|H. influenzae on a blood agar plate.|
(Lehmann & Neumann 1896)
Winslow et al. 1917
Haemophilus influenzae (formerly called Pfeiffer's bacillus or Bacillus influenzae) is a genome sequenced. The sequencing project was completed and published in 1995.
- Serotypes 1
- Diseases 2
- Culture 3.1
- 3.2 Latex particle agglutination
- Molecular methods 3.3
- Interaction with Streptococcus pneumoniae 4
- Treatment 5
- Prevention 6
- Sequencing 7
- Likely protective role of transformation 8
- See also 9
- References 10
- External links 11
In 1930, two major categories of H. influenzae were defined: the unencapsulated strains and the encapsulated strains. Encapsulated strains were classified on the basis of their distinct capsular antigens. There are six generally recognized types of encapsulated H. influenzae: a, b, c, d, e, and f. Genetic diversity among unencapsulated strains is greater than within the encapsulated group. Unencapsulated strains are termed nontypable (NTHi) because they lack capsular serotypes; however, they can be classified by multilocus sequence typing. The pathogenesis of H. influenzae infections is not completely understood, although the presence of the capsule in encapsulated type b (Hib), a serotype causing conditions such as epiglottitis, is known to be a major factor in virulence. Their capsule allows them to resist phagocytosis and complement-mediated lysis in the nonimmune host. The unencapsulated strains are almost always less invasive; they can, however, produce an inflammatory response in humans, which can lead to many symptoms. Vaccination with Hib conjugate vaccine is effective in preventing Hib infection, but does not prevent infection with NTHi strains.
|Haemophilus influenzae infection|
|Classification and external resources|
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, reduced immune function or chronically inflamed tissues, e.g. from allergies) create an opportunity. They infect the host by sticking to the host cell using trimeric autotransporter adhesins.
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, epiglottitis and acute bacterial meningitis. On occasion, it causes cellulitis, osteomyelitis, 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 the vaccine is not widely used. Unencapsulated H. influenzae strains are unaffected by the Hib vaccine and cause ear infections (otitis media), eye infections (conjunctivitis), and sinusitis in children, and are associated with pneumonia.
Clinical features may include initial symptoms of an upper respiratory tract infection mimicking a viral infection, usually associated with fevers, often low-grade. This may progress to the lower respiratory tract in a few days, with features often resembling those of a wheezy bronchitis. Sputum may be difficult to expectorate and is often grey or creamy in color. The cough may persist for weeks without appropriate treatment. Many cases are diagnosed after presenting chest infections do not respond to penicillins or first-generation cephalosporins.
Clinical diagnosis of H. influenzae is typically performed by
- Hib information on the World Health Organization (WHO) site.
- Fact sheet on the Centers for Disease Control and Prevention (CDC) site.
- Hib Initiative—from WHO
- November 2nd: World Pneumonia Day Website
- Centers for Disease Control and Prevention (2012). "Ch. 7: Haemophilus influenzae". In Atkinson W; Wolfe S; Hamborsky J. Epidemiology and Prevention of Vaccine-Preventable Diseases (12th ed.). Washington DC: Public Health Foundation. pp. 87–100.
- "Haemophilus influenzae". NCBI Taxonomy Browser. 727.
- Kuhnert, P; Christensen, H, eds. (2008). Pasteurellaceae: Biology, Genomics and Molecular Aspects. Caister Academic Press.
- Ryan, KJ; Ray, CG, eds. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. pp. 396–401.
- Slack, MP; et al. (1998). "Enhanced surveillance of invasive Haemophilus influenzae disease in England, 1990 to 1996: impact of conjugate vaccines". Pediatr Infect Dis J. 17 (9 suppl): S204–7.
- Behrman, Richard E.; Robert M Kliegman & Hal B. Jenson (2004). Nelson Tratado de Pediatría. Elsevier. p. 904.
- Puri J; Talwar V; Juneja M; Agarwal KN; et al. (1999). "Prevalence of antimicrobial resistance among respiratory isolates of Haemophilus influenzae". Indian Pediatr 36 (10): 1029–32.
- Levine OS; Schuchat A; Schwartz B; Wenger JD; Elliott J; Centers for Disease Control (1997). type B"Haemophilus influenzae"Generic protocol for population-based surveillance of (PDF). World Health Organization. WHO/VRD/GEN/95.05.
