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PCR versus culture isolation: what is better for detecting acanthamoeba from keratitis samples?

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Session Details

Session Title: Inflammation in Ocular Infections

Session Date/Time: Wednesday 17/09/2014 | 08:00-09:30

Paper Time: 08:36

Venue: Capital Hall A

First Author: : R.Kowalski USA

Co Author(s): :    M. Melan   L. Karenchak   L. Raju        

Abstract Details


Acanthamoeba keratitis is a severe eye infection that must be definitively diagnosed for appropriate therapy. The diagnosis of acanthamoeba keratitis is commonly ascertained with a combination of clinical presentation, isolation in culture, observation on stained material, and confocal microscopy. Our institution has validated polymerase chain reaction (PCR) to detect acanthamoeba DNA from keratitis samples to complement testing.


On-going diagnostic study from specialized ophthalmic microbiology laboratory.


The laboratory records of patients with a differential of acanthamoeba keratitis were reviewed (May 2012 to January 2014), without recording patient identifiers, for 1) acanthamoeba culture isolation and 2) acanthamoeba DNA detection by PCR. For acanthamoeba isolation, corneal samples were planted on non-nutrient agar (Noble Agar) overlaid with Enterobacter aerogenes and monitored for growth over 7 days. Validated PCR (May 2012) for acanthamoeba DNA was processed at the Division of Molecular Diagnostics, UPMC, Pittsburgh, PA, USA.


Culture isolation and PCR were processed on 114 patients with a differential diagnosis of acanthamoeba keratitis. Of these, 95 (83.3%) were (culture-neg, PCR-neg); 12 (10.5%) were (culture-pos, PCR-pos); 4 (3.5%) were (culture-neg, PCR-pos); and, 3 (2.6%) were (culture-pos, PCR-neg). Culture and PCR were statistically equivalent for detecting acanthamoeba from corneal samples (p=1.0, McNemar’s). Seventeen (17.9%) of the (culture-neg, PCR-neg) corneal samples were positive for other pathogens (5 Pseudomonas aeruginosa, 2 Aspergillus species, 2 Klebsiella pneumoniae, and one each of MRSA, MSSA, Moraxella lacunata, Alcaligenes xylosoxidans, Nocardia species, Fusarium species, Candida albicans, and HSV).


The present study indicated no statistical difference of PCR over culture isolation for acanthamoeba detection. Our laboratory data suggests that although acanthamoeba may be the primary suspect in specific cases of severe persistent keratitis, other pathogens such as bacteria, fungus, and virus must still be considered as part of the differential diagnosis. Our plan is to continue to use PCR as part of a complementary test for the support of acanthamoeba keratitis.

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