The frog palate mucosa as a model for studying bacterial adhesion to mucus-coated respiratory epithelium

Development and application of a dose-response model for Elizabethkingia spp

Elizabethkingia spp. are common environmental pathogens responsible for infections in more vulnerable populations. Although the exposure routes of concern are not well understood, some hospital-associated outbreaks have indicated possible waterborne transmission. In order to facilitate quantitative microbial risk assessment (QMRA) for Elizabethkingia spp., this study fit dose-response models to frog and mice datasets that evaluated intramuscular and intraperitoneal exposure to Elizabethkingia spp. The frog datasets could be pooled, and the exact beta-Poisson model was the best fitting model with optimized parameters α  = 0.52 and β = 86,351. Using the exact beta-Poisson model, the dose of Elizabethkingia miricola resulting in a 50% morbidity response (LD50) was estimated to be approximately 237,000 CFU. The model developed herein was used to estimate the probability of infection for a hospital patient under a modeled exposure scenario involving a contaminated medical device and reported Elizabethkingia spp. concentrations isolated from hospital sinks after an outbreak. The median exposure dose was approximately 3 CFU/insertion event, and the corresponding median risk of infection was 3.4E-05. The median risk estimated in this case study was lower than the 3% attack rate observed in a previous outbreak, however, there are noted gaps pertaining to the possible concentrations of Elizabethkingia spp. in tap water and the most likely exposure routes. This is the first dose-response model developed for Elizabethkingia spp. thus enabling future risk assessments to help determine levels of risk and potential effective risk management strategies.

Aspects on the interaction of Streptococcus pneumoniae and Haemophilus influenzae with human respiratory tract mucosa

Haemophilus influenzae and Streptococcus pneumoniae are common causes of respiratory tract infections. H. influenzae attach to receptor epitopes in mucins and in epithelial cell membranes. Attachment is followed by an epithelial cell cytokine response. Secreted cytokines then initiate inflammation, upset the integrity of the mucosal barrier, and lead to disease. S. pneumoniae do not bind to mucins but attach to respiratory tract epithelial cells. Attachment is increased by viral infection of the epithelial cells. Unlike H. Influenzae, S. pneumoniae induce apoptosis in epithelial cells, thus disrupting the mucosal barrier. Attachment and persistence is counterbalanced by antiadhesive as well as bactericidal molecules in secretions such as human milk. These examples illustrate the balance between host defenses and microbial virulence as it has coevolved to maintain the health of the respiratory mucosa.

Binding of Haemophilus influenzae to purified mucins from the human respiratory tract

Mucins are high-molecular-weight glycoproteins and major constituents of the mucus layer which covers the airway surface. We have studied the interactions between bacteria, mucins, and epithelial cells from the human respiratory tract. Nontypeable strains of Haemophilus influenzae were found to bind to purified airway mucins in suspension and on solid phase. Mucins in suspension inhibited the attachment of these strains to nasopharyngeal epithelial cells, while mucin coating of the cells enhanced their binding. In contrast, strains of Streptococcus pneumoniae and encapsulated and other nontypeable H. influenzae strains failed to interact with mucins. These H. influenzae strains used other strategies for adherence to epithelial cells. The type b strain 770235 attached via fimbriae but also expressed a subcapsular adhesin that was detected in a capsule- and fimbria-defective mutant. Mucin pretreatment of these bacteria did not inhibit adherence, but mucin pretreatment of epithelial cells inhibited adherence, probably by shielding of the receptors for these adhesins. Non-mucin-binding nontypeable and encapsulated H. influenzae strains would, therefore, adhere only after disruption of the mucus layer and exposure of cellular receptors. Differences in tissue toxicity and invasiveness among H. influenzae strains may also be influenced by the mucin interactions of the strains.

Interaction of pneumolysin-sufficient and -deficient isogenic variants of Streptococcus pneumoniae with human respiratory mucosa

