Haemophilus influenzae

Haemophilus influenzae satelliting colonies (pin point) near Staphylococcus aureus (yellow) on blood agar plate.

Chest X-ray in a case of COPD exacerbation where a nasopharyngeal swab detected Haemophilus influenzae: Opacities (on the patient's right side) can be seen in other types of pneumonia, as well.

ActHIB (Hib-vaccine)

Haemophilus influenzae, previously known as Pfeiffer's bacillus or Bacillus influenzae, is a Gram-negative, coccobacillary, facultatively anaerobic bacterium belonging to the Pasteurellaceae family. First described in 1892 by Richard Pfeiffer during an influenza pandemic, it was initially considered to be the causative agent of influenza. This understanding persisted until 1933 when the viral nature of influenza was confirmed. Nevertheless, infections caused by H. influenzae are still informally referred to as bacterial influenza.

Overview and Types

H. influenzae is capable of causing a variety of localized and invasive infections. The bacterium exists in both encapsulated (typeable) and nonencapsulated (nontypeable) forms. The encapsulated strains are classified into six serotypes (a through f) based on their distinct polysaccharide capsules. Among these, H. influenzae type b (Hib) was once a significant cause of bacterial meningitis in children.

Pathogenesis and Clinical Manifestations

H. influenzae is commonly found in the human respiratory tract and usually does not cause disease. However, under certain conditions, such as a weakened immune system or in the absence of adequate vaccination, the bacterium can cause diseases. These range from mild illnesses like otitis media (middle ear infection) and sinusitis to severe conditions like pneumonia, meningitis, and epiglottitis.

Genome Sequencing

In 1995, H. influenzae became the first free-living organism to have its entire genome sequenced. The completed sequence, comprised of approximately 1.83 million base pairs, has been instrumental in expanding our understanding of bacterial genomes and their organization. This accomplishment marked a significant milestone in the field of genomics, opening new avenues in microbial genomics and biotechnology.

Diagnosis and Treatment

The diagnosis of H. influenzae infections often involves culturing the bacterium from samples of blood, cerebrospinal fluid, or other body fluids. Polymerase chain reaction (PCR) is another tool that can be used for diagnosis, offering rapid and accurate detection.

H. influenzae infections are typically treated with antibiotics. However, the emergence of antibiotic-resistant strains is a growing concern and underscores the need for prudent use of antibiotics and for ongoing development of new drugs.

Vaccination

A significant reduction in the incidence of invasive disease caused by H. influenzae type b has been achieved through the use of Hib conjugate vaccines, which are part of routine childhood immunization programs in many countries.

See Also

• Pasteurellaceae
• Bacterial meningitis
• Otitis media
• Antibiotic resistance
• Genome sequencing

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