Neisseria Sicca: Infection, Transmission & Diseases

Neisseria sicca is a bacterial species with individual strains that fall into the genus Neisseria and are classified in the superordinate family Neisseriaceae. The bacteria live as commensals in the respiratory tract of humans and require oxygen for their metabolism. The aerobes have been observed in immunocompromised humans as causative agents of pneumonia and meningitis.

What is Neisseria sicca?

The domain of bacteria is divided into different divisions. One of these is the division of Proteobacteria, which is one of the most diverse bacterial divisions of all. The division is divided into several classes with different orders. One class of Proteobacteria is the Betaproteobacteria, which includes orders such as the so-called Neisseriales. This order includes the family Neisseriaceae, which includes the genus Neisseria. Individual bacterial species in the genus Neisseria are bacteria with Gram-negative staining behavior. The genus is named after bacteriologist Albert Neisser, who discovered Neisseria gonorrhoeae and thus the gonorrhea pathogen. Neisseria bacteria can occur in the form of diplococci, in which case they appear as pairs of spherical bacterial cells. Many species of the genus are of particular medical relevance and are thought to be human pathogenic. One species of the Neisseriaceae family is the bacteria of the species Neisseria sicca, the individual strains of which have not yet been conclusively investigated. So far, the involvement of the bacteria in diseases has not been conclusively proven. Nevertheless, a possible human pathogenic property is under discussion.

Occurrence, distribution, and characteristics

Bacteria of the species Neisseria sicca are aerobic microorganisms. Consequently, the bacteria require oxygen for their metabolism and cannot grow in an oxygen-deficient environment. Oxygen is mainly used for oxidative conversion in energy metabolism. Chemically, all aerobic processes can be understood as oxidations. Bacteria possess the enzyme oxidase for oxygen utilization, so they are oxidase-positive. They are equipped with an O-repeat structure in the lipopolysaccharide. For multiplication and attachment to the cells of their host, the bacteria carry so-called pili. These are proteinergic adhesins that enable the Neisseria sicca species to attach between border zones. Adhesins ensure, for example, that the bacteria are not washed away in liquid culture media. The bacteria do not carry flagella. In addition, they do not form spores. Their optimal growth is at temperatures between 32 and 36 degrees Celsius, and they do not form pigments. Neisseria sicca are found in the human body in the mucous membranes of the upper respiratory tract, where they have access to sufficient oxygen. They usually live as commensals in the human organism. This means that in most cases colonization with the bacteria neither harms nor benefits humans. However, the bacteria can enter the blood through wounds and cause bacteremia. For people with healthy immune systems, this does not seem too likely a scenario. The bacteria are recognized by their defense system as foreign particles, attacked and contained within a very short time. In age-physiologically immunocompromised individuals, sick people, or immunosuppressed individuals, the bacteria can probably cause endogenous infections, according to speculation. The infection is called ‘endogenous’ because in this case the pathogen originates from the person’s own body. Since Neisseria sicca colonize the upper respiratory tract as commensals, infections primarily affect the area of the respiratory organs when the immune system is weak. However, a wide spread of the infection is not considered to be generally excluded.

Diseases and complaints

In the worst case, bacteremia can lead to blood poisoning in the sense of sepsis. In septic shock caused by bacteria, the circulatory system may collapse. Septic conditions are acute systemic inflammatory reactions of the entire body and are associated with danger to life. Bacteria, especially in immunocompromised individuals, can proliferate without immune system intervention and are transported through the bloodstream to various organs where they can cause infections. The extent to which bacteria of the species Neisseria sicca can cause sepsis has not yet been clarified.As pathogens, however, they appear to be associated with meningitis for immunodeficient patients. This is an inflammation of the meninges of the brain and spinal cord. Because of the close proximity of this inflammation to the brain and spinal cord, bacterial meningitis should be understood as a life-threatening condition. The most common symptoms of meningitis (inflammation of the meninges) are more or less severe headache, stiff neck, fever and loss of consciousness. There may also be nausea and hypersensitivity to light and sound. Older children in particular are relatively likely to contract Neisseria meningitidis, which is caused preferentially by meningococci of the genus Neisseria. However, since Neisseria sicca were also detectable in the cerebrospinal fluid of meningitis patients in individual cases, meningitis can probably also be caused by them. As a rule, the bacteria of these species are considered commensals until the immune system is weakened. In immunodeficient patients, the bacteria have caused pneumonia in the past, while they colonized the lungs of immune-healthy patients without pathological consequences. In connection with pneumonia, bacteria of the species Neisseria sicca can therefore not be generally described as pathogens, but only as pathogens on immunocompromised persons. The same is apparently true for meningitis caused by Neisseria sicca. Pneumonia caused by the bacterial species has primarily affected senile patients, and administration of penicillin has resulted in healing of the inflammation in every case documented to date.