Adherence of ocular isolates of staphylococcus epidermidis to ACRYSOF intraocular lenses. A scanning electron microscopy and molecular biology study.
OBJECTIVE
To investigate the adherence of two clinically relevant ocular isolates of Staphylococcus epidermidis to ACRYSOF intraocular lenses (IOLs) (Alcon Surgical, Fort Worth, Texas) and to determine whether the strains under study carried the intercellular adhesion (ica) locus, which encodes production of S. epidermidis antigens mediating adherence to biomaterials.


METHODS
Experimental study.


METHODS
The authors examined the in vitro adherence of two clinically relevant ocular isolates of S. epidermidis (S. epidermidis 1 and S. epidermidis 2). Adherence was tested on six ACRYSOF IOLs.


METHODS
Three IOLs were placed in three separate test tubes containing 5 ml of S. epidermidis 1 suspension, and three other IOLs were placed in three test tubes containing 5 ml of S. epidermidis 2 suspension. At different times (3, 30, and 90 minutes), the IOLs were removed from the test tubes and rinsed in sterile phosphate buffered solution. The lenses were then fixed in glutaraldehyde, postfixed in osmium tetroxide, and serially dehydrated in ethyl alcohol. After critical point drying, they were sputter-coated with gold and then examined with a scanning electron microscope. In addition, polymerase chain reaction amplification was used to investigate whether the isolates under study carried the ica locus.


METHODS
The number of adhered bacteria per area (square millimeters) of IOL optic was calculated. Statistical analysis included calculation of arithmetic means and 95% confidence intervals (t test). Polymerase chain reaction amplification products were visualized in ethidium bromide-stained agarose gel.


RESULTS
Direct counting of adherent bacteria in scanning electron microscopy photographs revealed that the total amount of adhered bacteria per area of IOL optic after 3, 30, and 90 minutes of incubation in bacterial suspension was 1306/mm(2), 3389/mm(2), and 7195/mm(2) (S. epidermidis 1) and 778/mm(2), 1056/mm(2), and 3861/mm(2) (S. epidermidis 2). Differences at 30 and 90 minutes were statistically significant (P: = 0.01 and 0.02, respectively). Polymerase chain reaction amplification revealed that S. epidermidis 1 contained the ica locus, whereas S. epidermidis 2 was ica negative.


CONCLUSIONS
Different ocular isolates of S. epidermidis may differ significantly with regard to adherence to ACRYSOF IOLs. Adherence appeared to be greater when the bacterial DNA contained the ica locus. Strains of S. epidermidis carrying the ica locus may play an important role in the pathogenesis of some forms of endophthalmitis occurring after cataract surgery.
Pinna
A
A
Institute of Ophthalmology, University of Sassari, Sassari, Italy.
Sechi
L A
LA
Zanetti
S
S
Delogu
D
D
Carta
F
F
D000179:Acrylates; D001422:Bacterial Adhesion; D015169:Colony Count, Microbial; D017931:DNA Primers / Q000737:chemistry; D004269:DNA, Bacterial / Q000032:analysis; D004587:Electrophoresis, Agar Gel; D015818:Eye Infections, Bacterial / Q000382:microbiology; D005784:Gene Amplification; D007910:Lenses, Intraocular / Q000382:microbiology*; D008855:Microscopy, Electron, Scanning; D016133:Polymerase Chain Reaction; D013212:Staphylococcus epidermidis / Q000302:isolation & purification / Q000502:physiology* / Q000648:ultrastructure
D000179:Acrylates; D017931:DNA Primers; D004269:DNA, Bacterial; C036658:acrylic acid