Haemophilus influenzae

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  • Haemophilus influenzae morphology and culture

    image Haemophilus influenzae

    Morphologically it is Haemophilus influenzae are small (1-1.5 m mx 0.3 m m) immovable, partly to encapsulated, spore-free gram-negative rods, which often have a cocci similar appearance. H. influenzae is, as the name puts it, to the hemophilic bacteria. As a haemophiliac such bacteria are referred to the need to increase their growth factors that are found in the blood. H. influenzae required for the growth factors, the two X (hemin) and V (NAD and NADP), are present in erythrocytes. The culture thus possible only to such culture medium, both of which contain a sufficient amount of growth factors (eg, chocolate agar or nutrient media which X and V was added). Normal blood agar contains too little free V-factor. H. influenzae is grown on blood agar but in close proximity to colonies of b-haemolytic Staphylococcus aureus as S. aureus V sufficient factor is released into the medium (so-called satellite).

    To encapsulated strains are differentiated by the chemical structure of the capsular polysaccharide serotypes AF, of which the capsule type b (Hib) causes most infections.

    Therapy

    For oral therapy of infections in ENT and infections of the lower respiratory tract are primarily aminopenicillins, if recommended in combination with a b-lactamase inhibitor, and cephalosporins such as cefuroxime axetil (various trademarks). Possess the older Oralcephalosporine no sufficient activity. The alternatives are the fluoroquinolones ciprofloxacin (Cipro, etc.), levofloxacin (TAVANIC etc.) and moxifloxacin (Avelox, etc.) are available. By contrast, the in vitro activity of macrolides against H. influenzae inadequate. See www.medicatione.com for medications.

    In the sensitivity test is especially the detection of resistance to aminopenicillins important. Most of the resistance is caused by b-lactamases. Available b-lactamase inhibitors in combination with aminopenicillins capture and b-lactamase-producing strains. In the case of beta-lactamase-negative, ampicillin-resistant strains (BLNAR), the resistance is due to altered penicillin binding proteins. T he incidence of ampicillin resistance in Germany is 5-10%. Elsewhere but sometimes significantly higher rates of resistance were determined. Strains with resistance to amoxicillin / clavulanic acid (Augmentin, etc.), Haemophilus effective cephalosporins or fluoroquinolones are rarely seen in this country.

    When meningitis as early as possible initiation of antibiotic treatment is necessary. The treatment of choice for calculated therapy is ceftriaxone (Rocephin, etc.) about seven days. Ceftriaxone also detected BLNAR strains of H. influenzae. Children with Hib meningitis also receive dexamethasone (Fortecortin others) for suppression of inflammation (twice daily 0.4 mg / kg for 2 days or 4 times daily 0.15 mg / kg for 4 days, starting 20 - 30 minutes before the first antibiotic administration). Environment as rifampicin prophylaxis (eg RIFA; twice daily 10 mg / kg) for 4 days is recommended.

    NameDosage
    Chloramphenicol250500 mg3 - 4 times a day for 7 - 10 days

    Pathogenesis and clinical pictures

    H. influenzae is found only in humans. There he colonizes the mucosa of the nasopharynx. Outside the organism it is viable only for a short time. The carriage rate varies between 30% and 50%. Mostly it is in the colonizers to unbekapselte strains with low virulence. Support of bekapselten tribes are mostly children (2-4% incidence). The proliferation of the bacteria is by droplet infection and contact.

    The most important virulence factor is the capsule, which offers protection against the phagocytosis. Invasive infections (meningitis, sepsis, epiglottitis) are usually caused by type B strains of the capsule. Serious diseases by H. influenzae occur due to a lack of antibodies against the capsular antigens, especially in children between six months and five years of age. Therefore, vaccination with Hib vaccine is recommended in the first and second year of life.

    H. influenzae infections in adults manifested mostly as a complication of existing underlying diseases or immune deficiency. They are caused by unbekapselte tribes. The most frequent disease is acute exacerbation of chronic obstructive bronchitis. Even as pneumonia pathogen is H. influenzae common. For the community-acquired pneumonia that occur following an influenza makes H. influenzae after a CAPNETZ information of the approximately 7% of the detectable pathogens. Other infections are conjunctivitis, otitis media and sinusitis.

    Diagnosis

    The detection of the pathogen is through culture. The study is Depending on the site of infection blood, cerebrospinal fluid, pus, purulent sputum, and conjunctival Sinuspunktat considered. Due to the low environmental resistance of H. influenzae are the use of suitable transport media, a short delivery time as well as rapid processing of the material is very important in the laboratory for the detection. The material on blood agar with an inoculation of S. aureus (see above) be seeded as a nurse and on chocolate agar. For Fildes enrichment broth or brain-heart broth containing sufficient X-and V-factor is used. After incubation at 37 C in CO 2-containing atmosphere.

    The Hib meningitis is a medical emergency dar. for the quick diagnosis of a microscopic specimen preparation and the detection of capsular antigens in Liquorpunktat, blood or urine using agglutination tests come into consideration. The antigen detection also brings a positive result when bacteria are not culturable, eg after antibiotic treatment. The division into serotypes done using antibodies against the capsule substance.

    Compulsory registration

    According to 7 is a roll-call notification requirement for the direct detection of H. influenzae from blood or CSF.