Journal of the British Contact Lens Association, Vol. 14, No. 1, pp 13-16, 1991 ©1991 British Contact Lens Association Printed in Great Britain

EFFICACY OF AN ULTRAVIOLET LIGHT CONTACT LENS DISINFECTION UNIT AGAINST MICROBIAL PATHOGENIC

ORGANISMS

Walter Palmer*, Peter Scanlon-~ and Cliodna McNulty$ (Received 19th September 1990, in revised form 20th October 1990)

Abstract - Microbial keratitis has been shown to be significantly associated with contact lens wear. The efficacy of a commercial 253.7nm ultraviolet (UV) light~ultrasonic contact lens disinfection unit against Staphylococcus aureus, Pseudomonas aeruginosa, Serratia marcescens, Micrococcus luteus and Candida albicans w&s measured. The machine was found to reduce organism numbers, but the survivors were present at unacceptably high levels to give confidence in

efficient disinfection.

KEY WORDS: Contact lenses, UV light, ultrasonication, contamination.

Introduction

I N microbial keratitis related to contact lens wear the predominant organisms have been shown to

be staphylococci, streptococci and pseudomonas. 1'2 The conventional methods of contact lens disinfection with chemicals have resulted in poor patient compli- ance, due to the complexity and expense of these methods. In a recent survey of ulcerative keratitis, it was found that in the control group (daily wear lens patients who were symptomless) 50% did not disinfect their contact lenses daily. 2

The machine tested utilises ultrasound to dislodge material that has adhered to contact lenses and this is claimed to act synergistically with ultraviolet light at wavelength 254nm to kill organisms. Lenses are placed in individual cups which are half filled with saline and the cycle is started by closing the lid. Both the ultraviolet lamp and sonicator operate initially, the sonicator switching off after 6 minutes and the ultraviolet lamp continuing until the cycle finishes after 22 minutes.

The literature promoting the machine claims that ultrasonic agitation will enable adequate irradiation of organisms. There is a 'quick clean' option, in which the lenses may be removed after the sonic cleaning has ended. In theory, the machine could be used at night and the lenses left in place until the following morning for added convenience.

This study was designed to assess the disinfecting efficiency of the machine for low water content hydro- phfiic lenses. No attempt was made to assess the cleaning capabilities of the ultrasonic part of the cycle alone.

*FIMLS. tMRCP, MCOphth. SMRCPath.

Materials and Methods The organisms used to test the disinfection efficiency of the machine were selected from the FDA guide- lines 3 and British Pharmacopoeia 4 (Table 1). Each strain was inoculated into Tryptone Soya Broth (Oxoid) (10ml) and incubated at 37°C for 18 hours. The broth was subsequently diluted in sterile normal saline to achieve a cell suspension close to 105 colony forming units/ml (cfu/ml).

Table 1. Challenge organisms.

NCTC 10788 Staphylococcus aureus NCTC 6749 Pseudomonas aeruginosa, V.

erthrogenes NCTC 10211 Serratia marcescens NCTC 2665 Micrococcus luteus

NCPF 3155 Candida albicans

Between each test run the lenses (Cooperthin back vertex power -3.00 strength) were disinfected over- night in hydrogen peroxide and neutralised for 20 minutes in sodium pyruvate ('10.10' system Ciba- Vision), followed by rinsing in sterile normal saline before the next cycle. Both cups of the machine were half filled with a challenge organism suspension (lml volume) and a disinfected lens was placed into each cup. The disinfection unit was run according to the manufacturer's instructions. At the end of each cycle the total volume of saline was removed from each cup and added to 9ml of sterile phosphate buffered saline (PBS), pH 7.2. A further tenfold dilution was made and survival counts on horse blood agar were assessed. All counts were made using a surface drop technique where ten drops (each 20ttl) were deposited onto the surface of blood agar for each dilution.

13

WALTER PALMER ET AL.

