|Year : 1971 | Volume
| Issue : 3 | Page : 130-135
Bacterial and fungal flora of the normal eye
Hari Saxena, Promila Goswami
Department of Pathology & Bacteriology, G. S. V. M. Medical College, Kanpur, India
Department of Pathology & Bacteriology, G. S. V. M. Medical College, Kanpur
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Saxena H, Goswami P. Bacterial and fungal flora of the normal eye. Indian J Ophthalmol 1971;19:130-5
Ocular infections are commonly treated with broad spectrum antibiotics and or corticosteroids without microbiologic studies and it is only clinical failure in therapy that suggest incorrect diagnosis. One of the main reasons for irrational treatment is lack of swift methods of laboratory verification of microbiologic agents and their sensitivity results, available in most laboratories, Rising incidence of mycotic infections of the eye has been well documented, Haggerty and Zimmerman,  and Anderson, Roberts, Gonzales and Chick, ).
It has been suggested that the incidence is associated with increasing use of antibiotics and or corticosteroids. Mitsui and Hana reported four cases of cor-busa  neal ulcer due to fungi following cortisone therapy and also demonstrated that the use of topical corticosteroids for three weeks in previously negative persons yielded fungus in almost 50% eyes. Ainley and Smith  however failed to obtain such results in similar study. Experimentally Agarwal, Malik, Mohan and Khosla  produced mycotic corneal ulcers with intracorneal injections of Aspergillus and Candida species.
The incidence of normal fungal flora in healthy eyes shows considerable variation in reported series from 2.9% (williamson, Gordon, Wood, Dyer and Yahya,  ) to 27.9 % (Ainley and Smith  ). In India surprisingly very few studies have been done. Sinha and Das  reported 13.4% incidence in Gujeratees of Calcutta. The need for many such surveys is obvious. The present study was planned to determine the indigenous bacterial and fungal flora of the eye in both sexes at all ages and to study the effect of topical corticosteroids on its incidence.
| Material and Methods|| |
A total of 307 individuals form the material for this communication. All were considered normal on the basis of Clinical evaluation of the eye with special emphasis on absence of erythema oedema and discharge from the eyes, atleast for a fortnight before. The subject were either patients who attended the out patient department for minor ailments not related to eyes or comprised of medical students and technical staff of the college. It was thought desirable to include equal number of both sexes of different ages to represent infant, child, adult, middle age and old age.
Conjunctival swabs were taken from both eyes for smear and culture and streaked over the surface of blood agar, nutrient agar and sabouraud's dextrose agar for bacteria and fungi. Bacterial cultures were incubated at 37° C for 24-48 hours and colonies identified by conventional methods.
The cultures for fungi were incubated at 25° C and screened for growth every week for four weeks before being labelled as negative. The fungi were identified on the basis of colonial characters, microscopy, and sugar fermentation reactions. Candida albicans was diagnosed on the basis of chlamydospore formation on corn meal agar.
For control blank cultures were exposed to the atmosphere in the vicinity of patient for roughly the same time, taken for swabbing of eye and inoculation over the media and incubated for the same length of time.
| Observations|| |
Of a total number of 307 individuals included in this study for investigation, 55 were infants upto the age of 1 month, 68 children between ages of 1-12 years, 64 adults between 15-40 years and 62 middle aged between 41-55 years and 58 old persons between 56-82 years. The number of males and females were 156 and 151 respectively. Each group was almost equal distribution of sexes. Culture for bacterial microbes were positive in all eyes in all cases although organisms isolated from both eyes in the same individual were not necessarily the same. [Table - 1], shows the species and the frequency of organisms isolated. The commonest organism was co-agulase negative staphylococcus albus in 264 eyes (43%), followed by C, xerosis in 216 eyes, (35.1%). C.xerosis seems to have more affinity for eyes of adults and old persons. No influence of sex was noted in the colonisation of bacteria.
Fungi were isolated in 54 eyes (8.7%) of 43 persons (14.0%), with the lowest incidence in infants (0.32%) and the highest incidence in the middle aged (2.9%) and old persons (2.7%). The predominant species isolated was Penicillium in 21 eyes (38.8%) of 16 persons. Candida was isolated in 20 eyes (38.4%) of .15 persons. Of a total of 43 persons in whom fungus was grown 29 were females and 14 males. Candida was more commonly seen in females (13) eyes and Penicillium was more common in male eyes (16) eyes. The species of Candida were C. albicans (13) eyes, C. pseudotropicalis (5 eyes and C. parapsilosis, 2 eyes).
