Microbiological examination of eye and ear discharge

Eye Infection Diagnostics

Microbiological diagnostics is indicated for various purulent-inflammatory processes of the visual organ, such as conjunctivitis, keratitis, or blepharitis. The success of the study is largely determined by the preanalytical stage.

The procedure must be performed by an ophthalmologist observing all aseptic rules. The most crucial condition is the discontinuation of any ophthalmic drugs and therapeutic procedures 5–6 hours before collecting the material, which is performed at the peak of the inflammatory process.

Collection technique depends on the site of the lesion:

• Conjunctiva: material is collected using a sterile loop or a special glass rod.
• Abundant purulent discharge: collection is carried out with a sterile cotton swab from the inner surface of the lower eyelid, moving towards the inner corner of the eye. It is critically important to securely fix the eyelids with your fingers so that the swab does not touch the eyelashes — this will prevent sample contamination with extraneous microflora.
• Eyelid margins: formed crusts are carefully removed with sterile forceps.
• Ulcers: scraping or smear is taken directly at the base of the eyelashes.
• Cornea: material is taken with a sterile loop; the procedure requires prior local anesthesia.
• Contact lenses: if necessary, their inner surface (adjacent to the eye) is examined.

Immediately after collecting the material, a smear must be prepared on a glass slide for immediate bacterioscopy. The microscopy result can be issued to the clinician as a preliminary report. Inoculation of the clinical material is performed immediately (in the physician's office or "at the patient's bedside") onto specialized media: serum broth and thioglycollate medium. Further identification tactics are based on the suspected type of pathogen.

Ear Infection Diagnostics

For diseases of the auditory organ, a differentiated approach is applied depending on the depth of the pathological process localization (lesions of the external, middle, or inner ear).

1. External ear (external otitis):

Rigorous preparation is required prior to collecting purulent discharge. The skin of the external auditory canal must be treated with 70% alcohol and then thoroughly rinsed with normal saline. This procedure is necessary to remove the saprophytic flora constantly inhabiting the skin. Only after this is the pus collected with a sterile cotton swab.

1. Middle and inner ear:

Material for examination includes punctates, as well as tissue or fluid samples obtained during surgical interventions. To maintain microorganism viability, such material is transported to the laboratory exclusively in sterile tubes or using specialized transport media.

Diagnostic Algorithm and Interpretation

The work of a microbiologist with the obtained samples includes several consecutive stages:

• Primary inoculation of the material onto a standard set of nutrient media.
• Evaluation of the growth pattern with quantitative characteristics (recording single colonies, moderate, or abundant bacterial growth).
• Isolation of a pure culture of the microorganism.
• Final identification of the pathogen.

Interpretation of the etiological significance of the isolated microorganisms depends on their pathogenicity. If obligate pathogens are detected in the culture, this unequivocally indicates the cause of the disease.

The situation is more complex with opportunistic bacteria (OB), since normal microflora is present in certain niches (e.g., in the external auditory canal).

To confirm the etiological role of OB, strict criteria are used:

• Quantitative indicator: the microbe must be detected in a high concentration (high titer).
• Reproducibility: the same culture must be stably isolated upon repeated tests in a series of studies.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Characteristics of bacterial growth on thioglycollate medium and serum broth
• Methods for quantitative evaluation of bacterial growth in primary cultures
• Types of transport media for middle and inner ear punctates
• Spectrum of normal microflora of the external auditory canal

Other topics in the «Clinical Microbiology» section

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