medically important gram negative

Cards (32)

  • Fastidious Gram Negative Bacteria
    Bacteria that are difficult to grow in the laboratory and have specific growth requirements
  • Fastidious Gram Negative Bacteria
    • Haemophilus
    • Neisseria
    • Legionella
    • Bordetella
  • Haemophilus
    • Microman12345 / CC BY-SA [Image] (2019). Available from: https://commons.wikimedia.org/wiki/File:Haemophilus_influenzae_sputum_1000x_edited.jpg
  • Haemophilus influenzae
    Requires X-factor (haemin) and V-factor (NAD) for growth
  • Lab Diagnosis of H. influenzae
    1. Candle jar/Anaerobic jar/Gas pack
    2. API (Analytical Profile Index) biochemical tests
  • API Test
    Classification of bacteria based on biochemical tests
  • Neisseria
    Contains 2 notable human pathogens: Neisseria meningitidis (causes meningitis and meningococcaemia) and Neisseria gonorrhoeae (causes gonorrhoea)
  • Neisseria meningitidis Serotypes
    • A
    • B
    • C
    • W135
    • X
    • Y
  • Neisseria meningitidis
    • Type A most prevalent in Africa and Asia, Type B & C most predominant in North America and Europe
  • Lab Diagnosis of Neisseria meningitidis
    1. Smear and culture of blood and spinal fluid samples
    2. Culture on chocolate agar, Thayer Martin agar, New York City agar at 35-36.5°C with 5% CO2
    3. Biochemical tests: Oxidase+, API NH
  • Legionella
    Legionella pneumophila (and other legionellae) causes pneumonia (Legionnaires' disease)
  • Legionella spp. are Gram-negative bacilli that stain faintly with standard Gram stain</b>
  • Legionellae in lung biopsy sections do not stain by H&E so need special methods e.g. Dieterle silver impregnation stain
  • Prevention and Treatment
    • Prevention = Chemoprophylaxis and immunization
    • Treatment = Penicillin or ceftriaxone (cephalosporin)
  • Either rifampin or ciprofloxacin can be used for prophylaxis in people who have had close contact with an infected person
  • NHS vaccination schedule: https://www.nhs.uk/conditions/vaccinations/nhs-vaccinations-and-when-to-have-them/
  • Fastidious Gram Negative Bacteria
  • Legionella
    Causes pneumonia
  • Legionella spp.
    • 16 serogroups (1 = most pneumonia cases)
    • ~ 400 cases of legionellosis per year in UK (over ½ associated with foreign travel)
    • 10-15% mortality in healthy individuals
  • Legionnaires' disease
    Outbreak of pneumonia among people attending the American Legion convention in Philadelphia in 1976
  • Legionella spp.
    • Gram-Negative Bacilli, but stain faintly with standard Gram stain
    • Legionellae in lung biopsy sections do not stain by H&E so need special methods e.g. Dieterle silver impregnation stain
  • Legionellae widely distributed in environmental water sources = ponds, hot and cold water systems, air conditioning units
  • Legionellae can replicate to large #s in free-living amoebas in these water sources
  • The amoebas also enhance the survival of Legionellae
  • Under adverse environmental conditions the amoebas encyst
  • Legionella spp. - Clinical findings
    • From mild influenza-like illness to a severe pneumonia
    • Cough is a prominent symptom, sputum is frequently scanty and non-purulent
    • Hyponatremia
    • Can be fatal
    • Atypical pneumonia; need to distinguish from others
    • Pontiac fever = mild form of legionella infection
  • Legionella spp. - Lab diagnosis
    • Sputum Gram stains reveal many neutrophils but no bacteria
    • Buffered charcoal yeast agar in aerobic conditions in humidified incubator at 37°C
    • Indirect IF assay from convalescent serum
    • Urine antigen test for L. pneumophilia (only serogroup 1)
    • Legionella direct IF test environ-mental samples
    • Latex agglutination test
    • The cold-agglutinin titer does not rise
  • Azithromycin or erythromycin
    Treatment of choice for Legionella spp.
  • Penicillins and cephalosphorins are less effective for treating Legionella spp.
  • Prevention of Legionella spp.
    • Reducing cigarette and alcohol consumption
    • Eliminating aerosols from water sources
    • Reducing the incidence of Legionella in hospital water supplies by using high temperatures and hyperchlorination
    • There is no vaccine
  • Bordetella pertussis - A Brief Overview
  • Bordetella pertussis
    • Causes whooping cough (pertussis)
    • Small, coccobacillary, encapsulated GNB
    • B. pertussis was identified and isolated by Jules Bordet and Octave Gengou in 1906
    • Virulence factors: pertussis toxin, adenylate cyclase toxin, filamentous hæmagglutinin, pertactin, fimbria, and tracheal cytotoxin
    • Bordet-Gengou medium, aerobic, 37°C
    • Human pathogen
    • Transmitted by airborne droplets
    • Incubation period is 7–10 days on average (range 6–20 days)
    • Isolated from nasopharyngeal swabs taken during the paroxysmal stage
    • Produces multiple antigenic and biologically active products that are responsible for the clinical features of pertussis