic inflammation (serum IL-6). In parallel, DSS induced more severe mucositis in splenectomy mice than sham-DSS mice, as indicated by mortality, stool consistency, gut barrier defect, serum cytokines, and blood bacterial burdens. The presence of green fluorescent-producing (GFP) E. coli in the spleen of sham-DSS mice after an oral gavage supported a crucial role of the spleen in the control of bacteria from gut translocation. Additionally, LPS administration in splenectomy mice induced lower serum cytokines (TNF-α and IL-6) than LPS-administered sham mice, perhaps due to LPS tolerance from pre-existing post-splenectomy endotoxemia. In macrophages, LPS tolerance (sequential LPS stimulation) demonstrated lower cell activities than the single LPS stimulation, as indicated by the reduction in supernatant cytokines, pro-inflammatory genes (iNOS and IL-1β), cell energy status (extracellular flux analysis), and enzymes of the glycolysis pathway (proteomic analysis). In conclusion, a gut barrier defect after splenectomy was vulnerable to enterocyte injury (such as DSS), which caused severe bacteremia due to defects in microbial control (asplenia) and endotoxemia-induced LPS tolerance. Hence, gut dysbiosis and gut bacterial translocation in patients with a splenectomy might be associated with systemic infection, and gut-barrier monitoring or intestinal tight-junction strengthening may be useful.

SIDS, prone sleep position and infection: An overlooked epidemiological link in current SIDS research? Key evidence for the "Infection Hypothesis"

Mainstream researchers explain the etiology of SIDS with the cardiorespiratory paradigm. This has been the focus of intense study for many decades without providing consistent supporting data to link CNS findings to epidemiological risk factors or to the usual clinicopathological findings. Despite this, and the apparent oversight of the link between prone sleep position and respiratory infection, papers citing CNS, cardiac and sleep arousal findings continue to be published. Discovery of the prone sleep position risk factor provided tangential support for the cardiorespiratory control hypothesis which defines the mainstream approach. Despite many decades of research and huge expenditure, no aetiological answer has been forthcoming. In asking why?This paper exposes some of the shortcomings regarding this apparent oversight by mainstream SIDS researchers and examines the role of respiratory infection and puts the case for the “Infection Hypothesis.” In addition, the paper provides encouragement to neuropathologists to examine the potential link between CNS findings and cardiac function (as opposed to respiratory function) in relation to infection and to examine possible correlates between CNS findings and established risk factors such as recent infection, contaminated sleeping surfaces, maternal/obstetric/higher birth, ethnicity, non-breast-feeding, male gender, etc. or with the usual gross pathological findings of SIDS (intrathoracic petechial hemorrhages, liquid blood, congested lungs). The shortcomings exposed through this review invite questions over current research directions and hopefully encourage research into other more plausible hypotheses, such as the infection paradigm.•

Mainstream SIDS researchers appear to have overlooked the key relationship between prone sleep position and infection.

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This omission has major implications for current and future SIDS research.

Hypothesis: Bacterial induced inflammation disrupts the orderly progression of the stem cell hierarchy and has a role in the pathogenesis of breast cancer

BACKGROUND

The hierarchical model of stem cell genesis is based on the idea that the number of cell divisions between the zygote and fully differentiated epithelial cells is kept close to the minimum, which is log to the base 2 of the total number of cells produced in a human lifetime. The model assumes the orderly progression of stem cell divisions requires precise control at every stage in development. If the orderly progression is maintained then cancer will be rare. A prediction of the model is that if the orderly progression of the stem cell hierarchy is disturbed by trauma, ulceration or inflammation then cancer will occur.

HYPOTHESIS

Bacterial induced inflammation in breast ducts disturbs the stem cell hierarchy and is a cause of breast cancer.

EVIDENCE

Mammalian milk is not sterile. It contains a range of bacteria, derived endogenously by the entero-mammary circulation. The dominant flora consists of lactose fermenting bacteria. Pregnancy and breast feeding reduce the risk of subsequent breast cancer. The implication is that a lactose fermenting bacterial flora in breast ducts is protective. Malignant and benign breast tissue contains bacteria derived endogenously, but studies so far have not revealed a specific flora associated with malignancy. Periodontitis is associated with oral, oesophageal, colonic, pancreatic, prostatic and breast cancer. The pathogenic bacteria which cause periodontitis spread endogenously to cause inflammation at other epithelial sites. Meta-analysis of epidemiological studies shows that the consumption of yoghurt is associated with a reduction in the risk of breast cancer.

