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      A Laboratory Assessment of Factors That Affect Bacterial Adhesion to Contact Lenses

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      Author(s): 1 , 2 , * , 1
      Publication date (Electronic):
      Journal: Biology
      Publisher: MDPI
      Keywords: Bacterial adhesion, contact lens, Pseudomonas aeruginosa, Staphylococcus aureus

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          Abstract

          Adhesion of pathogenic microbes, particularly bacteria, to contact lenses is implicated in contact lens related microbial adverse events. Various in vitro conditions such as type of bacteria, the size of initial inoculum, contact lens material, nutritional content of media, and incubation period can influence bacterial adhesion to contact lenses and the current study investigated the effect of these conditions on bacterial adhesion to contact lenses. There was no significant difference in numbers of bacteria that adhered to hydrogel etafilcon A or silicone hydrogel senofilcon A contact lenses. Pseudomonas aeruginosa adhered in higher numbers compared to Staphylococcus aureus. Within a genera/species, adhesion of different bacterial strains did not differ appreciably. The size of initial inoculum, nutritional content of media, and incubation period played significant roles in bacterial adhesion to lenses. A set of in vitro assay conditions to help standardize adhesion between studies have been recommended.

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          Risk factors and causative organisms in microbial keratitis.

          Matthew Green, Andrew Apel, Fiona Stapleton (2008)
          To establish the risk factors, causative organisms, levels of antibiotic resistance, patient demographics, clinical presentations, and clinical outcomes of microbial keratitis at a tertiary hospital in Australia. Patients who had a corneal scraping for culture over a 5-year period were identified through the local microbiology database, and a retrospective audit of their medical records was carried out. Clinical information was gathered from medical records, and smear, culture, and antibiotic resistance results were from the microbiology database. An index of disease severity was calculated for each patient from scores for the magnitude of the epithelial defect and anterior-chamber reaction and the location of the lesion. Associations between risk factors for keratitis and variables such as patient demographics, causative organism and antibiotic resistance, disease severity, and outcome were analyzed by using analysis of variance and chi tests with appropriate correction for multiple comparisons. Two hundred fifty-three cases of microbial keratitis in 231 patients were included. Sixty percent of patients were men, and there was a bimodal distribution in the age of presentation. Common risk factors for keratitis were contact lens wear (53; 22%), ocular surface disease (45; 18%), ocular trauma (41; 16%), and prior ocular surgery (28; 11%). Gram stains were positive in 33%, with a sensitivity of 53% and specificity of 89%. Cultures of corneal scrapings were positive in 65% of cases, and Pseudomonas aeruginosa (44; 17%), coagulase-negative staphylococci (22; 9%), Staphylococcus aureus (19; 8%), and fungi (7; 3%) were commonly recovered. P. aeruginosa was more common than other culture results in contact lens-related cases (55% vs. 0%-23%; P < 0.001), and S. aureus was more common than other culture results in ocular surgery-related cases (29% vs. 0%-21%; P < 0.001). Patients with keratitis related to prior ocular surface disease had more severe keratitis at the time of scraping (P = 0.037). Cultures positive for Fusarium, P. aeruginosa, and other Gram-negative organisms had statistically significantly more severe keratitis at the time of scraping, whereas patients with negative cultures had milder keratitis (P = 0.030). Only 2% of all bacterial isolates were resistant to ciprofloxacin, 20% of Gram-positive isolates were resistant to cephalothin, and no Gram-negative isolates were resistant to gentamicin. In this series, the most common risk factor for keratitis was contact lens wear and the most commonly isolated organism was P. aeruginosa.
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            A novel cationic-peptide coating for the prevention of microbial colonization on contact lenses.

