Eye infection - Laboratory diagnosis
Laboratory diagnosis of eye infection
The laboratory diagnosis of eye infection beings with collection of samples.
Specimen
conjunctival swab
corneal scrappings
exudates
* collected by kimura spatula
Direct examination
Gram, Giemsa, and PAS (Periodic acid Schiff) stains can be used for direct examination
Polymorphonuclear leukocytes predominate bacterial conjunctivitis
If the sample volume is large (ophthalmic specimens), must be concentrated by centrifugation before additional studies are performed.
Culture
Media
BA, MA, CA = 5-10% CO2
Cystine-tellurite medium, Loeffler’s medium (Corynebacterium diphtheriae)
Modified NYC medium, Thayer Martin Agar (Neisseria gonorrhoeae)
Loeffler’s medium (Moraxella lacunata)
* the organism often leads to proteolysis and pitting of medium but non-proteolytic strains may be isolated
cycloheximide–treated McCoy cells (Chlamydia)
During inoculation, the media must be divided into two parts left (L) and right (R) in which the sample is inoculated into its corresponding sides.
Observation
If Cornebacterium diptheriae is suspected
Gram staining
pleomorphic, long, thin, and curved forms can be seen club-shaped rods can also be seen
Culture
grows aerobically
temperature => 20-40°C; optimum = 35-37°C
In tellurite whole blood agar Corynebacterium diphtheriae reduces tellurite producing gray-black colonies measuring 0.5-2mm in diameter. Strains can be hemolytic, slightly hemolytic, and non-hemolytic.
Confirmation is done by the ELEK GEL precipitation test
If Moraxella lacunata is suspected
they are gram-negative, obligatory aerobes
for culture, protein enriched medium such as Loeffler’s serum medium is required
when grown on a protein medium in a CO2-enriched atmosphere, it produces holes of liquefaction (change in liquid).
Non- culture methods
ELISA
DFA (Direct Fluorescent Antibody)
PCR