Neisseria flavescens are a bacterial species belonging to the division Proteobacteria, the class Betaproteobacteria, and the order Neisseriales, and belong to the genus Neisseria of the family Neisseriaceae. The obligate aerobic bacteria are basically apathogenic and live as commensals in the upper respiratory tract of humans. However, they have now been linked as pathogens to cases of meningitis, pneumonia, and endocarditis.
What are Neisseria flavescens?
Bacteria of the genus Neisseria are a group of bacteria with Gram-negative staining behavior that are classified in the family Neisseriaceae and thus the only family in the order Neisseriales of Beta-Proteobacteria. The parent division corresponds to the multiform group of cell-nucleated Proteobacteria. The Neisseria were named after bacteriologist Albert Neisser. He is considered the first describer of the gonorrhea pathogen Neisseria gonorrhoeae. The individual species of Neisseria occur inform of diplococci. Thus, they occur in paired arrangements of spherical bacterial cells. Four different species of Neisseria are of high medical relevance. One of them is the species Neisseria flavescens, which is characterized by the golden yellow coloration of its colonies. Like all other Neisseria, the species Neisseria flavescens is obligately aerobic. At their contact sites, the bacteria bear a flattened shape that makes them resemble a coffee bean. Neisseria flavescens include different strains. They are generally considered to be apathogenic. However, their role as pathogens is so far unclear to controversial, as they could be isolated from different infections in recent times. Normally, they inhabit humans as commensals.
Occurrence, distribution, and characteristics
Neisseria flavescens form colonies in culture with typically golden yellow coloration. Their metabolism is obligate aerobic. That is, they depend on oxygen for growth and undergo oxidation by means of the enzyme oxidase. The elemental oxygen is essentially required by them for metabolism within the energy metabolism. Obligate aeroby applies to all species of Neisseria. Many other bacteria have an extremely adaptable metabolism and are thus not obligatorily dependent on oxygen. Thus, aerobicity of Neisseria is an important feature in differentiating them from other bacteria. Neisseria flavescens form polysaccharides from sucrose and are susceptible to colistin. In addition to oxidase, the bacteria possess the enzyme catalase. Nevertheless, unlike many other bacteria, they cannot convert lactose, fructose, mannose, glucose and similar substances to acid. The constant temperature in the human body provides ideal growth conditions for the species Neisseria flavescens. Since they depend on oxygen, they particularly colonize the human respiratory tract. The mucous membranes of the upper airways are a particularly favored environment. The bacteria live there as commensals. Commensals neither harm nor benefit their host. This neutral colonization is most likely to occur in bacteria that have been using humans as hosts for a long time. The longer a bacterium has inhabited a particular organism, the more likely mutual adaptation has occurred. Since bacteria of the species Neisseria flavescens colonize a human’s upper respiratory tract without causing symptoms, they are generally considered apathogenic. Nonetheless, medical science considers the species’ bacteria to be a major factor in epidemics, such as the not-too-long ago meningitis outbreak in Chicago.
Diseases and ailments
Neisseria flavescens apparently can play a pathogenic role under certain circumstances. They were isolated from an epidemic in the Chicago meningitis outbreak. The bacteria were present in the cerebrospinal fluid of infected individuals. In about forty-seven cases of meningitis at that time, about fourteen persons carried Neisseria flavescens. Because the mortality rate among the fourteen individuals with Neisseria flavescens in their cerebrospinal fluid was higher than that of the other patients, the relevance of the bacterium to meningitis has been emphasized ever since. Beyond meningitis, the bacterial species can apparently cause sepsis if it is carried into the bloodstream. This may be the case, for example, after upper respiratory surgery.The risk of sepsis exists above all for persons who are immunocompromised due to age or illness. A healthy immune system attacks the bacteria after they enter the blood system and usually renders them harmless before they can cause blood poisoning (sepsis). As a pathogen, the bacterial species can apparently present with fever, chills, headache, and muscle pain or joint pain and rash. Swabs from skin lesions or blood cultures can be used to identify the pathogens. In addition to meningitis and sepsis, the species Neisseria flavescens has been isolated in the past from inflammation in the lower respiratory tract. However, pathogen identification in the context of pneumonia and empyema has so far occurred exclusively in a diabetic patient. This association suggests that aspiration (ingestion) of bacteria from the upper respiratory tract carries the risk of pneumonia, at least in constitutionally debilitated patients. The bacteria of the species Neisseria flavescens have also been identified as the causative agent of endocarditis. Endocarditis occurs primarily when bacteria are carried into the blood and reach the heart via the blood. Patients with an already damaged heart are apparently particularly susceptible to this form of infection. For strains of the species Neisseria flavescens, penicillin administration is usually an ineffective treatment. Administration of cefotaxime showed improvement of symptoms in most cases of infection.
