Emma B.H. Hume

A novel cationic-peptide coating for the prevention of microbial colonization on contact lenses.

Aims:  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.

Role of quorum sensing by Pseudomonas aeruginosa in microbial keratitis and cystic fibrosis

Pseudomonas aeruginosa is a ubiquitous bacterium that causes opportunistic infections in a range of host tissues and organs. Infections by P. aeruginosa are difficult to treat and hence there is interest in the development of effective therapeutics. One of the key mechanisms that P. aeruginosa uses to control the expression of many virulence factors is the N-acylated homoserine lactone (AHL) regulatory system. Hence, there is considerable interest in targeting this regulatory pathway to develop novel therapeutics for infection control. P. aeruginosa is the principal cause of microbial keratitis and of infections in cystic fibrosis (CF) sufferers, and AHL-dependent cell-to-cell signalling has been shown to be important for both infection types. However, keratitis tends to be an acute infection whereas infection of CF patients develops into a chronic, life-long infection. Thus, it is unclear whether AHL-regulated virulence plays the same role during these infections. This review presents a comparison of the role of AHL signalling in P. aeruginosa-mediated microbial keratitis and chronic lung infections of CF patients.

In Vivo Performance of Melimine as an Antimicrobial Coating for Contact Lenses in Models of CLARE and CLPU

PURPOSE One strategy to minimize bacteria-associated adverse responses such as microbial keratitis, contact lens-induced acute red eye (CLARE), and contact lens induced peripheral ulcers (CLPUs) that occur with contact lens wear is the development of an antimicrobial or antiadhesive contact lens. Cationic peptides represent a novel approach for the development of antimicrobial lenses. METHODS A novel cationic peptide, melimine, was covalently incorporated into silicone hydrogel lenses. Confirmation tests to determine the presence of peptide and anti-microbial activity were performed. Cationic lenses were then tested for their ability to prevent CLPU in the Staphylococcus aureus rabbit model and CLARE in the Pseudomonas aeruginosa guinea pig model. RESULTS In the rabbit model of CLPU, melimine-coated lenses resulted in significant reductions in ocular symptom scores and in the extent of corneal infiltration (P < 0.05). Evaluation of the performance of melimine lenses in the CLARE model showed significant improvement in all ocular response parameters measured, including the percentage of eyes with corneal infiltrates, compared with those observed in the eyes fitted with the control lens (P < or = 0.05). CONCLUSIONS Cationic coating of contact lenses with the peptide melimine may represent a novel method of prevention of bacterial growth on contact lenses and consequently result in reduction of the incidence and severity of adverse responses due to Gram-positive and -negative bacteria during lens wear.

Immunization with alpha-toxin toxoid protects the cornea against tissue damage during experimental Staphylococcus aureus keratitis.

ABSTRACT Alpha-toxin is a major virulence factor in Staphylococcus aureus keratitis. Active or passive immunization with alpha-toxin toxoid could protect against corneal damage. Results show that either form of immunization did not kill bacteria but did significantly protect against corneal pathology, especially epithelial erosion.

Lysostaphin is effective in treating methicillin-resistant Staphylococcus aureus endophthalmitis in the rabbit

Purpose. To determine the effectiveness of lysostaphin treatment of experimental endophthalmitis caused by methicillin-resistant Staphylococcus aureus (MRSA). Methods. In one experiment, rabbits were injected in the mid-vitreous with 50 or 200 CFU of S. aureus; untreated groups and groups injected intra-vitreally at 8 or 24 hours postinfection with vehicle or lysostaphin (0.1 mg/ml) were compared in terms of CFU/ml vitreous at 24 or 48 hours postinfection. Histopathology of untreated and treated eyes was also compared. To quantify the potency of lysostaphin, additional rabbits were injected with 50 CFU of S. aureus and untreated eyes and eyes treated at 8 hours with 0.001, 0.01 or 0.05 mg/ml were compared in terms of CFU/ml vitreous at 24 hours postinfection. Results. Vitreous of untreated eyes or vehicle-treated eyes injected with 50 or 200 CFU of S. aureus contained 5–10 million CFU/ml at 24 or 48 hours postinfection. All eyes treated with lysostaphin at 8 hours postinfection had less than 1 log CFU/ml in the vitreous (P = 0.0001). Similarly, eyes treated with lysostaphin at 24 hours postinfection had approximately 1 log of CFU/ml at 48 hours postinfection. None of the untreated eyes were sterile and 88% or 50% of the eyes treated at 8 or 24 hours postinfection, respectively, were sterile. Eyes treated with lysostaphin at 8, but not 24, hours postinfection had less pronounced pathologic changes than the untreated eyes (P = 0.002). A significant reduction in the CFU/ml vitreous at 24 hours postinfection was obtained by treating infected eyes at 8 hours postinfection with lysostaphin at concentrations of =0.001 mg/ml (P = 0.0034). Conclusions. Lysostaphin is effective in treating experimental endophthalmitis mediated by MRSA.

Experimental Pseudomonas aeruginosa keratitis in interleukin-10 gene knockout mice.

ABSTRACT Pseudomonas aeruginosa keratitis is one of the most destructive diseases of the cornea. The host response to this infection is critical to the outcome. The cytokine interleukin-10 (IL-10) is thought to play an important role in modulating excessive inflammation and antimicrobial defenses. We have found that in IL-10−/− mice there is a significant decrease in bacterial load in corneas at 7 days postchallenge with P. aeruginosa. This decrease was accompanied by a reduction in neutrophil numbers in the cornea and changes in cytokine levels compared to those of wild-type mice. A characteristic increase in neovascularization in the cornea was found in the IL-10−/− mice. This increased angiogenesis correlated with an increased expression of KC, whereas the kinetics of macrophage inflammatory peptide 2 expression correlated with neutrophil numbers. This finding suggests that KC may play a role in corneal angiogenesis. The source of IL-10 in mouse corneas was identified as a subpopulation of infiltrating cells and keratocytes. This study demonstrates that IL-10 plays an important role in regulating the balance of inflammatory mediators during P. aeruginosa infection of the cornea.

