Antimicrobial activity of Poly-ε-lysine peptide hydrogels against Pseudomonas aeruginosa

Abstract

Purpose : Corneal bandage contact lenses offer no antimicrobial properties and are used in conjunction with topical antibiotics to minimise the risk of infection following surgery. The purpose of this study was to investigate the antimicrobial activity of poly-ε-lysine (pεK) hydrogels covalently bound with pendant pεK (pεK+) against Pseudomonas (P.) aeruginosa keratitis isolates.

Methods : Peptide hydrogels were synthesised with pεK and octanedioic acid using carbodiimide chemistry (60% cross-linked and polymer density of 0.071 g/ml). pεK+ hydrogels were created by covalently binding pεK to the hydrogel using N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide coupling (Gallagher AG. et al. Adv Healthc Mater. 2016; 5: 2013-2018). Antimicrobial activity of hydrogels was tested against the PA01 type strain and cytotoxic (ExoU) and invasive (ExoS) P.aeruginosa keratitis isolates at 1x10⁶ cfu/ml for 4 and 24 hours (h) at 37°C. Bacteria associated with pεK+ and pεK hydrogels, Luria-Bertani (LB)/agar and culture media was assessed via viable plate counts. Threshold limits for bacterial detection was 3x10² cfu/ml. Statistical analysis was carried out using a one-way ANOVA with Tukey’s post-test analysis, n=3.

Results : The number of viable PA01 associated with the pεK+ hydrogel at 4 h showed a 3 log₁₀ and 4 log₁₀ reduction compared to pεK hydrogel and LB/agar, respectively (P<0.05). P.aeruginosa keratitis isolates (ExoU and ExoS) showed a 3 log₁₀ reduction in bacteria associated with the pεK+ hydrogels at 4 h, compared to pεK hydrogels and LB/agar (P<0.05). The number of viable P.aeruginosa keratitis isolates within the culture medium from pεK+ hydrogels was reduced 4 log₁₀ and 3 log₁₀, compared to culture medium from pεK hydrogels and LB/agar, respectively (P<0.05). At 24 h there was >5 log₁₀ reduction in all P.aeruginosa associated with the pεK+ hydrogels (below detection level), compared to pεK hydrogels (P<0.05).

Conclusions : This study demonstrates that pεK+ hydrogels possess increased antimicrobial activity against ExoU and ExoS P.aeruginosa compared to pεK hydrogels. A reduction in the number of bacteria associated with the hydrogel and in the culture media was observed at 4 and 24 h. pεK+ hydrogels have the potential to be used as prophylactic antimicrobial bandage contact lenses with innate antimicrobial characteristics to reduce the risk of bacterial infection following surgery.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.