a Medical Service Department, Square Pharmaceuticals Ltd, Dhaka b Department of Microbiology, National Diagnostic Network, Diabetic Association of Bangladesh,Dhaka c Department of Ophthalmology, Dhaka Medical College Hospital, Dhaka, Bangladesh
Sir,
The present study was undertaken to evaluate the in-vitro activities of commonly usedophthalmic antibiotic preparations against external ocular pathogens.
The patients were residents of Dhaka City with clinical diagnoses of acute bacterialconjunctivitis
who had not received systemic or intra-ocular antibiotics in the preceding 4weeks. The diagnosis
was based on the presence of conjunctival hyperaemia and one or both of apurulent exudate or
crusting on the eyelids. Conjunctival swabs were processed at a centrallaboratory according to
standard laboratory techniques and the isolates obtained afterovernight culture were identified by
standard procedures. Isolates were regarded as pathogensif they met one of the following criteria:
Gram-negative bacillus; ß-haemolytic streptococcus; Streptococcus pneumoniae;
10 colonies of an
-haemolytic streptococcus or Staphylococcus aureus; or
100 colonies of a coagulase-negative staphylococcus (CoNS).
1
The susceptibilities of the isolates were determined by the disc diffusion method accordingto recommendations of the National Committee for Clinical Laboratory Standards (NCCLS). 2 The medium used was MuellerHinton agar, supplemented with 5% sheep blood forstreptococci, or chocolate agar for Haemophilus spp. The following antibiotics were tested: tetracycline (30 µg), chloramphenicol (30 µg), gentamicin (10 µg), trimethoprim/ sulphamethoxazole (25 µg), penicillin (10 µg), erythromycin (15 µg), ciprofloxacin (30 µg), lomefloxacin (30 µg), bacitracin (10 µg), tobramycin (10 µg) and neomycin (30 µg). All of the discs were obtained from Oxoid, Unimed Co. Ltd (UK) and the isolates werecategorized as susceptible or resistant according to inhibition zone diameter breakpointsrecommended by the NCCLS. 2
Ninety-eight presumed pathogens were recovered. S. aureus was the most common isolate (accounting for 62% of the pathogens), followed by CoNS (24%), although the roles of these organisms as causes of acute conjunctivitis are controversial. The susceptibilities of the isolates are summarized in the Table. The ranking of the antibiotics interms of percentage susceptible strains (in descending order) was as follows: bacitracin; gentamicin; ciprofloxacin; tobramycin; lomefloxacin; chloramphenicol; trimethoprim/sulphamethoxazole; neomycin; tetracycline; erythromycin; and penicillin. While chloramphenicol is the most commonly used ophthalmic antibiotic in Bangladesh, followed by ciprofloxacin and gentamicin (S. Hossain, personal communication), it was active against fewer isolates than the latter two drugs. Ciprofloxacin was active against a marginally higherpercentage of isolates than lomefloxacin and, of the aminoglycosides tested, gentamicin was active against the highest percentage of strains.
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Acknowledgments
We are grateful to the Diabetic Association of Bangladesh for providing financial support for this study. We would also like to thank Mr Shazeed Hossain of Square Pharmaceuticals Ltd, Dhaka,for providing the unpublished data referred to in this article.
Notes
* Correspondence address. Medical Service Department, Square Pharmaceuticals Ltd, Square
Center, 48 Mohakhali CA, Dhaka 1212, Bangladesh. Tel: +880-2-887729; Fax:
+880-2-888608/9; E-mail: square{at}bangla.net
References
1 . Jacobsen, J. A., Call, N. B., Kasworm, E. M., Dirks, M. S. & Turner, R. B. (1988). Safetyand efficacy of topical norfloxacin versus tobramycin in the treatment of external ocularinfections. Antimicrobial Agents and Chemotherapy 32, 18204.[ISI][Medline]
2 . National Committee for Clinical Laboratory Standards. (1993). Performance Standards for Antimicrobial Disc Susceptibility TestsFifth Edition:Approved Standard M2-A5. NCCLS, Villanova, PA.
3 . Woodland, R. M., Darougar, S., Thaker, U., Cornell, L., Siddique, M., Wania, J. et al. (1992). Causes of conjuctivitis and keratoconjuctivitis in Karachi, Pakistan. Transactions of the Royal Society of Tropical Medicine and Hygiene83 , 31720.