Abstract
Staphylococcus epidermidis is a common commensal of healthy conjunctiva and it can cause endophthalmitis, however its presence in conjunctivitis, keratitis and blepharitis is unknown. Molecular genotyping of S. epidermidis from healthy conjunctiva could provide information about the origin of the strains that infect the eye. In this paper two collections of S. epidermidis were used: one from ocular infection (n = 62), and another from healthy conjunctiva (n = 45). All isolates were genotyped by pulsed field gel electrophoresis (PFGE), multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec), detection of the genes icaA, icaD, IS256 and polymorphism type of agr locus. The phenotypic data included biofilm production and antibiotic resistance. The results displayed 61 PFGE types from 107 isolates and they were highly discriminatory. MLST analysis generated a total of 25 STs, of which 11 STs were distributed among the ocular infection isolates and lineage ST2 was the most frequent (48.4%), while 14 STs were present in the healthy conjunctiva isolates and lineage ST5 was the most abundant (24.4%). By means of a principal coordinates analysis (PCoA) and a discriminant analysis (DA) it was found that ocular infection isolates had as discriminant markers agr III or agr II, SCCmec V or SCCmec I, mecA gene, resistance to tobramycin, positive biofilm, and IS256+. In contrast to the healthy conjunctiva isolates, the discriminating markers were agr I, and resistance to chloramphenicol, ciprofloxacin, gatifloxacin and oxacillin. The discriminant biomarkers of ocular infection were examined in healthy conjunctiva isolates, and it was found that 3 healthy conjunctiva isolates [two with ST2 and another with ST9] (3/45, 6.66%) had similar genotypic and phenotypic characteristics to ocular infection isolates, therefore a small population from healthy conjunctiva could cause an ocular infection. These data suggest that the healthy conjunctiva isolates do not, in almost all cases, infect the eye due to their large genotypic and phenotypic difference with the ocular infection isolates.
Highlights
Staphylococcus epidermidis is a common inhabitant of the skin and mucous membranes, in recent decades it has gained interest due to its high frequency of isolation in hospital acquired infections [1]
The molecular genotyping of S. epidermidis isolates by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) type assignment [5] and the whole genome sequencing [6] have exhibited a high diversity; which makes difficult to discriminate between opportunistic pathogenic strains of Staphylococcus epidermidis from the commensal strains
Healthy conjunctiva isolates had more genetic diversity than the ocular infection isolates, 31 PFGE types was presented in healthy conjunctiva isolates, 19 PFGE types in ocular infection, and only 11 PFGE types were shared between both sources of isolation (Table 1)
Summary
Staphylococcus epidermidis is a common inhabitant of the skin and mucous membranes, in recent decades it has gained interest due to its high frequency of isolation in hospital acquired infections [1]. S. epidermidis can cause infection and the most common examples include conjunctivitis, blepharitis, corneal ulcers and endophthalmitis. The main cause of ocular infection is the use of contact lenses (in the case of conjunctivitis and corneal ulcer) [7] or during ocular surgery (endophthalmitis). High incidences of ocular infection by S. epidermidis have been reported [8], even in some cases superior than those achieved by S. aureus [9]. The eye is an organ continuously exposed to the environment, and it is in contact with various microorganisms Despite this high exposure, the hazard of ocular infection during a person’ life is low. One possible explanation against bacterial infection in the eye is the production of molecules associated to innate immunity; such as lysozyme, lactotransferrin, secretoglobin family 2A [10], antimicrobial peptides [11], cytokine modulators [12] and TLRs [13], which help to remove the bacteria on the ocular surface
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