            Nerida Cole, Mark Willcox, Emma Hume … (2008)
            To develop an antimicrobial peptide with broad spectrum activity against bacteria implicated in biomaterial infection of low toxicity to mammalian cells and retaining its antimicrobial activity when covalently bound to a biomaterial surface. A synthetic peptide (melimine) was produced by combining portions of the antimicrobial cationic peptides mellitin and protamine. In contrast to the parent peptide melittin which lysed sheep red blood cells at >10 microg ml(-1), melimine lysed sheep red blood cells only at concentrations >2500 microg ml(-1), well above bactericidal concentrations. Additionally, melimine was found to be stable to heat sterilization. Evaluation by electron microscopy showed that exposure of both Pseudomonas aeruginosa and Staphylococcus aureus to melimine at the minimal inhibitory concentration (MIC) produced changes in the structure of the bacterial membranes. Further, repeated passage of these bacteria in sub-MIC concentrations of melimine did not result in an increase in the MIC. Melimine was tested for its ability to reduce bacterial adhesion to contact lenses when adsorbed or covalently attached. Approximately 80% reduction in viable bacteria was seen against both P. aeruginosa and S. aureus for 500 microg per lens adsorbed melimine. Covalently linked melimine (18 +/- 4 microg per lens) showed >70% reduction of these bacteria to the lens. We have designed and tested a synthetic peptide melimine incorporating active regions of protamine and mellitin which may represent a good candidate for development as an antimicrobial coating for biomaterials. Infection associated with the use of biomaterials remains a major barrier to the long-term use of medical devices. The antimicrobial peptide melimine is an excellent candidate for development as an antimicrobial coating for such devices.
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              Pseudomonas aeruginosa-mediated cytotoxicity and invasion correlate with distinct genotypes at the loci encoding exoenzyme S.

              K. Mostov, Frances T. Yen, D Kanada … (1997)
              Pseudomonas aeruginosa, an opportunistic pathogen, is capable of establishing both chronic and acute infections in compromised hosts. Previous studies indicated that P. aeruginosa displays either a cytotoxic or an invasive phenotype in corneal epithelial cells. In this study, we used polarized MDCK cells for in vitro infection studies and confirmed that P. aeruginosa isolates can be broadly differentiated into two groups, expressing either a cytotoxic or an invasive phenotype. In vivo infection studies were performed to determine if cytotoxic and invasive strains displayed differential pathology. Invasion was assayed in vivo by in situ infection of mouse tracheal tissue followed by electron microscopy. Both cytotoxic and invasive strains entered mouse tracheal cells in situ; however, more necrosis was associated with the cytotoxic strain. In an acute lung infection model in rats, cytotoxic strains were found to damage lung epithelium more than invasive strains during the short infection period of this assay. The expression of cytotoxicity requires a functional exsA allele. In the strains tested, the ability to invade epithelial cells in vitro appears to be independent of exsA expression. Since ExsA is a transcriptional regulator of the exoenzyme S regulon, chromosomal preparations from invasive and cytotoxic strains were screened for their complement of exoenzyme S structural genes, exoS, encoding the 49-kDa ADP-ribosyltransferase (ExoS), and exoT, encoding the 53-kDa form of the enzyme (Exo53). Invasive strains possess both exoS and exoT, while cytotoxic strains appear to have lost exoS and retained exoT. These data indicate that the expression of cytotoxicity may be linked to the expression of Exo53, deletion of exoS and perhaps other linked loci, or expression of other ExsA-dependent virulence determinants. In the absence of a functional cytotoxicity pathway (exsA::omega strains), invasion of eukaryotic cells is detectable.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Biology (Basel)
                Journal ID (iso-abbrev): Biology (Basel)
                Journal ID (publisher-id): biology
                Title: Biology
                Publisher: MDPI
                ISSN (Electronic): 2079-7737
                Publication date (Electronic): 01 November 2013
                Publication date Collection: December 2013
                Volume: 2
                Issue: 4
                Pages: 1268-1281
                Affiliations
                [1 ]School of Optometry and Vision Science, The University of New South Wales, Sydney NSW 2052, Australia
                [2 ]Brien Holden Vision Institute, Sydney NSW 2052, Australia; E-Mail: m.willcox@ 123456unsw.edu.au
                Author notes
                [* ]Author to whom correspondence should be addressed; E-Mail: debarun.dutta@ 123456unsw.edu.au ; Tel.: +612-9385-7546; Fax: +612-9385-7401.
                Article
                Publisher ID: biology-02-01268
                DOI: 10.3390/biology2041268
                PMC ID: 4009790
                SO-VID: 0b27af4b-8153-4c0b-8d33-d5c0450cbe5b
                Copyright © © 2013 by the authors; licensee MDPI, Basel, Switzerland.
                License:

                This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/3.0/).

                History
                Date received : 18 July 2013
                Date revision received : 01 October 2013
                Date accepted : 29 October 2013
                Categories
                Subject: Article

                Keywords: bacterial adhesion,contact lens,pseudomonas aeruginosa,staphylococcus aureus
                Data availability:
                Keywords: bacterial adhesion, contact lens, pseudomonas aeruginosa, staphylococcus aureus

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