- John TJ; Cherian T; Steinhoff MC; Simoes EA; et al. (1991). "Etiology of acute respiratory infections in children in tropical southern India". Rev Infect Dis 13: Suppl 6:S463–9.
- Kennedy WA; Chang SJ; Purdy K; LE T; et al. (2007). "Incidence of bacterial meningitis in Asia using enhanced CSF testing: polymerase chain reaction, latex agglutination and culture". Epidemiol Infect 135 (7): 1217–26.
- Pericone, Christopher D.; Overweg, Karin; Hermans, Peter W. M.; Weiser, Jeffrey N. (2000). "Inhibitory and Bactericidal Effects of Hydrogen Peroxide Production by Streptococcus pneumoniae on Other Inhabitants of the Upper Respiratory Tract". Infect Immun 68 (7): 3990–3997.
- Lysenko E; Ratner A; Nelson A; Weiser J (2005). "The role of innate immune responses in the outcome of interspecies competition for colonization of mucosal surfaces". PLoS Pathog 1 (1): e1.
- Chang CM; Lauderdale TL; Lee HC; et al. (August 2010). among nursing home residents in southern Taiwan"Haemophilus influenzae"Colonisation of fluoroquinolone-resistant . J. Hosp. Infect. 75 (4): 304–8.
- Roberts MC; Soge OO; No DB (January 2011). isolated from children with cystic fibrosis"Haemophilus influenzae"Characterization of macrolide resistance genes in . J. Antimicrob. Chemother. 66 (1): 100–4.
- Bar-On ES; Goldberg E; Hellmann S; Leibovici L (2012). "Combined DTP-HBV-HIB vaccine versus separately administered DTP-HBV and HIB vaccines for primary prevention of diphtheria, tetanus, pertussis, hepatitis B, and Haemophilus influenzae B (HIB)". Cochrane Database Syst Rev 4 (4): CD005530.
- type B (HiB)"Haemophilus influenzae". Health Topics A to Z. Retrieved 2011-03-29.
- Fleischmann R; Adams M; White O; Clayton R; et al. (1995). Rd"Haemophilus influenzae"Whole-genome random sequencing and assembly of . Science 269 (5223): 496–512.
- Naylor EJ; Bakstad D; Biffen M; et al. (August 2007). induces neutrophil necrosis: a role in chronic obstructive pulmonary disease?"Haemophilus influenzae". Am. J. Respir. Cell Mol. Biol. 37 (2): 135–43.
- Sánchez-Rincón DA; Cabrera-Juárez E (October 1991). "Haemophilus influenzae"Lethal and mutagenic action of hydrogen peroxide on . J. Bacteriol. 173 (20): 6632–4.
- Michod RE; Bernstein H; Nedelcu AM (May 2008). "Adaptive value of sex in microbial pathogens". Infect. Genet. Evol. 8 (3): 267–85. } As PDF
- Maurice Hilleman
- Hattie Alexander
- Hib vaccine
- Haemophilus influenzae cellulitis
- Haemophilus meningitis
- Trimeric Autotransporter Adhesins (TAA)
H. influenzae mutants defective in the rec1 gene (a homolog of recA) are very sensitive to killing 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, and is likely an adaptation for repairing DNA damages in the resident chromosome (as suggested in Transformation (genetics)#Transformation, as an adaptation for DNA repair).
Unencapsulated H. influenzae is often observed in the airways of patients with chronic obstructive pulmonary disease (COPD). Neutrophils are also observed in large numbers in sputum from patients with COPD. The neutrophils phagocytize H. influenzae, thereby activating an oxidative respiratory burst. However instead of killing the bacteria the neutrophils are themselves killed (though such an oxidative burst likely causes DNA damage in the H. influenzae cells). The lack of killing of the H. influenzae appears to explain the persistence of infection in COPD.
