The presence of unique signature bands in the three groups of isolates might give additional information on the factors essential for the development of infection. In silico analysis showed that most of the
S. epidermidis isolates from endophthalmitis had differential amplification of three genomic regions mapped to the
ebh,
tagD, and
ptsI genes in comparison with keratitis isolates
(Table 2) . Most of the keratitis isolates did not show amplification of these three genes, perhaps because of mutation. Genes such as
ebh (or
embp),
tagD, and
ptsI encode for extracellular matrix-binding protein homologue (a fibronectin binding protein), teichoic acid biosynthesis protein, and phospho-enol pyruvate phosphotransferase (involved in energy and signal transduction), respectively. These three molecules seem to have definite roles in human infections.
30 31 32 The recombinant embp or Ebh protein from both
S. epidermidis and
S. aureus has been found to bind human fibronectin specifically.
30 Ebh has been shown to be produced during human infection, as serum samples taken from patients with confirmed
S. aureus infections were found to contain anti-Ebh antibodies.
S. aureus Ebh has 57% protein similarity and 39% identity with that of
S. epidermidis Ebh. TagD is glycerol-3-phosphate cytidylyltransferase, a precursor protein involved in biosynthesis of teichoic acid in
S. aureus.
31 The penicillin-binding protein (
pbp4) gene that is responsible for intrinsic β-lactam resistance in
S. aureus is flanked downstream by the open reading frame
tagD.
32 It has been shown earlier that precise deletion of
tagD and controlled depletion of its product, leads to irregular morphology and lysis of
Bacillus subtilis growing at physiological temperature.
33 S. epidermidis TagD has 98% similarity and 95% identity to the
S. aureus TagD as well 88% similarity and 69% identity to the
B. subtilis TagD. One of the recent studies showed LD50 of the
S. aureus ptsI mutant for mice to be more than 10 times higher than the 50% lethal dose for the virulent parent strain, indicating that the mutation affects virulence.
34 S. epidermidis PtsI has 96% similarity and 89% identity to the
PtsI of
S. aureus and is very likely to have a similar role to enact. Keratitis isolates have modified
ebh,
tagD, and
ptsI genes
(Table 2)that may not have vital roles in the disease process, as their disease etiology is only superficial, whereas all of them appear to be essential in the endophthalmitis isolates.