Oman Journal of Ophthalmology

: 2012  |  Volume : 5  |  Issue : 1  |  Page : 16--18

Normal conjunctival flora and their antibiotic sensitivity in Omanis undergoing cataract surgery

Belur R Keshav1, Somansu Basu2,  
1 Department of Ophthalmology Sur Regional Hospital, Sur, Oman
2 Department of Microbiology, Sur Regional Hospital, Sur, Oman

Correspondence Address:
Belur R Keshav
P.O. Box 823, pc411, Sur


Purpose: To evaluate the normal conjunctival flora and to ascertain their sensitivity to antibiotics. Materials and Methods: Prospective study was undertaken with 56 patients scheduled for cataract surgery. In each of these patients, conjunctival swab was taken from both eyes before instilling any antibiotic drops or local anesthetics and were sent for culture sensitivity by inoculating the samples in blood agar plates. The un-operated eyes served as controls for the study. The results were tabulated and analyzed by applying confidence intervals at 95% confidence limits. Results: Of the 112 eyes studied, positive cultures were obtained from 54 eyes (48.3%) preoperatively, and included both operated and control eyes. Coagulase-negative staphylococcus was isolated in 44 eyes (81.5%). Maximum sensitivity was found with vancomycin, gentamycin, chloramphenicol, and ciprofloxacin and maximum resistance with fusidic acid, penicillin, and oxacillin. Conclusion: We conclude that coagulase-negative staphylococcus are the most common bacteria isolated from the conjunctival sac, and vancomycin followed by gentamycin and ciprofloxacin are most effective against normal conjunctiva l flora, and fusidic acid the most ineffective of all the antibiotics tested.

How to cite this article:
Keshav BR, Basu S. Normal conjunctival flora and their antibiotic sensitivity in Omanis undergoing cataract surgery.Oman J Ophthalmol 2012;5:16-18

How to cite this URL:
Keshav BR, Basu S. Normal conjunctival flora and their antibiotic sensitivity in Omanis undergoing cataract surgery. Oman J Ophthalmol [serial online] 2012 [cited 2019 Aug 24 ];5:16-18
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Cataract surgery is one of the most frequently performed operations in the world, with approximately 1.5 million cases done in the United States annually. [1] In Oman, unoperated cataract was the cause of 35% of estimated blindness. [2] Endophthalmitis is one of the most dreaded complications of cataract surgery. It may result in permanent loss of vision if not recognized and treated properly.

Eye surgeons use several pre-and postoperative methods to prevent the occurrence of endophthalmitis, the most common of which is the administration of topical antibiotic drops at regular intervals. [3] Use of antibiotic prophylaxis pre-and postoperatively in reducing the risk of endophthalmitis remains controversial. There also are no standard guidelines on the type of antibiotic to be used in this setting. Bacteria are the most common cause of endophthalmitis. Knowing the organisms found most frequently in the ocular flora and their antibiotic sensitivity may provide a better guide in choosing an antibiotic for prophylaxis of postoperative endophthalmitis. The most common site of the organism that is known to cause endophthalmitis is the conjunctiva itself. [4] Several studies have shown coagulase-negative staphylococcus to be the most common organism causing endophthalmitis and also the most common organism isolated among the conjunctival flora. [5],[6]

Although there are many published articles [3],[4],[5] from Western countries pertaining to normal flora of the eye and their sensitivity pattern to antibiotics, these data cannot be applied directly to Omani patients, as several factors affect the type and sensitivity and resistance patterns of bacteria. Moreover, this kind of a study must be done regularly due to the dynamic nature of bacterial resistance to antibiotics. [5]

In Oman with a wide prevalence of trachoma in the past, resulting in alteration of ocular surface subtly in many individuals and markedly in some, the conjunctival flora may be different. And as is well-known going by the various studies, [3],[4],[5],[6],[7],[8] every region may have a different sensitivity pattern.

This study was undertaken to ascertain the normal conjflora in the region and its sensitivity pattern and change following preoperative prophylactic antibiotic use.

 Materials and Methods

A prospective study was conducted with patients who underwent cataract surgery between February and August 2010. Hundred and twelve eyes of 56 patients admitted for cataract surgery in Sur regional hospital, a secondary care center with state of the art laboratory facilities, were enrolled in this study. The fellow eye of these patients served as controls. Patients with ocular surface disease such as meibomitis, dry eye, and chronic dacryocystitis were excluded from the study. After obtaining consent, conjunctival swab was taken 1 day before cataract surgery from both eyes before applying any antibiotic or anesthetic drops. Specimen was taken from the inferior conjunctival fornix with sterilized loop without touching the eyelids. The sample was inoculated aseptically by "C"-shaped streaking onto blood agar medium at the bedside. The plates were then incubated at 37°C for 48 hours under standard aerobic conditions. [7] Any positive bacterial growth was further identified and susceptibility testing done according to Kirby-Bauers method using standard CLSI guidelines. [8] Conjunctival swab was taken from both eyes and processed similarly on the first postoperative day. Chloramphenicol eye drops four times a day were instilled into the eyes of patients undergoing surgery 1 day preoperatively, and iodine (50-50 dilution of 10% povidone iodine) wash preoperatively was performed. No medications were applied to the control eyes of these patients either preoperatively or postoperatively.

