|Year : 1994 | Volume
| Issue : 2 | Page : 71-74
Donor corneoscleral rim contamination by gentamicin-resistant organisms
Usha Gopinathan1, Vinay Agrawal2, Savitri Sharma1, Gullapalli N Rao3
1 Sri Devchand Nagardas Jhaveri Microbiology Centre, Hyderabad, India
2 Sight Savers' Cornea Training Centre, L.V. Prasad Eye Institute, Hyderabad 500 034, India
3 Sri Devchand Nagardas Jhaveri Microbiology Centre,& Sight Savers Cornea Training Centre, L.V. Prasad Eye Institute, Hyderabad 500 034, India
L.V. Prasad Eye Institute, Road No. 2, Banjara Hills, Hyderabad 500 034
Source of Support: None, Conflict of Interest: None
Gentamicin is the most widely used antibiotic in the decontamination of donor cornea for penetrating keratoplasty. However, the incidence of resistance to gentamicin is on the rise. Bacterial isolates from 178 donor corneal rims were studied for gentamicin sensitivity. The overall rate of gentamicin resistance was 63.4%. At 86.2% the Pseudomonas. species had the highest rate of resistance, followed by Streptococci at 84.6%. The high rate of gentamicin resistance encountered by us and others suggest that either addition of a second antibiotic to corneal storage media or replacement of gentamicin by an antibiotic with a broader spectrum of activity may help reduce the risk of endophthalmitis following penetrating keratoplasty
Keywords: Gentamicin resistance - Donor cornea - Bacteria - Endophthalmitis - Penetrating keratoplasty
|How to cite this article:|
Gopinathan U, Agrawal V, Sharma S, Rao GN. Donor corneoscleral rim contamination by gentamicin-resistant organisms. Indian J Ophthalmol 1994;42:71-4
Despite the advances made in corneal preservation with the introduction of new media allowing enhanced duration of corneal storage, the ideal environmental conditions for corneal storage and sterilisation are not well defined.
Bacterial endophthalmitis remains a serious and often a devastating complication of penetrating keratoplasty. The reported incidence of bacterial endophthalmitis after penetrating keratoplasty is 0.8%, [1 ] compared to 0.09% incidence reported after extracapsular cataract extraction.  Gram-positive bacteria, particularly Staphylococcus and Streptococcus species are the most common causative organisms, while gram-negative organisms occur less frequently.
Gentamicin is the only antibiotic contained in all commercially available corneal storage media.  Previous studies have shown the broad-spectrum bactericidal activity of gentamicin. .  In a study on cultures taken from 4,167 donor eyes, it was found that more than 90% of all bacterial isolates were sensitive to gentamicin alone. 
This study was conducted to ascertain whether the widespread use of gentamicin has in anyway altered the sensitivity pattern of the bacterial isolates and to assess the emerging trends in antibiotic resistance in media and moist chamber preserved corneas.
| Materials and methods|| |
The corneoscleral rims included in this study were obtained from moist chamber preserved donor globes or corneal storage media (Optisol or McCareyKaufman). Prior to keratoplasty the rims from donor globes were soaked in 0.3% gentamicin solution for one hour. The storage media with rims were left at room temperature (23°C) before usage. Following the removal of corneal buttons for keratoplasty, the rims were sent immediately to the laboratory in a dry sterile bottle where they were processed according to a standard protocol. Briefly, the rim was cut into five pieces using aseptic techniques and each piece was placed in a different medium. The media used, the duration and atmospheric condition of incubation are shown in [Table - 1]. Growth in any one or more media was considered as positive.
The organisms recovered were identified employing standard microbiological methods and all bacterial isolates were subjected to tests for antibiotic susceptibility using Kirby-Bauer disc diffusion method. Disc containing 10 ug of gentamicin (Hi-media, Bombay) were used on a standard bacterial suspension lawn made on Mueller-Hinton agar. Following 18 hours incubation at 35°C, an inhibitory zone of 12 mm or less was recorded as resistance to gentamicin.
| Results|| |
A total of 648 corneoscleral rims from donor corneal buttons were cultured from April 1991 to March 1993. Of the 648 rims, 311 (47.9%) were culture positive for microorganisms. The total number of isolates, however, were 414 as more than one organism was isolated from 72 (11.1%) rims.
Bacteria accounted for 242 (58.4%) of the 414 isolates and fungi were seen in 172 (41.5%) isolates. Among the bacteria, 72.3% were gram-positive and 27.7% were gram-negative. Coagulase-negative staphylococci at 127 (52.4%) isolates were the most common bacteria isolated. Next in frequency were Pseudomonas aeruginosa (26, 10.7%) and Acinetobacter calcoaceticus (24, 9.9%), respectively [Table - 2].
