Week 3 Flashcards
GENERAL CHARACTERISTICS Haemophilus
- Gram-negative
- Pleomorphic small bacilli - sometimes almost coccal in shape, sometimes as short filaments
- Non-motile, do not form spores
- Encapsulated (typeable) or non-encapsulated (non-typeable)
- aerobic, facultatively anaerobic - generate energy for growth either oxidatively (preferred) or fermentatively
- oxidase positive
- Most species have fastidious nutritional requirements e.g.
- Factor X (haemin) and/or
- Factor V (nicotine adenine dinucleotide)
- optimal growth at 35oC to 37oC in humid atmosphere containing 5% to 10% CO2
NATURAL HABITAT Haemophilus
- Most non-encapsulated Haemophilus species are normal inhabitants of the
upper respiratory tract of humans and other animals - 85% of adults harbour these organisms as part of normal bacterial flora in nasopharynx and oropharynx
- Encapsulated H. influenzae may also be found as part of the normal upper respiratory tract flora of both children and adults
- Colonisation by H. influenzae capsular serotype b strains is uncommon in healthy infants (0.7%), children (3% to 5%), rare in adults
- But most infections are caused by H. influenzae capsular serotype b
- Haemophilus ducreyi is a pathogen of the genital tract
VIRULENCE FACTORS Haemophilus
- Capsule − major antigenic determinant of encapsulated H. influenzae - capsular polysaccharide
−this polysaccharide confers type specificity on the organism, the basis for grouping of organism into 6 serotypes (a, b, c, d, e, f)
−strains associated with invasive disease belong to serotype b
serotype b capsular polymer unique:
* contains pentose sugars (e.g., ribose) and ribitol-phosphate (polyribosilribitol-phosphate - PRP, inhibits phagocytosis and intracellular killing by neutrophils)
* instead of hexoses or hexosamines as found in other serotypes
- Pili
- IgA1 protease
- Adhesins
- Bacteriocin - haemocin
− protein able to inhibit growth of strains of same or related species (for competition) - Outer Membrane Proteins (OMPs)
− responsible for attachment, invasiveness, resistance to phagocytosis - Lipooligosaccharide (LOS)
− outer membrane component that exerts paralysing action on ciliated respiratory epithelium
− promotes proliferation of organisms in bronchial tree
CLINICAL SIGNIFICANCE - HAEMOPHILUS INFLUENZAE
- world-wide in distribution, endemic in nature
- infection occurs after inhalation of infected droplets from:
−clinically active cases
−convalescent patients
−carriers
MENINGITIS
* most cases in infants and children younger than age of 6 years
* more than 90% of isolates belong to capsular serotype b
* clinically resembles meningococcal meningitis
* complications unusual, may include:
− brain abscess
− pericarditis
−abscess formation at other body sites
* in adults, usually complicates underlying diseases or conditions including:
− head trauma
−chronic sinusitis, otitis media
− diabetes, chronic alcoholism
−tracheobronchitis, pneumonia
−immunodeficiency states
OTITIS MEDIA
* only 10% of isolates are serotype b
* symptoms include ear pain with or without ear drainage
SINUSITIS
* causes 20% to 40% of acute sinusitis in children and adults
* usually a secondary invader following a viral sinus infection
* most isolates are non-encapsulated
EPIGLOTTITIS
* typically in children between 2 and 7 years of age
* most common cause is serotype b
* infection acute, with abrupt onset of obstructive laryngeal oedema
UPPER AND LOWER RESPIRATORY TRACT INFECTIONS
* causes acute pharyngitis and laryngitis
* pre-existing viral infection usually present
* chronic bronchitis, acute exacerbations of purulent bronchitis, acute febrile tracheobronchitis caused by non-encapsulated strains
* pneumonia
BACTERAEMIA AND ENDOCARDITIS
* usually accompanied by:
− cellulitis
− arthritis
− osteomyelitis
UROGENITAL, MATERNAL, AND PERINATAL INFECTIONS* non-encapsulated strains cause:
