Haemophilus influenzae bacteria

Haemophilus influenzae

Haemohilus influenzae picture haemophilus influenzae animated image

Encapsulated strain of Haemophilus influenzae on chocolate agar plate. Encapsulated strains may produce larger colonies with a glistening mucoid quality. Haemophilus influenzae requires two accessory growth factors: factor X (haemin or other porphyrins) and V factor (NAD). The X and V factor requirement is usually demonstrated by the absence of growth on porphyrin and NAD deficient but otherwise nutritionally adequate media except near paper disc impregnated with X and V factors. H.influenzae grown on agar plates usually shows a highly regular shape under microscope. The rounded ends of short bacilli make many appear round, hence the term coccobacilli.

Haemophilus influenzae, formerly called Pfeiffer's bacillus, is a non-motile Gram-negative pleomorphic rod-shaped bacterium first described in 1892 by Richard Pfeiffer during an influenza pandemic. It is facultatively anaerobic. H. influenzae was mistakenly considered to be the cause of influenza until 1933, when the viral etiology of the flu became apparent. Still, H. influenzae is responsible for a wide range of clinical diseases.


Most strains of H. influenzae are opportunistic pathogens - that is, they usually live in their host without causing disease, but cause problems only when other factors (such as a viral infection or reduced immune function) create an opportunity. Naturally-acquired disease caused by H. influenzae seems to occur in humans only. In infants and young children, H. influenzae type b (Hib) causes bacteremia, pneumonia, and acute bacterial meningitis. Occasionally, it causes cellulitis, osteomyelitis, epiglottitis, and infectious arthritis. Due to routine use of the Hib conjugate vaccine in the U.S. since 1990, the incidence of invasive Hib disease has decreased to 1.3/100,000 in children. However, Hib remains a major cause of lower respiratory tract infections in infants and children in developing countries where vaccine is not widely used. Unencapsulated H. influenzae causes ear (otitis media) and eye (conjunctivitis) infections and sinusitis in children, and is associated with pneumonia.


Bacterial culture of H. influenzae is performed on Chocolate agar at 37°C in an enriched CO2 incubator. Blood agar growth is only achieved as a satellite phenomenon around other bacteria. H. influenzae will grow in the hemolytic zone of Staphylococcus aureus on blood agar plates. The hemolysis of cells by S. aureus releases nutrients vital to the growth of H. influenzae. H. influenzae will not grow outside the hemolytic zone of S. aureus due to the lack of nutrients in these areas.

Colonies of H. influenzae appear as raised or convex, smooth, pale, grey or transparent. Gram-stained and microscopic observation of a specimen of H. influenzae will show Gram-negative coccobacilli with no specific arrangement. Further serological is necessary to distinguish the capsular polysaccharide and differentiate between H. influenzae b and non-encapsulated species. H. influenzae is a finicky bacterium to culture, and any modification of culture procedures can greatly reduce isolation rates. Poor quality of laboratories in developing countries has resulted in poor isolation rates of H. influenzae.

Abbreviated from Wikipedia.

Haemophilus influenzae basic characteristics


Identification of Haemophilus influenzae

  • requirement of X+V factor in cultivation media; X = hematin, V = nicotinamide adenine dinucleotide(NAD)
  • growth on chocolate agar but not on blood agar (when cultivated in pure culture)
  • satelite phenomenon with Staphylococcus aureus (on blood agar)

Antibiotic treatment of Haemophilus influenzae infections

Should be always guided by in vitro susceptibility tests!!
Selection of appropriate antibiotics depends on diagnosis!!

  • ampicillin
  • amoxicillin
  • ampicillin/sulbactam
  • amoxicillin/clavulanate

  • cefuroxime
  • ceftriaxone
  • cefotaxime

  • Trimethoprim-Sulfomethoxazole(TMP-SMX)
  • azithromycin
  • clarithromycin
  • doxycicline

  • List of antibiotics (Wikipedia)

Haemophilus influenzae on chocolate agar

Haemophilus influenzae growing on chocolate agar plate Hib colonies on chocolate agar Haemophilus influenzae virulent strain, pure culture on agar plate H.influenzae b (Hib) virulent, strongly mucoid strain chocolate agar plate with haemophilus influenzae colonies of Haemophilus influenzae growing on chocolate agar haemophilus influenzae colonies photo colonies of haemophilus on chocolate agar close-up colony morphology of H.influenzae Haemophilus influenzae colonies detail of H.influenzae colonies on chocolate agar H. influenzae Haemophilus influenzae virulent strain, Hib, haemophilus group b bacterial colonies of Haemophilus influenzae comparison of mucoid and non-mucoid strains of Haemophilus influenzae H.influenzae, Hib, virulent, encapsulated strain virulent H.influenzae colony characteristics colony morphology of virulent Haemophilus influenzae haemophilus influenzae colony appearance haemophilus influenzae serotype b (Hib) colony morphology on agar haemophilus influenzae Hib

Haemophilus influenzae dependence on X and V factors

haemophilus influenzae haemophilus influenzae

Haemophilus influenzae satellite phenomenon (the satellite test)

haemophilus influenzae haemophilus influenzae the satellite test haemophilus influenzae satelliting haemophilus influenzae growth on blood agar

Haemophilus influenzae Gram-stain

haemophilus influenzae haemophilus influenzae gram stain, micrograph

Haemophilus influenzae 3D

haemophilus influenzae

Useful Links