APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Feb. 1979, p. 233-236 0099-2240/79/02-0233/04$02.00/0
Vol. 37, No. 2
Evaluation of Microbial Flora of the Eye During Wear of Soft Contact Lenses MOLLIE E. McBRIDE
Department of Dermatology, Baylor College of Medicine, Houston, Texas 77030 Received for publication 3 November 1978
The microflora of the eye has been monitored in 21 patients during a 6-month period to study changes resulting from wear of soft contact lenses. A minimum of 20 cul-de-sac cultures were taken from each patient. Fifty-one percent of cultures taken prior to lens wear were positive for microbial growth, whereas, after lens wear, positive cultures ranged from 14.3% to 30.9% over the 6-month period. There was no qualitative change in the flora during the 6-month period. Staphylococcus epidermidis was the most frequently isolated organism, followed by Micrococcus spp., diphtheroids, and Bacillus spp. Nonfermentative, gram-negative rods and fungi were isolated sporadically. Bacterial growth was sparse from all specimens, but individual differences were found. The microflora of the eye appears to resemble that of the skin, suggesting that the eye has no real flora of its own, but has a transient flora supplied from the skin, possibly the eyelid. lenses were issued to patients at the time of lens fitting with instructions for cleansing, storing, and disinfecting lenses when not in use. The patients were instructed to empty the cases each morning, rinse with physiological saline, and air dry. After wear, lenses were washed in physiological saline and placed in the cases with fresh saline solution. Disinfection was carried out each night by placing the cases containing the lenses in an Aquaflex Disinfection Unit; this is an automatic closed hot-water bath which heats to boiling temperature for 20 min. After cooling (usually overnight), the lenses were ready for wear. Lenses were fungi. The purpose of this study was to monitor the removed by inverting the cases over the hand. The in saline and shaken dry. Lens cases microbial flora of eyes prior to and during a 6- cases were rinsed the clinic and cultured at the same brought to month period of soft contact lens wear in a group were patients reported for cul-de-sac cultures, which of 21 subjects, to determine whether changes in time was over 12 h after the disinfection procedure. No microbial flora of the eye could be detected. detergents or disinfectants were used in the cleaning procedure. MATERIALS AND METHODS Microbiology. Cul-de-sacs and lens storage cases Subjects. Thirty adult male and female patients were sampled with calcium alginate swabs moistened attending a private ophthalmology clinic in Houston, in phosphate-buffered saline (pH 7.2) containing 20% Tex., were selected on the basis of whether their vision glycerol. The swab was returned to 0.5 ml of the could be corrected by wear of hydrophilic soft contact buffered solution and blended in a Vortex mixer for 30 lenses (Aquaflex). Patients were enrolled over a 1-year s, and the entire specimen used as inoculum was period and wore their lenses ad libitum throughout divided between Casman sheep blood agar, chocolate the study; hence the number of hours a day of lens agar, and mycosel agar. Chocolate and blood agar wear was not constant. Twenty-one patients com- plates were incubated in CO2 jars at 37°C for 1 week, pleted the 6-month observation period; 9 had cul-de- and mycosel agar tubes were incubated at 22°C for 5 sac sampling once prior to lens fitting, and 12 had weeks. Microorganisms were characterized using stanthree cul-de-sac samples taken before lens fitting. Cul- dard methods (1, 5). Pathogens, such as Staphylococde-sac cultures were taken at the following time inter- cus aureus, were identified at the species level, but vals after lens fitting: 2 days, 1 week, 2 weeks, and normal flora organisms, such as Micrococcus sp., were monthly up to 6 months; hence a total of either 24 or characterized only at the generic level. Data were 30 cultures were taken from each subject. All cultures compiled by designating the microorganisms isolated were taken between 1:00 and 3:00 p.m. after lens wear into the following groups: Staphylococcus spp.; Microvarying between 0 and 6 h. None of the subjects used coccus spp.; Streptococcus spp.; Corynebacterium spp.; including lipophilic species; enteric gram-negaophthalmic preparations. Lens storage cases. Cases for night storage of tive bacteria (Enterobacteriaceae); nonfermentative 233
The introduction of new polymers (3, 4) for the manufacture of contact lenses has raised the question of their safety with regard to the initiation of microbial infection of the eye. The risk of infection exists for several reasons. Sufficient heat to provide sterilization is not always possible without deterioration of the lens material; therefore, sterilization may be incomplete. Furthermore, the lens material itself may become colonized by microorganisms, particularly by
234
APPL. ENVIRON. MICROBIOL.