An assessment of the effects of overnight storage of lenses in the machine was made using P. aerugi- nosa as the challenge organism. At the end of the 22 minute cycle and after overnight storage at room tempera ture the saline in each cup was well mixed and an aliquot (10#1) was added to PBS (90#1) and diluted further, to 1:10. The total volume of each dilution was inoculated, as five drops (each 20#1), onto blood agar and incubated at 37°C for 18 hours. I t was observed that the disinfection unit gained heat during the cycle. To investigate this, thermocouple wires were placed in each cup and measurements were taken throughout the cycle and at intervals up to 3 hours from the star t of the cycle.

The short 'quick clean' method was investigated only with S. aureus and P. aeruginosa. These two isolates were also used to test the effectiveness of the machine without lenses present for the full 22 minute cycle.

R e s u l t s With lenses present it was not possible to demon- strate a satisfactory log kill, as represented by 90%

destruction of the challenge dose on any organism, except for S. aureus. The presence of lenses created a wide range of survival rates (Table 2). The average kills are demonstrated in Figure 1 for all test organisms.

Without a lens present more consistent results were achieved (Table 3), with S. aureus being destroyed to a level of 99%. However, for P. aeruginosa, although more closely grouped, on average poorer results were obtained than with contact lenses present.

When the machine was left overnight (Table 4), the count after 15 hours was higher than the initial challenge owing to multiplication. The tempera ture of the fluid in the cups was shown to rise to a level of 38°C during the cycle, which took approximately 2.5 hours to fall to room temperature with the lid closed (Figure 2).

The shortened cycle, which is intended to be used as a 'quick clean' method, did not appear to be markedly less effective than the full cycle with S. aureus, whereas with P. aeruginosa it was less efficient (Table 5).

Table 2. Survival counts with lenses in place, a

Challenge Surviving Organisms Kill (%)*

L R L R

Staphylococcus aureus

Pseudomonas aeruginosa

Serratia marsescens

Micrococcus luteus

Candida albicans

3.2 X106 1.1 ×103 2.3 xl04 99.9 99 3.45×106 8.5 xl04 8.8 xl04 97 97 2.5 xlO 5 6.2 xl03 2.4 xlO 2 97 99.9 9.0 xlO 3 6.0 xl02 3.5 xl03 93 61 8.0 x 104 4.85x 104 1.95x 104 39 75

85* 86*

3.3 xl05 9.73x104 9.6 x104 70 71 1.2 xl05 4.2 xl04 4.4 xl04 65 63 6.6 xlO 4 2.4 xlO 4 2.5 xl04 63 62 7.5 xl04 3.8 x104 4.3 xl04 49 42 6.9 xl04 5.8 xl04 5.7 xlO 4 16 17

53* 51"

9.5 xl04 6.4 xl04 6.2 xl04 33 35 9.5 xl04 5.3 xlO 4 5.7 xl04 44 40 9.8 xl04 6.1 x l 0 ' 6.0 xl04 38 39 9.8 xl04 5.9 xlO 4 5.8 xl04 40 41 9.1 xl04 6.0 xl04 6.1 xl04 34 33

38* 38*

1.3 xl05 9.1 xl04 9.3 xlO 4 30 28 1.3 xl05 9.0 xl04 9.1 xl04 31 30 4.2 xl05 2.5 xl05 2.1 xlO 5 40 50 6.8 xl04 5.4 xl03 5.5 xlO 3 21 19 6.4 xl04 5.3 xl04 5.5 xl04 17 14

28* 28*

2.3 x104 1.5 x104 1.8 x104 35 28 2.3 xl04 1.6 xl04 1.8 xlO 4 30 28 8.0 xl04 5.7 xl04 6.0 xl04 29 25 8.7 xl04 6.2 xl04 4.9 xl04 29 44 6.8 xl04 4.2 xl04 4.7 zl04 38 31

32* 31"

a Results of five test runs for each organism, total volume 1 ml. Both cups in the machine were sampled, left and right. * Average.