Sensitivity to gentamicin was assessed in 178 of the culture-positive rims. The analysis is shown in [Table - 3]. Resistance to gentamicin was seen in 113 (63.4%) of the 178 isolates. Amongst gram-positive organisms, the incidence of resistance was 53.8%. Gram-negative organisms" showed resistance to gentamicin in 81.9% of the isolates. The individual species of bacteria showed a varying frequency of occurrence of resistance. Pseudomonas species at 86.2% of the isolates showing resistance to gentamicin had the highest incidence. Streptococcus species at 84.6% and Acinetobacter calcoaceticus at 81.8% also showed a high incidence of gentamicin resistance. Staphylococcus epidermidis, the commonest bacterial isolate showed gentamicin resistance in 50% cases and Staphylococcus aureus had a 57% rate of resistance.
| Discussion|| |
Gentamicin is the most frequently used antibiotic in all commercially available corneal storage media today, as it has been proven to be effective against a wide variety of bacteria. It is also used extensively in decontamination of donor globes. Various methods have been tried to minimize bacterial contamination of donor cornea. Irrigation of harvested corneas using either neomycin and polymyxin B solution sub or povidone-iodine  has, been shown to markedly decrease the incidence and extent of colonization. Fong et a1  have shown that the use of gentamicin 100 gg/ ml in preservation media reduced the incidence of their donor contamination from 43% in whole globe storage to 14% in M-K and K-Sol stored corneas.
Resistance to gentamicin among ocular pathogens is reported to be on the increase.  A comparison of gentamicin resistance in common bacterial contaminants from donor rims in some studies is shown in the Figure. The overall incidence of gentamicin-resistant organisms in our study was 63.4%. This is similar to the range of 49 to 70% reported previously. ,,
The incidence of gentamicin resistance for grampositive and gram-negative organisms in our study was 53.8% and 81.9%, respectively. In the grampositive group, Streptococci demonstrated a resistance in 84.6% of isolates. This serves to emphasize the poor activity of gentamicin against Streptococcus species.  A variation from the past studies is the increased incidence of Pseudomonas species (16.2%) and its high rate of gentamicin resistance (86.2%). In most of the earlier studies ,,[13 ]Pseudomonas species does not figure in the list of donor rim contaminants.
Baer et all  have demonstrated that warming the globe for an hour before intended surgery may not eliminate even sensitive organisms from the donor tissue. Longer periods of preoperative warming may more effectively eradicate bacteria, but their effect on donor corneal tissue is unknown and needs further study.
The relationship of bacteria cultured from corneal storage media or donor cornea and development of postoperative endophthalmitis is not conclusively established.  Several studies on donor corneal contamination reveal no postoperative infections ,, Leville et al  have, however, reported a 22-fold increased risk of endophthalmitis among recipients of contaminated donor corneas compared to those receiving culture-negative tissue (1.3% vs 0.06%). Kloess et a1  have shown that donor rim cultures were positive in 31(56%) of 55 cases (13 cases with unknown culture status included) of post-penetrating keratoplasty endophthalmitis reviewed by them and that in 30 of these 31 culture-positive donor rims the same organism was isolated from the endophthalmitis and corneal rim cultures. They also reported that in 13 of the 31 cases (32%), the causative bacteria were resistant to gentamicin.
It is apparent from the data that the frequency of contaminated donor tissue relative to that of the incidence of endophthalmitis is much higher. Possibly, most of the bacteria and fungi are eliminated by either one or a combination of the following: action of residual antibiotics from the preservation media;  rinsing of the donor cornea before grafting,  antibiotics given to the recipient postoperatively, , or the host immune response.
In view of the above facts and the definite increase in the incidence of gentamicin resistance documented, we believe that the incidence of endophthalmitis following penetrating keratoplasty can be reduced further by the following measures:
Use of povidone-iodine in the decontamination of donor globes. 
Addition of other antibiotics or using those with a broader spectrum of activity in the corneal storage media.
Routine culture of donor rims in all patients as this may provide a guide to early therapy in case of occurrence of infection.
Increased frequency of initial follow-up visits in patients whose donor corneal rim cultures isolate potentially virulent organisms.
Use of antibiotics other than gentamicin during the initial period following penetrating keratoplasty.
| Acknowledgement|| |
This study was funded by the Hyderabad Eye Research Foundation, Hyderabad.
| References|| |
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Yab CW, Busin M, Avni I, et al. Antibacterial effect of donor cornea stored in gentamicin-enriched Mc.CareyKaufman medium. Arch Ophthalmol. 104:263-267, 1986.
[Figure - 1]
[Table - 1], [Table - 2], [Table - 3]
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