Culture media exposed to atmosphere near the eyes showed bacterial growth in one out of 25 plates (4%), comprising of co-agulase negative staphylococci. All media (25) for fungal growth were negative.
Effect of topical hydrocortisone:
In 31 adults initially negative for fungi, topical hydrocortisone was instilled twice a day for three weeks and culture repeated afterwards. Fungi were grown in 9 eyes (29.0%) of 7 persons (22.5%) No appreciable difference was observed in both sexes. [Table - 3] gives the details.
| Discussion|| |
The present study amply confirms that bacterial flora appear soon after birth n the external eye and continue to be present at all ages in both sexes. Similar observations were reported by Wilson, Abeam, Jones and Sexton  who showed a 10O% presence of bacteria in their investigation of 312 eyes. However, Sinha and Das  could find bacteria in 56.7% of 67 healthy eyes. Diphtheroids, mainly C. xerosis along with staphylococcus albus form the predominant bacteria in the eyes and both are normally considered coomnensals. Staphylococcus aureus was grown in 3.4 0/c of eyes and our figure compares favour Sinha ably with the finding of and Das  who reported 2.9% incidence.
Fungi were isolated from 43 persons (14%) in 54 eyes (8.7%). Our incidence is lower than that reported in published series in India and other countries and the data are summarised in [Table - 4].
This variable incidence suggests the importance of ecological differences in temperature, and humidity of the place and of course the number of eyes investigated and the methods employed.
Fungal isolation seems to be affected by age as infants had the lowest (0.32%) incidence which increased to 2.9% in the middle aged. Hammeke and Ellis  also demonstrated this variation, with 0.1 % incidence in infants and 10.3% in adults and postulated that the lower incidence in infants is due to lesser chance of exposure on account of infant eyes being closed, most of the time.
Females harbour fungi more commonly than males and the ratio in present work was almost 2:1. This could be attributable to increasing use of cosmetics, mascara and other beauty aids, already contaminated by fungi. Wilson,  et al grew C. parapsilosis from mascara. Apart from the varying incidence of fungi in the external eye there seems to be agreement on the species of yeast and mycelia isolated in the present study with reported work in the literature. Thus Penicillium, Aspergillus and Candida species are common in all studies. Rhodotorula reported by most workers in other countries has not been isolated by us. The only other Indian publication on fungal flora of the eye by Sinha and Das  does not mention isolation of Candida species.
The over all incidence of normal fungi from the eye is however quite low and it does not seem probable that oculomycosis is due to activation of these normal fungi. It rather suggests that any fungi isolated in the normal eye are transient in nature and has been shown by Williamson," et al, in their experiments. A repeat culture after 4 weeks in 32 positive cases, showed fungi in only 4 and the species isolated were also not similar.
It is however well documented that corticosteroids may well potentiate these commensal fungi to pathogeniciety, (Ley,  ) . Agarwal,1 et al submitted experimental proof of producing corneal ulcer after injection of fungi and showed that corticosteroids enhance the virulence. Mitsui and Hanabusa  have suggested that antibiotics and or corticosteroids therapy might convert nonpathogenic fungi into pathogenic types. They reported 4 cases of occulomycosis after cortisone therapy.
Ainley and Smith  failed to demonstrate the role of cortisone on the incidence of normal fungal flora. Our incidence of 29% after cortisone is almost four times more than that without topical corticosteroids, and is fairly significant.
Candida albicans is now regarded as the cause of many corneal infections (Mitsui and Hanabusa). Manchester and George reported fungal keratitis due to C. parapsilosis.
| Summary|| |
Normal healthy eyes were investigated for bacterial and fungal flora in 307 persons of both sexes in varying age periods.
Bacteria were present in all the eyes, predominant organism was co-agulase negative staphylococcus albus (43%) followed by C. xerosis in 35.1% eyes.
Fungi were grown in 54 (8.7%) eyes of 43 persons (14%). The incidence was lowest in infants (0.32%) and highest in the middle aged (2.9%). Penicillium was the commonest species isolated (38.8%) followed by Candida (38.4%).
Use of topical hydrocorticone in the eyes for three weeks increased the incidence to 29%.
| References|| |
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LEY, A. P.: Experimental fungus infections of the Cornea., Amer. J. Ophthal. 42: 59 (1956).
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[Table - 1], [Table - 2], [Table - 3], [Table - 4]