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia, and pneumolysin, a hemolytic toxin, is thought to be an important virulence factor. We have studied the interaction of a pneumolysin-sufficient type II S. pneumoniae strain (PL+) and an otherwise identical pneumolysin-deficient derivative (PL-) with human respiratory mucosa in an organ culture with an air interface for up to 48 h. Ciliary beat frequency (CBF) was measured by a photometric technique, and adherence to and invasion of the epithelium were assessed by scanning and transmission electron microscopy. PL+ and PL- caused a progressive fall in CBF compared with the control which became significant (P < 0.01) at 24 h for PL+ and at 48 h for PL-. At 24 h, there was a significant increase in the percentage of the mucosa of the organ culture that was damaged for PL+ compared with the control (P < 0.01) and PL- (P < 0.02). At 48 h, there was a significant increase in mucosal damage for both PL+ (P < 0.005) and PL- (P < 0.05) compared with the control. At 24 and 48 h, PL+ and PL- adhered predominantly to mucus and damaged cells. PL+ infection alone caused separation of tight junctions between epithelial cells, and at 48 h PL+ cells were adherent to the separated edges of otherwise healthy unciliated cells. PL+ and PL- both caused damage to the epithelial cell ultrastructure. S. pneumoniae infection caused patchy damage to the respiratory mucosa and a lowered CBF. These changes were more severe and occurred earlier with the pneumolysin-sufficient variant.

Quantitative X-ray microanalysis of P, Ca, and S in the mucus secretory granules of the cryofixed frog palate epithelium

In respiratory epithelium, the mucus is densely packed inside the secretory granules (SG) of secretory cells (SC) before being released by exocytosis in the airway lumen. We have previously shown that the frog palate is a representative model of respiratory epithelium and that rapid cryofixation is a very effective technique in preserving the integrity of the mucus SG. The concentration of phosphorus (P), sulphur (S), and calcium (Ca) were analysed inside the SG of the SC of frog palate after quick freezing, cryosubstitution, and embedding in Lowicryl resin at low temperature. The experiments were carried out using X-ray microanalysis conducted with energy dispersive spectrometry (EDS) at 100 kV. The quantitation was carried out using the continuum method with reference to Agar standards. The cryofixation permitted us to distinguish two types of SG depending on whether they were electron dense (serous cells) or electron-lucent (mucous cells). A significant (P < 0.001) difference in the S concentration was observed between the individual serous (239 +/- 79 mmol.kg-1) and the mucous SG (161 +/- 48 mmol.kg-1). No significant difference could be identified in the Ca concentration between the two SG phenotypes. In the serous SG, the P content was high (41 +/- 17 mmol.kg-1) compared with the mucous SG where it was not measurable. The comparison of the three element concentrations in each type of secretory cells showed that significant differences in concentration of S and Ca concentration could be observed from one SC cell to another.(ABSTRACT TRUNCATED AT 250 WORDS)

Preservation of tracheal mucus by nonaqueous fixative

Two nonaqueous fixatives, composed of fluorocarbon solvents with dissolved osmium tetroxide, were used to determine the feasibility of preserving the mucous coat in bovine and rat trachea for light and electron microscopy. Aqueous fixatives, while providing excellent cytological preservation, wash away the mucous lining, precluding ultrastructural analysis. Inclusion of ruthenium red or alcian blue within aqueous fixative improved retention of mucus, but provided incomplete, patchy results. Fixation with nonaqueous fluorocarbon solvent and dissolved osmium tetroxide preserved a continuous mucous epiphase layer above a clear hypophase layer. Subcomponents of the mucus included an electron dense surface layer, interrupted patches of mucus above the surface layer and electron dense membrane-like material within the mucus. This method of fixation will preserve mucus for light, scanning and transmission electron microscopy, using either intratracheal or immersion methods of fixation. The latter would enable use of materials from large animal models, autopsy or an abattoir.

The role of bacterial adhesion in cystic fibrosis including the staphylococcal aspect

The bacteriology of cystic fibrosis shows a unique and predictable progression of colonizing micro-organisms. The reason for this sequence is still not known, but thought must be given to the idea that it may be related to the genetic disorder in some way. If this were to be true, an understanding of the colonization mechanisms at all stages in this progression could provide valuable insights for the development of novel therapies. As far as can be ascertained from published studies, mucus is the site of colonization in cystic fibrosis. While there is no doubt that the major pathogen, Pseudomonas aeruginosa, adheres to injured cells more avidly than to intact cells, the overwhelming evidence indicates that it also attaches more avidly to mucus than to intact airway cells by means of specific adhesin-receptor mechanisms. Studies with Staphylococcus aureus, the other major pathogen, are also in progress. These indicate that this organism also has an affinity for mucus. At this time the studies suggest a lesser affinity than P. aeruginosa, at least with adult mucins. These two organisms do not however appear to share the same receptor. In addition to these two major pathogens, Haemophilus influenzae and Streptococcus pneumoniae, pathogens of lesser importance also adhere to mucus. Therefore adhesion to mucus or mucins may be a recurring theme in all airway colonization. A knowledge of the factors which control these tropisms ought to provide insights into the bacterial specificity seen in cystic fibrosis and other diseases.