What is the Life Cycle of Haemophilus Influenzae

Haemophilus Influenzae is a species of small bacteria that is common and usually not harmful, but can sometimes cause life-threatening illness. According to the Online Textbook of Bacteriology, an estimated 75 percent of healthy children and adults harbor H. influenzae in the nasopharynx (the upper part of the throat that connects to the nose). There are seven different types, the most virulent of which is H. influenzae type b (Hib).

Reproduction & Growth

• H. influenzae reproduces through a process called binary fission. Unlike humans, who have 23 pairs of chromosomes, H. influenzae (and most other bacteria) has only a single circular chroomsome. During binary fission, the chromosome is replicated or copied; the original and the copy migrate to opposite ends of the cell as the membrane grows inward and the one cell splits up into two daughter cells. The life cycle of H. influenzae is like that of most bacteria comparatively simple: growth alternating with binary fission.

Pathogenesis

• In most healthy people who carry it, H. influenzae doesn't cause any problems. The reasons why H. influenzae only occasionally causes disease are not fully understood. It is know, however, that encapsulated forms of the bacterium (bacteria that have formed an additional layer or capsule outside their cell wall) are able to adhere to the lining of the mucous membranes and penetrate them to break into the capillaries. The capsule helps to protect the bacterium from immune system counterattack; it resists both the complement system (a protein cascade that kills invaders in your bloodstream) and phagocytosis (a process whereby some of your white blood cells like macrophages engulf and digest invaders). Hib may spread to the meninges (the membranes of the central nervous system) and cause meningitis, a potentially life-threatening condition, or it may cause epiglottitis (inflammation of the epiglottis) or other conditions. Infection and illness is generally in children younger than 5, although, according to eMedicine, 5 to 10 percent of adult meningitis cases are caused by Hib.

Transmission

• Transmission from one host to the next also plays an important role in the life cycle of H. influenzae. Direct contact or inhalation of bacteria in droplets from sneezing or coughing transmit H. influenzae, although the bacteria seldom cause illness.

NTHi

• Some other strains called NTHi or nontypable H. influenzae often spread in the same fashion, but exhibit a few peculiarities. NTHi can colonize the lower respiratory tract and cause pneumonia, and NTHi is actually a common cause of pneumonia in immunocompromised patients. There are also some cases in which NTHi causes disease in newborns, usually within 24 hours of birth; the bacteria colonize the maternal genital tract and infect the baby during delivery.

Considerations

• H. influenzae is typically not pathogenic; it most often causes illness in children younger than5 and immunocompromised patients. Even in these cases, antibiotics are typically able to effect a cure, although H. influenzae seems to be exhibiting an increased level of resistance to antibiotics, especially penicillins. Vaccination is perhaps the most effective strategy--indeed, immunization against Hib has already dramatically reduced the incidence of this disease in the United States. By teaching the immune system to recognize the bacteria upon entry, vaccination helps prevent Hib from establishing a foothold in tissues where it can cause damage.