Гемофильная палочка: характеристика, патогенность и вакцинопрофилактика.

Species of bacterium

Haemophilus influenzae (formerly called Pfeiffer's bacillus or Bacillus influenzae) is a Gram negative, non motile, coccobacillary, facultatively anaerobic, capnophilic pathogenic bacterium of the family Pasteurellaceae. The bacteria are mesophilic and grow best at temperatures between 35 and 37 °C. H. influenzae was first described in 1893 by Richard Pfeiffer during an influenza pandemic when he incorrectly identified it as the causative microbe, which is why the bacteria was given the name "influenzae". H. influenzae is responsible for a wide range of localized and invasive infections, typically in infants and children, including pneumonia, meningitis, or bloodstream infections. Treatment consists of antibiotics; however, H. influenzae is often resistant to the penicillin family, but amoxicillin/clavulanic acid can be used in mild cases. Serotype B H. influenzae have been a major cause of meningitis in infants and small children, frequently causing deafness and mental retardation. However the development in the 1980s of a vaccine effective in this age group (the Hib vaccine) has almost eliminated this in developed countries. This species was the first organism to have its entire genome sequenced.

H. influenzae is a small Gram negative bacterium, approximately 0.3 micrometer to 1 micrometer. Like other Gram negative bacteria, H. influenzae has a thin peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharide. Some types of H. influenzae contain a polysaccharide capsule around the outer membrane to aid in protection and colonization. The bacteria are pleomorphic, meaning the shape of the bacterium is variable, however it is typically coccobacillus or rod shaped. H. Influenzae contains pili, which are specialized to adhere to the human nasopharynx. The H. Influenzae pili, unlike those of E. coli, resist unwinding, allowing for stronger adhesion to resist expulsion when coughing or sneezing. A minority of non typeable, or unencapsulated, H. influenzae employ a variety of attachment techniques, such as pili, adhesins, or Hia and Hap proteins. Though the bacteria possess pili, they are not used for traditional movement or motility, and the bacterium is still considered to be non motile. The cell wall of H. influenzae bacterium contains various proteins, referred to as autotransporters, for adherence and colony formation. H. influenzae prefers to bind to mucus linings or non ciliated epithelial cells, which is facilitated by Hap𝘴 autotransporters in the cell wall binding with unknown receptors within the epithelium. The Hap𝘴 autotransporters also facilitate the formation of microcolonies of the bacteria. These microcolonies are likely responsible for the formation of various biofilms within the body, such as those responsible for middle ear or lung infections. These proteins are the targets blocked by penicillin and other beta lactam antibiotics that bind to PBPs, hence their name. Some antibiotic resistant isolates of H. Influenzae contain modified PBPs that resist beta lactam action by producing beta lactamases to degrade these antibiotics. This resistance is likely due to a N526K mutation, or R517H substitution in conjunction with another unknown mutation. The R517H substitution alone did not have a lower affinity for penicillin, and therefore cannot cause resistance alone.

H. influenzae isolates were initially characterized as either encapsulated (having an extracellular polysaccharide layer, the bacterial capsule) or unencapsulated. Encapsulated strains were further classified on the basis of the immune response to the type of polysaccharides in their capsule. The six generally recognized types of encapsulated H. influenzae are: a, b, c, d, e, and f. H. Influenzae type b, also known as Hib, is the most common form, recognizable by its polyribosyl ribitol phosphate (PRP) capsule, and found mostly in children. Types a, e, and f have been isolated infrequently, while types d and c are rarely isolated. Unencapsulated strains are more genetically diverse than the encapsulated group. Unencapsulated strains are termed nontypable (NTHi) because they lack capsular serotypes; however, all H. influenzae isolates can now be classified by multilocus sequence typing and other molecular methods. Most NTHi strains are considered to be part of the normal human flora in the upper and lower respiratory tract, genitals, and conjunctivae (mucous membranes of the eye). H. influenzae has been found in both aerobic and anaerobic environments, as well as environments with different pH's. Conjugative plasmids (DNA molecules that are capable of horizontal transfer between different species of bacteria) can frequently be found in H. influenzae. It is common that the F+ plasmid of a competent Escherichia coli bacterium conjugates into the H. influenzae bacterium, which then allows the plasmid to transfer among H. influenzae strands via conjugation.

H. influenzae mutants defective in their rec1 gene (a homolog of recA) are very susceptible to being killed by the oxidizing agent hydrogen peroxide. This finding suggests that rec1 expression is important for H. influenzae survival under conditions of oxidative stress. Since it is a homolog of recA, rec1 likely plays a key role in recombinational repair of DNA damage. Thus, H. influenzae may protect its genome against the reactive oxygen species produced by the host's phagocytic cells through recombinational repair of oxidative DNA damages. Recombinational repair of a damaged site of a chromosome requires, in addition to rec1, a second homologous undamaged DNA molecule. Individual H. influenzae cells are capable of taking up homologous DNA from other cells by the process of transformation. Transformation in H. influenzae involves at least 15 gene products,