Q: Occasionally, Id like to culture certain suspicious corneal ulcers, but Im not sure about yields with transport media, and I hate to carry blood and chocolate plates for the rare times that I need them. Are there any other culture devices or techniques that have a high yield and are cost-effective?

A: Absolutely says optometrist Paul M. Karpecki, of Kansas City, Mo. He uses a Mini-Tip Culturette (Becton Dick- inson Microbiology Systems), which is a rayon-tipped swab attached to a flexible and extendable aluminum wire. The swab has one ampule of 0.5ml of modified Stuarts bacterial transport medium (sodium glycerophosphate, 1.0%; sodium thioglycolate, 0.1%; calcium chloride, dihydrate, 0.01% and water) and comes in a sealed package.

Dr. Karpecki points to a study done by the Krieger Eye Institute in Baltimore that showed the Mini-Tip Culturette has a high yield and is cost-effective. The study compared the efficacy of the swab (both with and without moistened non-bacteriostatic normal saline) to a platinum spatula in culturing rabbit and human bacterial keratitis. In rabbits, all three culturing methods had 100% sensitivity and speci-ficity. In humans, the Mini-Tip Culturette had a sensitivity of 83.3% and a specificity of 100%.1 In addition, after the researchers assessed the cost of processing the cultures, the platinum-spatula culture cost $92.50 versus the Mini-Tip Culturette, which cost $83.30.1

The Mini-Tip Culturette is a culture device used for corneal ulcers that has a high yield and is cost-effective for those practitioners who dislike carrying blood and chocolate plates.

Ophthalmologist Andrew Lee Moyes, of Kansas City, Mo., adds, I used to do all of the plating onto the Sabarouds media, the blood agar, the chocolate agar and the thioglycolate broth, but all of this has become supplanted by using these Mini-Tip Culturettes.

Still, not all practitioners use these swabs correctly. I think a lot of practitioners get poor yields because they just sort of brush the swab over the top of the lesion, Dr. Karpecki says. You really have to be aggressive at getting at the infiltrate. Dr. Moyes adds that some practitioners make the mistake of sticking the swab in the soupy mucous or pus located in the middle of the ulcer. This goo does not contain many active bac-teria, he says. You really need to be rubbing at the hard infiltrated edge of the lesion. (If, however, this pus precludes you from getting down to the lesions base, he suggests using a cotton tip to remove it.) Dr. Moyes also says that practitioners must be sure that the swab does not touch the patients lids, lashes, or anything else, as contamination can cause a false positive or a questionable result.

Optometrist Andrew S. Gurwood, of the Eye Institute at Pennsylvania College of Optometry in Philadelphia, says that many clinicians question the need for culturing because they have observed the exceptional potency and rapid killing properties of the topical fluorinated quinolones. Nevertheless, he says, culturing suspicious ulcers must remain a priority. Culture results are the only means of identifying the actual (correct, not presumed) underlying etiology in the rare event that healing does not proceed as predicted or if in fact, the condition worsens, he says.

Editors note: In researching other mini swabs used for corneal ulcers, we discovered the CalgiSwab Type 1, (Puritan). However, there may be others on the market, so we encourage you to choose these products at your own discretion.

  1. Epley KD, Katz HR, Herling I, Lasky JB.Platinum spatula versus Mini-tip Culturette in culturing bacterial keratitis. Cornea 1998 Jan;17(1):74-8.

Vol. No: 141:11Issue: 11/15/04