Neisseria sicca is a common Gram-negative bacterium found in the human body. It is generally considered a harmless component of the normal human microbiota, coexisting with its host without causing disease.
Understanding Neisseria sicca
Neisseria sicca is a Gram-negative bacterium, appearing as cocci arranged in pairs (diplococci). It naturally inhabits various human mucosal surfaces, primarily the upper respiratory tract and oral cavity, and sometimes the genitourinary tract.
Laboratory identification involves observing specific metabolic properties and colony characteristics. It tests positive for oxidase and catalase enzymes and produces acid from carbohydrates like glucose, maltose, fructose, and sucrose, but not lactose. On agar plates, Neisseria sicca forms dry, wrinkled, and adherent colonies, which is where its name “sicca” (Latin for dry) originates.
A Benign Member of the Neisseria Family
The genus Neisseria includes well-known human pathogens, which can lead to confusion regarding Neisseria sicca. It is important to distinguish Neisseria sicca from pathogenic species such as Neisseria gonorrhoeae and Neisseria meningitidis, responsible for diseases like gonorrhea and bacterial meningitis.
Despite belonging to the same genus, Neisseria sicca generally lacks the specific virulence factors that make its pathogenic counterparts harmful. Pathogenic species like Neisseria meningitidis possess protective capsules and surface proteins, while Neisseria gonorrhoeae uses pili for attachment. In contrast, Neisseria sicca does not possess such factors, limiting its ability to cause widespread disease.
As a commensal organism, Neisseria sicca lives in harmony with its human host. Its presence is part of the natural, healthy microbial balance on mucosal surfaces. Finding Neisseria sicca in a sample does not indicate an infection or pose a health threat.
When Neisseria sicca Becomes Notable
While Neisseria sicca is generally harmless, rare instances associate it with clinical infections. These cases are exceptional and usually arise in individuals with weakened immune systems, or when the bacteria gain access to normally sterile sites within the body. Such access might occur due to trauma, medical procedures, or prosthetic devices.
Reported infections are uncommon but can include endocarditis, meningitis, pneumonia, and conjunctivitis. For example, endocarditis caused by N. sicca has been documented in patients with pre-existing heart conditions. Cases of meningitis have been linked to instances where the bacterium was introduced into the central nervous system, such as after spinal injection procedures. Even in these rare occurrences, Neisseria sicca acts as an opportunistic pathogen rather than a primary one.