L15 Haemophiles, Bordetella, Legionella Flashcards
Hemophilus microbiological characteristics:
Gram-positive/negative?
Anaerobic/Aerobic?
Culture?
Other?
- small Gram-negative coccobacilli
- facultative anaerobe
- Cultured on Chocolate Agar
- require growth factors to grow on culture media
X factor
- supplied by heat-stable iron-containing pigments haemin, haemoglobin, haematin
- concentrated within erythrocytes
V factor
- supplied by nicotinamide adenine dinucleotide (NAD), nicotinamide adenine dinucleotide phosphate (NADP), or nicotinamide nucleoside (NN)
- present in erythrocytes, lysis required for release
Haemophilus Influenzae Description?
Unique Characteristics?
Transmission/Colonization?
small Gram-negative anaerobic coccobacilli that requires X and V factors for growth on Chocolate Agar
Exhibits satellitism: pinpoint colonies in zone of haemolysis surrounding S. aureus streak
Nontypeable: strains of H. influenzae that lack a capsule are non-reactive with typing antisera raised against each of the six capsules
Spread by inhalation of respiratory droplets or direct contact with secretions, colonizes nasopharynx and conjunctiva
Haemophilus Influenzae Virulence Factors (5)
- Polysaccharide Capsule: Resistance to phagocytosis and bacteriolysis
- Pili: Attachment to epithelial cells
- IgA Protease: Inactivates IgA and facilitates evasion of local immune response
- Outer Membrane proteins: Attachment
- LPS: Aids in invasion
Clinical Manifestations of Haemophilus Influenzae
Invasive: Colonization=> penetration of nasopharyngeal mucosa => bloodstream
Non-invasive: Physiological or anatomical abnormality
Treatment of Haemophilus Influenzae?
Treatment
Serious Infection: Third-generation cephalosporins (Ceftraxone or Ceftaxime)
Non-Typeable: amoxicillin, amoxicillin-clavulanic acid, fluoroquinolones, newer macrolides (e.g., azithromycin, clarithromycin), and various extended-spectrum cephalosporins.
Prevention of Haemophilus Influenzae?
Hib vaccine:
–all infants at 2, 4 and 6 months with a booster dose at 13 months
–unvaccinated aged 1 to 10 years should be given 1 dose
Bordetella microbiological characteristics?
Gram-positive/negative?
Anaerobic/Aerobic?
Culture?
Bordetella microbiological characteristics:
- small gram-negative coccobacilli
- strictly aerobic
- fastidious–special media required
- Bordet-Gengou agar
- charcoal blood agar, made selective w/ antibiotics (Regan-Lowe media)
Bordetella Pertussis description?
Transmission?
spread by droplets, highly contagious
Pre-vaccine era nearly all children infected between the ages of 1 and 5 years.
adults with waning vaccine-induced immunity are increasingly infected
often goes undiagnosed because infection may be atypical.
Bordetella Pertussis Virulence factors (7)
-
Pertussis Toxin (PT)
- AB Toxin activates adenyl cyclase => increased cAMP
- Promotes lymphocytosis
- Hypoglycemia due to islet cell activation
- blocks immune effector cells
- increased Histamine sensitivity
- Pertacin (PRN): outer membrane protein involved in adhesion
- Pili
- Filamentous Hemagglutinin (Fha): attachment of B Pertusus to cuilliated rtespirator epithelia
- Lipooligosachirade
- Adenylate Cyclase Toxin: Enters leucocytes interfering w/ their function
- Tracheal Cytotoxin: Causes allostasis, inhibits DNA synthesis killing ciliated epithelial cells
- Dermonecrotic Toxin: Causes vascular smooth muscle contraction resulting in focal ischemic necrosis
Mechanisms of Bortetella Perusis’s Pertussis Toxin?
-
Pertussis Toxin (PT)
- AB Toxin activates adenyl cyclase => increased cAMP
- Promotes lymphocytosis
- Hypoglycemia due to islet cell activation
- blocks immune effector cells
- increased Histamine sensitivity
Stages of Bordetella Pertussis Infection?
