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Gram Negative Coccobacilli


  1. Bordetella
    1. B. pertussis; B. parapertussis: Whooping cough
    2. B. bronchiseptica (motile by peritrichous flagella): dogs; may occasionally infect humans & produce a disease like whooping cough
    3. GN, coccobacilli; strict aerobes
  1. B pertussis: non motile
    1. Culture: “thumb print” appearance
    2. Metachromatic granules
    3. Bordet Gengou medium: “bisected pearl”, “mercury drop”, “aluminum paint” appearance
    4. Catalase and oxidase positive, non fermenter.
  2. Antigens & Virulence factors:
    1. Agglutinogens: associated with capsular K antigen or fimbriae, attachment to respiratory epithelium,   useful in serotyping
    2. Pertussis toxin: hexamer, toxoided
    3. Filamentous haemagglutinin (FHA), PT, Lipid factor: adhesion to respiratory epithelium, “piracy of adhesins”, used in acellular vaccines
    4. Adenylate cyclase: Heat labile toxin
    5. Tracheal cytotoxin
    6. Lipopolysaccharide

  1. Pathogenicity:
    1. Obligate human parasite
    2. I/ P: 1-2 weeks
    3. Chronic carriers not known
    4. Immunity following natural infection not complete
    5. “cough plate” method, West’s postnasal swab, pernasal swab (best results)
    6. Antigen detection in nasopharyngeal secretions by direct immunofluorescence 3 stages: catarrhal (most infective, can be stopped by antibiotics), paroxysmal, convalescent lasting   for 2 weeks
  2. Complications:


Prophylaxis: DPT, Acellular vaccines; Efficacy 70-90%

  1. Brucella
  1. Zoonosis; goat, sheep, cattle, buffaloes, pigs etc
  2. Mediterranean fever, Malta fever, Undulant fever
  3. Intracellular pathogen affecting the reticuloendothelial system
  4. B melitensis (goat), B abortus (cattle), B suis (pigs), B canis (canines), B ovis (sheep), B neotome (desert wood rats)
  5. Bipolar staining, non-motile GN coccobacillus
  6. Strict aerobes, Capnophilic (B. abortus)
  7. Serum dextrose agar & broth, Trypticase soy agar & broth
  8. Erythritol: stimulatory effect on growth
  9. Antigenic structure: two main determinants i.e. A & M (present in different amounts in 3 major species)
  10. Tblisi phage as the reference phage
  11. Transmitted via skin by direct contact with infected tissues, inhalation of aerosolised bacteria, ingestion of  contaminated meat, unpasteurized milk or milk products.
  12. Brucella possesses a number of antigens which cross react with Yersinia enterocolitica, Vibrio cholerae, E. coli, Strenotrophomonas maltophila and group N Salmonella.
  13. Treatment of adults-Doxycycline for 45d + Streptomycin for 2 wks-best therapy OR Doxy with rifampicin for 6 weeks. Children-Cotrimoxazole + Rifampicin/ Gentamicin
  1. Pathogenicity:
    1. B. melitensis is most pathogenic
    2. I/ P: 10 –30 days
    3. Most common cause of acute undulant fever: B. melitensis
    4. “Strauss’ Reaction” in male guinea pigs
    5. Ingestion, inhalation, contact, accidental inoculation; most important is raw milk; among animals   through tick bite
    6. Blood culture- Castaneda’s technique
    7. Serology is the mainstay in most cases. SAT-tube agglutination test in acute brucellosis
    8. CFT, ELISA (IgM and IgG)- in acute/chronic brucellosis
    9. False positive serology in cholera/ IgG antibodies-2-mercaptoethanol test
    10. Incomplete / blocking antibodies IgG detected by Coomb’s test
    12. Animals: Rapid plate agglutination test, Rose Bengal card test, Milk ring test, Whey agglutination test

  1. Haemophilus
  • Blood loving

  • Requirement for one or more of the accessory factors: X & V in blood
  • Pfeiffer’s bacillus” or H influenzae
  • Pleomorphic coccobacillus, non-motile, non-sporing,
  • Capsulated- polysaccharide capsule- Pittman’s classification into 6 capsular types. Type b is most virulent and capsular polysaccharide is polyribosyl ribitol phosphate. Some strains- non-capsulated
  • Stain: methylene blue or dilute carbol fuchsin, Gram’s-counterstain for 3 min
  • X: hemin or porphyrin required for aerobic respiration; heat stable
  • V: heat labile, NAD or NADP
  • Poor growth on blood agar, Satellitism on blood agar with S.aureus streak, chocolate agar-good growth
  • Levinthal’s agar (iridescent colonies of capsulated strains), Filde’s agar (best for primary isolation)
  • 8 biotypes; Biotype I for meningitis
  • Oxidase +, catalase +
  • Refrigeration kills
  • Antigenic properties- Capsule: a – f; 95% type b; (PRP/ polyribose ribitol phosphate capsule)
  • OMP- sub-serotypes
  • LOS
  1. Pathogenicity:
  • Humans only. 2 types of infections
  1. Invasive infections caused by capsulated type b strains:
    1. meningitis (most common in children between 2 mo and 2yrs),
    2. arthritis,
    3. laryngo- epiglottitis, epiglottitis
    4. pneumonia,
    5. bacteremia, brain abscess
    6. endocarditis,
    7. pericarditis; capsulated
  2. Non invasive:
    1. By Non, capsulated;
    2. sinusitis, otitis media
    3. COPD; adults

