Bacterial interactions with contact lenses; effects of lens material, lens wear and microbial physiology.

Contact lens wear is a successful form of vision correction. However, adverse responses can occur during wear. Many of these adverse responses are produced as a consequence of bacterial colonization of the lens. The present study demonstrated that during asymptomatic contact lens wear lenses are colonized by low levels of bacteria with gram-positive bacteria, such as coagulase negative staphylococci, predominating. Gram-negative bacteria are frequently the causative agents of adverse responses during contact lens wear. Measuring the adhesion of different strains and/or species of bacteria to different contact lens materials demonstrated considerable differences. In particular. Pseudormonas aeruginosa strains Paerl and 6294 and Aeromonas hydrophilia strain Ahyd003 adhered in larger numbers to the highly oxygen permeable contact lenses Balafilcon A compared to hydrogel lenses manufactured from either Etafilcon A or HEMA. Furthermore, after Balafilcon A lenses had been worn for 6 h during the day bacteria were able to adhere in greater numbers to the worn lenses compared to the unworn lenses with increases in adhesion ranging from 243% to 1393%. However, wearing Etafilcon A lenses usually resulted in a decrease in adhesion (22-48%). Bacteria were able to grow after adhesion to lenses soaked in artificial tear fluid and formed biofilms, visualized by scanning confocal microscopy. Chemostat grown bacterial cultures were utilized to enable control of bacterial growth conditions and bacteria were shown to adhere in the greatest numbers if grown under low temperature (25 degrees C compared to 37 degrees C). The changes in growth temperature was shown. using 2D gel electrophoresis, to change the experssion of cell-surface proteins and, using ID gel electrophoresis, to change the expression of surface lipopolysaccharide of P. aeruginosa Paerl. Thus, these surface changes would have been likely to have mediated the increased adhesion to Etafilcon A contact lenses.

Association of acinetobacter species with contact lens-induced adverse responses.

PURPOSE: To determine the levels of Acinetobacter species associated with normal soft contact lens wear and to determine whether Acinetobacter species are involved in adverse reactions that occur during contact lens wear. METHODS: Patients wore soft contact lenses on an extended-wear basis. The bacteria on lenses and ocular swabs during asymptomatic and symptomatic lens wear were identified using standard microbiologic methods. RESULTS: Acinetobacter species were isolated and identified from 16 (13%) of 126 patient samples. Greater numbers of Acinetobacter species were isolated from lenses of patients experiencing adverse responses than from asymptomatic patients. Acinetobacter species were isolated from patients experiencing symptomatic adverse responses in 4 (13%) of 32 cases. CONCLUSION: It appeared that Acinetobacter species colonized the eye of extended contact lens wearers at a time when the normal functioning of the eye was compromised by contact lens wear. When Acinetobacter species were in high numbers on a contact lens, an adverse response occurred. This may implicate Acinetobacter species as a contributing factor to adverse responses associated with contact lens wear.

Bacterial populations on 30-night extended wear silicone hydrogel lenses.

PURPOSE: Ocular infection and inflammation during hydrogel lens extended wear is often associated with colonization of the lenses with bacteria. This study compares colonization of a high Dk silicone hydrogel contact lens (lotrafilcon A) worn on a 30-night extended wear basis to a low Dk HEMA-based lens (etafilcon A) worn on a 6-night extended wear schedule. METHODS: The group wearing the low Dk/t soft contact lens (n = 63) replaced their lenses weekly and the group wearing high Dk/t soft contact lenses replaced their lenses monthly (n = 64). Lens allocation was assigned randomly at enrollment. Worn lenses, from one eye only, were collected aseptically and placed in sterile vials. Microbial growth on various media was enumerated and the number of colony forming units (cfu) per lens was calculated in categories of normal ocular microbiota (such as coagulase-negative staphylococci and Propionibacterium spp.) and known ocular pathogens (such as Staphylococcus aureus and gram-negative bacteria). The proportion of samples colonized with these bacteria and the extent of colonization were compared between the two groups. The proportion of sterile lenses was calculated, and the types of bacteria on each lens group were compared. RESULTS: No differences between the low and high Dk/t Soft contact lens groups were observed in the proportion of lenses colonized by Propionibacterium spp. (48% vs 43%, P = 0.4) or coagulase-negative staphylococci (47% vs 54%, P = 0.2). Similarly, no differences were found for lenses colonized by S. aureus (0% vs 2%, P = 0.1) or gram-negative bacteria (3% vs 2%, P = 0.8). The types of bacteria isolated from the high and low Dk/t lenses were similar. There were no differences in the number of sterile samples (28% vs 27%, P = 0.8) from each group. CONCLUSIONS: These findings suggest that high Dk/t silicone hydrogel materials are colonized by similar numbers and types of microorganisms during extended wear compared to HEMA-based material. Most lenses were colonized by commensal bacteria during 30-night extended wear with high Dk/t lenses and during 6-night extended wear with low Dk/t lenses. The incidence of sterile samples was the same between the high and low Dk/t soft contact lens groups.

