Genital culture is the use of enrichment and selective mediatoisolate andidentify organisms that cause genital infections such as urethritis, cervicitis, and salpingitis (pelvic inflammatory disease). The primary reason for a genital culture is to isolate Neisseria gonorrhoeae, the causative agent of gonorrhea. Other organisms that cause genital infections and that can be cultured are Gardnerella vaginalis, Candida albicans, Neissria meningitidis, Haemophilus ducreyi, Mycoplasma hominis, and Ureaplasma urealyticum.
Genital culture is performed on persons who have signs of abnormal discharge or skin lesions in the genital area, or complaints such as itching or pain on urination. It is performed on persons who have evidence of other sexually transmitted diseases for which culture is not routinely performed because of the high prevalence of concomitant infection. For example, there are approximately three million new cases of Chlamydia trachomatis infection in the United States each year and many infected persons also will test positive for N. gonorrhoeae. Genital culture is also performed on any person who may be a victim of a sexual assault. Genital culture may be performed as a screening test on patients who have no symptoms, but are at increased risk for infection because of sexual behavior, since many sexually transmitted diseases can be carried silently. Also, pre and postnatal genital cultures for gonococcus and group B streptococcus are performed routinely on obstetrical patients.
Although most genital infections are sexually transmitted, children or elderly persons are also at risk. In children, skin or wound infections may cause vaginal or urethral infections, especially when there has been physical injury to the genital area. People with deficient immune function and those on prolonged antibiotic treatments are more susceptible to vaginal yeast infections (e.g., Canidida albicans or Torulopsis glabratainfection). Abscesses may form in the pelvic area and Bartholin's gland following pregnancy, abortion, malignancy, obstetrical procedures, obstruction, and other conditions, and these often involve anaerobic bacteria.
Some infections, particularly gonorrhea, can be difficult to culture. In males it may be necessary to culture other sites that may be infected, such as the anus and mouth, if the patient has corresponding sexual habits putting him or her at risk. Up to 35% of males and 50% of females who are positive for gonococcal infection will test positive for Chlamydia trachomatis. This organism as well as Treponema pallidum, the causative agent of syphilis, Trichomonas vaginalis, human immunodeficiency virus, cytomegalovirus, herpes simplex 2, and human papilloma virus are not generally cultured. Because of their high prevalence, tests for these organisms (i.e., immunoassays, DNA probes, tests for antibodies) may also be performed. When performing genital cultures, universal precautions for prevention of transmission of bloodborne pathogens must be observed.
Neisseria gonorrhoeae causes approximately 650,000 genital infections in the United States each year. If untreated, gonorrhea can result in permanent damage to the reproductive organs (pelvic inflammatory disease), gonococcal arthritis, skin infection, and neonatal conjunctivitis (when transmitted via pregnancy).
The female patient will be in the dorsal lithotomy position typical for Pap testing. A speculum is moistened with warm water (no lubricant should be used) and inserted into the vagina to secure good visualization of the cervix. Any excess cervical mucous should be removed with a cotton ball (held by ring forceps). A sterile cotton swab is inserted just inside the opening of the cervix (the os) and rotated gently for 30 seconds. Genital swabs are usually placed in transport media that contains charcoal to absorb toxins that inhibit the growth of gonococcus.
Care should be taken not to touch the vaginal surfaces with the swab in order to avoid the transfer of normal vaginal flora. For culture, the sample is placed in Stuart's or Amies transport medium with charcoal added and delivered to the laboratory at room temperature. For DNA probe testing (in which organisms are not cultured, but the presence or absence of their genetic material is confirmed) the swab is broken off at the top of the sterile tube provided, and the tube is capped and sent to the laboratory. For immediate viewing, a swab sample may be placed in normal saline. One drop can then be placed between a slide and coverslip, and viewed beneath the microscope. This is called a "wet prep." A wet prep is useful for diagnosing yeast infection and trichomoniasis. Pelvic inflammatory disease samples and samples from genital lesions such as chancres are collected by aspiration. Plating for H. ducreyi should be done from the chancre aspirate and performed immediately because the organism is fastidious.
In the male patient, a smaller sterile cotton swab is used to remove cells and any discharge from the last 2 cm of the urethra, and the swab is transported for culture or DNA probe testing as described for the female patient. If visible discharge is present on the surface of the penis, this should be swabbed, and it is unnecessary to enter the urethra. If prostate infection is suspected, urine culture should be performed. If infection of the prostate, epididymus or testes is suspected, seminal fluid should be cultured.
