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Biomedical subjects

M S Gilmore

Publications and source records attributed to M S Gilmore.

At least 37 records · Page 2Linked to original sources
PubMed1997

Host/parasite interactions in bacterial endophthalmitis.

Bacterial infections within the eye arise as complications of intraocular surgery, penetrating injury, or hematogenous spread from distant anatomical sites. Because: 1) the interior surfaces of the eye are lined with sensitive, nonregenerating tissues, 2) the inner chambers of the eye are relatively sequestered from circulating immunological components, 3) the integrity of blood-ocular barriers provides poor penetration of systemically administered antibiotics, and 4) aqueous and vitreous humor represent rich, relatively acellular culture media; endophthalmitis often progresses rapidly and total loss of vision frequently results. Years of clinical experience have shown that current therapies for endophthalmitis, including antimicrobials, antiinflammatory agents, and vitrectomy, are frequently unsuccessful in ameliorating destruction of intraocular tissues. While bacterial and host factors were thought to play key roles in the course and severity of endophthalmitis, it is only recently that their contributions have been experimentally defined. Molecular-based techniques are gaining increased use in the study of infectious eye diseases. Current findings regarding the host/parasite interactions within the eye are reviewed, and a resulting integrative model of the natural course of endophthalmitis proposed. A molecular-level understanding of the roles of both bacterial and host factors during endophthalmitis will likely reveal potential targets for therapeutic intervention aimed at salvaging vision.

Bacterial Capsules↗
PubMed1997

Staphylococcal accessory regulator (sar) in conjunction with agr contributes to Staphylococcus aureus virulence in endophthalmitis.

Previous studies showed that an agr mutant strain of Staphylococcus aureus was partially attenuated in virulence compared to a parental strain in experimental endophthalmitis. The purpose of this study was to determine whether the sar locus, either alone or through interactions with agr, contributes to the regulation of virulence in S. aureus endophthalmitis. Experimental endophthalmitis was established by the midvitreous injection of approximately 30 CFU of S. aureus RN6390 or the isogenic attenuated strains RN6911 (agr mutant), ALC136 (sar mutant), and ALC135 (agr sar double mutant). Unexpectedly, the rate of reduction in electroretinographic B-wave amplitude in eyes infected with strain ALC136 (sar mutant) was not significantly different from the parental strain on postinfection day (PID) 5 (10% retention). In contrast, ALC135 (agr sar double mutant)-infected eyes retained 73% of preoperative B-wave amplitude on PID 5. Therefore, unlike agr, a mutation in the sar locus alone does not alter the overall virulence of wild-type S. aureus in experimental endophthalmitis. However, the combined effect of insertional mutations in both the sar and agr global regulators leads to near-complete attenuation of virulence.

Bacterial Proteins↗
PubMed1997

Chromosomal localization of a human mucin gene (MUC8) and cloning of the cDNA corresponding to the carboxy terminus.

A partial cDNA (pAM1) encoding a major airway mucin glycoprotein with novel tandem repetitive sequence has recently been cloned (Shankar, V., M. S. Gilmore, R. C. Elkins, and G. P. Sachdev. 1994. Biochem. J. 300:295-298). In this article, we report additional new sequence derived by 3'-rapid amplification of cDNA ends technique. The sequence corresponds to a stop codon, 3'-untranslated region of 458 bp, a polyadenylation signal, and poly A+ tail, and represents the extreme carboxy terminus of MUC8. A plasmid construct (pAM3) in pBluescript was generated by in-frame ligation of pAM1 to the 479-bp 3'UTR of MUC8. A 5'-end 325-bp fragment of this cDNA subcloned into the protein fusion and expression vector pET28b(+) was used to generate fusion protein under the control of T7 promoter. The purified fusion protein as well as synthetic peptide corresponding to the MUC8 repeat sequence (TSCPRPLQEGTPGS) were used to raise polyclonal antibodies in rabbits. The antiserum to the fusion protein and to the synthetic peptide reacted with the deglycosylated major tracheobronchial mucin. Immunohistochemical studies using the above antibodies localized the MUC8 protein product to submucosal glands in human tracheal epithelium. Furthermore, the gene from which this cDNA is derived, was mapped to chromosome 12 using DNA from a panel of human-mouse somatic cell hybrids. Fluorescence in situ hybridization was used to assign the regional localization to 12q24.3. Since the eight known human mucin genes map to other chromosomes, we have named this gene MUC8, in accordance with mucin gene nomenclature.

Amino Acid Sequence↗
PubMed1996

Enterococcus faecalis cytolysin and lactocin S of Lactobacillus sake.