Infiltrative keratitis associated with extended wear of hydrogel lenses and Abiotrophia defectiva.

PURPOSE: Infiltrative keratitis is a common complication associated with extended wear of hydrogel lenses. Causative bacteria are often isolated from the lens at the time of an event. We report a case where three repeated occurrences of infiltrative keratitis were associated with contamination of the contact lenses by Abiotrophia defectiva. METHODS: A 34-year-old man participating in a clinical trial of extended wear hydrogel contact lenses experienced three episodes of infiltrative keratitis. The clinical presentation was observed using a biomicroscope. At the time of each event, the contact lenses were removed aseptically and ocular swabs were taken for bacterial identification and enumeration. The condition was monitored until full resolution. RESULTS: The condition was characterized by irritation, marked bulbar and limbal injection, and multiple focal subepithelial infiltrates. Many of the infiltrates also showed overlying staining with fluorescein. In each of the three events of infiltrative keratitis, A. defectiva was cultured from the contact lens and ocular swabs. CONCLUSION: This is the first reported occurrence of infiltrative keratitis associated with A. defectiva contamination of contact lenses.

Co-incubation of Acanthamoeba castellanii with strains of Pseudomonas aeruginosa alters the survival of amoeba.

Enhanced survival of Acanthamoeba castellanii has previously been reported following co-incubation with a single strain of Pseudomonas aeruginosa. The aim of this study was to evaluate the impact of different strains of P. aeruginosa on amoebae survival. Four contact lens solutions were challenged with A. castellanii for between 6 and 24 h, and survival rates of amoeba were calculated. Subsequently, A. castellanii was co-incubated with different strains of P. aeruginosa (strain 6294, an invasive isolate; 6206, a cytotoxic isolate; and Paer 001, a null isolate). Differences in amoeba survival over time between solutions for each bacterial strain were analysed. Non-neutralized hydrogen peroxide was the most effective system against A. castellani at all time points (P<0.05). Survival rates were not different between multipurpose solutions and neutralized hydrogen peroxide. Co-incubation with P. aeruginosa altered amoeba survival, and maximum survival occurred in the presence of the invasive strain of P. aeruginosa. Enhanced amoeba survival may occur in the presence of certain strains of Gram-negative bacteria, and with certain types of contact lens disinfection systems.

Incidence of contamination of preserved saline solutions during normal use.

PURPOSE: To ascertain the incidence of microbial contamination of preserved contact lens saline solutions with normal patient use. METHODS: Eight different brands of preserved saline were dispensed to 40 patients attending optometric practices in the Sydney area. After specific periods of time (7 to 28 days), the samples were collected and the solution bottle nozzles and contents underwent microbial analysis. RESULTS: The overall contamination rate was approximately 26% for contents only and 55% for nozzles of preserved saline solutions. This rate remained constant for all periods of use. Coagulase-negative Staphylococci were most frequently isolated. No Acanthamoebae were isolated. Saline preserved with ethylene-diamine-tetraacetic acid (EDTA) in conjunction with sorbic acid showed the highest percentage of sterility. CONCLUSIONS: The results of this study show that preserved saline became contaminated with gram-positive bacteria. This is in contrast to our previously published paper using unpreserved saline, where contamination was predominantly with gram-negative bacteria. The overall contamination rates with preserved saline were lower than for unpreserved saline.

Does Acanthamoeba protect Pseudomonas aeruginosa from the bactericidal effects of contact lens disinfecting systems?

