Authors: Ritesh Gupta, Gayathri Sivakumar, Rookaya Mather
Author Disclosure Block: R. Gupta: None. G. Sivakumar: None. R. Mather: None.

Abstract Body:

Purpose: To determine the profile of bacterial isolates from submitted ocular cultures in London, Ontario and evaluate their susceptibility to common antibiotic agents.
Study Design: A retrospective quality improvement analysis of all ocular culture specimens was performed using the electronic database hosted by the London Health Sciences Microbiology Lab in London, Ontario between 1999 to 2017.
Methods: Data was analyzed to determine most common bacterial specimens in submitted conjunctival, corneal, and vitreous fluid cultures. Antimicrobial susceptibility data was extracted only between 1999 to 2011 due to data availability.
Results: A total sample of 3,367 isolates were included from ocular cultures analyzed in the LHSC electronic database. In these specimens, there were 2,760 conjunctival, 390 corneal, and 217 vitreous fluid cultures with bacterial isolates. The leading bacterial pathogens associated with conjunctivitis in the geographic region of London, ON were Coagulase negative staphylococcus (CoNS; n=778, 28.2%), Staphylococcus aureus (n=552, 20.0%), Haemophilus species (n=292, 10.6%), and Streptococcus pneumoniae (n=147, 5.3%). Conjunctival isolates positive for Staphylococcus aureus and CoNS demonstrated 76% and 100% susceptibility to ciprofloxacin, respectively. CoNS (n=119, 30.5%), Staphylococcus aureus (n=49, 12.6%), Pseudomonas aureus (n=25, 6.4%), and Streptococcus species (n=29, 7.4%), were among the most prevalent pathogens associated with keratitis. Isolates from contact lens-wearers in ocular infections included Gram-negative pathogens such as Enterobacter, Klebsiella, Serratia, and Pseudomonas species. Gram-positive bacteria were predominant in endophthalmitis consisting of CoNS (n=88, 40.6%), Streptococcus species (n=15, 6.9%), and Staphylococcus aureus (n=10, 4.6%). Gram-positive organisms in keratitis and endophthalmitis culture specimens demonstrated 100% susceptibility to vancomycin. Cefazolin showed an antimicrobial efficacy of 86%, while gentamicin showed an efficacy of 90% for gram-negative endophthalmitis specimens.
Conclusions: Gram-positive cocci appear to be the most common cause of ocular infections in London, ON. Susceptibility data suggests that most gram-positive ocular pathogens showed in vitro susceptibility to ciprofloxacin and vancomycin. Currently, fourth-generation fluoroquinolones are not routinely tested for susceptibility at our centre. Gram-negative species should be borne in mind for keratitis, especially in the setting of contact-lens wear. Gram-positive bacteria are most commonly isolated from vitreous samples. Intravitreal vancomycin and ceftazidime is the current standard for empiric regimen in the treatment of endophthalmitis at our centre. While gentamicin demonstrated excellent efficacy against gram-negative species in the setting of endophthalmitis, there are concerns for possible retinal toxicity due to a narrow therapeutic range.