Numerous problems affect the culture of Neisseria gonorrhoeae. A screening culture for gonorrhea detects only 65-85% of infected women. The yield of those cultures is improved by careful sampling and the use of a second specimen. Several selective media enhance the growth and isolation of Neisseria, but 3% of the strains are inhibited by those media. Sixteen percent fewer infections are detected when long-term transport of gonorrhea culture specimens is used instead of on-site bacteriologic testing.
PIP: The diagnosis of gonorrhea in men can be established by observing gram-negative intracellular diplococci in Gram's stained urethral discharge, but more sensitive screening is required for women, who may be asymptomatic in 80% of cases. Routine screening for gonorrhea detects only 65-85% of infected women. Careful sampling from the endocervix and use of a 2nd specimen can improve the yield. Care should be taken to avoid disenfectants and lubricants that might inhibit culture growth. Allowing adequate time for absorption of organisms onto the swab and prewarming the culture medium improve the recovery rate. Dacron and calcuim alginate swabs are theoretically better than cotton because they do not contain fatty acids hostile to N. gonorrhoeae. 3 media are recommended by the Centers for Disease Control: Martin-Lewis (ML), modified Thayer-Martin (MTM), and modified New York City (MNYC). Each of the 3 has unique advantages and disadvantages, and each can enhance growth and isolation of Neisseria. Strains inhibited by the vancomycin in all 3 media can be detected by parallel cultures on chocolate agar, a procedure not always practical for routine screening. 16% fewer infections are detected when longterm transport of gonorrhea culture specimens is required instead of on-site bacteriologic testing. For longterm transport, culture media in a CO2 enriched environment are best. The JEMBEC system with a CO2 generating tablet enclosed in a ziploc bag is a convenient system. The cultures must be incubated before transport. For onsite testing and transport lasting less than 3 hours, a nonnutrient system such as modified Stuart's medium is sufficient. The JEMBEC system and direct plating on selective media with transport in a candle jar are also acceptable for short-term transport. Presumptive identification is based on 1) the opaque, convex, and gray-white appearance of colonies incubated for 24-48 hours at 35 degrees Celsius with increased CO2 2) identification of typical gram-negative diplococci on Gram's staining of a characteristic colony, and 3) demonstration of the presence of cytochrome oxidase in the colonies. Presumptive identification is at least 98% specific. Confirmation is usually based on carbohydrate utilization tests or immunologic methods, including fluorescent antibody and coagglutination systems. These tests are quicker than carbohydrate utilization tests but have a 2-3% false-positive rate. Carbohydrate utilization techniques require 48-72 hours but are more specific than immunologic methods and should be used for medicolegal cases.