Strains of Enterococcus faecalis and Lactobacillus sake have been found to express lantibiotics with unusual properties. The enterococcal lantibiotic is unusual in that it consists of two dissimilar subunits, both putatively containing modifications consistent with those found in other lantibiotics. The enterococcal lantibiotic is also unusual in the number of proteolytic steps involved in secretion signal removal and activation. Moreover, it has been observed to contribute to enterococcal disease in humans and in animal models. Structural studies of lactocin S, expressed by a strain of L. sake highlight unique properties including the presence of D-alanine within its structure, and a protease putatively responsible for lactocin S secretion signal peptide removal which, itself, lacks a signal or propeptide sequence. Despite the unusual properties of each of these lantibiotics, the operons encoding each, and accompanying auxiliary functions, are collinear suggesting a common ancestry. The accretion of interdigitating DNA sequences between genes encoded within the lactocin S determinant are unique to that determinant, however, and are of unknown function.

Amino Acid Sequence↗
PubMed1996

Structural analysis and proteolytic activation of Enterococcus faecalis cytolysin, a novel lantibiotic.

Clinical isolates of Enterococcus faecalis more commonly produce a cytolysin than do commensal isolates. Epidemiologic evidence and animal-model studies have established a role for the cytolysin in the pathogenesis of enterococcal disease. The cytolysin consists of two structural subunits, CylLL and CylLS, that are activated by a third component, CylA. Genetic and biochemical characterization of CylA indicate that it is a serine protease, and that activation putatively results from cleavage of one or both cytolysin subunits. Genetic evidence also suggests that the cytolysin subunits are related to the rapidly growing class of bacteriocins termed lantibiotics. However, unlike lantibiotics, the cytolysin is lytic for eukaryotic as well as prokaryotic cells, and it consists of two structural subunits. This report describes the purification and characterization of the cytolysin subunits and detection of lanthionine-type post-translational modifications within their structures. Furthermore, the cleavage specificity of the CylA activator is reported and it is shown that proteolytic activation of both subunits is essential for activity.

Amino Acid Sequence↗
PubMed1995

Frequency of aggregation substance and cytolysin genes among enterococcal endocarditis isolates.

Enterococcus faecalis blood isolates were probed for the serine protease activator of cytolysin (cylA) and aggregation substance (asa1), traits that generally reside on pheromone-responsive plasmids, to determine how commonly these genotypes were associated with disease. In dot blot assays, no significant difference was found in the frequency of asa1 for blood isolates [55 of 103 (54%)] and isolates recovered from stool [9 of 14 (60%); P > 0.1, chi 2 test]. In contrast, cylA occurred more frequently among bacteremia isolates [34 of 68 (50%)] than endocarditis [4 of 35 (11%)] or stool isolates (0 of 14; P < 0.001; chi 2 test). However, when the clonality of isolates was accounted for, the frequency of asa1 and cylA among unrelated strains was not significantly different among the three sets of strains (P > 0.2, chi 2 test). The lack of enrichment for asa1 or cylA among clonally unrelated E. faecalis bloodstream isolates fails to support a role for plasmid-encoded aggregation substance or cytolysin in the transition from bacteremia to endocarditis. Clonally related, cytolytic strains, however, demonstrated an increased propensity to cause bloodstream infection.

Amino Acid Sequence↗
PubMed1995

Enterococcus faecalis cytolysin without effect on the intestinal growth of susceptible enterococci in mice.

A murine model was developed to determine whether the Enterococcus faecalis cytolysin, through its bacteriolytic action on gram-positive bacteria, could promote intestinal overgrowth of cytolytic strains. Sets of E. faecalis strains with varying cytolytic production and susceptibility to cytolytic activity were mixed 1:1 and allowed to compete in vitro in broth or in vivo after orogastric administration in mice pretreated with antibiotics. In general, cytolytic strains outgrew, by as much as 2000-fold, competing cytolysin-susceptible or -hypersusceptible strains in vitro. In contrast, no growth advantage was observed in vivo, despite similar transient colonization of the murine intestinal tract by both cytolytic and cytolysin-susceptible strains. These data suggest that cytolysin plays little role in promoting intestinal overgrowth of enterococci through bacteriolytic activity.

Animals↗
PubMed1995

Accessory gene regulator controls Staphylococcus aureus virulence in endophthalmitis.