CONCLUSION

The hypothesis, although not proven, is supported by the available evidence. Lactose fermenting bacteria protect but pathogenic bacteria which induce inflammation raise the risk of breast cancer. The consumption of yoghurt also appears to be protective.

Optimise the microbial flora with milk and yoghurt to prevent disease

Pathogenic bacteria, which are temporary or permanent members of our microbial flora, cause or contribute to a wide range of human disease at all ages. Conditions include Alzheimer's disease, atherosclerosis, diabetes mellitus, obesity, cancer, autoimmunity and psychosis, amongst others. The mechanism of damage is inflammation which can be chronic or acute. An optimal microbial flora includes a wide range of pathogenic bacteria in low dose. This allows specific immunity to be developed and maintained with minimal inflammatory damage. Human milk has evolved to deliver an optimal microbial flora to the infant. Cow's milk has the potential, following appropriate fortification, to maintain an optimal human microbial flora throughout life. Yoghurt is a fermented milk product in which bacteria normally present in milk convert sugars to lactic acid. The acid suppresses the growth of pathogens in the oral cavity, oropharynx and oesophagus. Thus yoghurt can restore an optimal flora in these regions in the short term. Since bacteria are transported between epithelial surfaces, yoghurt will also optimise the flora elsewhere. The judicious use of milk and yogurt could prevent a high proportion of human disease.

Effect of salivary agglutination on oral streptococcal clearance by human polymorphonuclear neutrophil granulocytes

Salivary agglutination is an important host defense mechanism to aggregate oral commensal bacteria as well as invading pathogens. Saliva flow and subsequent swallowing more easily clear aggregated bacteria compared with single cells. Phagocytic clearance of bacteria through polymorphonuclear neutrophil granulocytes also seems to increase to a certain extent with the size of bacterial aggregates. To determine a connection between salivary agglutination and the host innate immune response by phagocytosis, an in vitro agglutination assay was developed reproducing the average size of salivary bacterial aggregates. Using the oral commensal Streptococcus gordonii as a model organism, the effect of salivary agglutination on phagocytic clearance through polymorphonuclear neutrophil granulocytes was investigated. Here we describe how salivary aggregates of S. gordonii are readily cleared through phagocytosis, whereas single bacterial cells showed a significant delay in being phagocytosed and killed. Furthermore, before phagocytosis the polymorphonuclear neutrophil granulocytes were able to induce a specific de-aggregation, which was dependent on serine protease activity. The data presented suggest that salivary agglutination of bacterial cells leads to an ideal size for recognition by polymorphonuclear neutrophil granulocytes. As a first line of defense, these phagocytic cells are able to recognize the aggregates and de-aggregate them via serine proteases to a more manageable size for efficient phagocytosis and subsequent killing in the phagolysosome. This observed mechanism not only prevents the rapid spreading of oral bacterial cells while entering the bloodstream but would also avoid degranulation of involved polymorphonuclear neutrophil granulocytes, so preventing collateral damage to nearby tissue.

Microbes, molecular mimicry and molecules of mood and motivation

The hypothesis proposed is that functional disorders, such as irritable bowel syndrome, chronic fatigue syndrome and anorexia nervosa are caused by auto-antibodies to neuronal proteins induced by molecular mimicry with microbial antigens. The age incidence of these conditions, the marked female excess, increase with economic and technological advance, precipitation by infection, and the paucity of histological changes are all consistent with the hypothesis. It can be tested directly using human sera to search for cross reaction with brain proteins in model systems such as Drosophila melanogaster. The conditions might be amenable to treatment using pooled immunoglobulin. Identification and elimination from the microbial flora of the bacteria that express the cross reacting antigens should be possible.

Gut Microbiota and Immunity: Possible Role in Sudden Infant Death Syndrome

The gut microbiome influences the development of the immune system of young mammals; the establishment of a normal gut microbiome is thought to be important for the health of the infant during its early development. As the role of bacteria in the causation of sudden infant death syndrome (SIDS) is backed by strong evidence, the balance between host immunity and potential bacterial pathogens is likely to be pivotal. Bacterial colonization of the infant colon is influenced by age, mode of delivery, diet, environment, and antibiotic exposure. The gut microbiome influences several systems including gut integrity and development of the immune system; therefore, gut microflora could be important in protection against bacteria and/or their toxins identified in SIDS infants. The aims of the review are to explore (1) the role of the gut microbiome in relation to the developmentally critical period in which most SIDS cases occur; (2) the mechanisms by which the gut microbiome might induce inflammation resulting in transit of bacteria from the lumen into the bloodstream; and (3) assessment of the clinical, physiological, pathological, and microbiological evidence for bacteremia leading to the final events in SIDS pathogenesis.

