Background

Chlamydia trachomatis is an obligate intracellular and small gram-negative bacterium. It is impaired in energy metabolism. The host cells of these bacteria are mostly epithelial cells that line the respiratory tract, conjunctiva, rectum, and urogenital tract. 

Cell culture was accepted as a standard before the PCR. The usage of cell culture is substantially decline because of the technical complexity, handling and time requirement, difficult nature of organism and expense. The sensitivity of cell cultures varies between 50 to 70 %. NAAT (nucleic acid amplification tests) has emerged as a standard criterion due to high sensitivity of 85 to 95 %. Cell culture is frequently performed due to the 100% specificity during the staining phase, properly utilizing and acquiring fluorescein-conjugated monoclonal antibodies. 

However, C. trachomatis culture is less sensitive than the NAATs, preserving the potential to perform this laboratory test is necessary. The novel Swedish strain of C. trachomatis, that evaded NAATs was discovered due to the organism could be cultivated. 

Indications/Applications

When the diagnosis of C. trachomatis is challenged, a culture should be conducted. CDC suggests that positive nonculture tests must be confirmed if the false-positive result might lead to adverse social, psychological, or social effects. Culture confirmation is needed, yet, if the nonculture test was NAATs, they have claimed that a second NAAT is enough than the obtaining the culture. 

The common indications to perform the test are child sexual abuse, suspected sexual assault, susceptibility testing in resistant organisms, and urinary tract infections (UTIs).  

The test is also performed for neonatal conjunctivitis, suspected trachoma, cervicitis, nongonococcal urethritis, salpingitis, endometritis, pelvic inflammatory disease, proctitis, acute urethral syndrome, epididymitis, lymphogranuloma venereum, perihepatitis (Fitz-Hugh-Curtis syndrome), and pneumonia in newborns. NAATs is the most common test which is used in these conditions due to instant turnaround and high sensitivity. 

Clinical Significance: 

The factors which can cause the false-positive results are: 

The patient has taken anti-C. trachomatis medications within a few days before the test. 

Men evacuated within 1 hour of the collection of samples. 

Women douched in 24 hours. 

Proper sample collection methods will not be performed.  

Contamination in the samples was caused by the fecal material in the rectal culture.  

A C. trachomatis culture test is performed in conditions like suspected urinary tract infection, sexual assault, or child sexual abuse. 

Reference Range

The normal result of this test lead to a negative culture and the below values of antibodies: 

Chlamydophila pneumoniae 

IgM: Less than 1:10 

IgG: Less than 1:64 

Chlamydophila psittaci 

IgM: Less than 1:10 

IgG: Less than 1:64 

Chlamydia trachomatis 

IgM: Less than 1:10 

IgG: Less than 1:64 

The normal result includes the negative detection of nucleic acids. 

Interpretation

Normal result: 

A correctly acquired negative culture confirms the 100% specificity. This confirms that there is no infection present of C. trachomatis. 

Abnormal result: 

A positive culture confirms that the infection of C. trachomatis with sensitivity ranges from 50 to 85%. The criteria standard has been supressed by NAAT which has a specificity of 99 to 100% and sensitivity from 85 to 95 %. CDC has updated the 2002 recommendations about the C. trachomatis screening tests. These include using NAAT to identify chlamydia. 

Positive culture results can lead to diagnoses like: 

Trachoma 

Nongonococcal urethritis 

Neonatal conjunctivitis 

Salpingitis 

Cervicitis 

Endometritis 

Pelvic inflammatory disease (PID) 

Proctitis 

Acute urethral syndrome 

Pneumonia of newborns 

Epididymitis 

Lymphogranuloma venereum (LGV) 

Perihepatitis (Fitz-Hugh-Curtis syndrome) 

Collection And Panels

Sample type: 

Epithelial cells can be collected from the urethra and endocervix (remove purulent exudate), eye, and rectum. Patient should not urinate for 3 to 4 hours before taking the samples from the genital tract. Female patients should not douche for 24 hours before the sample collection. 

Sample collection container: Swab transport system along with sucrose phosphate (2SP) transport medium 

Sample collection method: 

Epithelial cells should be obtained from the infected site, A rayon tipped swap or Dacron tipped swap is preferred. Cotton tipped or calcium alginate swaps sometimes toxic. Use a plastic or metal shaft due o wood shafts are toxic to the organisms.  

Urethral samples: The microbiological transport swab should be inserted into the urethra between 0. 75 to 2 inches (2 to 5 cm). Place the samples into a 2SP transport medium. 

Endocervix sample: The microbiologic transport swap or cytobrush is used. Place the samples into a 2SP transport medium. 

In infants, the samples should be obtained from eye, nasopharynx, throat, or aspirates. Place the samples into 2SP transport medium. 

Rectum: The microbiologic transport inserted into the anal canal from 2 to 3 cm. The sample should be collected from all walls of the rectum. 

Sample handling: The samples should be sent to laboratories at 4 °C. If the time between sample collection and inoculation into the culture is greater than 24 hours, freeze the 2SP transport medium, then send it to the laboratories with the dry ice. 

Growing: The organism cannot grow on an artificial medium. It can grow on cell lines which are treated with cycloheximide like HEp-2, buffalo green monkey cells, HeLa, and McCoy. 

References

https://ncbi.nlm.nih.gov/pmc/articles/PMC2563901/