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Biomedical subjects

M D Willcox

Publications and source records attributed to M D Willcox.

103 records · Page 6Linked to original sources
PubMed1988

In-vitro adherence of oral streptococci in the presence of sucrose and its relationship to cariogenicity in the rat.

Streptococcus sanguis I gave a significantly greater percentage coverage (cell-pellicle attachment) of saliva-coated glass in the presence of sucrose than did Strep. sanguis II (p less than 0.025), and both these gave greater percentage coverages than the other species tested, between which no significant differences were noted. There was a large number of significant differences in clump size (cell-cell attachment) between species-pairs. Among the mutans streptococci, there were significant differences in the percentage coverage between Streptococcus rattus/Streptococcus mutans (p less than 0.05) and Strep. rattus/Streptococcus sobrinus (p less than 0.01), and in clump size between all species-pairs with the exception of Streptococcus cricetus or Strep. sobrinus and Strep. mutans. The rank order of species in relation to fissure caries was mutans streptococci greater than Streptococcus salivarius greater than Streptococcus milleri greater than Strep. sanguis greater than Streptococcus faecalis greater than Streptococcus mitis greater than Streptococcus lactis. There was a significant correlation between percentage coverage in vitro and fissure caries in vivo for strains of Strep. sanguis (p less than 0.05) and pooled strains of Strep. mitis and Strep. sanguis (p less than 0.01). On comparing data for adherence in the presence or the absence of sucrose, the sugar had no effect on the percentage coverage of the seven species tested, but significantly increased the clump size of the mutans streptococci (p less than 0.01) and Strep. sanguis (p less than 0.05).

Animals↗
PubMed1988

Partial characterisation of the inhibitory substances produced by Streptococcus oralis and related species.

The production of inhibitory substances was sought by deferred antagonism. Streptococcus oralis, Streptococcus mitis and Streptococcus sanguis produced bactericidal concentrations of hydrogen peroxide, but no detectable bacteriocin. Actinomycetes and Neisseria pharyngis were particularly susceptible to the lethal action of hydrogen peroxide. Streptococcus milleri produced bactericidal concentrations of hydrogen peroxide and bacteriocin-like substances. S. oralis strains were inhibited by the bacteriocin-like products of strains of Streptococcus bovis, Streptococcus faecalis, Streptococcus mutans and Streptococcus salivarius. Inhibition was due neither to complete bacteriophage nor to fermentation end-products. Extracellular polysaccharides formed during growth could not protect sensitive strains from the effect of hydrogen peroxide or bacteriocin-like substances.

Actinomycetales↗
PubMed1987

Relative cariogenicity and in-vivo plaque-forming ability of the bacterium Streptococcus oralis in gnotobiotic WAG/RIJ rats.

The rats, fed a high sucrose diet, were mono-infected with seven strains of Streptococcus oralis. Moderate levels of caries were induced by four strains, and three others induced low levels. Approximal lesions were induced by two strains; no buccal/lingual lesions were produced. Scanning electron microscopy showed that all strains colonized the tooth fissures, some strains producing a moderately abundant and dense plaque. The most cariogenic strains (PB178, PB180 and PB186) induced similar levels of caries to Streptococcus milleri.

Animals↗
PubMed1985

Relationship of adhesion in vitro and cariogenicity of oral Streptococcus species in germ-free rats.

Thirty-two strains of Streptococcus spp., of known cariogenicity in the gnotobiotic WAG/RIJ rat, were tested for their in vitro adhesion properties. Computerized image analysis measured percentage coverage by, and clump size of, cells adhering to saliva-coated glass. An analysis of variance revealed significant differences for percentage coverage for the majority of species-pairs. There were fewer significant differences for mean clump size between species-pairs. Within the Strep. mutans group there was a highly-significant difference between Strep. mutans/Strep. cricetus (p less than 0.01) with respect to mean clump size. There was a significant correlation between cariogenicity and percentage coverage (p = 0.05) but not clump size (p = 0.359) for pooled strains of Strep. mitis and Strep. sanguis combined.

Adhesiveness↗
PubMedDate not supplied

Differences in the pathogenesis of bacteria isolated from contact-lens-induced infiltrative conditions.