Hib PRP vaccine; not effective in < 2 years of age.

Conjugate vaccines- PRP-T, PRP-D, PRP-OMP conjugated with tetanus toxoid, diphtheria toxoid and outer membrane proteins of N. meningitides resp.

  • Treatment for invasive disease- Ceftriaxone
  • Rifampicin for prophylaxis
  1. H aegyptius (Koch’s - Week’s bacillus)- now a biotype of H. influenzae
    1. “Pink eye”  
    2. Brazilian purpuric fever
  2. H ducreyi: GN coccobacillus
    1. Chancroid: painful, LNs
    2. “School of fish” or “rail road track” appearance
    3. Medium used: chocolate agar with 1% isovitalex, vancomycin 93mg/ml), Chorioallantoic membrane of chick embryo, fresh clotted rabbit blood


About H. influenza, all true except? (AIIMS Nov 10)
A. Requires factor X and V for growth
B. Rarely presents as meningitis in children less than 2 months of age
C. Capsular polypeptide protein is responsible for virulence
D. M. C invasive disease of H influenza is meningitis


Ans- C.

  1. HACEK group of organisms
    1. Fastidious slow growing bacteria, normal resident of oral cavity
    2. Grow on BA after 2-3 days, capnophiles. No growth on Mac
    3. Share an enhanced capacity to produce endocardial infections.
    4. They are responsible for 5-10% of cases of infective endocarditis (IE) involving native valves
    5. Hemophilus species, Actinobacillus actinomycetecomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae
  2. Mycoplasma

  1. Medically important genera: Mycoplasma, Ureaplasma
  2. 0.2-0.3µm, can pass through bacterial filters
  3. Absence of cell wall, pleomorphic, resistant to cell-wall active antibiotics
  4. Cell membrane contains sterols
  5. Lack several synthetic enzymes
  6. Poorly stained with grams stain, stained well by Geimsa
  7. Solid medium: fried egg colony. Diene’s stain used to demonstrate the tiny colonies
  8. M. pneumonia- primary human to human transmission. Immunocompetent individuals.
  9. Tracheobronchitis, pharyngitis, primary atypical pneumonia
  10. Serological tests-IFAT, CFT
  11. Cold agglutinins: agglutination of O Rh negative erythrocytes at 4°C, appear one week after infection. 4 fold rise or ≥ 64 is suggestive of M. pneumoniae infection.
  12. Streptococcus MG agglutinins also raised in M. pneumoniae infection. Heterophile antibodies
  13. Treatment – Macrolides, Doxycycline, Levofloxacin

U. urealyticum

Urease test positive. Requires sterols and urea for growth.

  1. Non gonococcal urethritis, epididymitis, cervicitis
  2. Chorioamnionitis, chronic lung disease of premature infant

M. hominis- Salpingitis, endometritistubo-ovarian abscess, pelvic abscess, septic abortion, puerperal infection, septic arthritis      

M.genitalium- NGU, PID, infertility

  1. Calymmatobacterium Granulomatis
    1. Gram negative
    2. Donovanosis/ granuloma inguinale
    3. Painless ulcer, without lymphadenopathy, also causes pseudo elephantiasis
    4. “safety pin” appearance
    5. “Donovan bodies” : phagosomes of large macrophages
    6. Yolk sac inoculation, great difficulty on fresh egg yolk agar
  2. Legionella Pneumophila
    1. Reservoir: natural or artificial aquatic environs
    2. Can survive intracellularly in freeliving amebae
    3. Gram negative, strict aerobe, motile
    4. Does not take up Gram stain well. Dieterle’s silver stain used
    5. Buffered charcoal yeast extract medium (BCYE), Iron and cysteine required, cut glass appearance colonies
    6. Infection via inhalation of contaminated water aerosols
    7. Legionnaire’s disease: pneumonia which progresses to involve every system of body, more common in immunocompromised people, smokers, alcoholics, DM, lung carcinomas
    8. Pontiac fever: self limiting, brief, Influenza-like, healthy people
    9. Diagnosis: culture, antigen detection in specimen by DFAT, antigen detection in urine by ELISA
    10. Treatment-macrolides or fluoroquinolones

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