Final Report: Dr Esther Karanukaran- Developing a human model of the cornea to study keratitis

Keratitis, also known as ‘corneal ulcer,’ is an inflammation of the cornea – the clear, dome shaped window at the front of the eye that covers the iris and pupil. Keratitis affects twenty-three million people globally, each year. It is a condition that is hard to diagnose and without quick intervention, progresses rapidly, leading to painful damage to the cornea and blindness. Keratitis can be caused by injury or infection with a bacteria called Pseudomonas aeruginosa.

Using human corneas (unsuitable for corneal transplants), which would otherwise be wasted, Dr Esther Karanukaran has developed a novel, human-relevant tool to test and refine antibiotics for keratitis before they are used in clinical trials.  

Establishing and tracking keratitis infection in human corneas

Bacteria can live as free-floating (planktonic) cells or form ‘biofilms’, where numerous bacteria live in coordinated communities, enabling them to better survive. Some bacteria undergo genetic changes that give them the ability to defeat the drugs designed to kill them, something known as drug resistance. The emergence of such ‘superbugs ‘is one of the obstacles currently facing doctors treating keratitis, as it makes infections harder to treat and increases the risk of disease. Resistance is a major healthcare challenge as superbugs are outpacing the development of new antibiotics so new, effective treatments for keratitis are urgently needed.

In this research, Dr Karanukaran, (using human corneas unsuitable for corneal transplants which would otherwise be wasted) successfully developed a human corneal model infected with Pseudomonas aeruginosa. She sterilised the corneas with antibiotics (to rid them of bacteria) and then introduced a wound on the corneal surface, infected the cornea with Pseudomonas aeruginosa and monitored the growth of the bacteria over time. Dr Karanukaran used specialised microscopes to confirm that the bacteria were growing. This equipment enabled her to observe bacterial biofilms and free floating (planktonic) bacteria. She also used photography (shown in the image) to visualise the typical features of keratitis (such as ulceration and opacity) as the infection progressed.

Image: Human corneas infected with Pseudomonas aeruginosa – bacteria that commonly cause keratitis. As the infection progresses over time, features that are typical of keratitis (such as ulceration and opacity) are evident.

The impact of this research

Eye damage and subsequent keratitis can lead to blindness within 48h, so fast intervention is vital. In countries with effective medical provision, this is possible, and patients who receive prolonged antibiotic treatment can salvage their vision. In contrast, countries with poorer medical facilities see a much higher incidence of keratitis-associated blindness.

Animal experiments (using pig corneas) have shown that the number of planktonic bacteria progresses steadily over 24h, ultimately forming a biofilm, indicating a need for intervention within 1 day of eye damage.

Using this human-focussed model, Dr Karanukaran has shown however, that Pseudomonas aeruginosa infections progress differently in humans compared with animals. In human corneas, bacterial biofilms form within 2h as opposed to forming gradually. This shows the need for fast intervention and the crucial development of antibiotics that specifically target biofilms in order to eradicate infection.

Mice are commonly used to research keratitis. The animal is infected, leading to painful corneal ulcers and blindness before a drug is administered. This animal-free tool would also replace the many animals suffering in keratitis research.

This human-focussed model represents a more effective and efficient way of identifying and testing new antibiotics to tackle keratitis. In addition, antibiotics that don’t work or are unsafe could be eliminated from the testing pipeline earlier. This would remove the need for some animal testing stages and lead to fewer drug failures at subsequent clinical trial stages and better outcomes for patients.

Next steps

  • This work will feature in a forthcoming scientific publication by Dr Karanukaran
  • Dr Karanukaran will promote this human-relevant tool for potential uptake by research groups and companies involved in antibiotic development and testing in the UK and beyond
  • The interplay between the immune systems and the antibiotic is pivotal in how infections are cleared. Investigation into this will be the focus of further research that follows on from this pilot study.