Comparison of the antimicrobial effect of heavy silicone oil and conventional silicone oil against endophthalmitis-causing agents.

PURPOSE: To conduct an in vitro experimental study comparing the effectiveness of conventional silicone oil and heavy silicone oil against endophthalmitis-causing agents.
MATERIALS AND METHODS: The antimicrobial activity of conventional silicone oil (RS OIL 5000) and heavy silicone oil (heavySil 1500) was tested. The antimicrobial effects of both silicone oils were determined by the growing capability of the microorganism.
RESULTS: The number of Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans decreased to zero levels at the second day of inoculation in heavy silicone oil. In conventional silicone oil, the microorganisms survived longer than in heavy silicone oil.
CONCLUSION: Heavy silicone oil seems to be more effective than conventional silicone oil against endophthalmitis-causing agents.

Infectious endophthalmitis is one of the most devastating complications of ophthalmic surgeries and penetrating injuries. Although the microbial etiology of infectious endophthalmitis varies according to the clinical settings, the most common isolated microorganisms are Gram-negative bacilli, Staphylococci, Gram-positive bacilli, Streptococci, and fungi. Despite agressive therapeutic and surgical interventions, endophthalmitis generally results in partial or complete visual loss, often within a few days of microbial inoculation. It has been hypothesized that complete vitrectomy in patients with endophthalmitis might ensure complete removal of both the vitreoretinal tractions and the microbial load within the vitreous cavity.[1]

Silicone oil is a group of clear, inert, and hydrophobic polymers, chemically derived from siloxane. Currently, the main indications of its use are complicated cases and infectious endophthalmitis.[23] They help by providing tamponade to inadvertent breaks, decreasing the spread of the microorganisms by compartmentalizing the eye. Experimental studies suggested that conventional silicone oil has bactericidal activity against various microorganisms.[45]

The purpose of this study was to compare the effect of the conventional and heavy silicone oils on in vitro bacterial growth of selected microrganisms Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans.

Materials and Methods

An in vitro experimental study was conducted in the Laboratory of Microbiology of the Kırıkkale University School of Medicine. The antimicrobial activities of the two intraocular tamponades, conventional silicone oil (RS OIL, 5000, Alchimia, Italy) and heavy silicone oil (heavySil 1500, Alchimia, Italy), against S. aureus, S. epidermidis, E. coli, P. aeruginosa, and C. albicans were tested. The bacteria were suspended in physiologic saline to get 1-Mc Farland turbidity. Two samples of 0.1 ml and two samples of 0.5 ml were obtained from the microbial suspension. Two samples of 0.1 ml were inoculated into the 0.9-ml conventional silicone oil and heavy silicone oil. The 0.5-ml samples were inoculated into 4.5-ml brain-heart infusion, physiologic saline for bacteria, and Sabouraud broth for fungus. Negative controls were brain-heart infusion and physiologic saline without any inoculations.

The antimicrobial effect of both silicone oils was determined by the growing capability of the microorganism. The sterilized Müeller-Hinton agar growth medium was prepared (4 mm thick) for determining the bacterial growth daily. Before sampling, the tubes were carefully vortexed at 2500 rpm until bacteria/fungus and silicone oil mixture with evenly distributed microorganisms was obtained. Samples were taken from these liquids each day. A 10-ml sample was taken from the intraocular liquids and controls. The samples were inoculated and spreaded with single-use loop on Müeller-Hinton agar or Sabouraud broth. After 24 h in the incubator, bacterial growth was evaluated daily. After a 24-h period, growing colonies were counted as colony forming unit (CFU).

Results

Figs 1–5 show the antimicrobial effects of the two silicone oils against endophthalmitis causing agents.

Figure 1

The growth of S. aureus in silicone oils and controls. HS: Heavy silicone, CS: Conventional silicone, BH: Brain-hearth broth, SF: Saline, SDB: Sabouraud dextroz broth

Figure 5

The growth of C. albicans in silicone oils and controls. HS: Heavy silicone, CS: Conventional silicone, BH: Brain-hearth broth, SF: Saline, SDB: Sabouraud dextroz broth

Coventional silicone oil demonstrated a significant decrease in bacterial load at third day against S. aureus, at first day against S. epidermidis, at fourth day against E. coli, at eigth day against P. aeruginosa, and these antibacterial effects stayed same for 16 days. Candida albicans grew at third day significantly (300 CFU) and after a decrease of 100 CFU at fourth day, the colonies stayed stable up to 15 days.

The growth of S. epidermidis in silicone oils and controls. HS: Heavy silicone, CS: Conventional silicone, BH: Brain-hearth broth, SF: Saline, SDB: Sabouraud dextroz broth

The growth of E. coli in silicone oils and controls. HS: Heavy silicone, CS: Conventional silicone, BH: Brain-hearth broth, SF: Saline, SDB: Sabouraud dextroz broth

The growth of P. aeruginosa in silicone oils and controls. HS: Heavy silicone, CS: Conventional silicone, BH: Brain-hearth broth, SF: Saline, SDB: Sabouraud dextroz broth

In heavy silicone oil, the number of all microorganisms survived only 2 days, and then their numbers declined to zero levels at the end of second day and this effect remained the same up to 16 days. In controls, all pathogens grew rapidly in brain-heart infusion broth and Sabouraud Dextroz broth, while they decreased in saline.

Discussion

Endophthalmitis cases have been treated with several routes of antibiotic administration, including intravitreal, systemic, topical, and subconjunctival previously.[67] With the advent of vitrectomy techniques, pars plana vitrectomy combined with intravitreal antibiotics became the standard treatment for all forms of endophthalmitis. Vitreoretinal surgeons have also used silicone oil in cases of endophthalmitis with extensive retinal damage as intraocular tamponade in order to prevent retinal detachment over the past two decades.[8910]

The potential antimicrobial properties of silicone oil in vitro have been reported in the literature.[45] Özdamar et al.[4] have shown that conventional silicone oil had antimicrobial activity against endophthalmitis-causing agents like S. aureus, S. epidermidis, P. aeruginosa, and C. albicans in in vitro conditions. In our study, we compared the antimicrobial effectiveness of heavy silicone oil and conventional silicone oil against the endophthalmitis-causing microorganisms. Conventional silicone oil decreased the colony numbers of all bacteria except for C. albicans, but heavy silicone oil demonstrated a superior antimicrobial effect on all pathogens including C. albicans.

Although a mechanism of the antimicrobial effect of silicone oils has not yet been clearly determined, physical and chemical properties may help us to understand the bioactivity of this material.[11] Being highly hydrophobic and having hydrogen bonding interactions, silicone oils might have damaged the cellular membrane of the infectious agents and improved the efficacy of human defence mechanisms.

Concurrent endophthalmitis and retinal detachment have a poor visual and anatomical outcome, especially when retinal detachment is an intraoperative complication.[121314] Therefore, vitrectomy with silicone oil tamponade may result in faster and better visual rehabilitation and reduced risk of retinal detachment and decrease the need for additional procedures. The role of heavy silicone oil in the treatment of endophthalmitis cases may be assessed by a prospective study with larger amount of patients to confirm the findings of this study.