PURPOSE: To evaluate the contribution of toxins to the severity of Staphylococcus aureus endophthalmitis. METHODS: Experimental endophthalmitis was established by injecting rabbit eyes with wild type S. aureus ISP479 and the isogenic attenuated strain, ISP546, defective in expression of the global regulator locus agr. agr regulates expression of at least 19 exoproteins that are potentially important in the pathogenesis of endophthalmitis. Infections were evaluated using electroretinography, slit lamp biomicroscopy, and histology. Two concentrations (approximately 10 and 1000 organisms) of bacteria were injected. RESULTS: The agr- strain consistently resulted in slower loss of b-wave response when compared to the wild type strain, irrespective of inoculum size. Clinical signs were less severe among the agr- group at 24 and 48 hours when 10 organisms were injected. However, when the number of bacteria injected was increased to 1000, earlier onset of clinical signs was observed, with both groups showing maximum cell and flare and a white fundal reflex at 48 hours after infection. Histologic examination of eyes enucleated 36 hours after inoculation revealed that the wild type strain induced focal retinal destruction and mild vitritis, whereas eyes infected with the agr- strain remained completely normal. Histologic examination carried out when loss of B-wave response was 100% revealed that retinal changes for both groups could not be distinguished. CONCLUSIONS: These data indicate that toxin production by S. aureus contributes to severity of endophthalmitis by accelerating the rate of onset of retinal damage. Therefore, toxin-targeting therapies instituted early in the course of infection could preserve retinal function.

Animals↗
PubMed1995

Evaluation of therapeutic measures for treating endophthalmitis caused by isogenic toxin-producing and toxin-nonproducing Enterococcus faecalis strains.

PURPOSE: Management of endophthalmitis typically includes antibiotic combinations to arrest bacterial growth and antiinflammatory agents to limit inflammatory damage to sensitive tissues. Little research has been reported that systematically evaluates the contribution of each therapeutic component for treating infections caused by organisms of varying virulence. The authors determined the relative value of the antinflammatory corticosteroid, dexamethasone, as an intravitreal therapeutic adjunct for the treatment of infection caused by either Enterococcus faecalis expressing a cytolytic toxin previously shown to contribute to the course and severity of infection, or an otherwise identical strain of E. faecalis specifically attenuated in expression of the cytolytic toxin. METHODS: Endophthalmitis in rabbits was monitored using electroretinography (ERG). Eyes were infected with 100 colony forming units of either the cytolytic or the noncytolytic E. faecalis strain. Intravitreal ampicillin and gentamicin were administered at postinfection day 1, and intravitreal dexamethasone was either omitted or administered at day -1, 1, or 1.5. RESULTS: ERG B-wave amplitude declined precipitously throughout the course of infection with cytolytic toxin-producing E. faecalis, despite the administration of antibiotics and regardless of the time of dexamethasone administration. In fact, the ultimate course of infection caused by cytolytic E. faecalis did not differ from the course in untreated controls. In contrast, infections caused by specifically attenuated, noncytolytic strains of E. faecalis responded well to antibiotics augmented by antiinflammatory therapy when the latter was administered either 1 or 1.5 days after the initiation of infection. In these cases, no loss in ERG B-wave response was observed. CONCLUSIONS: These results underscore the importance of bacterial toxins in infectious diseases of the eye and their contribution to treatment failures. These results further suggest that in cases of endophthalmitis caused by toxin producing bacteria, significant improvement in clinical outcome will require specific therapeutic targeting of the toxins involved.

Ampicillin↗
PubMed1995

The Enterococcus faecalis cytolysin determinant and its relationship to those encoding lantibiotics.

The E. faecalis cytolysin represents a new class of cytolytic agents which are related to a family of antibacterial peptides termed lantibiotics. Despite considerable similarity at the genetic level, the E. faecalis cytolysin differs from the lantibiotics in several respects. First, the E. faecalis cytolysin consists of two dissimilar precursors, both of which are required to effect target cell lysis. A second important difference is that the E. faecalis cytolysin is active against eukaryotic as well as Gram-positive prokaryotic cells. Originally identified as a haemolysin [32], the E. faecalis cytolysin has been shown to make a contribution to bacterial virulence in endocarditis [8, 33] and endophthalmitis [7] models, and the cytolytic phenotype is enriched among clinical isolates of the organism [2, 3]. Similarities between the E. faecalis cytolysin and lantibiotics such as nisin (which is used as a food preservative in several countries [34] and is the subject of continuing attempts at rational design of lantibiotic-based food preservatives [25]), and the observation of an association between the E. faecalis cytolysin and bacterial virulence indicate that it may be possible to engineer lantibiotics to a point where undesired toxic or cytolytic activities will arise. Further comparison of the chemical, structural and biological properties of the E. faecalis cytolysin and classical lantibiotics will define these limits.

Amino Acid Sequence↗