Haemophilus refers to a genus of 16 different species of rod-shaped, gram-negative, bacteria, all of which are members of the Pasteurellaceae family. The facultative (temporarily) anaerobic bacteria can colonize mucous membranes and require certain growth factors contained in erythrocytes for their growth. Some of the 16 species can cause respiratory infections or the venereal disease “soft chancre” or “ulcus molle.”
What is Haemophilus?
The genus Haemophilus gram-negative bacteria includes 16 different species of facultative anaerobic rod-shaped bacteria, a few of which are pathogens. Their generic name, Haemophilus, is in agreement with their requirement for certain growth factors contained in hemoglobin. Haemophilus bacteria do not form spores and cannot actively move. A few species of the bacteria can cause respiratory infections, the venereal disease ulcus molle, conjunctivitis of the eyes, and nonspecific inflammation of the vagina and uterus. In rare cases, subsets of the bacteria can also cause inflammation of the inner lining of the heart (endocarditis) and meningitis (meningitis). Basically, the encapsulated Haemophilus bacterial strains are classified as pathogenic because their control by the body’s own phagocytes (macrophages) is more difficult. The unencapsulated bacterial strains are more likely to be part of the normal bacterial flora of the mucous membranes and only develop pathogenicity when the immune system is impaired and the epithelium of the mucous membranes is pre-damaged.
Significance and function
Significance and functions of nonpathogenic Haemophilus bacteria for the metabolism of the body and specifically for the mucous membranes of the respiratory organs are not known. Unencapsulated – nonpathogenic – species are quasi-omnipresent in the mucous membranes of the respiratory tract, especially in the upper respiratory tract, and are part of the natural bacterial flora. Most Haemophilus bacteria are viable outside the body for only a short time. Since they do not develop spores, infection or transmission of the bacteria from person to person is only possible via droplet infection. A characteristic of the bacteria is their need for hemin and NAD, which is contained in the red blood cells (erythrocytes) and plays an important role in the energy balance of the cells in the controlled oxidation process. Since the bacteria themselves are unable to obtain the required substances via hemolysis of the erythrocytes, they need other bacteria, e.g. staphylococci, which have the ability to release hemoglobin via hemolysis of the erythrocytes. This process can be readily observed in laboratory cultures and is known as the nurse phenomenon. Because infants and young children are particularly at risk, the Standing Committee on Vaccination (STIKO) recommends vaccination to prevent infection with influenza bacterium type b in infants as young as 2 months of age. Before the introduction of vaccination in 1990, there were approximately 2,000 cases of infection with the influenza bacterium in Germany. The number of new cases dropped dramatically thereafter, and only 70 cases were registered in 2004. A proven infection with Haemophilus influenzae, type b, is reportable by name in Germany. The incubation period from infection to disease outbreak is a few days.
Diseases and symptoms
Known dangers come mainly from the few pathogenic species of Haemophilus bacteria at the same time attacked immune system. The best-known bacterium with the greatest pathogenic potential is Haemophilus influenzae. This bacterium – also known as the Pfeiffer influenza bacterium – colonizes almost exclusively the mucous membranes of the nose, throat and bronchial tubes and can lead to infections there. Because the bacterium was almost always detected in influenza patients, there was a long-held belief that the bacterium itself was the causative agent of influenza, an assumption that has long been clearly refuted. Six different variants of Haemophilus influenzae are known, each of which differs in the structure of its capsular walls made of polysaccharides (types A to F), with type B being considered particularly pathogenic. In the case of a weakened immune system or damage to the corresponding mucous membrane, the different types of the influenza bacterium can cause diseases such as bronchitis, pneumonia, inflammation of the middle ear, inflammation of the laryngeal cap, conjunctivitis and even meningitis.Haemophilus parainfluenzae, closely related to the influenza bacterium, also colonizes the mucous membranes of the respiratory organs, but is only occasionally pathogenic if certain conditions are met. In exceptional cases, the bacterium can lead to serious respiratory infections, meningitis, or even sepsis. Another species closely related to the influenza bacterium is Haemophilus aegypticus, which is widespread in North Africa and has been identified as the causative agent of conjunctivitis. The bacterium Haemophilus ducreyi, causative agent of the venereal disease ulcus molle (soft chancre), which is widespread in the tropics, has already developed resistance to some antibiotics. Infection with Haemophilus aphrophilus can result in purulent abscesses, and if infection with the bacterium occurred through the bloodstream (bacteremia), endocarditis (inflammation of the inner lining of the heart) or even sepsis can develop. Infections with Haemophilus bacteria can be treated with targeted antibiotic treatment with a good prognosis, but preexisting resistance to certain antibiotics must be expected.