Likely protective role of transformation
H. influenzae was the first free-living organism to have its entire genome sequenced. Completed by Craig Venter and his team, Haemophilus was chosen because one of the project leaders, Nobel laureate Hamilton Smith, had been working on it for decades and was able to provide high-quality DNA libraries. The genome consists of 1,830,140 base pairs of DNA in a single circular chromosome that contains 1740 protein-coding genes, 2 transfer RNA genes, and 18 other RNA genes. The sequencing method used was whole-genome shotgun, which was completed and published in Science in 1995 and conducted at The Institute for Genomic Research.
Hib vaccines cost about seven times the total cost of vaccines against measles, polio, tuberculosis, diphtheria, tetanus, and pertussis. Consequently, whereas 92% of the populations of developed countries was vaccinated against Hib as of 2003, vaccination coverage was 42% for developing countries, and only 8% for least-developed countries.
Macrolide antibiotics (e.g., clarithromycin) may be used in patients with a history of allergy to beta-lactam antibiotics. Macrolide resistance has also been observed.
Haemophilus influenzae produces beta-lactamases, and it is also able to modify its penicillin-binding proteins, so it has gained resistance to the penicillin family of antibiotics. In severe cases, cefotaxime and ceftriaxone delivered directly into the bloodstream are the elected antibiotics, and, for the less severe cases, an association of ampicillin and sulbactam, cephalosporins of the second and third generation, or fluoroquinolones are preferred. (Fluoroquinolone-resistant Haemophilus influenzae has been observed.)
It is unclear why H. influenzae is not affected by the immune response.
- When H. influenzae is attacked by S. pneumoniae, it signals the immune system to attack the S. pneumoniae
- The combination of the two species triggers an immune system response that is not set off by either species individually.
Two scenarios may be responsible for this response:
Lab tests showed neutrophils exposed to dead H. influenzae were more aggressive in attacking S. pneumoniae than unexposed neutrophils. Exposure to dead H. influenzae had no effect on live H. influenzae.
When both bacteria are placed together into a nasal cavity, within 2 weeks, only H. influenzae survives. When either is placed separately into a nasal cavity, each one survives. Upon examining the upper respiratory tissue from mice exposed to both bacteria species, an extraordinarily large number of neutrophils (immune cells) was found. In mice exposed to only one bacterium, the cells were not present.
Both H. influenzae and S. pneumoniae can be found in the upper respiratory system of humans. In an in vitro study of competition, S. pneumoniae always overpowered H. influenzae by attacking it with hydrogen peroxide and stripping off the surface molecules H. influenzae needs for survival.
Interaction with Streptococcus pneumoniae
Polymerase chain reaction (PCR) assays have been proven to be more sensitive than either LAT or culture tests, and highly specific. However, PCR assays have not yet become routine in clinical settings. Countercurrent immunoelectrophoresis has been shown to be an effective research diagnostic method, but has been largely supplanted by PCR.
The latex particle agglutination test (LAT) is a more sensitive method to detect H. influenzae than is culture. Because the method relies on antigen rather than viable bacteria, the results are not disrupted by prior antibiotic use. It also has the added benefit of being much quicker than culture methods. However, antibiotic sensitivity testing is not possible with LAT alone, so a parallel culture is necessary.
Latex particle agglutination
H. influenzae will grow in the hemolytic zone of Staphylococcus aureus on blood agar plates; the hemolysis of cells by S. aureus releases factor V which is needed for its growth. H. influenzae will not grow outside the hemolytic zone of S. aureus due to the lack of nutrients such as factor V in these areas. Fildes agar is best for isolation. In Levinthal medium, capsulated strains show distinctive iridescence.
Although highly specific, bacterial culture of H. influenzae lacks in sensitivity. Use of antibiotics prior to sample collection greatly reduces the isolation rate by killing the bacteria before identification is possible. Beyond this, 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.
catalase and oxidase tests, both of which should be positive. Further serological testing is necessary to distinguish the capsular polysaccharide and differentiate between H. influenzae b and nonencapsulated species.
Bacterial culture of H. influenzae is performed on agar plates, the preferable one being chocolate agar, with added X (hemin) and V (nicotinamide adenine dinucleotide) factors at 37 °C in a CO2-enriched incubator. Blood agar growth is only achieved as a satellite phenomenon around other bacteria. Colonies of H. influenzae appear as convex, smooth, pale, grey or transparent colonies.
infection. H. influenzae isolated from cerebrospinal fluid or blood would indicate H. influenzae However,