PURPOSE: The purpose of this study was to examine the ability of gram-negative bacteria isolated from the non-infectious condition contact-lens-induced acute red eye (CLARE) and infectious microbial keratitis (MK) to infect the eyes of mice. METHODS: One cornea of BALB/c mice was scratched with a needle and 5 x 10(6) bacteria applied. Bacterial types used were Pseudomonas aeruginosa, Haemophilus influenzae, Serratia marcescens, Stenotrophomonas moltophilia and Aeromonas hydrophilia. The mice were killed after 1, 4 and 24 h and examined by slit lamp, histology and microbiology. RESULTS: CLARE strains were unable to infect the mouse corneas. The eyes inoculated with the CLARE strains had low levels of polymorphonuclear leucocytes (PMN) in the stroma. All eyes that had MK contained bacteria and large numbers of PMN after 24 h. CONCLUSIONS: The development of CLARE or MK is dependent on the type of bacteria with specific bacterial types being responsible for CLARE or MK.

Animals↗
PubMedDate not supplied

Comparison of potential pathogenic traits of staphylococci that may contribute to corneal ulceration and inflammation.

Staphylococcus epidermidis and Staphylococcus aureus are two of the commonest bacteria isolated from corneal ulcers. The aim of the current investigation was to determine the frequency of potentially pathogenic traits in the two staphylococcal species. Strains of both species, some isolated from eyes during active corneal inflammation, were screened for their ability to degrade a variety of proteins and hyaluronic acid and the production of cytotoxins. S. aureus produced more tissue-destructive enzymes than the S. epidermidis. S. aureus strains more commonly synthesized the cytotoxin, alpha-toxin. The production of elastase was more common among S. aureus strains isolated from ulcerative events. The production of alpha-toxin was inversely correlated with isolation from keratitis. This study has demonstrated that S. aureus is better equipped with a range of potentially damaging enzymes and toxins than S. epidermidis and that S. aureus elastase may be involved in the production of corneal ulcers.

Bacterial Toxins↗
PubMedDate not supplied

Detection of staphylococcal superantigens from contact-lens-induced inflammatory diseases.

PURPOSE: We investigated the correlation between the production of superantigens in Staphylococcus-aureus-induced ulcer and contact-lens-induced peripheral ulcer (CLPU) and infiltrative keratitis (IK). METHODS: Twenty-five S. aureus strains used in the study were isolated either from CLPU cases (six), or IK events (13) or asymptomatic eyes (six). A polymerase chain reaction (PCR) was employed to detect genes for superantigenic staphylococcal enterotoxins A-D, toxic shock syndrome toxin-1 and exfoliative toxins A and B. Reversed passive latex aggregation, enzyme-linked immunosorbent assay (ELISA) and immunoblot were used to examine the production of staphylococcal enterotoxins A-D and toxic shock syndrome toxin-1. RESULTS: The frequency of the superantigenic genes was not significantly different among the clinical isolates when asymptomatic isolates were compared with the strains isolated from CLPU and IK events. ELISA and immunoblot showed non-specific protein cross-reactions. CONCLUSIONS: The results suggest that detection of superantigenic toxin genes in ocular strains of S. aureus by PCR is a specific, sensitive, rapid and inexpensive alternative to traditional immunological assays. The role, if any, of the S. aureus superantigens in the production of CLPU/IK remains uncertain.

Bacterial Toxins↗
PubMedDate not supplied

Bacterial invasion of corneal epithelial cells.

PURPOSE: The normal ocular surface is frequently colonized by commensal gram-positive species. Gram-negative bacteria are often implicated in corneal infection and inflammation, particularly in association with soft contact lens wear. The aim of this study was to elucidate possible mechanisms of virulence in ocular bacteria. METHODS: The susceptibility of a human corneal epithelial cell line to bacterial invasion and association was evaluated using the gentamicin exclusion assay. Organisms tested included isolates from corneal ulcers, corneal inflammation and ocular sites in asymptomatic individuals. RESULTS: The commensal, non-pathogenic bacterium Staphylococcus epidermidis and some pathogenic strains of Serratia marcescens did not invade corneal epithelial cells. In contrast, pathogenic strains of Pseudomonas aeruginosa associated with and invaded corneal epithelial cells. CONCLUSIONS: The increased association of P. aeruginosa, compared to other bacterial types, might be a reason for the more frequent association of this bacterium with contact-lens-associated microbial keratitis.

Bacteria↗
PubMedDate not supplied

Effect of lysozyme on adhesion and toxin release by Staphylococcus aureus.

