Typically, when a patient presents with an out-of-control bug, we start them on our favorite antibiotic drop, bring them back in a few days, and watch them heal like nothing happened.
These are the patients you should consider culturing.
Whether your practice has invested in its own culturing materials or you use a local lab, knowing which patients need to be examined, when to collect your bacteria, and which testing materials should be utilized is key to successfully managing these difficult cases.
This article will give new grads a quick review of these key points of ocular culturing.
1. What presentations should be cultured?
Culturing can be performed on any patient that you wish; however, the following ocular infections should warrant strong consideration for testing:
- Central corneal ulcers
- Ulcers that have significantly thinned the stroma (“significant thinning” can be different from clinician to clinician. I would strongly recommend culturing anytime thinning reaches 50% or more due to risk of progression to perforation)
- Large K ulcers – the American Academy of Ophthalmology’s EyeNet article “Confronting Corneal Ulcers” recommends culturing any ulcer 2mm or larger
- Unresponsive conjunctivitis, K ulcers, or blepharitis
- Atypical K ulcers – extreme pain with minimal clinical signs, possible fungal etiology, etc.
- Suspected endophthalmitis – this will require a referral for an aqueous humor and/or vitreous tap; typically, these referrals are to a retinal specialist
2. When should cultures be taken?
One of the most important things to remember when culturing is that once a medication is applied to the eye, the chances of obtaining a good, pure sample are diminished.
If you suspect that your patient may have an atypical or particularly sight-threatening condition, it’s best to go ahead and culture at first presentation.
If you do not have full culturing abilities at your office, you should connect with a local lab and make sure you stock their preferred means of collection. This way, you’re always prepared for anything that lands in your exam chair.
Remember: Do not wait for the results of your culture to begin treatment. After gathering your sample, go ahead and start your patient on whichever therapy you feel is most appropriate. Be sure to educate him or her that your treatment plan may be altered after the results are obtained.
In some cases, an infection initially seems ordinary but does not respond to treatment in the manner you expected. If this is the case, go ahead and culture anyways. While it will not be the ideal scrape, there may be enough bacteria remaining to create a successful culture and help with your patient’s management.
3. Which tools and medium should be used for testing?
The tools you use should be tailored to the location you are scraping.
Corneal cultures should be performed with a spatula, blade, forceps, or moistened applicator.
Conjunctival and lid margin specimens may be taken with moistened applicators. Some labs will equip you with specific broth to wet the applicator with, though sterile saline will work as well. In addition, most labs will provide collection culturettes which will allow for sterile transport from your office to theirs.
The medium on which to culture will depend on which bacteria you suspect to be present. It is best to inoculate multiple different types of plates to get the best likelihood of growth and identification.
Whether you choose to work with a local lab in your area or would like to culture within your own office, it is important to remember to utilize this diagnostic tool.
Severe bacterial infections can be daunting, but proper ID of the culprit will mean faster resolution for your patient and less risk of permanent vision loss.
American Academy of Ophthalmology EyeNet “Confronting Corneal Ulcers.” http://www.aao.org/eyenet/article/confronting-corneal-ulcers?july-2012
The Charles T. Campbell Eye Microbiology Lab “Lab Diagnostic Testing: Bacteria.” http://eyemicrobiology.upmc.com/ Bacteria.htm