Bacteriology-Haemophilus| Quick Revision Notes for NEET-PG

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  1. Haemophilus influenzae
      • Blood loving
      • Gram negative coco bacillus
      • It is aka pfeiffer’s bacillus as it was discovered by Pfeiffer
      • Non-motile and non-sporing
      • Catalse postive and oxidease postive
      • Capsule may be present or absent
      • Fastidious organisms i.e it requires presence of one or more of the accessory growth factors-X and V in the blood

X factor-It consist of heat-stable compounds such as hemin,porphyrins and it is required for aerobic respiration by the organism.

        1. Scanty growth is seen on blood agar as only factor X is available in the medium.Factor V is intracellular and is present only inside RBC’s.
        2. It does not grow on ordinary media like nutrient agar and peptone water as it lacks X and V factor.
        3. Chocolate agar- At 75oC when blood is pored into  molten agar to form chocolate agarNADse gets inactivated and lyses RBC,in turn releasing factor V.Hence,it supports the growth of Haemophilus influenzae
        4. It shows satellitism
      1. V factor(heat labile)-present inside RBC’s NAD/NADP and the organism does not cause hemolysis.

There are 6 serotypes of capsulated strains of haemophilus influenzae-a,b,c,d,e and f[classified on the basis of surface antigen]

Out of the 6 serotypes,serotype b which possesses capsule made up of polyribosyl ribitol phosphate causes the more severe infection and death in man.

Infections caused of H. influenzae can be categorized as invasive and non-invasive

      1. Invasive-bacteria invade the blood stream and causes bacteremia(capsulated strains)
        • Epiglotittis(Note-most common cause of epiglottitis is S. Pneumoniae)
        • Pyogenic meningitis-It occur in children of age less than 2 and is charaterized by fever,neck    rigidity,headache,vomitting and altered sensorium.
        • Cellulitis in infants
        • Severe pneumonia in infants
      2. Non-Invasive-no bateremia, as in Non-capsulated bacteria
        • Most common cause of community acquired pneumonia
        • 2nd most common cause of acute otitis media

Diagnosis –

      • Specimen like CSF,blood,sputum should be collected immediately and never refrigerated.
      • Gram staining shows pleomorphic cocco bacilli
      • Capsule detection by quellung RXN
      • Antigen detection by latex agglutiunation test
      • Culture on blood agar with streak line of S. aureus to show atellitism
      • Culture on Filde’s agar and Levinthal’s agar
      • Biochemical test-Disk test for X and V requirement
      • Biotyping and serotyping
      • Antimicrobial susceptibility testing

Haemophilus ducreyi

It is the etiological agent of chancroid/soft chancre

    • It is a sexually transmitted disease characterized by
      • Painful genital ulcerations
      • Enlarged,tender inguinal lymph nodes
    • Incubation period of 4-7 days
    • Transmission-predominantly heterosexually
    • Diagnosis
      • Specimen to be collected-swab/exudate from edge of ulcer
      • Under microscope it can be seen as pleomorphic gram negative coccobacillus with school of fish/rail road track appearance
      • Culture on blood agar enriched with 1 % isovitalex and made selective by adding vancomycin.
    • Dug of choice- Azithromycin
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