Sexually transmitted diseases cultures

Definition

Sexually transmitted diseases are infections spread from person to person through sexual contact. A culture is a test in which a laboratory attempts to grow and identify the microorganism causing an infection.

Purpose

Sexually transmitted diseases (STDs) produce symptoms such as genital discharge, pain during urination, bleeding, pelvic pain, skin ulcers, or urethritis. Often, however, they produce no immediate symptoms. Therefore, the decision to test for these diseases must be based not only the presence of symptoms, but on whether or not a person is at risk of having one or more of the diseases. Activities, such as drug use and sex with more than one partner, put a person at high risk for these diseases.

STD cultures are necessary to diagnose certain types of STDs. Only after the infection is diagnosed can it be treated and further spread of the infection prevented. Left untreated, consequences of these diseases range from discomfort to infertility to death. In addition, these diseases, if present in a pregnant woman, can be passed from mother to fetus.

Description

Gonorrhea, syphilis, chlamydia, chancroid, herpes, human papillomavirus, human immunodeficiency virus (HIV), and mycoplasma are common sexually transmitted diseases. Not all are diagnosed with a culture. For those that are, a sample of material is taken from the infection site, placed in a sterile container, and sent to the laboratory.

Bacterial cultures

In the laboratory, a portion of material from the infection site is spread over the surface of several different types of culture plates and placed in an incubator at body temperature for one to two days. Bacteria present in the sample will multiply and appear on the plates as visible colonies. They are identified by the appearance of their colonies and by the results of biochemical tests and a gram stain. The Gram stain is done by smearing part of a colony onto a microscope slide. After it dries, the slide is stained with purple and red stains, then examined under a microscope. The color of stain picked up by the bacteria (purple or red), the shape (such as round or rectangle), and the size provide valuable clues as to the identity and which antibiotics might work best. Bacteria that stain purple are called Gram-positive; those that stain red are called gram-negative.

The result of the gram stain is available the same day or in less than an hour if requested by the physician. An early report, known as a preliminary report, is usually available after one day. This report will tell if any microorganisms have been found yet, and if so, their Gram stain appearance-for example, a Gram-negative rod or a gram-positive cocci. The final report, usually available in one to seven days, includes complete identification and an estimate of the quantity of the microorganisms isolated.

A sensitivity test, also called antibiotic susceptibility test, commonly done on bacteria isolated from an infection site, is not always done on bacteria isolated from a sexually transmitted disease. These bacteria often are treated using antibiotics that are part of a standard treatment protocol.

Gonorrhea

Neisseria gonorrhoeae, also called gonococcus or GC, causes gonorrhea. It infects the surfaces of the genitourinary tract, primarily the urethra in males and the cervix in females. On a gram stain done on material taken from an infection site, the bacteria appear as small gram-negative diplococci (pairs of round bacteria) inside white blood cells. Neisseria gonorrhoeae grows on a special culture plate called Thayer-Martin (TM) media in an environment with low levels of oxygen and high levels of carbon dioxide.

The best specimen from which to culture Neisseria gonorrhoeae is a swab of the urethra in a male or the cervix in a female. Other possible specimens include vagina, body fluid discharge, swab of genital lesion, or the first urine of the day. Final results usually are available after two days. Rapid nonculture tests are available to test for GC and provide results on the same or following day.

Chancroid

Chancroid is caused by Haemophilus ducreyi. It is characterized by genital ulcers with nearby swollen lymph nodes. The specimen is collected by swabbing one of these pus-filled ulcers. The gram stain may not be helpful as this bacteria looks just like other Haemophilus bacteria. This bacteria only grows on special culture plates, so the physician must request a specific culture for a person who has symptoms of chancroid. Even using special culture plates, Haemophilus ducreyi is isolated from less than 80% of the ulcers it infects. If a culture is negative, the physician must diagnose chancroid based on the person's symptoms and by ruling out other possible causes of these symptoms, such as syphilis.

Mycoplasma

Three types of mycoplasma organisms cause sexually transmitted urethritis in males and pelvic inflammatory disease and cervicitis in females: Mycoplasma hominis, Mycoplasma gentialium, and Ureaplasma urealyticum. These organisms require special culture plates and may take up to six days to grow. Samples are collected from the cervix in a female, the urethra or semen in a male, or urine.

Syphilis

Syphilis is caused by Treponema pallidum, one in a group of bacteria called spirochetes. It causes ulcers or chancres at the site of infection. The organism does not grow in culture. Using special techniques and stains, it is identified by looking at a sample of the ulcer or chancre under the microscope. Various blood tests also may be done to detect the treponema organism.

Chlamydia

Chlamydia is caused by the gram-negative baterium Chlamydia trachomatis. It is one of the most common STDs in the United States and generally appears in sexually active adolescents and young adults. While chlamydia often does not have any initial symptoms, it can, if left untreated, lead to pelvic inflammatory disease and sterility. Samples are collected from one or more of these infection sites: cervix in a female, urethra in a male, or the rectum. A portion of specimen is combined with a specific type of cell and allowed to incubate. Special stains are performed on the cultured cells, looking for evidence of the chlamydia organism within the cells.

Viral cultures

To culture or grow a virus in the laboratory, a portion of specimen is mixed with commercially prepared animal cells in a test tube. Characteristic changes to the cells caused by the growing virus help identify the virus. The time to complete a viral culture varies with the type of virus. It may take several days or up to several weeks.