PURPOSE: The aim of this study was to test the hypothesis that Pseudomonas aeruginosa that have been internalized in Acanthamoeba are protected against the action of contact lens disinfecting solutions. METHODS: The experiments were divided into two parts. First, five commercially available disinfecting solutions, hydrogen peroxide and non-peroxide based, were tested for their efficacy against four strains of P. aeruginosa and one strain of A. castellanii. Cells were inoculated into working concentrations of disinfecting solutions, incubated for 18 h and the numbers of viable bacteria or amoeba were analysed after appropriate growth on agar plates. Second, two strains of P. aeruginosa were allowed to interact with A. castellanii for 4 h prior to addition to disinfecting solutions. The numbers of P. aeruginosa after incubation with the disinfecting solutions were measured after growth on agar plates. RESULTS: In general, disinfecting solutions containing hydrogen peroxide were most effective against the micro-organisms. Solutions containing only traces of polyaminopropyl biguanide were least effective. CONCLUSIONS: For strains of P. aeruginosa, the presence of the amoebae did not protect the bacteria against the disinfecting agents. The amoeba appeared to kill the bacteria, perhaps using them as a food source.

Preliminary studies on the amoebicidal efficacy of contact lens disinfection systems.

PURPOSE: This preliminary study evaluated the efficacy of contact lens disinfection systems against Acanthamoeba castellanii, tested with and without co-incubation with Pseudomonas aeruginosa. METHODS: First, disinfection systems containing 3% hydrogen peroxide, 0.00005% polyaminopropyl biguanide or 0.001% polyquaternium were challenged with A. castellanii for 72 h. Surviving cells were enumerated. Second, A. castellanii were co-incubated with P. aeruginosa for 48 h, then exposed to the disinfectants for 6 h. RESULTS: There was zero survival of A. castellanii in hydrogen peroxide and variable survival in multipurpose systems. Following co-incubation, A. castellanii survival increased significantly (P = 0.015). CONCLUSIONS: Multipurpose systems have variable anti-amoeba activity and storage cases contaminated by bacteria may enhance amoeba survival.

Identification and enumeration of staphylococci from the eye during soft contact lens wear.

PURPOSE: An extensive study was conducted to identify and enumerate staphylococcal microbiota found on ocular sites during asymptomatic soft contact lens (SCL) wear. METHODS: A biochemical identification system separately grouped the eight clinically relevant staphylococci. Total counts and isolation frequencies from SCLs and ocular sites were evaluated. RESULTS: The epidermidis group was the most numerous isolate from extended wear (EW) lenses; the capitis/warneri group was the most numerous (p < 0.05) from daily wear (DW) lenses. In both DW and EW, the greatest isolation frequency (p < 0.05) was recorded for the capitis/warneri group. The remaining six groups were isolated infrequently and in low numbers. DISCUSSION: These results show that, in addition to Staphylococcus epidermidis, other staphylococcal species may be important members of the normal microbiota of the ocular surface during SCL wear. Furthermore, an increase and a shift in staphylococcal microbiota between DW and EW regimes was highlighted.

Potential sources of bacteria that are isolated from contact lenses during wear.

PURPOSE: The aim of this paper was to determine the possible contamination sources of contact lenses during wear. METHODS: Potential sources of the microbiota that colonized hydrogel contact lenses during wear were examined. The microorganisms that colonize contact lenses were grown, identified, and compared to those microorganisms that colonized the lower lid margins, upper bulbar conjunctiva, hands, and contact lens cases of contact lens wearers. In addition, the incidence of contamination of the domestic water supply in the Sydney area was obtained, and this was compared to the incidence of colonization of contact lenses by microorganisms in general and gram-negative bacteria in particular. RESULTS: There was a wide diversity of bacteria that were isolated from each site sampled. Coagulase-negative staphylococci and Propionibacterium spp. were the most common isolates from all ocular sites examined, and constituted the normal ocular microbiota. Other bacteria, including members of the families Enterobacteriaceae and Pseudomonadaceae, were isolated infrequently from all sites, but most frequently from contact lens cases. Statistical analysis revealed that there was a correlation between the isolation of bacteria from the contact lens and the lower lid margin (p < 0.001). Analysis of this correlation revealed that this was true for the normal microbiota. A correlation was also noted between the colonization of contact lenses by gram-negative bacteria and contamination of the domestic water supply. DISCUSSION: This study has demonstrated that the likely route for the normal ocular microbiota colonizing contact lenses is via the lid margins, whereas colonization by gram-negative bacteria, including potential agents of microbial keratitis, is likely to be from the domestic water supply.