Slime production as a virulence factor in Staphylococcus epidermidis isolated from bacterial keratitis

A total of 126 coagulase negative staphylococci (CONS) isolated from corneal scrapings of patients of bacterial keratitis and 50 isolates from healthy eyes (controls) were tested for slime production. Eighty eight (69.84%) of 126 isolates from patients and 11 (22%) of 50 isolates from controls were slime producing (P < 0.001). Of these 88 isolates, 42 were Staphylococcus epidermidis biotype II, 30 were S. epidermidis biotype I, 8 were S. epidermidis biotype III and the rest belonged to CONS other than S. epidermidis. Amongst the corneal ulcer isolates, multidrug resistance (resistance to 3 or more antibiotics) was observed in 82.9 per cent (73/88) slime producing organisms as against only 18.4 per cent (7/38) nonslime producing organisms (P < 0.001). Similarly, of the total 99 slime positive and 77 slime negative isolates, 79 (79.8%) and 22 (28.6%) respectively were multidrug resistant (P < 0.001). Although, slime production is known to be one of the major virulence factors of CONS in extraocular systemic staphylococcal infections, the present study detected slime in isolates from ocular infections. It was found that S. epidermidis I and II were the common biotypes associated with bacterial keratitis and, slime production and multidrug resistance were the two important virulence factors. These observations have clinical and therapeutic significance.