Journal of the British Contact LensAssociation, Vol. 16, No. 3, pp 113-117, 1993 © 1993 British Contact Lens Association Printed in Great Britain BACTERIAL ADHERENCE AND GLYCOCALYX FORMATION ON UNWORN HYDROGEL LENSES Fiona Stapleton*, John K. Dart*, Melville Matheson*, and E. Geoffrey Woodward* (Received 24th May 1992; in revisedform 26th October 1992) Abstract-- Bacterial adherence and colonisation of hydrogel contact lenses may be a relevant factor in contact lens-related infec- tions, particularly in users of disposable extended-wear contact lenses or of sterile contact lens care materials. The adherence of one strain ofPseudomonas aeruginosa to unworn hydrogel contact lenses was evaluated to elucidate the initial time course of adher- ence and to examine the effects of material charge. Adherence was evaluated using quantitative bacteriology and scanning electron microscopy (SEM). With 75% water-content non- ionic contact lenses, bacterial adherence increased with time and reached a maximum after 30-60rain. Organisms adhered in higher numbers to unworn non-ionic contact lenses compared with ionic lenses (p<O.01). SEM showed no preferential adherence of bacteria to lathing marks or surface defects. After 30rain incubation, a thin fixed film was visible with SEM and adherent bacteria were associated with fibrous material. There was little further change in appearance with longer incubation times. KEY WORDS: Bacterial adherence, hydrogel, contact lenses. Introduction C ORNEAL infection is the most severe complica- tion of contact lens wear and is most frequently associated with hydrogel lenses, particularly those used on an overnight basis. 1 Bacteria, particularly Pseudomonas aeruginosa, are often implicated in these infections? ,~ Organisms may be carried via the contact lens from contaminated lens cases to the ocular sur- face. 4 In infectious keratitis arising where lens storage cases are sterile, or in disposable extended-wear lens users, organisms may have been transferred manually to the lens. Bacterial adherence to hydrogel lenses and subse- quent formation of a polysaccharide-rich glycocalyx on lens surfaces has been suggested as a possible initial event in the pathogenesis of lens-related keratitis. ~,6 The predominant method of growth for bacteria in nature is within glycocalyx-enclosed microcolonies, forming a biofilm on surfaces. 7 This mode of growth affords the organisms protection from antimicrobial agents. 8,9 Glycocalyx-enclosed microcolonies on lenses or in lens-storage cases may be similarly protected from antimicrobial agents in lens-care systems. 1° Part of the biofilm's function may be the continued adher- ence of organisms to the substratum, and the biofilm itself may enable corneal inoculation with bacteria in the event of a corneal epithelial defect. Several in-vitro studies have shown that bacteria will actively adhere to both new and worn, rigid and hydrogel lenses. 6,11,12 There is, however, considerable controversy in the literature as to whether bacteria adhere in greater numbers to new or worn lenses. * PhD. tDM. *BSc. Several studies have shown that lens surface deposits increase bacterial attachment.m4 However, other studies have shown no predictable differences in bac- terial adherence, using new or worn lenses. 15,16 One study has shown that the predominantly lysozyme surface coating formed during wear of Etafilcon A inhibits adherence of one strain of Pseudomonas aeruginosa. 17 Similar findings have been demon- strated using rabbit-worn lenses. 18 Once initial adher- ence has occurred, colonisation of the lens surface and biofilm production has been demonstrated in an animal model. 5 This study aimed to examine the rate of bacterial adherence to hydrogel lenses, following exposure to known concentrations of organisms, and the kinetics of bacterial glycocalyx formation using SEM. Differences in the levels of adherence to ionic and non-ionic lens materials and the effects of hydrogel water content on bacterial adherence were also compared. Methods Bacterial suspensions were prepared from an 18h static culture of Pseudomonas aeruginosa used to generate organisms in log phase. This occurs when organisms replicate in a logarithmic manner. The organism was derived from a contact lens-related corneal ulcer, and had been purity plated and stored in 25% glycerol broth at -20°C. The glycerol broth culture was regenerated by an 18h static incubation in nutrient broth. Bacteria were centrifuged and the supernatant removed; the resultant pellet was washed three times in sterile phos- phate-buffered saline (PBS) before being resuspended in 5ml of PBS to give a final concentration of 107organ - isms/ml. The concentration of viable organisms was checked using a colony-counting technique 19 for log dilutions of the suspension, for each freshly prepared bacterial culture. 113