McBRIDE
gram-negative bacteria, which included such organisms as Acinetobacter, Moraxella, and Bacillus spp.; fungi; and yeasts. Statistics. Student's t test was used to test the significance of the differences in percentage of positive cultures from cul-de-sacs taken before and after lens wear. The paired t test was used to determine the significance of differences in percentage of positive cultures in lens storage cases taken throughout the 6month test period. The percentage of positive cultures from cases during the first month of lens wear was compared to the percentages from the second- and third-month cultures and to the values obtained for the final 3-month period. RESULTS
Qualitative results. Microflora of the culde-sac was found to be scant both in the types and number of organisms present. Table 1 summarizes the frequency of isolation of microorganisms prior to soft contact lens wear and at each culture period throughout 6 months of surveillance. The percentage of pre-lens control cultures that were positive for microorganisms of any kind was 51%, as compared to values ranging from 14.3 to 30.9% during the first 6 months of contact lens wear. The predominant genera isolated were Staphylococcus and Micrococcus, occurring in 25.6 and 22.2% of pre-lens cul-de-sacs, respectively. Corynebacterium spp. were isolated with the next greatest frequency, 8.8%; these were further differentiated into lipophilic and nonlipophilic species, since lipid-dependent organisms have not been described in cul-desacs heretofore. Bacillus spp. were isolated with the next greatest frequency, 4.4%, and nonfermentative, gram-negative rods were found in only 1.1% of pre-lens cultures, as were Streptococcus spp. The nonfermentative, gram-negative rods included species of Moraxella, King groups, and Acinetobacter calcoaceticus. Neither yeasts
nor fungi nor any significant pathogens were isolated in the pre-lens period. The decline in the number of positive cultures in the cul-de-sac with soft contact lenses proved to be statistically significant (P = 0.001) after 2 days of lens wear and throughout the 6-month surveillance period. The frequency of isolation of individual species was examined statistically to see if the decrease in total percentage of positive cultures could be attributed to any one group of microorganisms. When Staphylococcus spp. and Micrococcus spp. were treated together, the decline in frequency of isolation proved to be significant (P = 0.001), whereas separately their significance was not large (P = 0.022 for Staphylococcus spp. and P = 0.031 for Micrococcus spp.). The fluctuations in the isolation of Corynebacterium spp. did not prove to be significant (P = 0.917). The only significant pathogen occurring after lens wear was one colony of S. aureus, isolated on a single occasion at the 5-month period. Aspergillus species was also isolated on a single occasion from one eye at the 2-day post-lens culture period; its presence was transitory, how-
ever.
The majority of cul-de-sacs had only one isolate, regardless of the length of time of lens wear (Fig. 1). Over the 6-month period of soft contact lens wear, however, there was an increase in the number of cul-de-sac cultures that had two isolates. The month-5 culture period was found to have the greatest microbial load, but this did not persist to the 6-month culture period. In only one subject were there five different organisms isolated; this occurred after 5 months of lens wear, but this increase in the number of isolates did not persist. Individual variation was noted in the numbers of isolates present in cul-de-sacs. Some patients
TABLE 1. Frequency of isolation of microorganisms in cul-de-sac cultures before and during soft contact lens wear % Positive cultures
Microorganisms isolated
Total flora Staphylococcus epidermidis Micrococcus spp. Corynebacterium spp. Lipophilic Bacillus spp. Gram-negative rods, nonfermentative Streptococcus spp. Fungi Staphylococcus aureus
Prior to lens
Time interval of lens wear
wear
2 days
51
23.8
1 wk 14.3
2 wk 19.0
1 mo 23.8
2 mo 28.6
3 mo 19.0
4 mo 23.8
5 mo 30.9
6 mo 26.2
25.6
7.1
11.9
9.5
9.5
9.5
16.6
7.1
21.4
9.5
22.2 8.8 3.3
11.9 9.5 7.1
7.1 2.4 0
7.1 11.8 4.7
11.9 7.1 2.4
11.9 7.1 2.4
4.7 7.1 2.4
16.6 4.7 4.7
16.6 16.7 2.4
9.5 7.1 4.7
4.4
2.4
2.4
2.4
2.4
2.4
4.7
0
2.4
4.7
1.1
2.4
2.4
0
2.4
0
0
0
2.4
0
1.1 0 0
0 2.4 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 2.4
0 0 0
0 0 0
VOL. 37, 1979
EYE MICROFLORA WITH SOFT CONTACT LENS WEAR
235
M One isolate Two isolates U Three isolates 30 Four isolates 30-
40
Vol. 37, No. 2
Evaluation of Microbial Flora of the Eye During Wear of Soft Contact Lenses MOLLIE E. McBRIDE
Department of Dermatology, Baylor College of Medicine, Houston, Texas 77030 Received for publication 3 November 1978
