Gram Negative Bacteria Neisseria

Gram Negative Bacteria

Neisseria:

The genus Neisseria consists of gram-negative, catalase –ve, oxidase +ve, non motile, diplococci. Grows well at aerobic conditions and some spp. are facultative anaerobes. 5% CO2 enhance the growth of N., some spp. are capsulated and others are not. N. spp. are very fastidious in their growth.
Two Neisseria species are pathogenic for humans:
1. Neisseria gonorrhoeae (Gonococcus) causes “Gonorrhoea”.
2. Neisseria meningitidis (Meningicoccus) causes “Meningitis”.
Both spp. frequently observed inside polymorphonuclear leukocytes (Nutrophils) of clinical samples obtained from infected patients, but cannot be distinguished from each other under the microscope. However, they can be differentiated in the lab by sugar use patterns, and the sites of their primary infections. Both bacteria are classified as pyogenic cocci because infections by these organisms are also characterized by the production of purulent (pus-like) material comprised largely of white blood cells.
Neisseria gonorrhoeae: is usually transmitted during sexual contact or, more rarely, during the passage of a baby through an infected birth canal. It does not survive long outside the human body because it is highly sensitive to dehydration.
Lab. Diagnosis:
1. Specimens: Include material from genital sources (for both ? and ?) like uretheral, vaginal discharge [creamy yellowish color] and extra-genital specimens in disseminated gonococcal infections eg. skin, joint fluid and blood.
2. Direct stain: Gram stain is made to the specimens above and will show G –ve, diplococci, non-capsulated by (capsular stain).
3. Growth conditions for cell culture: N. gonorrhoeae grows best under aerobic conditions in the presence of CO2, cannot grow at temp. below 22°C, the colonies are non hemolytic, gray to white in color. N. gonorrhoeae ferments glucose but not maltose, lactose, or sucrose. [Note: N. meningitidis ferments glucose and maltose]. All members of the genus are oxidase-positive. [Note: The oxidase test is used to identify neisseriae, but does not distinguish between gonococci, meningococci, and non-pathogenic neisseriae.]
4. Culture: N. is fastidious grows on enriched media like chocolate agar and the selective one is Thayer Martin medium which is chocolate agar supplemented with several antibiotics that suppress the growth of nonpathogenic neisseriae and other normal and abnormal flora) is typically used to isolate gonococci. The use of this medium is important for cultures that are typically obtained from sites such as the genitourinary tract or rectum, where there is normally an abundance of flora. On nonselective media, the normal flora overgrows the gonococci.