Ability of silver-impregnated contact lenses to control microbial growth and colonisation

Purpose To examine the ability of silver nano-particles to prevent the growth of Pseudomonas aeruginosa and Staphylococcus aureus in solution or when adsorbed into contact lenses. To examine the ability of silver nano-particles to prevent the growth of Acanthamoeba castellanii.

Efficacy of contact lens multipurpose solutions against serratia marcescens.

Purpose. To compare the susceptibilities of clinical isolates of Serratia marcescens and the standard ISO ATCC 13880 strain to five contact lens multipurpose disinfection solutions (MPDSs). Methods. Five commercially available MPDSs, containing either a polymeric biguanide or polyquaternium, were tested using ISO/CD 14729 stand-alone test for contact lens care products against four ocular isolates of S. marcescens and the strain ATCC 13880. An average log reduction in bacterial numbers at the manufacturers minimum recommended disinfection time was determined and compared with the criteria for stand-alone disinfection products for each MPDS against each bacterial strain. Results. All the MPDSs tested met the stand-alone criteria of 3-log reduction of viable bacteria against the ATCC strain of S. marcescens. However, there was more variability in their ability to meet disinfection criteria when tested against the clinical isolates. Two of the clinical isolates were significantly more resistant to disinfection than was the recommended ISO strain (p ≤ 0.034). Two of the polyquaternium-1-based disinfection solutions (solutions D and E, p ≤ 0.005) were less effective overall than the other MPDSs against S. marcescens. Conclusions. The importance of strain selection for the testing of MPDSs is indicated, and the use of a single laboratory strain may be insufficient to provide assurance that the disinfection solution will be effective against clinical isolates. Furthermore, clinical isolates of S. marcescens may show increased resistance to disinfection with polyquaternium.

Soft contact lens disinfection solution efficacy: clinical Fusarium isolates vs. ATCC 36031.

Purpose. To compare the disinfecting efficacy of five soft contact lens multipurpose disinfection solutions (MPDS) against Fusarium solani clinical isolates and the ISO standard ATCC 36031 strain. Methods. Three commercially available and two recalled MPDS were tested using the ISO/CD 14,729 stand-alone test for contact lens care products against 10 ocular isolates of F. solani and the ATCC 36031 strain. The effect of filtering the fungal suspension before incubating in MPDS was also tested. An average log reduction in colony forming units at the manufacturer’s minimum recommended disinfection time was determined and compared with criteria for stand-alone disinfection products for each MPDS against each strain. Results. No difference between filtered and unfiltered fungal suspensions was observed for the ISO standard, whereas in one MPDS the representative clinical isolate showed significantly increased resistance when unfiltered. All but one solution met the stand-alone criteria of 1.0-log reduction of colony forming units against the recommended ISO standard strain ATCC 36031. However, there was wide variation in the ability of MPDS to meet the ISO disinfection criteria when tested against clinical isolates. Among the commercially available MPDS, the two polyquaternium-based solutions showed a higher disinfecting efficacy than the biguanide-based solution. The two recalled solutions showed a lower disinfecting efficacy than the polyquaternium-based solutions. Further, the clinical isolates were significantly more resistant to disinfection than was the recommended ISO strain. Conclusions. The effect of filtering the fungal suspension to remove hyphae seems to be relevant in the clinical isolate tested, but not in the ISO strain. Clinical isolates were significantly more resistant to disinfection than the recommended ISO strain in the presence of both the commercially available and the recalled MPDS. The use of clinical isolates in stand-alone disinfection testing is indicated. Because there were significant differences in increased resistance exhibited by clinical isolates and in a mixed (unfiltered) culture the use of a single laboratory strain may be insufficient to provide assurance that the disinfection solution will be effective against clinical isolates.

The role of CXC chemokine receptor 2 in Pseudomonas aeruginosa corneal infection

Pseudomonas is one of the leading causes of contact lens‐related microbial keratitis. Despite the use of antibiotics, the host inflammatory response continues to cause damage to the cornea, which may lead to blindness. CXCR2‐binding chemokines have been implicated in the pathogenesis of Pseudomonas keratitis, and the exact role of this receptor remains to be elucidated. Corneas of CXCR2 knockout and wild‐type mice (Cmkar 2−/− and Cmkar 2+/+) were scratched, and 2 × 106 CFU/mL Pseudomonas 6294 or 6206 was added to corneas. Twenty‐four hours postinfection, mice were killed, and eyes were harvested for enumeration of bacteria, myeloperoxidase (MPO) levels, and inflammatory mediators. Cmkar 2−/− had 20‐ to 100‐fold more bacteria than Cmkar 2+/+ mice. There were no differences in MPO levels between gene knockout and Cmkar 2+/+ mice. Histology revealed PMN were restricted to the limbal area. Levels of CXCR2 chemokines (keratinocyte‐derived chemokine and MIP‐2) were elevated significantly in gene knockout mice. A lack of CXCR2 leads to an inability to control bacterial numbers as a result of the inability of PMN to reach the site of infection in the avascular cornea. These results imply that CXCR2 is critical to the extravasation of neutrophils into the avascular cornea.