The microflora of the eye has been monitored in 21 patients during a 6-month period to study changes resulting from wear of soft contact lenses. A minimum of 20 cul-de-sac cultures were taken from each patient. Fifty-one percent of cultures taken prior to lens wear were positive for microbial growth, whereas, after lens wear, positive cultures ranged from 14.3% to 30.9% over the 6-month period. There was no qualitative change in the flora during the 6-month period. Staphylococcus epidermidis was the most frequently isolated organism, followed by Micrococcus spp., diphtheroids, and Bacillus spp. Nonfermentative, gram-negative rods and fungi were isolated sporadically. Bacterial growth was sparse from all specimens, but individual differences were found. The microflora of the eye appears to resemble that of the skin, suggesting that the eye has no real flora of its own, but has a transient flora supplied from the skin, possibly the eyelid. lenses were issued to patients at the time of lens fitting with instructions for cleansing, storing, and disinfecting lenses when not in use. The patients were instructed to empty the cases each morning, rinse with physiological saline, and air dry. After wear, lenses were washed in physiological saline and placed in the cases with fresh saline solution. Disinfection was carried out each night by placing the cases containing the lenses in an Aquaflex Disinfection Unit; this is an automatic closed hot-water bath which heats to boiling temperature for 20 min. After cooling (usually overnight), the lenses were ready for wear. Lenses were fungi. The purpose of this study was to monitor the removed by inverting the cases over the hand. The in saline and shaken dry. Lens cases microbial flora of eyes prior to and during a 6- cases were rinsed the clinic and cultured at the same brought to month period of soft contact lens wear in a group were patients reported for cul-de-sac cultures, which of 21 subjects, to determine whether changes in time was over 12 h after the disinfection procedure. No microbial flora of the eye could be detected. detergents or disinfectants were used in the cleaning procedure. MATERIALS AND METHODS Microbiology. Cul-de-sacs and lens storage cases Subjects. Thirty adult male and female patients were sampled with calcium alginate swabs moistened attending a private ophthalmology clinic in Houston, in phosphate-buffered saline (pH 7.2) containing 20% Tex., were selected on the basis of whether their vision glycerol. The swab was returned to 0.5 ml of the could be corrected by wear of hydrophilic soft contact buffered solution and blended in a Vortex mixer for 30 lenses (Aquaflex). Patients were enrolled over a 1-year s, and the entire specimen used as inoculum was period and wore their lenses ad libitum throughout divided between Casman sheep blood agar, chocolate the study; hence the number of hours a day of lens agar, and mycosel agar. Chocolate and blood agar wear was not constant. Twenty-one patients com- plates were incubated in CO2 jars at 37°C for 1 week, pleted the 6-month observation period; 9 had cul-de- and mycosel agar tubes were incubated at 22°C for 5 sac sampling once prior to lens fitting, and 12 had weeks. Microorganisms were characterized using stanthree cul-de-sac samples taken before lens fitting. Cul- dard methods (1, 5). Pathogens, such as Staphylococde-sac cultures were taken at the following time inter- cus aureus, were identified at the species level, but vals after lens fitting: 2 days, 1 week, 2 weeks, and normal flora organisms, such as Micrococcus sp., were monthly up to 6 months; hence a total of either 24 or characterized only at the generic level. Data were 30 cultures were taken from each subject. All cultures compiled by designating the microorganisms isolated were taken between 1:00 and 3:00 p.m. after lens wear into the following groups: Staphylococcus spp.; Microvarying between 0 and 6 h. None of the subjects used coccus spp.; Streptococcus spp.; Corynebacterium spp.; including lipophilic species; enteric gram-negaophthalmic preparations. Lens storage cases. Cases for night storage of tive bacteria (Enterobacteriaceae); nonfermentative 233
The introduction of new polymers (3, 4) for the manufacture of contact lenses has raised the question of their safety with regard to the initiation of microbial infection of the eye. The risk of infection exists for several reasons. Sufficient heat to provide sterilization is not always possible without deterioration of the lens material; therefore, sterilization may be incomplete. Furthermore, the lens material itself may become colonized by microorganisms, particularly by
234
APPL. ENVIRON. MICROBIOL.