Gut microbiome in sudden infant death syndrome (SIDS) differs from that in healthy comparison babies and offers an explanation for the risk factor of prone position

The role of bacteria in the causation of sudden infant death syndrome (SIDS) is gaining acceptance. Mainstream research favouring respiratory compromise has failed to provide a plausible pathogenetic mechanism despite many years of investigation and thousands of research papers. Bacterial colonisation of the colon of the human infant is influenced by many factors including age, mode of delivery, diet, environment, and antibiotic exposure. The gut microbiome influences development of the immune system. The gut microflora could be important in protection against the bacteria and/or their toxins purportedly involved in SIDS pathogenesis. The aim was to perform a preliminary investigation of the gut microflora in sudden infant death syndrome (SIDS) compared with live comparison babies. The intestinal contents from 52 SIDS, and 102 faecal samples from age-matched live comparison infants were screened by PCR to target 16s RNA genes of Clostridium innocuum, Cl. Perfringens, Cl. difficile, Bacteroides thetaiotaomicron and Staphylococcus aureus. Gut colonisation of the babies with these bacteria was analysed in relation to age, gender and type of feeding; and for SIDS babies sleeping position. Cl. difficile, Cl. innocuum and B. thetaiotaomicron were significantly associated with SIDS with 25%, 46% and 30% of cases PCR positive for these respective bacteria compared with only 6%, 23% and 8.8% respectively in the comparison group. SIDS babies had dual colonisation by both Cl. perfringens and Cl. difficile significantly more often than comparison babies and also with triple colonisation by Cl. perfringens, Cl. difficile and Cl. innocuum. SIDS babies were more often colonised by S. aureus than comparison babies. In addition, SIDS babies found prone were significantly more likely to be colonised by S. aureus than for other positions recorded (OR = ∞; CI = 2·04 - ∞). No significant differences between breast and bottle-fed SIDS babies was observed in regard to each clostridial bacterium, or S. aureus, however Cl. innocuum was found to be significantly associated with formula feeding in the comparison cohort. Comparison of breast and formula feeding of SIDS babies with live comparison babies revealed significant differences with regards to some of the clostridial bacteria. Age-specific differences in gut bacterial microbiome were observed in both SIDS and comparison healthy babies. This study gives an insight into differences in the gut bacterial microbiome of SIDS babies compared with healthy babies. These differences could be important in contributing to a baby's susceptibility to infection and therefore to SIDS. The association of S. aureus colonisation with prone sleep position supports the hypothesis that prone sleep position could increase the risk of ingestion/inhalation of bacteria contaminating the sleeping surface and could account for the increased risk of SIDS in babies who are put to sleep prone. The study provides impetus for broader studies into the gut microbiome of babies and could lead to effective approaches to SIDS prevention.

Time-dependent post mortem changes in the composition of intestinal bacteria using real-time quantitative PCR

Post mortem or even normal changes during life occurring in major gut bacterial populations are not known. We investigated Bacteroides sp., Bifidobacterium sp., Clostridium leptum, Clostridium coccoides, Streptococcus sp., Lactobacillus sp. and Enterobacteriacaea ratios in 7 fecal samples from healthy volunteers and in 61 autopsies rectum and cecum samples and studied the effect of post mortem time using quantitative real-time PCR. Bacterial ratios in stool samples from volunteers and rectum samples from autopsy cases were similar and did not change significantly up to 5 days post mortem. In cecum, significant post mortem time-dependent differences were observed in ratios of Bacteroides sp. (p = 0.014) and Lactobacillus sp. (p = 0.024). Our results showed that ratios of Bacteroides sp., Bifidobacterium sp., Clostridium leptum, Clostridium coccoides, Streptococcus sp., Lactobacillus sp. and Enterobacteriacaea can be investigated in autopsy rectum samples up to 5 days after death.

Evaluation of postmortem bacterial migration using culturing and real-time quantitative PCR

Postmortem bacteriology can be a valuable tool for evaluating deaths due to bacterial infection or for researching the involvement of bacteria in various diseases. In this study, time-dependent postmortem bacterial migration into liver, mesenteric lymph node, pericardial fluid, portal, and peripheral vein was analyzed in 33 autopsy cases by bacterial culturing and real-time quantitative polymerase chain reaction (RT-qPCR). None suffered or died from bacterial infection. According to culturing, pericardial fluid and liver were the most sterile samples up to 5 days postmortem. In these samples, multigrowth and staphylococci were not or rarely detected. RT-qPCR was more sensitive and showed higher bacterial positivity in all samples. Relative amounts of intestinal bacterial DNA (bifidobacteria, bacteroides, enterobacter, clostridia) increased with time. Sterility of blood samples was low during the studied time periods (1-7 days). The best postmortem microbiological sampling sites were pericardial fluid and liver up to 5 days after death.

