Phenotypic and plasmid pattern analysis of Staphylococcus epidermidis in bacterial keratitis.
BACKGROUND
Staphylococcus epidermidis, a commensal of the conjunctival sac has been incriminated as the commonest etiological agent of bacterial keratitis. However, the pathogenic potential of this commensal organism is not clearly known.


OBJECTIVE
To determine any phenotypic, molecular markers of S. epidermidis pathogenicity in bacterial keratitis.


METHODS
A total of 382 corneal ulcer isolates of S. epidermidis and 87 S. epidermidis isolates from healthy eyes (controls) were studied. Speciation, biotyping and antibiotic sensitivity testing were performed by conventional methods. Tube slime and adherence tests were carried out by recommended techniques. Plasmid analysis was conducted by a standard protocol.


METHODS
Chi-square test was employed for calculations.


RESULTS
Out of 382 corneal ulcer isolates (Pathogens) 284 (74.3%) belonged to biotypes I and II. Slime was detected in 164 (42.9%) of 382 pathogens vs. 21 (24.1%) of 87 controls (P<0.001). Sixty-five (39.6%) of 164 slime positive isolates were multidrug-resistant as compared to only 49 (22.4%) of 218 slime negative isolates (P<0.001). A significantly higher number i.e, 73.1% (120/164) of slime-producers possessed a 21 Kb plasmid in contrast to only 53.2% (116/218) of nonslime-producers (P<0.001). Presence of this plasmid had a statistical correlation of low significance with multidrug resistance (P=0.04). One hundred and seventy-two (45.0%) of 382 pathogens and 24 (27.6%) of the 87 controls were adherent to artificial surfaces (P=0.003) and the majority of the adherent organisms (99/172, 57.6%) were slime producers (P<0.001).


CONCLUSIONS
Slime was associated with multidrug resistance in corneal ulcer isolates of S. epidermidis. The 21 Kb plasmid could determine virulence as it was responsible for slime production and adherence.
Nayak
Niranjan
N
Department of Microbiology and Cornea Services, Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India. niruni2000@yahoo.com
Satpathy
Gita
G
Vajpayee
Rasik B
RB
Mrudula
Srikantam
S
D003320:Corneal Ulcer / Q000382:microbiology; D024901:Drug Resistance, Multiple, Bacterial; D006801:Humans; D007634:Keratitis / Q000382:microbiology*; D010641:Phenotype; D010957:Plasmids; D013203:Staphylococcal Infections / Q000382:microbiology*; D013212:Staphylococcus epidermidis / Q000235:genetics* / Q000472:pathogenicity* / Q000502:physiology