Examination in Eye Infections
Microbiological diagnostics is indicated for various purulent-inflammatory conditions of the eye, such as conjunctivitis, keratitis, or blepharitis. The success of the study is largely determined by the pre-analytical phase.
The procedure must be performed by an ophthalmologist in compliance with aseptic rules. A crucial condition is the cessation of all ophthalmic medications and therapeutic procedures 5–6 hours before sampling, which is conducted during the peak of the inflammatory process.
Collection technique depends on the site of infection:
- Conjunctiva: material is collected using a sterile loop or a specialized glass rod.
- Abundant purulent discharge: collection is carried out with a sterile cotton swab from the inner surface of the lower eyelid, moving toward the inner canthus. It is critically important to securely hold the eyelids open with your fingers so that the swab does not touch the eyelashes—this prevents contamination of the sample by extraneous microflora.
- Eyelid margins: any crusts formed are gently removed with sterile forceps.
- Ulcers: scrapings or smears are taken directly from the base of the eyelashes.
- Cornea: material is collected with a sterile loop; the procedure requires prior topical anesthesia.
- Contact lenses: if necessary, their internal surface (facing the eye) is examined.
Immediately after material collection, a smear on a glass slide must be prepared for prompt bacterioscopy. Microscopy results may be provided 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 pathogen.
Examination in Ear Infections
For hearing organ disorders, a differentiated approach is applied depending on the anatomical depth of the pathological process (involvement of the external, middle, or internal ear).
- External ear (external otitis):
Prior to collecting purulent discharge, strict preparation is required. The skin of the external auditory meatus must be treated with 70% alcohol and then thoroughly rinsed with normal saline. This procedure is necessary to remove saprophytic flora that constantly inhabit the skin. Only after this is the pus collected with a sterile swab.
- Middle and inner ear:
Materials for examination include aspirates, tissue samples, or fluids obtained during surgical interventions. To maintain the viability of microorganisms, such material is transported to the laboratory exclusively in sterile tubes or using specialized transport media.
Diagnostic Algorithm and Interpretation
The microbiologist's work with the received samples includes several consecutive stages:
- Primary inoculation of the material onto a standard set of culture media.
- Evaluation of growth characteristics with quantitative grading (single colonies, moderate, or abundant bacterial growth).
- Isolation of a pure culture.
- Final identification of the pathogen.
Interpretation of the etiological significance of 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 pathogens, as certain sites (such as the external auditory meatus) harbor resident normal microflora.
To confirm the etiological role of opportunistic bacteria, strict criteria are applied:
- Quantitative indicator: the microbe must be detected in a high concentration (high titer).
- Reproducibility: the same culture must be consistently isolated in repeated analyses across a series of tests.