All swabs or aspirates are plated on modified Thayer-Martin (MTM) agar or New York City (NYC) agar. These media are selective for the growth of N. gonorrhoeae. MTM is chocolate agar (heated sheep blood agar) containing colistin to inhibit the growth of gram negative bacilli, nystatin, or anisomycin to inhibit yeast, vancomycin to inhibit growth of gram-positive bacteria, and trimethoprin to inhibit Proteus spp. NYC agar contains amphotericin B instead of nystatin and consists of clear proteosepeptone supplemented agar. In addition, the sample is plated on either 5% sheep blood agar or Columbia agar with 5% sheep blood and colistin and nalidixic acid (CNA) to isolate yeast and Gardnerella vaginalis. In addition, special selective and differential agar may be used to isolate Mycoplasma hominis and Ureaplasma urealyticum. Plates are incubated at 36°C in 5-10% carbon dioxide. MTM or NYC agar are examined for growth at 24 hours and if negative again at 48 hours. After 24 hours, any suspicious colonies are Gram-stained and tested for oxidase, which provides presumptive identification of Neisseria if positive. Further biochemical testing may be performed to differentiate N. gonorrhoeae from N. meningitides which is sometimes isolated from homosexual males. Isolated colonies should also be tested for penicillin resistance. Plates may be discarded at 48 hours if no growth is seen. Other plates are observed at 24 hours, and any suspecious colonies are isolated and tested biochemically to identify the organism. No growth or negative plates are held an additional 24 hours. Anaerobic cultures are performed on abscesses and by request. Pathogens other than N. gonorrhoeae are also tested for antibiotic susceptibility.
Microscopic analysis should always be included with genital culture. Wet preparations can identify both yeast and Trichomonas vaginalis. A Gram stain of the swab material can identify gram-negative diplococci, which is presumptive evidence of gonococcal infection. In males, a positive finding on the Gram stain obviates the need for culture and the patient can begin antibiotic treatment. In females, the diplocicci must be located intracellularly in order to make a presumptive diagnosis of gonorrhea infection, and culture must be performed to confirm the diagnosis. The presence of clue cells, epithelial cells containing gram-negative or gram-variable coccobacilli, can signal the presence of Gardnerella vaginalis. In homosexual males engaging in anal intercourse, microscopic examination may reveal Giardia lamblia or Entamoeba histolytica that originated in the intestinal tract.
For both male and female patients, urine tests for the DNA of Chlamydia trachomatis and Neisseria gonorrhoeae are available. In recent years, use of these nucleic acid amplification tests (NAATs) has increased, particularly for screening and where urethral and vervical culture samples are not possible because patients do not accept the procedure or because of logistics. These tests measure bacterial DNA that is amplified either by the ligase chain reaction (LCR) or the polymerase chain reaction (PCR). Both methods can detect the organisms within four hours, affording more rapid treatment. However, the tests do not detect any other genital tract pathogens that might be present in the patient.
Male patients can improve the accuracy of test results by not urinating for one hour prior to testing. Females should avoid douching for at least 24 hours prior to testing. If one of the DNA tests is to be used, it may be preferable to collect the first urine sample of the day. Women should be informed that having cultures performed is no more uncomfortable than routine Pap testing. Men may experience some temporary discomfort. It is preferred that these tests be done before any antibiotics are started, so that the growth of the causative agent is not suppressed.
Patients should be instructed to have no sexual contacts until test results are back.
The minor discomforts of genital testing are short lived, and no significant complications are common.
A normal result would be no growth of pathologic organisms, or no evidence of infectious organisms on DNA probe or LCR assay. Any infection identified, or organisms seen, can be appropriately treated and the patient counseled regarding prevention, if the causative agent is transmitted sexually. Yeast infections and bacterial vaginosis do not generally represent sexually transmitted diseases (STDs), whereas gonorrhea, chlamydia, herpes, and trichomonas infections are classed as STDs.
Health care team roles
Genital cultures are ordered by a physician and collected by a physician, nurse, or physician assistant. Culture, microscopic analysis, immunoassay, and DNA testing are performed by clinical laboratory scientists/medical technologists. Wet preparations may also be performed by the physician or physician assistant or nurse practitioner with appropriate training.
Nursing staff have a very important task in educating the patient in what to expect, assisting with obtaining samples, and helping to explain test results to patients. Many patients undergoing genital testing are in need of counseling regarding the risks of careless sexual behavior, and the opportunity should be used by staff for patient education to reduce risks in the future.
Group B streptococcus— A serotype of Streptococcus, Streptococcus agalactiae, which is beta hemolytic and can cause neonatal sepsis, pneumonia, or meningitis if present in the birth canal at the time of delivery especially when the delivery is difficult.
Os— The opening of the cervix, which is the mouth of the uterus.
Fishbach, Frances Talaska. A Manual of Laboratory and Diagnostic Tests, 6th ed. Lippincott, 2000: 563-565.
Malarky, Louise M., and Mary Ellen McMorrow. Nurses Manual of Laboratory Tests and Diagnostic Procedures. WB Saunders Co., 2000:177-179.
Tierney, Lawrence M., Stephen J. McPhee, and Maxine A. Papadakis. Current Medical Diagnosis and Treatment 2001. Lange Medical Books/McGraw-Hill, 2001:1309.
Campos-Outcalt, Doug. "Sexually Transmitted Disease: Easier Screening Tests, Single-dose Therapies." The Journal of Family Practice (December 2003):965-969.
Centers for Disease Control. 〈http://www.cdc.gov/nchstp/dstd/disease-info.htm〉.
National Library of Medicine. 〈http://www.nlm.nih.gov/medlineplus/ency/article/001345.htm〉.