Neisseria
Neisseria species bacteria are from the family Neisseriaceae and differ from other pyogenic (pus-producing) cocci in their fundamental properties, as well as in the specific kinds of diseases they produce. Neisseria are Gram-negative, nonmotile, diplococci, which commonly have a flattened or concave side. The pathogenic strains are fermentive. They are easily killed by drying, chilling, sunlight, acids, or alkalies. There are several species of Neisseria with two of them taking their names from the diseases they produce. N. meningitidis, commonly referred to as meningococcus, is the leading cause of adult meningitis. N. gonorrhoeae, usually called gonococcus, is the cause of the most frequently reported sexually transmitted disease. Although these two species are similar in their structure and physiological makeup, they produce vastly different diseases.
Neisseria gonorrhoeae is responsible for the ancient disease of gonorrhea. It was first described in 3500 BCE, and syphilis a short time later. Chinese writings referred to it as "different from all the others," the Greeks called it a urinary blockage, and the Bible refers to it as a "discharge." Neisseria gonorrhoeae is a part of the group of "venereal" diseases named after Venus, the goddess of "love." The bacterium responsible for gonorrhea was named after Albert Neisser, a German bacteriologist who isolated it in 1879. Until 1937 with the discovery of sulfa drugs and penicillin, there was no cure for the disease. However, the bacterium has learned how to resists these antibiotics, causing the spread of the disease with mutant forms. There is no natural immunity nor any vaccine, and millions worldwide are still being infected. The incubation period is three to five days after initial contact, and, if left untreated, infectiousness can last for months, but, with antibiotic treatment, infectiousness can be cleared within twenty-four hours.
Only about 10% of men and 20% of women show any signs or symptoms of gonnorhea. Most remain asymptomatic carriers who spread the disease but do not suffer significantly themselves. For men, symptoms have been described as being equal to the feeling of razor blades during urination. They will often have a thick white or yellow puslike discharge. Many women have an abnormal green or yellow discharge, vaginal bleeding between periods, pelvic discomfort, and pain during urination. Some will develop PID (pelvic inflammatory disease) that leads to infertility, but this is only one of the myriad of internal problems it can cause. Very few pregnant women have symptoms. Although lesbians rarely pass on this disease to their partners, gay men do, causing infections in the rectum and the throat. Non-sexual transmission does happen, as in the cases of infants who contract the disease in their eyes during birth from an infected mother. This is the reason that silver nitrate is applied to the eyes of a newborn. Older children who have contracted the disease are almost always as the result of sexual abuse.
Non-specific urethritis and non-gonococcal urethritis are initially indistinguishable from gonorrhea, and are caused by Chlamydia trachomatis, a bacterium that commonly infects the cervix and urethra. A rare complication is Reiter's syndrome, characterized by conjunctivitis and arthritis, mostly affecting the lower back and legs of young men, in addition to the urethritis. Reiter's syndrome is also associated with certain infections caused by Shigella species, Yersinia species, and Campylobacters.
Neisseria meningitidis is responsible for one type of meningitis, known as meningococcus. Meningitis is a disease in which the membranes surrounding the brain and spinal cord become painfully inflamed. Neisseria meningitidis species can be divided into thirteen different serogroups. Group A, sometimes called the epidemic strain, is the most frequent cause of the meningococcal disease around the world. In the US, however, the responsible strains are typically serotypes B, C, Y, and W-135. Meningococcus is not a rare bacterium. It inhabits the back of the throat in most humans as normal flora. Transmitters of the diseases are usually asymptomatic carriers who cough and sneeze as part of every day life. Most people breathe in the organism, causing no ill effects, but, when those with weakened or compromised immune systems breathe it in, it turns into a threatening disease.
When the organism enters the body, it is deposited in various tissues, including the skin, meninges, joints, and lungs. Within a few days, signs and symptoms of an infection develop. Symptoms begin with a stiff neck and fever progressing to hemorrhages, coma, and death within a day.
Meningococcal meningitis can have a death rate as high as 85% if not treated. But even with treatment, the mortality rate still averages 10%. Most of the time, the bacterium remains harmless. No one knows exactly why it will suddenly turn on its host, but those with weakened or compromised immune systems are known to be at a higher risk. Disease occurs when the bacteria escape the membranes of the throat, invade the bloodstream, and multiply unchecked.
The meningiococcal bacterium is similar to the polio virus and seems to follow a twenty-year pattern throughout the 19th century. In an outbreak in Nigeria in the late 1940s, over 14,000 died from the disease and 80% of the children succumbed. An outbreak in 1974 was stopped by an unprecedented massive vaccination campaign that saw some eighty million people in São Paulo, Rio de Janeiro, and other Latin American cities vaccinated against the disease. However, despite this campaign, more than ¼ million people contracted the disease, and more than 11,000 died, leaving 1/3 of the survivors neurologically damaged. The Brazilian outbreak was compounded by the fact that two strains were raging simultaneously. Type A was new, yet treatable with antibioticss. Type C was not new and proved to be drug-resistant. Both are now controlled by other drugs, but as with most bacteria, this will last for only a short period of time before a new strain evolves. Several clusters of C infection occurred in the US in 1993, but about half of all severe incidents of meningococcal disease in America are caused by type B.
A new vaccine against meningitis type C is made from a small part of the meningococcal bacteria. It stimulates the body's immune system to produce antibodies that act as a defence against group C meningococcal disease. The new vaccine does not prevent infection by other viruses or bacteria, including group B meningococcus. The general population is not usually immunized against the disease as incidents are relatively rare. However, military recruits are vaccinated, as well as those with sickle cell anemia. Interestingly, the main reason for not immunizing the populace as a whole is that the vaccination predisposes them to N. meningitidis infection.
Acinetobacter is a member of the family Neisseriaceae, with one species, A. calcoaceticus, and two subspecies -- A. anitratus and A. lwoffi. These organisms are not closely related to the pseudomonads, but do fit the description of nonfermenting Gram-negative bacilli. Acinetobacter is an oxidase negative, nonmotile, non-spore-forming coccobacillus that is normally found in soil, water, and in moist areas of the skin. Infections are mainly seen in those whose immune systems have been compromised and are in a hospital setting. Most infections are of the lower repiratory nature, but urinary tract infections do occur, as well as bacteremia following an insertion of an IV catheter.
