High-resolution genome profiling differentiated Staphylococcus epidermidis isolated from patients with ocular infections and normal individuals

Aparna Duggirala, Prashanth Kenchappa, Savitri Sharma, Justine K Peeters, Niyaz Ahmed, Prashant Garg, Taraprasad Das, Seyed E Hasnain
Investigative Ophthalmology & Visual Science 2007, 48 (7): 3239-45

PURPOSE: To investigate the potential phenotypic and genetic differences among the Staphylococcus epidermidis isolates obtained from control subjects (lower conjunctival sac; n = 14) with those from patients with keratitis (corneal scrapings; n = 18) or endophthalmitis (vitreous; n = 24).

METHODS: Biofilm-forming capacity was detected by PCR for the icaAB gene and phenotyping by microtiter plate assay and congo red agar plate. Genotyping was performed by using fluorescence-amplified fragment length polymorphism (FAFLP) and in silico analysis of the FAFLP profiles.

RESULTS: Biofilm phenotyping (congo red agar/microtiter plate) differentiated disease-causing strains from control subjects. PCR assays (mecA, icaAB) were not useful in differentiating disease-causing strains from that of control subjects. The biofilm-forming capability appeared more critical in the pathogenesis of keratitis than in that of endophthalmitis. Cluster analysis of FAFLP data generated 11 clusters comprising 4 major clusters (I, II, III, and V) and 7 minor ones. FAFLP analysis clearly showed clustering of most of the commensal isolates in cluster I, separate from keratitis and endophthalmitis isolates. In silico analysis mapped signature bands to genes such as ebh, tagD, ptsI, and sepA, which might have a significant role in transforming less virulent populations of S. epidermidis to more virulent ones.

CONCLUSIONS: The population dynamics of S. epidermidis revealed that there are significant genetic variations that can be detected through FAFLP between ocular disease causing isolates and the commensal population.

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