Comprehensive postmortem analyses of intestinal microbiota changes and bacterial translocation in human flora associated mice

Background

Postmortem microbiological examinations are performed in forensic and medical pathology for defining uncertain causes of deaths and for screening of deceased tissue donors. Interpretation of bacteriological data, however, is hampered by false-positive results due to agonal spread of microorganisms, postmortem bacterial translocation, and environmental contamination.

Methodology/Principal Findings

We performed a kinetic survey of naturally occurring postmortem gut flora changes in the small and large intestines of conventional and gnotobiotic mice associated with a human microbiota (hfa) applying cultural and molecular methods. Sacrificed mice were kept under ambient conditions for up to 72 hours postmortem. Intestinal microbiota changes were most pronounced in the ileal lumen where enterobacteria and enterococci increased by 3–5 orders of magnitude in conventional and hfa mice. Interestingly, comparable intestinal overgrowth was shown in acute and chronic intestinal inflammation in mice and men. In hfa mice, ileal overgrowth with enterococci and enterobacteria started 3 and 24 hours postmortem, respectively. Strikingly, intestinal bacteria translocated to extra-intestinal compartments such as mesenteric lymphnodes, spleen, liver, kidney, and cardiac blood as early as 5 min after death. Furthermore, intestinal tissue destruction was characterized by increased numbers of apoptotic cells and neutrophils within 3 hours postmortem, whereas counts of proliferative cells as well as T- and B-lymphocytes and regulatory T-cells decreased between 3 and 12 hours postmortem.

Conclusions/Significance

We conclude that kinetics of ileal overgrowth with enterobacteria and enterococci in hfa mice can be used as an indicator for compromized intestinal functionality and for more precisely defining the time point of death under defined ambient conditions. The rapid translocation of intestinal bacteria starting within a few minutes after death will help to distinguish between relevant bacteria and secondary contaminants thus providing important informations for routine applications and future studies in applied microbiology, forensic pathology, and criminal medicine.

Postmortem cerebrospinal fluid pleocytosis: a marker of inflammation or postmortem artifact?

The aim of this paper is to reassess the significance of postmortem cerebrospinal fluid pleocytosis. Published articles of CSF changes after death were reviewed, and reanalysis, in the light of modern views on the significance of bacterial postmortem isolates, was undertaken. There is theoretical and experimental evidence that the blood brain barrier to the movement of protein and cells is preserved in the first few hours after death. The number of mononuclear cells in the cerebrospinal fluid does rise in the first 24 hours after death, and this is most probably due to detachment of leptomeningeal lining cells. But the marked increase in lymphocyte counts seen in some cases of sudden infant death syndrome (SIDS) and in other deaths in the paediatric age range could well be a marker of inflammation.

Sudden infant death syndrome and cardiac arrhythmias

There is a considerable body of evidence that common bacterial toxins, absorbed from the mucosal surface or delivered as part of a transient bacteremia, have a pathogenic role in sudden infant death syndrome (SIDS). The candidate organisms are Staphylococcus aureus and Escherichia coli. Death in SIDS is rapid, with infants progressing from well, or only mildly unwell, to death in less than 20 min. This mode of death is not typical of infection but it is consistent with toxin action on cardiovascular or respiratory control. Both S. aureus and E. coli secrete toxins (cytolysins and colicins) that create channels in cell membranes and disturb ion currents. Recent evidence indicates that between 5 and 15% of SIDS cases carry potentially lethal loss-of-function mutations in cardiac channelopathy genes. However, only a minority of individuals with these mutations die of SIDS and the hypothesis proposed is that toxin-gene interaction could explain the deaths. Furthermore, channelopathy mutations predispose to sudden death at all ages and since episodes of transient bacteremia occur throughout life the idea of toxin-gene interaction could have wider applicability. These ideas can be investigated and answered in the near future using the new science of proteomics.

Hypothesis: increased male mortality caused by infection is due to a decrease in heterozygous loci as a result of a single X chromosome

Inbreeding in experimental animals leads to loss of heterozygous loci and a marked increase in morbidity and mortality. Males have fewer heterozygous loci than females because of a single X chromosome. It is suggested that heterozygous loci protect against infection and that increased male mortality in humans at all ages is secondary to infection. The specific testable hypothesis is that episodes of bacteraemia occur throughout life leading to toxin secretion causing sudden death in infancy (SUDI), accelerating the development of atherosclerosis and precipitating sudden death in old age.