Laboratory diagnosis of Acanthamoeba keratitis using buffered charcoal-yeast extract agar

To evaluate the use of buffered charcoal-yeast extract agar for the isolation of Acanthamoeba from clinical specimens.

We retrospectively reviewed laboratory records of patients with ocular acanthamebic infection from October 1993 to September 1997 to compare the recovery of Acanthamoeba from clinical specimens inoculated onto various media. We then compared the experimental recovery of 10 corneal isolates of Acanthamoeba on buffered charcoal-yeast extract and blood agars.

Paired data for buffered charcoal-yeast extract and blood agars were available from 24 cultures performed in 13 cases of ocular acanthamebic infection. Acanthamebic trails were detected on both buffered charcoal-yeast extract and blood agars in nine cultures, only on buffered charcoal-yeast extract agar in nine cultures, and only on blood agar in one culture (P = .027). In the experimental study, all 10 clinical isolates produced trails on buffered charcoal-yeast extract agar, and the mean recovery after 10 days of incubation ranged from 38% to 95% of the original inoculum number. For seven of the 10 isolates, more than 70% of the original inoculum was recovered on buffered charcoal-yeast extract agar. Only two of the 10 strains produced persistent trails on the blood agar, and the mean recoveries after 10 days of incubation were 0.67% and 1.17%. Recovery was significantly better on buffered charcoal-yeast extract agar than blood agar (P < or = .0003).

Buffered charcoal-yeast extract agar is an excellent commercially available culture medium for the recovery of Acanthamoeba.