Bacteriological findings in patients with ocular infection and antibiotic susceptibility patterns of isolated pathogens

Khosravi AD, Mehdinejad M, Heidari M
Correspondence: Dr Azar Khosravi, khosraviaz@yahoo.com

ABSTRACT
Introduction Isolation of common pathogens involved in ocular infection, and their in-vitro susceptibility to commonly-used ocular antibiotics, as well as the trends in antibiotic resistance developed by these pathogens, were investigated.
Methods Corneal scrapings were obtained from 318 hospitalised patients and inoculated directly onto enriched and differential culture media. Subcultures were performed on selective media. The necessary biochemical tests were conducted and the organisms identified using standard procedures. Susceptibility of isolated pathogens to commonly-used ocular antibiotics was examined using standard susceptibility testing.
Results 70 different organisms were isolated. Gram-positive cocci accounted for 47 (67.2 percent) and gram-negative bacilli for 23 (32.8 percent) bacterial isolates. Coagulase-negative Staphylococci (33 percent) and Pseudomonas species (24 percent) were the most commonly-isolated organisms. In susceptibility testing, Gentamycin had coverage against 35 (74.5 percent) of 47 gram-positive cocci and 19 (82.6 percent) of 23 gram-negative bacilli tested. The coverage of Tetracycline, Cephalotin and Ceftriaxon against gram-positive cocci were 61.7, 55 and 53 percent, respectively. All the tested gram-positive cocci showed resistance to Cefotaxime and Penicillin. Ceftriaxon and Tobramycin had coverage against 17 (73.9 percent) and 14 (60.8 percent) of 23 gram-negative bacilli isolates, respectively. The coverage of Vancomycin against coagulase-negative Staphylococci was 100%, but all the isolates of Staphylococcus aureus were resistant to Vancomycin.
Conclusion Susceptibility analysis revealed that antibiotic with the greatest coverage was Gentamycin (77.1 percent of 54 isolates). Gentamycin also had good coverage against gram-positive cocci, which constituted the majority (67.1 percent) of ocular isolates.

Keywords: antibiotic susceptibility, bacteria, ocular infection, susceptibility patterns
Singapore Med J 2007; 48(8): 741–743