Bacte lec finals

• Organisms covered


  • Haemophilus
  • HACEK
  • Legionella
  • Other Fastidious Gram-Negative Bacilli

  
• Organisms


  • Miscellaneous
  • Fastidious
  • Pleomorphic (many shapes)
  • Small, gram-negative bacilli
  • Require special nutrients for isolation and identification
• Family: Pasteurellaceae


  • Haemophilus
  • Actinobacillus
  • Pasteurella
  • Aggregatibacter

  
• HACEK Group


  • Haemophilus
  • Aggregatibacter
  • Cardiobacterium
  • Eikenella
  • Kingella

  
• Other Fastidious Gram-Negative Bacilli

  • Capnocytophaga
  • Brucella
  • Francisella
• Haemophilus


  Greek word meaning "blood lover"
• Haemophilus gram-stain appearance


  • Gram-negative pleomorphic coccobacilli or rods
  • Coccobacilli in direct smears
  • Rods with occasionally long filamentous rods from colony growth

  
• Haemophilus biochemical reactions


  • Nonmotile, oxidase positive, catalase positive, nitrate reduction, ferments carbohydrates

  
• Haemophilus species associated with humans

  • H. influenzae
  • H. parainfluenzae
  • H. haemolyticus
  • H. parahaemolyticus
  • H. pittmaniae
  • H. aegyptius
  • H. ducreyi

  
• Most Haemophilus species are nonpathogenic or produce opportunistic infections

  
• Major pathogenic Haemophilus species

  • H. influenza
  • H. aegyptius
  • H. ducreyi

  
• Haemophilus definition


  Organisms prefer growth factors present in blood

  
• X factor


  Hemin, hematin
• V factor


  Nicotinamide-adenine dinucleotide (NAD)
• Species with the prefix Para require only V factor
• H. parainfluenzae


  Produces X factor, requires V factor
• Differential characteristic


  • Hemolysis of 5% horse or rabbit blood agar
  • Sheep blood agar (SBA) only contains X factor and not V factor
  • Chocolate (CHOC) agar releases X and V factor and deactivates NADases
• Satellitism


  Growth of fastidious organisms around other bacteria that release the necessary growth factors or break down toxic products
• Clinically significant exception—H. ducreyi
• Haemophilus species constitutes approximately 10% of normal flora of the upper respiratory tract in adults
• Haemophilus species constitutes 2% to 6% of normal flora in children from birth through childhood, with a higher percentage colonization in daycare centers

  
• As they mature, children convert from encapsulated to non-encapsulated Haemophilus strains
• H. influenzae was erroneously named during the influenza worldwide pandemic (1889–1890)

  
• H. influenzae virulence factors

  • Capsule
  • Immunoglobulin A (IgA) proteases
  • Adherence by fimbriae and other structures
  • Outer membrane proteins and lipopolysaccharide (LPS)

  
• H. influenzae capsule serotypes


  • a
  • b
  • c
  • d
  • e
  • f

  
• Serotype b (Hib)


  • Consists of unique polymer composed of ribose, ribitol, and phosphate
  • Evidence suggests antiphagocytic and anticomplement activity
• Hib vaccine is useful in reducing incidence of disease
• Nontypable H. influenzae (NTHi)


  • Some strains are not encapsulated (no capsule)
  • Invade the respiratory tract and tissues located around the same area
  • Cause localized infections

  
• H. influenzae other virulence factors

  • Immunoglobulin A (IgA) protease cleaves IgA on mucous membranes
  • Adherence mechanisms not well defined
  • Outer membrane components not well defined

  
• Two patterns of H. influenzae disease

  • Invasive disease caused by encapsulated strains (septicemia, meningitis, arthritis, epiglottitis, tracheitis, pneumonia)
  • More localized infection due to Hib vaccination by contiguous spread of NTHi (conjunctivitis, sinusitis, Otitis media with effusion)

  
• H. influenzae meningitis


  • Before Hib vaccine, most cases occurred in children ages 3 months to 6 years
  • Bloodstream invasion and bacteremic spread follow colonization, invasion, and organism replication in the respiratory mucous membranes

  
• H. influenzae epiglottitis


  • Acute inflammation and swelling, causing airway obstruction
  • Affects children 2 to 4 years old
  • Requires emergency tracheostomy
• H. influenzae bacterial tracheitis


  • Life-threatening disease in young children
  • Arises after an acute, viral respiratory infection
  • Mild to moderate illness for 2 to 7 days that progresses rapidly
  • Use of broad-spectrum antibiotics imperative because thick secretions can occlude trachea

  
• Infections associated with H. aegyptius and H. influenzae biogroup aegyptius

  • Conjunctivitis
  • Brazilian purpuric fever (BPF)

  
• Brazilian purpuric fever (BPF)


  • Occurs in warm tropical climates
  • Recurrent conjunctivitis, high fever, vomiting, petechiae, purpura, septicemia, shock, and vascular collapse
  • High mortality, as high as 70% within 48 hours after onset
• H. ducreyi infections


  • Sexually transmitted infection called genital ulcer disease (GUD)
  • Chancroid
  • Incubates 4 to 14 days
  • Painful lesion with an irregular edge in genital and perianal areas
  • Enlarged and draining lymph nodes (buboes)
• H. parainfluenzae infections


  • Low incidence of pathogenicity
  • Otitis media, acute sinusitis
  • Endocarditis (rare)
  • May be a cause of some cases of pharyngitis in absence of other pathogens

  
• Specimen processing and isolation

  • Organisms known to die rapidly, plated within 10 minutes for maximum recovery
  • H. ducreyi - clean specimen site, swab base of ulcer, can also aspirate pus from buboes
• Media selection

  • H. influenzae - CHOC agar with bacitracin
  • H. aegyptius - CHOC agar supplemented with 1% IsoVitaleX
  • H. ducreyi - GC agar, enriched chocolate, or Mueller-Hinton agar with 5% chocolatized lysed horse blood

  
• Growth requirements


  • Incubate in 5-10% CO2, 35-37°C, high humidity
  • H. ducreyi - grow at 33°C, 5-10% CO2, 7 days before reporting negative
  • H. aegyptius - same as H. ducreyi, but incubate for 4 days