Specimen Collection and Transport

Purulent material from the surface of the lower conjunctiva sac and inner canthus (angle) of the eye is collected on a sterile swab for cultures. Both eyes should be cultured separately. Chlamydial cultures are taken with a dry calcium alginate swab and placed in 2-SP (2-sucrose phosphate) transport medium. An additional swab may be rolled across the surface of a slide, fixed with methanol, and sent if direct fluorescent antibody (DFA) chlamydia stains are used for detection.

In the patient with keratitis, an ophthalmologist collects scrapings of the cornea with a heat-sterilized platinum spatula. Multiple inoculations with the spatula are made to blood agar, chocolate agar, an agar for the isolation of fungi, thioglycollate broth, and an anaerobic blood agar plate. Other special media may be used if indicated. Corneal specimens for culture of HSV and adenovirus are placed in viral transport media. Recently, the collection of two corneal scrapes (one used for Gram stain and the other transported in brain heart infusion medium and used for culture) was determined to provide a simple method for diagnosis of bacterial keratitis.

Cultures of endophthalmitis specimens are inoculated with material obtained by the ophthalmologist from the anterior and posterior chambers of the eye, wound abscesses, and wound dehiscence (splitting open). Lid infection material is collected on a swab in the conventional manner. For microbiologic studies of canaliculitis, material from the lacrimal canal should be transported under anaerobic conditions. Aspiration of fluid from the orbit is contraindicated in patients with orbital cellulitis. A patient history of sinusitis in association with orbital cellulitis is an indication for obtaining an otolaryngologist’s assistance in the collection of material from the maxillary sinus by antral puncture. Blood cultures should also be obtained. Tissue biopsy is essential for the micro biologic diagnosis of mucormycosis. Because cultures are usually negative, the diagnosis is made by histologic examination.

Direct Visual Examination

All material submitted for culture should be smeared and examined directly by Gram stain or other appropriate microscopic techniques. In bacterial conjunctivitis, polymorphonuclear leukocytes predominate; in viral infection, the host cells are primarily lymphocytes and monocytes. Specimens in which Chlamydia is suspected can be stained immediately with monoclonal antibody conjugated to fluorescein for the detection of elementary bodies or inclusions. Using histologic stains, basophilic intracytoplasmic inclusion bodies are seen in epithelial cells. Cytologists and anatomic pathologists usually perform these tests. Direct examination of conjunctivitis specimens using histologic methods (Tzanck smear; a scraping from the lesion for collection of cells) may reveal multinucleated epithelial cells typical of herpes group viral infections. However, DFA stains available for both HSV and VZV are recommended for rapid diagnosis of viral infections. In patients with kera titis, scrapings may be examined using Gram, Giemsa, periodic acid-Schiff (PAS), and methenamine silver stains. If Acanthamoeba or other amebae are suspected, a direct wet preparation should be examined for motile trophozoites, and a trichrome stain should be added to the regimen. For this diagnosis, however, culture is by far the most sensitive detection method for the identification of the organism. In patients with endophthalmitis, the specimen is examined using Gram, Giemsa, periodic acid-schiff (PAS), and methenamine silver stains. When submitted in large volumes of fluid, ophthalmic specimens must be concentrated by centrifugation before additional studies are performed.

Culture

 Because of the constant washing action of the tears, the number of organisms recovered from cultures of eye infections may be relatively low. Unless the clinical specimen is obviously purulent, using a relatively large inoculum and a variety of media is recommended to ensure recovery of the etiologic agent. Conjunctival scrapings placed directly onto media yield the best results. At a minimum, blood and chocolate agar plates should be inoculated and incubated under increased carbon dioxide tension (5% to 10% CO2). Because potential pathogens may be present in an eye without causing infection, it may be very helpful to culture both eyes. If a potential pathogen grows in cultures of the infected and the uninfected eye, the organism may not be causing the infection; however, if the organism only grows in culture from the infected eye, it is most likely the causative agent. When Moraxella lacunata is suspected, Loeffler’s medium may prove useful; the growth of the organism often leads to proteolysis and pitting of the medium, although non proteolytic strains may be isolated. If diphtheritic conjunctivitis is suspected, Loeffler’s or cystine-tellurite medium should be used. For more serious eye infections, such as keratitis, endophthalmitis, and orbital cellulitis, one should always include a reduced anaerobic blood agar plate, a medium for the isolation of fungi, and a liquid medium such as thioglycolate broth. Blood cultures are also important in serious eye infections.