Data obtained were subjected to statistical analysis by applying confidence intervals (CIs) at 95% confidence limits. This study was evaluated and approved by the ethics review committee members of the Ministry of Health in South Sharqiya region


A total of 112 eyes of 56 patients from whom the conjunctival swabs were taken were analyzed. In this study, 19 (33.9%) were males and 37 (66.1%) were females. The age group was 40-80 years. No bacterial growth was seen 51.7% eyes preoperatively (95% CI: 41.75%-61.25%), while 48.3% (95% CI: 38.75%-57.25%) showed bacterial growth [Table 1]. This included both control and operated eyes. Of the 54 eyes showing bacterial growth, 81.5% (95% CI: 71.12%-81.84%) grew coagulase-negative staphylococcus, 4 eyes (7.4%) grew Streptococcus pneumoniae, and 2 (3.7%) eyes grew Staphyloccus viridans, Staphylococcus aureus, S. corynebacterium, S. proteus, and S. enterococci were grown in one eye (1.8%) each [Table 2]. When preoperative and postoperative cultures were analyzed and compared, it was found that 11 eyes (20.3%) were showing the same growth pre- and postoperatively, 44.4% (95% CI: 30.76%-57.24%) of eyes operated for cataract showed growth preoperatively and no growth postoperatively, and 33.3% (95% CI: 20.46%-45.54%) of the unoperated eyes with growth preoperatively showed no growth [Table 3]. As regards to susceptibility pattern in case of all isolates, the organisms showed high sensitivity to choramphenicol, 63% (95% CI: 50.125%-88%), gentamycin 74% (95% CI: 62.3%-85.7%), ciprofloxacin 72% (95% CI: 60.2%-83.98%), and vancomycin 83% (95% CI: 72.98%-93.02%) and high resistance to penicillin, ampicillin, fusidic acid, and oxacillin [Table 4]. As regards to the sensitivity pattern in case of coagulase-negative staphylococci, the organisms were most susceptible to vancomycin, 97.72% (95% CI: 91.96%-102.04%), gentamycin, 86.36% (95% CI: 75.75%-96.25%), and ciprofloxacin 84% (95% CI: 73.17%-94.83%) and moderately susceptible to chloramphenicol 68.1% (95% CI: 54.2%-81.78%), augmentin 52.27% (95% CI: 37.24%-66.76%), oxacillin 50% (95% CI: 35.23%-64.77%), and methicillin 61.36% (95% CI: 49.59%-75.41%) and least susceptible to fusidic acid (29.5%; [Table 5]). Thus, coagulase-negative staphylococci showed maximum sensitivity to vancomycin followed closely by gentamycin and maximum resistance to fusidic acid.{Table 1}{Table 2}{Table 3}{Table 4}{Table 5}


Postoperative endophthalmitis is the most dreaded complication of cataract surgery and conjunctival flora has been blamed to be the primary and most frequent source of bacteria. So evaluation of the conjunctival bacterial flora and their sensitivity pattern is of utmost importance. In our study, we were able to isolate bacteria in 54 eyes (48.3%). In a study by Reza et al., [5] the percentage isolation was found to be 52.4%. Another study by Terence et al. [6] showed the isolation was of the order of 80%. In both cases, the inoculation was in blood agar and in the latter case the lid margin samples were also taken which could be the reason for such a high positivity.

In our study, it is shown that 44% of eyes having growth preoperatively and treated with perioperative iodine and chloramphenicol preoperatively showed no growth postoperatively, and 33% of the control eyes showing growth preoperatively and not treated with iodine perioperatively showed no growth postoperatively. The negative growth postoperatively in control eyes is difficult to explain. More number of cases treated with iodine showed negative growth postoperatively. Although statistically nonsignificant (P=0.2342), there was a trend suggesting that the practice of perioperatively washing eyes with iodine is a step in the right direction. A larger study in this regard may throw light on its significance in a better way.

The most common organism isolated in our study was coagulase-negative staphylococcus (81.5%) which is in confirmation with most of the studies. [5],[6],[7],[8] In all these studies, the isolation was above 80% with respect to coagulase-negative staphylococcus, thus confirming that this bacteria is the most common isolate in conjunctival bacterial flora worldwide.

With regards to sensitivity patterns particularly in case of CNS, ciprofloxacin, gentamycin, vancomycin, and chloramphenicol were found to be most effective. In a study by Terence et al., [7] almost identical sensitivity patterns were noticed. With respect to the resistance pattern, the organism was least sensitive to fusidic acid. Terence et al. found maximum resistance to polymyxin B, but fusidic acid was not tested for in their study.

In conclusion, our study is the first of its kind in Oman showing nearly 50% positive growth with coagulase-positive staphylococci predominating, which was most sensitive to vancomycin followed by ciprofloxacin, gentamycin, and chloramphenicol. The other bacteria were shown to be isolated in insignificant numbers. Perioperative conjunctival irrigation with iodine is an effective way of reducing bacterial flora. This study may act as a guide to choosing antibiotics for preoperative prophylaxis or postoperative prophylaxis and treatment.


We wish to thank the doctors and paramedical staff of ophthalmology and microbiology departments of Sur Hospital. We also wish to thank Dr. Puneet Jain Head, Department of Pathology, for his cooperation. Last but not the least we are grateful to our executive director for his cooperation. Finally, we wish to state that the study would not have been possible without the help of the patients and relatives involved in the study.


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