C. trachomatis is an obligate intracellular pathogen, and this culture may be used to diagnose C. trachomatis infections. Although tests based on nucleic acid amplification have emerged as the most sensitive methods for diagnosis of Chlamydia genital infections, Chlamydia culture is still required for specimen types for which molecular diagnostic tests have not been validated. Chlamydia cultures should also be performed in cases that may have legal implications, such as rape and child abuse.
Method:
Infected cells from patient specimens are inoculated onto cultured eukaryotic cells, most commonly McCoy cells.
Cultures are incubated for 48 " “72 hours.
Positive cultures are now most commonly detected by staining fixed monolayers with specific anti " “C. trachomatis antibodies; positive cultures show staining of intracellular inclusions. The sensitivity of cultures for C. trachomatis detection is improved by blind subculture of a primary culture after the initial incubation.
Turnaround time: Cultures are incubated for 72 hours. An additional 48 " “72 hours are required if primary cultures are subcultured prior to final examination.
Special Collection and Transport Instructions
It is critical to collect infected epithelial cells from infected sites using toxicity-tested swabs or other device. Swabs may be premoistened with sterile nonbacteriostatic saline before specimen collection. Scrapings or biopsy specimens may be submitted for some specimen types. (See specimens below.)
Place specimens into a Chlamydia transport medium, such as 2-SP, and transport to the laboratory at 4 ‚ °C. Deliver to the laboratory as quickly as possible.
Specimens commonly submitted for Chlamydia culture come from the following sites:
Cervix: Remove excess mucus from the exocervix. Insert a new swab approximately 1 cm into the cervical canal and gently rotate for 10 " “15 seconds.
Urethra: Clean the distal urethra and meatus with a swab. Insert a new thin-shafted swab 2 " “4 cm into the urethra and gently rotate for 10 " “15 seconds.
Conjunctiva: Remove excess purulent discharge with a swab. With a new swab, gently rotate over the affected conjunctival surface.
Anus: Insert a premoistened swab into the anorectal juncture and rotate gently. The swab should not be heavily stained with feces.
Fallopian tube or epididymis: Place aspirate into an equal volume of Chlamydia transport media.
Respiratory tract (neonate): Place aspirate or wash into an equal volume of Chlamydia transport media.
Biopsies (lymph node, endometrium, fallopian tube, lung) may be taken. Place the biopsy specimen in a sterile container with the Chlamydia transport medium.
Interpretation
Expected results: No growth
Positive results: Chlamydia culture is very specific for infection caused by C. trachomatis.
Negative results: Chlamydia infection is not ruled out by a negative culture. Repeat testing, using a nucleic acid amplification test if appropriate for the site, is recommended for patients with a high suspicion for chlamydial infection.
Limitations
Chlamydia culture is intrinsically less sensitive than molecular diagnostic techniques. Chlamydophila species, C. psittaci, and C. pneumoniae, are not isolated by C. trachomatis culture. The following specimens are not recommended for Chlamydia culture:
Peritoneal fluid
Urethral discharge
Urine
Cul-de-sac fluid
Vagina or vaginal fluid
Throat
Common pitfalls:
Poor specimen collection (sample selection or collection technique) or loss of viability during transport. Swabs may be toxic for C. trachomatis. Specific types and lots of swabs should be tested for toxicity before releasing before clinical use. Urethral specimens should not be collected within 1 hour after the patient has urinated.