Background:

Staphylococcus epidermidis is one of the prominent pathogens in ocular infection. The prevalence of mutations in the quinolone resistance determining region (QRDR) area in S epidermidis isolated from the ocular surface and its association with fluoroquinolone resistance has not been fully elucidated.

Methods:

Mutations in the QRDR of gyrA, gyrB, parC, and parE genes of 138 isolates of S epidermidis recovered from the human conjunctival flora were analysed. The minimal inhibitory concentrations (MICs) of four fluoroquinolones (levofloxacin, gatifloxacin, moxifloxacin and tosufloxacin) against these isolates were also determined using agar dilution methods.

Results:

The MIC90 values of levofloxacin, gatifloxacin, moxifloxacin and tosufloxacin were 3.13, 1.56, 0.78 and 3.13 μg/ml, respectively. The MIC values of all fluoroquinolones showed a bimodal distribution (susceptible strain and less susceptible strain). Mutations with amino acid substitution in the QRDR were present in 70 (50.7%) isolates. 19 different combinations of mutations were detected: 3 isolates (2.2%) had four mutations, 8 (5.8%) had three mutations, 43 (31.2%) had double mutations and 16 (11.6%) had single mutations. Isolates with mutations in the QRDR of both gyrA and parC (n = 53) were less susceptible to fluoroquinolones.

Conclusions:

The present findings show that approximately half the S epidermidis isolates from the normal human conjunctiva have mutation(s) in the QRDR. The presence of mutations in both gyrA and parC is strongly associated with reduced susceptibility to fluoroquinolones.

Aim:

This study was performed to independently assess the turnover rates of aqueous and lipid layers of the tear film.

Methods:

Two fluorescent dyes, fluorescein sodium and 5-dodecanoylaminofluorescein (DAF), which is a free-fatty-acid conjugate of fluorescein, were applied to the right eye of 12 healthy volunteers. Fluorescent intensity of the precorneal tear film was measured at the central cornea every minute for 10 min for fluorescein sodium, and every 5 min for 50 min for DAF. The turnover rate was calculated by plotting fluorescent intensity against time in a semilog plot and expressed as %/min.

Results:

Turnover rates of fluorescein sodium and DAF were 10.3 (SD 3.7)%/min and 0.93 (0.36)%/min, respectively. The turnover rate of DAF was significantly lower than that of fluorescein sodium (p<0.05, Mann–Whitney test). The turnover rate of DAF positively correlated with that of fluorescein sodium (r = 0.93, p<0.05).

Conclusion:

Our results indicate that the turnover of lipids in tears is much slower than the aqueous flow of tears, and that this lipid turnover is associated with the aqueous flow of tears in healthy adults.