17. Haemophilius, Bordetella, Legionella Flashcards
Haemophilus species and what they cause
- H. influenzae
-respiratory tract infection
-meningitis
-bloodstream infection - H. ducreyi
-chancroid (a sexually transmitted infection) - H. aphrophilius (now A. aphrophilus)
-HACEK endocarditis
H.influenza and H.aphrophilus colonise the upper respiratory tract
Where is H.influenzae found
nasopharynx of healthy adults and children
-capsulated or non-capsulated
Encapsulated H.influenzae type b strains
- severe invasive disease
- especially in young children in countries that do not include Hib vaccine in the infant schedule
- hyposplenism/asplenism
- congenital or acquired immunological deficiencies
- e.g. depletion of CD4 T-cell in HIV, complement deficiency
- has a anti-phagocytic polysaccharide capsule: PRP (polyribosylribitol phosphate) that:
a) makes it resistant to phagocytosis by PMN leukocytes in the absence of specific anti-capsular antibody
b) reduce the organism’s susceptibility to the bactericidal effect of serum
Non-encapsulated H.influenza
mainly associated with respiratory/mucosal infection
- acute exarcebation of chronic bronchitis
- otitis media, sinusitis, pneumonia
- may cause invasive disease
Capsulated H.influenza
divided into different strains using antisera against specific capsular polysaccharides
- 6 type: a-f
- b: Hib - most commonly associated with systemic disease
Virulence factors of capsulated H.influenzae
- capsule
- pili/fimbrae
- outer membrane proteins - adhesion proteins
- lipooligosaccharide
- antimicrobial resistance
Pathogenesis of infection with capsulated H.influenzae
- inhalation of respiratory droplets or direct contact with respiratory secretions
- colonization of oropharynx
- fimbriae/pili attachments to respiratory epithelial cells
- capsule is the critical virulence factor that facilitates invasion and haematogenous dissemination
- capsular and lack of anti-PRP antibody complement activation of endotoxin acting on the lipopolysaccharide
Virulence factors of non-capsulated H. influenzae and their biological role
- fimbrae - attachment to pharyngeal cells
- opacity-associated protein (Aap) - attachment to pharyngeal cell
- IgA protease - inactivate IgA in the nasopharynx
- lipooligosaccharide - endotoxin activity when the organism are lysed
- antimicrobial resistance (esp. beta-lactamase protein)
Pathogenesis of infection with non-capsulated H.influenzae
- commonly colonise patients with chronic pulmonary disease (e.g. COPD, cystic fibrosis)
- ciliated columnar epithelium is damaged by air pollutants, smoking
- damaged cilia or reduction in the number of ciliated cells allow collection/pooling of mucus
- biofilm formation
- predisposes to invasion by bacteria
- preceding or coincident viral infection may also precipitate infection
H. influenzae type B may cause
- respiratory tract infections in early childhood
- acute epiglottis
- pneumonia - meningitis
- untreated -> very high mortality
- deafness, seizures and intellectual impairment - septicaemia
- septic arthritis
- cellulitis (closed, spreading)
Non-capsulated H. influenzae may cause
- recurrent sinusitis
- acute/chronic bronchitis
- acute and chronic otitis media
- community-acquired pneumonia
- invasive infection (less common)
Laboratory features of haemophilus species
- pleomorphic gram negative bacilli/coccobacilli
- stain faintly
- facultatively anaerobic
- max growth in 5% CO2 - fastidious
- require either X factor (haemin) or V factor (NAD) or both
- both found in chocolate agar
- H.influenzae require both
Laboratory diagnosis of systemic infections such as epiglottis, bloodstream infection, cellulitis and septic arthritis
- blood culture
- joint fluid (septic arthritis)
- aspirate from area of cellulitis
- swab for culture and antibiotic susceptibility
Laboratory diagnosis of suspected meningitis
- blood culture and PCR
2. CSF for microscopy, culture and PCR
Antibiotic treatment for haemophilus species
- naturally resistant to penicillin
- beta-lactamase producers
- resistant to amoxicillin
1. In-patient treatment - IV co-amoxiclav (respiratory infection)
- IV cefotaxime/ceftriaxone (BSI, meningitis)
2. Out-patient treatment - oral co-amoxilav
- macrolide (e.g. clarithromycin)
What does Bordetella pertussis cause
whooping cough (pertussis)
What is bordetella pertussis
pertussis which is a highly contagious infection of the respiratory tract
-may occur at any age, but most severe in infants
What is the virulence factors of bordetella pertussis
- filamentous haemagglutinin adhesin