Specimen cultures for chlamydia and viruses should be inoculated to appropriate media from transport broth.

For Chlamydia isolation use cycloheximide-treated McCoy cells; for viral isolation the use of human embryonic kidney, primary mondey kidney and Hep-2 cell lines is recommended.

Nonculture Methods

Although acute and convalescent serologic tests for viral agents might be used in the event of epidemic conjunctivitis, they typically are not performed because the infections are self-limited. Enzyme-linked immunosorbent assay (ELISA) tests and DFA staining are available for the detection of Chlamydia trachomatis. An ELISA test of aqueous humor is available for the diagnosis of Toxocara infection. Finally, single and multiplex polymerase chain reaction (PCR) assays including both conventional and real-time formats have been used to diagnose viral and chlamydial keratoconjunctivitis and other ophthalmic infections including uveitis (inflammation in the middle layer of the eye).

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الشؤون الفكرية ينظّم برنامجًا تدريبيًّا لعدد من ملاكات المؤسسات الثقافية في ذي قار

إقامة المحاضرة الرابعة من محفل نهج البلاغة في مقام الإمام المهدي (عجل الله فرجه)

للعام التاسع.. المجمع العلمي يطلق 29 ختمة قرآنية رمضانية في النجف الأشرف

قسم الصيانة يجري أعمال الإدامة الدورية لجدران حرم مرقد أبي الفضل العباس (عليه السلام)

المزيد

الآخبار الصحية

مفاجأة.. تحسين القدرة على التحمل لا يعتمد العضلات فقط

المرتفعات والأكسجين.. دراسة "مبشرة" لمرضى السكري

علماء يبتكرون "آلية" تتوقع موعد ظهور أعراض الزهايمر

ماذا يحدث لجسمك عند التوقف عن تناول الخضراوات والفواكه؟

المزيد

الآخبار التكنلوجية

رصد "القرش النائم" في أحد أقسى الأماكن على وجه الأرض

أسماك أعماق البحر تكشف نظاما بصريا يتجاوز "المألوف"

زوكربيرغ أمام القضاء في قضية إدمان المراهقين

"علي بابا" تكشف عن نموذج جديد للذكاء الاصطناعي

المزيد

مواضيع ذات صلة

Laboratory Diagnosis of Central Nervous System Infections

Diagnosis and Differential Diagnosis of Paroxysmal Nocturnal Hemoglobinuria

Differential Diagnosis of Pancytopenia

Diagnosis of Aplastic anemia

Diagnosis of Upper Respiratory Tract Infections

tuberculosis testing (TB testing, Interferon gamma release assay [IGRA, T-Spot.TB], QuantiFERON-TB Gold [QFT, QFT-G, TB Gold test, TB blood test], Nucleic acid amplification for TB [NAAT], TB antibody)

thyrotropin-releasing hormone stimulation test (TRH stimulation test, Thyrotropin-releasing factor stimulation test [TRF stimulation test])

Laboratory Diagnosis of Lower Respiratory Tract Infections: Specimen Processing

Laboratory Diagnosis of Lower Respiratory Tract Infections: Specimen Collection and Transport

thyroid scanning (Thyroid scintiscan)

thyroid fine needle aspiration biopsy (FNAB, Skinny needle thyroid biopsy, Fine-needle aspiration [FNA])

thoracentesis and pleural fluid analysis (Pleural tap)