Herpes virus

Herpes simplex virus type 2 is the cause of genital herpes. Diagnosis is usually made based on the person's symptoms. If a diagnosis needs confirmation, a viral culture is performed using material taken from an ulcer. A Tzanck smear is a microscope test that can rapidly detect signs of herpes infection in cells taken from an ulcer. The culture takes up to 14 days.

Human papillomavirus

Human papillomavirus causes genital warts. This virus will not grow in culture; the diagnosis is based on the appearance of the warts and the person's symptoms. In late 2003, the U.S. Food and Drug Administration (FDA) approved a human papillomavirus (HPV) DNA test with a Pap smear for screening women age 30 and older. The combined test would help physicians determine which women were at extremely low risk for cervical cancer and which should be more closely monitored.

HIV

Human immunodeficiency virus (HIV) is usually diagnosed with a blood test. Cultures for HIV are possible, but rarely needed for diagnosis. However, newer rapid tests were developed in 2003 and awaiting approval from the FDA. These tests were cheaper and could deliver results in as little as 15 or 20 minutes.

Preparation

Generally, the type of specimen depends on the type of infection. Cultures always should be collected before the person begins taking antibiotics. After collection of these specimens, each is placed into a sterile tube containing a liquid in which the organism can survive while in route to the laboratory. The new rapid tests rely on blood samples but initial results are not sent to a lab but are processed onsite. An additional rapid test that could detect HIV antibodies in saliva also was under FDA approval application in late 2003.

Urethral specimen

Men should not urinate one hour before collection of a urethral specimen. The physician inserts a sterile, cotton-tipped swab into the urethra.

Cervical specimen

Women should not douche or take a bath within 24 hours of collection of a cervical or vaginal culture. The physician inserts a moistened, nonlubricated vaginal speculum. After the cervix is exposed, the physician removes the cervical mucus using a cotton ball. Next, he or she inserts a sterile cotton-tipped swab into the endocervical canal and rotates the swab with firm pressure for about 30 seconds.

Vaginal specimen

Women should not douche or take a bath within 24 hours of collection of a cervical or vaginal culture. The physician inserts a sterile, cotton-tipped swab into the vagina.

Anal specimen

The physician inserts a sterile, cotton-tipped swab about 1 inch into the anus and rotates the swab for 30 seconds. Stool must not contaminate the swab.

Oropharynx (throat) specimen

The person's tongue is held down with a tongue depressor, as a healthcare worker moves a sterile, cotton-tipped swab across the back of the throat and tonsil region.

Urine specimen

To collect a "clean-catch" urine, the person first washes the perineum, and the penis or labia and vulva. He or she begins urinating, letting the first portion pass into the toilet, then collecting the remainder into a sterile container.

Normal results

These microorganisms are not found in a normal culture. Many types of microorganisms, normally found on a person's skin and in the genitourinary tract, may contaminate the culture. If a mixture of these microorganisms grow in the culture, they are reported as normal flora.

Abnormal results

If a person has a positive culture for one or more of these microorganisms, treatment is started and his or her sexual partners should be notified and tested. Certain laws govern reporting and partner notification of various STDs. After treatment is completed, the person's physician may want a follow-up culture to confirm the infection is gone.

Key Terms

Culture

A laboratory test done to grow and identify microorganisms causing infection.

Gram stain

Microsopic examination of a portion of a bacterial colony or sample from an infection site after it has been stained by special stains. Certain bacteria pick up the purple stain; these bacteria are called gram positive. Other bacteria pick up the red stain; these bacteria are called gram negative. The color of the bacteria, in addition to their size and shape, provide clues as to the identity of the bacteria.

Sensitivity test

A test that determines which antibiotics will kill the bacteria isolated from a culture.

Sexually transmitted diseases (STD)

Infections spread from person to person through sexual contact.

For Your Information

Resources

Books

• Palella, Frank J., and Robert L. Murphy. "Sexually Transmitted Diseases." In The Biologic and Clinical Basis of Infectious Diseases, edited by Standford T. Shulman, et al. Philadelphia: W. B. Saunders Company, 1997.

• "Approval Sought for HIV-1 Test that Detects Antibodies in Oral Fluid or Plasma." AIDS Weekly (October 27, 2003): 23.
• Centers for Disease Control and Prevention. "1998 Guidelines for Treatment of Sexually Transmitted Diseases." Morbidity and Mortality Weekly Report (MMWR) (January 1998): RR-1.
• "1998 FDA Approves DNAwithPap for Screening Women (Greater than or Equal to) Age 30)." Contemporary OB/Gyn (October 2003): 105.
• Miller, Karl E. "Sexually Transmitted Diseases." Primary Care (March, 1997): 179-193.
• "New HIV Rapid Test Is 100 Percent Accurate." Health & Medicine Week (September 15, 2003): 194.
• "One-step HIV Test May Be Cheaper, Faster, Less Wasteful." Medical Letter on the CDC & FDA (October 5, 2003): 5.
• St. Lawrence, Janet S., et al. "STD Screening, Testing, Case Reporting, and Clinical and Partner Notification Practices: A National Survey of U.S. Physicians." The American Journal of Public Health (November 2002): 1784.

• American Social Health Association. PO Box 13827, Research Triangle Park, NC 27709. (800) 227-8922. http://sunsite.unc.edu/ASHA.
• Centers for Disease Control and Prevention. National Center for HIV, STD, and TB Prevention. 1600 Clifton Road NE, Atlanta, GA 30333. (404) 639-8000. http://www.cdc.gov/nchstp/od/nchstp.html.

Source: Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group

The Essay Authors are Nancy J. Nordenson, Teresa G. Odle.

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