PURPOSE: Staphylococcus aureus is a common cause of ocular infection and inflammation. We hypothesized that potential for S. aureus to cause an ocular infection would be enhanced if these bacteria are able to adhere to the biomaterials used in contact lenses. In turn, bacterial adhesion could also be influenced by other factors, such as properties of contact lenses and the absorbance of some tear components. We investigated the effect of the tear protein lysozyme on S. aureus adhesion to contact lenses and its effect on production of toxins or enzymes. METHODS: Bacterial adhesion on contact lenses was determined by counting the total number of bacteria as well as viable bacteria on lysozyme-coated or non-coated lenses, and by counting bacteria grown in the presence or absence of lysozyme in the medium. Toxin and enzyme production was assessed by haemolysis and proteolysis assays. RESULTS: Our results indicate that adhesion was significantly increased in the presence of lysozyme, both in the medium and coated onto contact lenses (P=0.04). The presence of lysozyme did not alter the production of alpha- or beta- toxins. However, the presence of lysozyme inhibited elastase activity. CONCLUSION: These results indicate that lysozyme deposition on contact lenses promoted S. aureus adhesion. The tear protein lysozyme might modify elastase activity and thus modulate the production of corneal degradation resulting from the action of this enzyme.

Bacterial Adhesion↗
PubMedDate not supplied

Secretory IgA epitopes in basal tears of extended-wear soft contact lens wearers and in non-lens wearers.

PURPOSE: To determine secretory IgA epitopes in tears of extended-wear soft contact lens wearers and non-wearing controls. METHODS: We developed enzyme-linked immunosorbent assays (ELISA) to determine the tear concentrations of two epitopes of secretory IgA, the IgA alpha-chain and the secretory component. These epitopes were measured in basal tears of 20 individuals in 6 nights of extended wear of etafilcon A soft contact lenses and in 19 non-lens-wearing individuals. RESULTS: Levels of IgA alpha-chain immunoreactivity were significantly decreased in the lens-wearing group compared to non-lens wearers. However, the level of secretory component immunoreactivity was not significantly different between groups. IgA alpha-chain and secretory component immunoreactvity were highly correlated; however, some samples showed a marked variation between these two values. CONCLUSION: Tear concentrations of sIgA epitopes are significantly reduced in extended-wear contact lens wearers, and may contribute to the increased susceptibility to ocular infection seen in this group.

Adult↗
PubMedDate not supplied

Effect of tear-specific immunoglobulin A on the adhesion of Pseudomonas aeruginosa I to contact lenses.

PURPOSE: The aims of the study were (i) to determine the immunodominant antigens of Pseudomonos aeruginoso 1 (Paer1) to tear secretory immunoglobulin A (sIgA); (ii) to study the role of sIgA in inhibiting bacterial adhesion to contact lenses. METHODS: SDS-PAGE and Western blotting were used to study the interaction of tear sIgA with Paer1; an adhesion assay was used to study the effect of sIgA on the adhesion of Paer1 to the contact lenses. RESULTS: The results of our study showed that the immunodominant molecules of Paer1 which reacted with tear sIgA were of molecular masses of 105, 50, 45 kDa; the binding of sIgA to Paer1 resulted in a reduction of the adhesion of Paer1 to worn Etafilcon A contact lenses. CONCLUSIONS: In conclusion, Paer1-specific sIgA are present in tears; the immunodominant molecules of Paer1 may be adhesins and tear-specific sIgA might play an important role in protecting the eye from contact-lens-induced corneal infection by preventing bacterial attachment to contact lenses and the ocular surface.

Bacterial Adhesion↗
PubMedDate not supplied

Induction of apoptosis in human corneal epithelial cells in vitro.

PURPOSE: The purpose of this study was to evaluate exhausted-medium-induced apoptosis in human corneal epithelial (HCE) cells in vitro. METHODS: Confluent HCE cells were maintained in tissue-culture medium for 5-7days. The supernatant was harvested and fresh HCE cells were exposed to the exhausted supernatant for 24-48 h over a range of pH conditions. The exhausted medium was assayed for cytokines interleukin 6 (IL-6), IL-8, interferon-gamma (IFN-gamma) and tumour necrosis factor alpha (TNF-alpha) by ELISA. Apoptotic cells were assessed using Hoechst 33342 Propidium iodide and AnnexinV-FITC staining and by the TUNEL assay. RESULTS: Human corneal epithelial (HCE) cells exposed to exhausted medium demonstrated a high incidence of apoptosis, which increased over time to 87+/-5% after 48 h. Apoptosis was independent of pH. Cytokine levels were not elevated in the exhausted medium. CONCLUSIONS: This study suggests that exhausted medium can be used as a simple, rapid and potent positive control for apoptosis of HCE cells.

Annexin A5↗