14

UV CONTACT LENS DISINFECTION AGAINST MICROBIAL PATHOGENIC ORGANISMS

100

90

,< ¢¢

50

Staphylococcus Pseudomona. Serratia Micrococcus Candida aureus aeruginosa mareescens luteus albicans

F i g u r e 1. Destruction of microbial challenge organisms. (A 90% kill of 1.0 x 105 organisms/ml would result in the survival of 1.0 x 104 organisms/ml.)

T a b l e 3. Survival counts without lenses.

Challenge Surviving Organisms

L R

Kill

L R

Staphylococcus aureus

Pseudomona's aernginosa

1.8 x 104 4.2 x 104 8.0 x 104 9.2 x 104 2.1×104

1 .5x lO s 3 .3x105 5 .2×10 5 5.8 x 104 8.9 x 104

1.5x102 1.9x102 99 5 .0x 102 6 .0x 102 99 9 .0x 102 8 .0x 102 99 1.1x 103 1.2x 103 99 2 .2x 102 3.0× 102 99

8 .0x 104 9.0× 104 46 2 .0x 105 2 .2x 104 39 2 .3x 10 s 2 .4x 10 s 55 3 .7x104 3.6x104 36 4 .2x 104 4 .1x 104 52

99 98.5 99 98.5 98.5

40 33 53 38 54

T a b l e 4. Lenses in place overnight.

Challenge Overnight End of Cycle (15h)

L R L R

Psuedo- monas aeruginosa 5.9x104 4.2x104 4:7x104 1.5x10 s 1.6x105

0 <_

40

30

20 0

I 20 40 / /

Time (min)

F i g u r e 2. Heat gain during cycle.

180

T a b l e 5. Short cycle (sonication time).

Challenge Surviving Organisms

L R

Kill (%)

L R

Staphylococcus aureus

Pseudomonas aeruginosa

2.1x105 1.9z105

3 .3x10 ~ 1.5x105

1.6x104 2.2x104 1.7x104 2.0x104

2 . 4 x 1 0 s 2 .7x105 1 .0x10 s 1.1x105

92 91

27 33

89 89

18 27

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WALTER PALMER ET AL.

Discussion The objective of this study was to assess the disinfec- tion capability of the 253.7nm UV/ultrasonic disinfec- tion unit. The concept of a small, easy-to-use machine with effective cleaning and disinfecting properties holds many attractions for patients and their contact lens practitioners. Compliance would be likely to be better because of the simplicity of the technique.

Hovding 5 has shown that lens wear does not appre- ciably alter the commensal flora associated with the eye. Other studies have shown that microbial keratitis relating to lens wear is usually caused by environ- mentally associated organisms. A survey analysing the incidence of microbial keratitis in patients pre- senting to the Department of Ophthalmolgy at Sahlgren's Hospital, Gothenburg, Sweden, showed that the predominant organism isolated in the moderate-to-severe group of soft lens wearers (daily and extended wear) was P. aeruginosa. 6

A survey examining the contact lens care system of 100 asymptomatic patients 7 showed contamination in 52 of the care systems. In total, 22 isolates of coagulase negative staphylococci, 12 isolates of Pseudomonas spp, seven isolates of Bacillus spp, and two isolates of Acanthamoebae (in home-made saline) were recorded.

In a separate review of Acanthamoeba contami- nation of care systems 8 (including seven patients with Acanthamoebae keratitis), all were associated with mixed organisms in lens cases.

Pseudomonas, staphylococci and streptococci were the predominant organisms cultured in a recent study of microbial keratitis 2, again emphasising the need to apply a rigorous lens disinfection system.

The use of UV light for contact lens disinfection is a relatively new concept. It has been used extensively for the treatment of water effluent, where its effici- ency is well documented. 9 UV light has been shown to be effective for contact lens disinfection in laboratory conditions using a high output 253.7nm UV light machine. 1° This machine, with an intensity of 1100/~W/cm 2 , destroyed most organisms within 3 minutes of exposure.