- pertactin
- outer membrane protein (P69 protein) - fimbriae
- capsule
- cytotoxin
- pertussis toxin
- endotoxin (LPS)
Pathogenesis of bordetella pertussis
- inhalation of droplets
- attach to respiratory mucosal cells in nasopharynx and trachea:
- filamentous haemagglutinin adhesin - ciliated cells
- pertactin (P69 protein) - tracheal cells
- fimbriae - ciliated cells - capsule to evade the immune system
- toxin to damage host cell
a) cytotoxin
- paralyes cilia
- causes paroxysms of coughing
b) Pertussis toxin
c) endotoxin
- causes disruption of host cell - shed in respiratory droplets with coughing or sneezing
Stages of whooping cough
- Catarrhal stage (1-2 weeks)
-non-specific symptoms: malaise, rhinorrhoea, mild cough
-most infective stage - Paroxysmal stage (2-4 weeks)
-paroxysmal cough - severe, vigorous cough that occur during a single expiration following by vigorous inspiration - whooping sound
-post-tussis vomiting - Convalescent stage (3-4 weeks)
-gradual reduction in the frequency and severity of the cough
Total: 3 months
Laboratory features of bordetella pertussis
- very small Gram negative cocco-bacillus
- 3 distinct serotypes: 1-3
- aerobic
- capsulated
- highly infectious - droplet spread
Diagnosis of pertussis
Microbiological tests
- culture (fastidious organism)
- aspiration of nasopharyngeal secretions or nasopharyngeal swab - special transport medium - rapid transport to laboratory
- selective and enriched medium
- charcoal-blood agar, antibiotics to inihibit normal flora (may take up to 10 days to grow)
- gram-negatve coccobacilli (tiny)
- lacks sensitivity
- blood culture are of no benefit because Bordetella do not enter the bloodstream! - serology
- anti-pertussis IgG detected on samples taken > 2 weeks after onset of symptoms - nucleic acid amplification tests (NAAT) - PCR on pernasal swab or nasopharyngeal aspirate
- more sensitive than culture and faster - Other supportive lab test
- increase white cell count with absolute lymphocytosis
Treatment of whooping cough
- primarily supportive
- fluid administration - erythromycin/clarithromycin
- if administered in the catarrhal stage, may elimated disease and prevent transmission
Which Legionella species is responsible for most infections
Legionella pneumophilia serogroup 1
Epidemiology of L.pneumophilia
colonisation is enhanced by warm temperature (25-42°C), stagnation, scale and sediment
-infection arises following inhalation of aerosols from contaminated water
Virulence factors of Legionella pneumophilia
- pili
- adherence - outer membrane proteins
- adherence - flagellae
- enzymes
- protease, phosphatase, lipase, DNAase, RNAse
- cell damage - LPS
- endotoxic activity - phagocytosis or invasion?
- L. pneumophilia is an intracellular pathogen, the bacteria avoid phagolysosome fusion and replicate within alveolar macrophages and epithelial cells in a vacuole
- virulence proteins secreted into the vacuole enable survival and replication
Clinical features of legionnaires’ disease
- male:female 2:1
- aged 50-60 years
- pontiac fever: brief flu-like illness
- cause of community-acquired pneumonia
- incubation period is 2-10 days
- abrupt onset of fever, chills, dry cough, headache
- may get multi-organ disease of GIT, CNS, liver
- renal involvement result in proteinuria, haematuria and hyponatraemia (due to renal tubular acidosis)
- higher mortality in patients with severely depressed cell-mediated immunity (transplant recipient) or if treatment is delayed
Predisposing factors to severe disease include
a) old age
b) cigarette smoking
c) immunosuppression
Diagnosis of legionnaires’ disease
- Culture
- require specific growth media
- e.g. buffered charcoal yeast extract (BCYE) agar and antibiotics to which the organism is resistant to inhibit growth of other bacteria
- sputum/tracheal aspirate/bronchoalveolar lavage
- colonies appear after 2-3 days incubation - Urinary antigen detection
- rapid - Serology - antibody detection
- antibody is detectable about the 8th day of the illness
- 4 fold increase in the level of antibodies produced between serum taken at acute stage of illness and repeated up to 2 weeks later - Immunofluorescent microscopy
- difficult to see L.pneumophilia by gram stain
- high specificity but lack sensitivity
Treatment of Legionnaires’ disease
- beta lactam agents are not effective
- drugs with good intracellular penentration is required
- respiratory fluroquinolones, e.g. levoflaxacin
- macrolides, e.g. azithromycin or clarithromycin
- may combine with rifampicin in the seriously ill
