Lipase production by ocular bacteria

Abstract

Purpose: Our previous study found that higher density of commensal bacteria on the eyelid is associated with clinical measures of decreased meibum quality and function. Changes in commensal bacterial profiles can result in altered expression of bacterial products such as lipases. Bacterial lipases might alter tear lipid spectrum and cause the increase of free fatty acids that are irritants to eyelid epithelia and may induce inflammation and hyperkeratinisation of meibomian orifice, contributing to development of blepharitis or meibomian gland dysfunction. The aim of the current study was to determine the levels of lipase production by various species of ocular bacteria.

Methods: Forty-eight isolates of most commonly isolated ocular commensal species Staphylococcus epidermidis (20 isolates), Propionibacterium acnes (8 isolates), and Staphylococcus aureus (20 isolates) were examined. Each test strain was cultured in 10 mL Tryptic Soy Broth at 37 ^oC for S. epidermidis and S. aureus, or in an anaerobic jar for P. acnes. After 24 h incubation, optical density of each culture was measured, and culture supernatants collected. Lipase activity in culture supernatant was determined by using a commercial lipase assay kit or tributyrin assay. Lipase activity for each test strain was normalized against bacterial growth. Bonferroni multiple comparison test in ANOVA was applied to compare the average lipase production among different species.

Results: All the test bacterial strains produced lipases. The levels of lipase production by different species were varied. The average of lipase production by S. aureus strains (2.37 ± 0.54 log units) was significantly higher than that of S. epidermidis (2.02 ± 0.37 log U, p = 0.038) and P. acnes (1.76 ± 0.14 log U, p = 0.004). Variation between strains in lipase production was also observed. The levels of lipase production ranged from 28 to 1711 U with median level of 266 U for S. aureus, from 38 to 543 U with median of 73 U for S. epidermidis, and from 30 to 87 U with median of 58 U for P. acnes.

Conclusions: The greatest bacterial lipolytic activity was found in the S. aureus ocular clinical isolates, and the levels of lipase production within this species were found to be strain specific. Whether high lipase production species or strains dominate to ocular microbiota in blepharitis or MGD related dry eye syndrome remains to be determined.

Keywords: 486 cornea: tears/tear film/dry eye