HACEK

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


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


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

  
• Family: Pasteurellaceae


  • Haemophilus
  • Actinobacillus
  • Pasteurella
  • Aggregatibacter
• HACEK Group


  • Haemophilus
  • Aggregatibacter
  • Cardiobacterium
  • Eikenella
  • Kingella

  
• Other Fastidious Gram-Negative Bacilli

  • Capnocytophaga
  • Brucella
  • Francisella
• Haemophilus


  Gram-negative pleomorphic coccobacilli or rods, Nonmotile, oxidase positive, catalase positive, nitrate reduction, ferments carbohydrates
• Haemophilus species


  • Approximately 13 species known to exist, 8 species associated with humans

  
• 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


  Greek word meaning "blood lover", 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
• Hemolysis of 5% horse or rabbit blood agar

  H. haemolyticus species and sometimes H. ducreyi
• Sheep blood agar (SBA) only contains X factor and not V factor, thus some will not grow without V factor added because NADases present in blood agar plate (BAP) destroy 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, 2% to 6% in children from birth through childhood, with a higher percentage colonization in daycare centers

  
• 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


  Possible antigenic distinct types—a, b, c, d, e, and f, Serotype b (Hib) consists of unique polymer composed of ribose, ribitol, and phosphate

  
• 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 development of a 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

  
• H. aegyptius and H. influenzae biogroup aegyptius

  Can cause conjunctivitis, Particularly in children, H. influenzae biogroup aegyptius can also cause Brazilian purpuric fever (BPF) - 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


  Causes sexually transmitted infection called genital ulcer disease (GUD) or chancroid - painful lesion with an irregular edge in genital and perianal areas, Incubates 4 to 14 days, Causes enlarged and draining lymph nodes (buboes)
• H. parainfluenzae


  Low incidence of pathogenicity, Can cause otitis media, acute sinusitis, and rare cases of endocarditis, May be a cause of some cases of pharyngitis in the 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 at 35-37°C, High humidity to prevent drying, H. ducreyi - grow at 33°C, 5-10% CO2 for 7 days, H. aegyptius - same as H. ducreyi but incubate for 4 days
• H. influenzae colony morphology

  Translucent, tannish, moist, smooth, convex, Mousy or bleach-like odor, Encapsulated strains appear more mucoid

  
• H. influenzae microscopic morphology

  Gram: small gram-negative coccobacilli or small rods to long filaments, Clear nonstaining areas (halos) may be seen

  
• H. ducreyi microscopic morphology

  Gram: coccobacilli
• Growth requirements for most species

  • Incubate in 5% to 10% CO2
  • 35–37° C
  • Place culture media into atmosphere with high humidity to prevent drying