Role of Liquid Culture Media in the Laboratory Diagnosis of Microbial Keratitis

Abstract

To determine whether liquid culture media are helpful in the diagnosis of infectious keratitis. Retrospective noncomparative case series. This is a retrospective review of microbiology records of 114 corneal scraping samples from infectious keratitis patients. Samples were processed by corneal smear microscopy (potassium hydroxide with calcofluor white and Gram stains) and culture examination (5% sheep blood agar, sheep blood chocolate agar, Sabouraud dextrose agar, brain heart infusion, thioglycolate broth, and Robertson's cooked meat broth. Cases where at least 1 liquid medium was taken were included in the study and all cases were required to have significant growth in culture as per the institutional criteria. Results of smear examination and culture growth were analyzed. Out of 114 cases, 44 (38.59%) were bacterial, 62 (54.38%) fungal, and 8 (7.01%) were mixed (bacteria+ fungus) infection. Thirty-eight out of 44 cases of bacterial keratitis (86.36%) were diagnosed by solid media alone (criterion 1) and 6 of 44 (13.63%) required liquid media for diagnosis (P < .001). In fungal keratitis, 61 of 62 cases (98.38%) were diagnosed using solid media alone (criterion 1) while 1 case required liquid media for diagnosis. In mixed infection, none of the cases required liquid media for diagnosis of fungal component; however, all 8 cases required liquid media for establishing bacterial component. Liquid culture media increase the chance of isolation of bacteria in pure bacterial and/or mixed infection; however, their role in isolating fungus is limited. Owing to overlap in clinical diagnosis of bacterial and fungal keratitis, we recommend inclusion of both solid and liquid culture media in the laboratory diagnosis of nonviral keratitis.