Corneal scrapes for microscopy and culture

This document details the requirements for collection of corneal scrape specimens for microscopy and culture of bacterial and fungal pathogens. For all requests, please ensure any relevant clinical details are provided on the request form. If there is any travel or tropical infections suspected, please highlight this on the request form as there will be additional safety precautions required for the staff in the laboratory.

Please ensure that all sample containers are securely tightened to prevent leakage during transport.

If investigation for viral infection, chlamydia or acanthamoeba, the corneal scrape sample should be sent in 200µl of sterile saline.

Procedure at the bedside

Prior to collection of the sample, the microbiology laboratory should be contacted on extension 52606 and a corneal scrape kit requested. This can be collected from pathology main reception. If the kit is not used immediately, it should be stored in the fridge until required. If stored, expiry dates should be checked regularly, and plates returned to the lab for disposal once the expiry date has been reached. If the kit has been in the fridge, it must be brought to room temperature prior to being used.   

The corneal scrape kit includes:

• 4 x agar pates (1 x each of blood, chocolate, SAB and FAA)
• 1 twinfrost slide (provided inside a slide case)

Each plate and the slide should be inoculated with corneal material using sterile technique and samples should be collected prior to antibiotic therapy where possible.

After culture media has been inoculated – the slide can then be inoculated. This must come last as it is the least sterile component. 

If there is not enough material to inoculate all, priority should be as follows:

1. Chocolate (this will grow all bacteria, yeasts and pathogenic fungi – except anaerobes)
2. FAA (this will grow all anaerobes)
3. Blood (this will grow all organisms)
4. SAB (this will grow yeasts and pathogenic mould only)
5. Slide (this only provides an indication of presence of organisms)

All plates must be labelled with patient details. If stickers are being used, these must be placed on the agar side of the plate – not on the lid.

The inoculated slide must be marked with pencil on the frosted end to indicate which side the sample has been inoculated onto.

Transport back to the laboratory:

• The inoculated plates should be sealed to prevent lids from falling off during transport back to the laboratory which could contaminate the sample.
• The slide must be placed back into the slide container for transport.
• Inoculated plates and slide must be sent to the laboratory for investigation following sampling as soon as is reasonably possible to preserve the integrity of the samples.
• If timely transport to the laboratory is not possible, the samples should be refrigerated until that can be transported.
• Samples for acanthamoeba should NOT be refrigerated. They should be kept at ambient temperature if transport for processing cannot be done within 8 hours. 

Procedure within the laboratory:

• On receipt patient information on the plates and slide are checked against the form to ensure they match.
• Clinical details are checked to assess for the risk of hazardous organisms.
• The form, plates and slide are labelled with an individual laboratory number.
• Plates are incubated immediately into the appropriate atmospheres and the slide is stained.
• The slide is examined for the presence of white blood cells, bacteria and yeasts. Results positive for bacteria or yeasts are phoned to the requesting source and a provisional report is issued. Negative results are sent out as a provisional report.
• Culture results will be provided at 48 hours for bacterial culture, and 14 days for fungal culture.

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