In a separate part of this study, the UV output of the machine used for our microbiological experiments was measured at 2.13#W/cm 2 after 17 cycles, and there was a drop to a level of 0.96/~W/cm 2 at the completion of 125 cycles, the number used in this study. The recording methods and calculations for the UV output are explained elsewhere. 11 We are therefore working with a machine of considerably lower output than that of the laboratory experiment quoted above. 1° A second new machine was found to have an output of 2.36#W/cm 2 after 50 cycles and 1.58/~W/cm 2 after 100 cycles. We, therefore, feel that the inability of the machine to adequately disinfect, which we have shown, cannot be explained as being due to a faulty machine.

Our findings with the machine tested show that the only organism that k approached 90% destruction after one cycle was S. (~ureus. The reason for the more consistent results without lenses present is possibly due to the position of the lens within the fluid imped- ing flow through the top layer of the bath. This would also account for the higher kill of S. aureus when lenses were not present in the cups. The poorer results for P. aeruginosa without lenses present may be interpreted as being due to the lowering of ~ the UV output of the machine during the experiments, because the tests without lenses were performed last. The reason for such a high level of P. ae~ginosa after overnight storage in the machine at room tern- perature was felt to be due to the rise in temperature of the fluid in the cups, which may encourage the multiplication of organisms.

A higher output machine with a good flow of fluid through the top of the bath or penetration of the UV light to the depth of the cups may adequately disinfect contact lenses, but this has yet to be shown. We were unable to show a satisfactory disinfection with the unit that we tested.

Acknowledgements We are grateful to J. Walton of Specialist Optical Source for the loan of the machines.

Address for Correspondence W. Palmer, FIMLS, Public Health Laboratory, Glou- cestershire Royal Hospital, Great Western Road, Gloucester GL1 3NN, England.

R E F E R E N C E S

' Schein, 0., Ormerod, D., Barraquer, E., Alfonso, E., Egan, K., Paton, B., Kenyon, K. Microbiology of contact lens-related keratitis. Cornea, 8(4), 281-285 (1989).

2 Schein, 0., Glynn, A., Poggio, E., Seddon, J., and Kenyon, K. The relative risk of ulcerative keratitis among users of daily- wear and extended-wear soft contact lenses. New Eng. Med. J., 321, 773-778 (1989).

3 F.D.A. Guidelines, Guidelines for Class III Contact Lenses. Microbiology Section (September 1982).

4 British Pharmacopoeia, A200-A203 Efficacy of Antimicrobial Preservatives in Pharmaceutical Products, Vol. II, Appendix XVIC (1988).

5 Hovding, G. The conjunctiva] and contact lens bacteria flora during lens wear. Acta. Ophthalmol., 59, 387-401 (1981).

6 Chalupa, E., Swarbrick, H., Holden, B., and SjSstrand, J. Severe corneal infections associated with contact lens wear. Ophthal- tool., 94, 17-22 (1987).

7 Donzis, P., Mondino, B., Weissman, B., and Bruckner, D. Micro- bial contamination of contact lens care systems. Am. J. Ophthal- mol., 104, 325-335 (1987).

8 Donzis, P., Mondino, B., Wiessman, B., and Bruckner, D. Micro- biol analysis of contact lens care systems contaminated with Acanthamoeba. A m J. Ophthalmol., 108, 53-56 (1989).

9 Qualls, R., Ossoff, S., Chang, J., Dorfman, A., Dumais, C., Lobe, D., and Johnson, J. D. Factors controlling sensitivity in ultraviolet disinfection of secondary effluents. J. War. PoL Control Fed., 75, 1006-1011 (1985).

~0 Dolman, P. and Dobrogowski, M. Contact lens disinfection by ultraviolet light. Am. J. Ophthalmol., 108, 665-669 (1989).

11 Scanlon, P. Presidential Address, J. Br. Contact Lens Assoc., in press.

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