− urethritis
−tubo-ovarian abscesses
−septic abortion
− postpartum bacteraemia
− neonatal sepsis with and without meningitis
CONJUNCTIVITIS
* causes contagious, acute conjunctivitis - “pinkeye”
BRAZILIAN PURPURIC FEVER
* caused by a single clone of Haemophilus influenzae biogroup aegyptius
* acute illness characterised by:
− high fever
− abdominal pain
− vomiting
− purpuric rash
− eventually vascular collapse, hypotensive shock, death
CLINICAL SIGNIFICANCE - HAEMOPHILUS PARAINFLUENZAE
- causes endocarditis
- higher incidence of vegetations on heart valves and septic complications
resulting from embolisation of these vegetations to large arteries - may cause secondary bacteraemia and urethritis in adults
CLINICAL SIGNIFICANCE - OTHER HAEMOPHILUS SPP. (not H. Influenzae or parainfluenzae)
- Aggregatibacter aphrophilus and Haemophilus paraphrophilus
−cause endocarditis and brain abscess
− may cause: pneumonia, meningitis, secondary bacteraemia
other species are rarely associated with infection
CLINICAL SIGNIFICANCE - HAEMOPHILUS DUCREYI
- causes chancroid, highly contagious, sexually transmitted infection* manifested by shallow genital ulcerations (sharply circumscribed, nonindurated, painful ulcers - “soft chancres”)
- may be accompanied by inguinal lymphadenopathy (suppurative buboes develop in ½ of patients)
- world-wide in distribution
COLLECTION, TRANSPORT, AND STORAGE OF SPECIMENS Haemophilus
- specimen collected depends on the area of involvement:
− blood
− other body fluids (CSF, synovial fluid, pericardial fluid, pleural fluid)
− middle ear aspirates, middle ear drainage fluid
− sinus aspirates, upper respiratory tract material
− sputum, bronchoalveolar lavage
− purulent ocular discharge
− material collected from exposed base or margin of genital lesion - Stuart’s or Amies Transport Medium adequately maintains organisms’ viability
CULTURE MEDIA Haemophilus
Selective media
* Haemophilus isolation agar medium
* Mueller-Hinton base chocolate agar medium supplemented with 1% IsoVitaleX(BBL Microbiology Systems) and 3µg/mL vancomycin
−adequately supports growth of Haemophilus ducreyi
Non-selective media
* Chocolate agar medium
−supplies factors necessary for growth of most Haemophilus spp.:
* haemin or haematin (X factor)
* nicotine adenine dinucleotide - NAD or NAD phosphate -NADP (V factor)
INCUBATION CONDITIONS Haemophilus
- 35oC to 37oC
- from 24 hours to 72 hours
- up to 7 days for Haemophilus ducreyi
- in 5% to 10% CO2
-enriched atmosphere
DIRECT EXAMINATION Haemophilus
- detection of specific polysaccharide capsular antigens in body fluids
DNA probe assays
* PCR-based
- Haemolytic reaction on horse blood agar
- Growth requirements for X and V factors
- MALDI-TOF MS
SEROLOGIC TESTS Haemophilus
- Serotyping methods
− relevant only for encapsulated (typeable) strains of Haemophilus influenzae
− agglutination of organisms in type-specific antisera - Detection of antibodies to Haemophilus spp.
− Enzyme Immunoassays (EIA) for Haemophilus ducreyi IgG and IgM antibodies
ANTIBIOTIC SUSCEPTIBILITIES Haemophilus
- recommended initial therapy for meningitis:
combination of ampicillin and chloramphenicol - ceftriaxone or cefotaxime alternative therapy
- treatment for chancroid: erythromycin or ceftriaxone
IMMUNISATION Haemophilus
Active immunisation
* availability of safe and effective vaccines against Haemophilus influenzaeserotype b altered incidence of serious infections
GENERAL CHARACTERISTICS Pasteurella
- Gram-negative coccobacilli or rods, show bipolar staining, no special arrangement (present singly, in pairs, short chains or small groups)
- non-motile, do not form spores
- facultatively anaerobic
- oxidase positive, catalase positive, fermentative
- reduce nitrate to nitrite
- virulent organisms produce a capsule
- generally susceptible to β-lactam antibiotics
