Bacterial Growth in Tissue Engineered Cornea Constructs

Abstract

Purpose: : To study the susceptibility of tissue engineered cornea substitutes to bacterial attack. The rationale is that apart from having optical clarity, adequate tensile strength and biocompatibility with living tissue, they should also not be more conducive to bacterial growth compared to human corneas.

Methods: : Three bacterial species that cause ocular infections, Staphylococcus aureus(SA), Streptococcus pneumoniae(SP), and Pseudomonas aeruginosa(PA) were studied. The ability of each bacterial species to proliferate was tested on 27 different tissue engineered contructs that comprised different ratios of water, collagen and synthetic polymer (PEO). Each construct (n=27 total) was injected with 100 µL of each bacterial strain (approximately 10⁷ CFU to start and serial dilutions to obtain a dose response). After the injection, the constructs were incubated at room temperature for 24 hours. They were then homogenized in saline and the bacterial counts determined. Human donor corneas from the Eye Bank and saline served as benchmarks for the engineered corneas.

Results: : The mean colony counts (±SD) for SA were 1.1x10⁵ (±1.6x10⁵) CFU/mL for the tissue engineered corneas, 2.4x10⁵ (±3.1x10⁵) CFU/mL for the human cornea, and 2.6x10⁵ (±2.3x10⁵) CFU/mL for saline. With SP there was no growth in the tissue engineered cornea, human cornea or saline. The mean colony counts for PA were 6.2x10³ (±8.6x10³) CFU/mL for the tissue engineered corneas, 6.8x10² (±7.2x10²) CFU/mL for the human cornea, and 9.1 x 10⁵ (±8.3x10⁵) CFU/mL for saline. There were no statistically significant differences in the colony counts of SA and PA in different cornea constructs, or as compared to human donor corneas (p–value for SA between constructs and human donor cornea is 0.6 and for PA, the p–value is 0.4). These results suggest that SA and PA replication within the tissue engineered corneas occurred at the same rate as that in human cornea. For SP, there was no growth in either engineered corneas or human corneas, presumably because this organism is fastidious and has more stringent growth requirements.

Conclusions: : Collagen–based tissue engineered corneas developed were similar to human donor corneas with respect to their susceptibility to bacterial growth. They are therefore not likely to be more attractive to bacteria than donor tissues.

Keywords: cornea: clinical science • keratitis • Staphylococcus