McBRIDE
gram-negative bacteria, which included such organisms as Acinetobacter, Moraxella, and Bacillus spp.; fungi; and yeasts. Statistics. Student's t test was used to test the significance of the differences in percentage of positive cultures from cul-de-sacs taken before and after lens wear. The paired t test was used to determine the significance of differences in percentage of positive cultures in lens storage cases taken throughout the 6month test period. The percentage of positive cultures from cases during the first month of lens wear was compared to the percentages from the second- and third-month cultures and to the values obtained for the final 3-month period. RESULTS
Qualitative results. Microflora of the culde-sac was found to be scant both in the types and number of organisms present. Table 1 summarizes the frequency of isolation of microorganisms prior to soft contact lens wear and at each culture period throughout 6 months of surveillance. The percentage of pre-lens control cultures that were positive for microorganisms of any kind was 51%, as compared to values ranging from 14.3 to 30.9% during the first 6 months of contact lens wear. The predominant genera isolated were Staphylococcus and Micrococcus, occurring in 25.6 and 22.2% of pre-lens cul-de-sacs, respectively. Corynebacterium spp. were isolated with the next greatest frequency, 8.8%; these were further differentiated into lipophilic and nonlipophilic species, since lipid-dependent organisms have not been described in cul-desacs heretofore. Bacillus spp. were isolated with the next greatest frequency, 4.4%, and nonfermentative, gram-negative rods were found in only 1.1% of pre-lens cultures, as were Streptococcus spp. The nonfermentative, gram-negative rods included species of Moraxella, King groups, and Acinetobacter calcoaceticus. Neither yeasts
nor fungi nor any significant pathogens were isolated in the pre-lens period. The decline in the number of positive cultures in the cul-de-sac with soft contact lenses proved to be statistically significant (P = 0.001) after 2 days of lens wear and throughout the 6-month surveillance period. The frequency of isolation of individual species was examined statistically to see if the decrease in total percentage of positive cultures could be attributed to any one group of microorganisms. When Staphylococcus spp. and Micrococcus spp. were treated together, the decline in frequency of isolation proved to be significant (P = 0.001), whereas separately their significance was not large (P = 0.022 for Staphylococcus spp. and P = 0.031 for Micrococcus spp.). The fluctuations in the isolation of Corynebacterium spp. did not prove to be significant (P = 0.917). The only significant pathogen occurring after lens wear was one colony of S. aureus, isolated on a single occasion at the 5-month period. Aspergillus species was also isolated on a single occasion from one eye at the 2-day post-lens culture period; its presence was transitory, how-
ever.
The majority of cul-de-sacs had only one isolate, regardless of the length of time of lens wear (Fig. 1). Over the 6-month period of soft contact lens wear, however, there was an increase in the number of cul-de-sac cultures that had two isolates. The month-5 culture period was found to have the greatest microbial load, but this did not persist to the 6-month culture period. In only one subject were there five different organisms isolated; this occurred after 5 months of lens wear, but this increase in the number of isolates did not persist. Individual variation was noted in the numbers of isolates present in cul-de-sacs. Some patients
TABLE 1. Frequency of isolation of microorganisms in cul-de-sac cultures before and during soft contact lens wear % Positive cultures
Microorganisms isolated
Total flora Staphylococcus epidermidis Micrococcus spp. Corynebacterium spp. Lipophilic Bacillus spp. Gram-negative rods, nonfermentative Streptococcus spp. Fungi Staphylococcus aureus
Prior to lens
Time interval of lens wear
wear
2 days
51
23.8
1 wk 14.3
2 wk 19.0
1 mo 23.8
2 mo 28.6
3 mo 19.0
4 mo 23.8
5 mo 30.9
6 mo 26.2
25.6
7.1
11.9
9.5
9.5
9.5
16.6
7.1
21.4
9.5
22.2 8.8 3.3
11.9 9.5 7.1
7.1 2.4 0
7.1 11.8 4.7
11.9 7.1 2.4
11.9 7.1 2.4
4.7 7.1 2.4
16.6 4.7 4.7
16.6 16.7 2.4
9.5 7.1 4.7
4.4
2.4
2.4
2.4
2.4
2.4
4.7
0
2.4
4.7
1.1
2.4
2.4
0
2.4
0
0
0
2.4
0
1.1 0 0
0 2.4 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 2.4
0 0 0
0 0 0
VOL. 37, 1979
EYE MICROFLORA WITH SOFT CONTACT LENS WEAR
235
M One isolate Two isolates U Three isolates 30 Four isolates 30-
40
