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Lab 16: Isolation and Identification of Neisseriae, Mycobacteria, and Obligate Anaerobes

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    The neisseriae are a group of Gram-negative diplococci 0.6-1.5 µm in diameter (see Fig. 1A). Two species of Neisseria, N. gonorrhoeae and N. meningitidis, are considered as true human pathogens. Both of these organisms possess pili and adhesins for adherence to host cells, produce endotoxins, and resist destruction within phagocytes. N. meningitidis also produces a capsule to resist phagocytic engulfment.

    • Scanning electron micrograph Neisseria gonorrhoeae; courtesy of Dennis Kunkel's Microscopy.
    • Scanning electron micrograph of Neisseria meningitidis. © Margaret Ketterer, author. Licensed for use, ASM MicrobeLibrary.
    • Transmission electron micrograph Neisseria gonorrhoeae; courtesy of CDC.

    In females, 30-50 percent of those initially infected are asymptomatic or show mild symptoms. They are, however, still infectious. Initially, the organism invades the cervix, the urethra, and frequently the rectum. In about 15 percent of the cases, the organism spreads up the reproductive tract and infects the fallopian tubes causing pelvic inflammatory disease (PID). The resulting inflammation and scar tissue formation may result in sterility or abnormal (ectopic or tubal) pregnancies.

    The gonococcus may also cause extragenital infections such as pharyngitis (from oral-genital sex), ophthalmia (from inoculation of the eyes with contaminated fingers), and proctitis (from anal sex). In 1% - 3% of infected women and a lower percentage of infected males, the organism invades the blood and disseminates, causing a rash, septic arthritis, endocarditis, and/or meningitis. Dissemination occurs more frequently in females. Congenital gonorrhea is known as ophthalmia neonatorum and occurs as a result of the eyes of newborns becoming infected as the baby passes through the birth canal.

    Neisseria meningitidis (the meningococcus) is the causative organism of meningococcal (epidemic) meningitis. There are between 2000 and 3000 cases of meningococcal meningitis per year in the U.S. Approximately 50% of the cases occur in children between 1 and 4 years old. N. meningitidis infects the nasopharynx of humans causing a usually mild or subclinical upper respiratory infection. Colonization of the nasopharynx may persist for months. However, in about 15% of these individuals, the organism invades the blood and disseminates, leading septicemia and from the there may cross the blood-brain barrier causing meningitis. A petechial skin rash, caused by endotoxin in the blood, appears in about 75 percent of the septic cases and fatality rates for meningococcal septicemia are as high as 30 percent as a result of the shock cascade. A fulminating form of the disease, called Waterhouse-Frederichsen syndrome, can be fatal within several hours due to massive intravascular coagulation and resulting shock, probably a result of massive endotoxin release. N. meningitidis is especially dangerous in young children.

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    Lab 16: Isolation and Identification of Neisseriae, Mycobacteria, and Obligate Anaerobes is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.