Catarrhal stage (1 –2 weeks)
–profuse rhinorrhoea, malaise, low-grade fever, cough
–indistinguishable from other URTI
Paroxysmal stage (1 –4 weeks)
–cough paroxysm consists of a series of short expiratory bursts,
=> followed by a characteristic inspiratory whoop
=> Vomiting frequently follows whoop
– Miserable and exhausted.
Convalescent stage (3 –4 weeks)
–decrease in intensity of cough and frequency of paroxysms
Complications of Bordetella Pertussis
Complications
- secondary bacterial infections such as pneumonia and otitis media.
- increased intra-thoracic pressures during coughing can result in:
Subconjunctival hemorrhage
Cerebral haemorrhages
Pneumothorax
umbilical and inguinal hernias
rectal prolapse
•convulsions, encephalopathy
Diagnosis of Bordetella Pertussis
Culture - sample from nasopharynx
PCR
Serology - later stages of disease, sample 2-8 weeks after cough onset
Management of Bordetella Pertussis
Management
Supportive care - Oxygen and hydration
Specific therapy - Erythromycin, clarithromycin or azithromycin
Prevention of Bordetella Pertussis
Pertussis vaccine
•Whole-cell pertussis vaccine (wP)
–contain a suspension of killed B. pertussis
•Acellularvaccine (aP)
–purified pertussis antigens (Fha, PT toxoid, pertactin, pili)
–significantly less local and systemic side-effects
Indication for Vaccine:
–all infants at 2, 4 and 6 months with a booster at 4-5 years
–further booster (Tdap w/low dose acellular pertussis) at 11-14 years
Bordetella Pertussis Pathogenesis?
Pathogenesis:
B. pertussis Inhalation
=> adheres to ciliated epithelium of trachea and bronchi (tropism)
=>bacilli begin to multiply, producing toxins
=> organisms remain localized on respiratory epithelium and DO NOT INVADE
Legionella pneumophila Description:
Gram-positive/negative?
Anaerobic/Aerobic?
Culture?
Other?
Legionella pneumophila
•Gram-negative bacilli (unencapsulated- stain poorly with Gram stain)
•strict AEROBE
•does not grow on standard media. Needs buffered charcoal yeast extract (BCYE) supplemented with l-cysteine, α-ketoglutarate and ferric ions.
Other: consists of 15 serogroups, serogroups 1, 4, 6 predominant–serogroup 1 causes 70-90% of cases
Epidemiology of Legionella pneumophila
aquatic environment
Natural: surface waters of rivers, lakes, streams and thermally polluted waters
Man-Made: cooling towersm hot water tanks, air conditioners, whirlpool spas
Growth aided by:
–co-existing micro-organisms, which provide nutrients
–free-living amoebae, in which Legionella reside and multiply
– Found in BIOFILMS => less susceptible to chlorine
dissemination from environment to host
Aerosolization of water
Aspiration of contaminated water
Direct inoculation (surgical wound infection)
NO PERSON TO PERSON TRANSMISSION
Legionnaire’s Disease pathogenesis?
L. pneumophila’s ability to grow in macrophages is central to pathogenesis.
intracellular multiplication
=> neutrophils, macrophages, and erythrocytes infiltrate alveoli
=> capillary leakage
=> edema
cell-mediated immunity primary host defense, humoral immunity secondary
Clinical Manifestation of Legionnaire’s Disease
Extrapulmonary common
1. neurological Headaches, Confusion, Obtundation (slowed level of response), Seizures
2. gastrointestinal, diarrhoea, nausea and vomiting, abdominal pain
Usually unilateral, lower lobe predominance=> progresses to bilateral
pleural effusion (1/3) and cavitations in immunocompromised
progresses despite appropriate antibiotic therapy, may take up to 4 months to resolve
Diagnosis of Legionnaire’s Disease
Legionnaire’s Stains poorly with Gram Stain
Culture is GOLD STANDARD
-
Special complex needed (Buffered Charcol Yeast Extract)
- L-cysteine and ferric ions support growth
- antibiotics prevent overgrowth of other organisms
- Dyes impart color on legionnella
-
Colonies take 3-5 days to apear
- GROUND GLASS apperance
- white, gray, pale blue, purple
Treatment of Legionella?
Duration?
Effective antibiotics are capable of achieving high intracellular concentrations:
Macrolides (clarithromycin and azithromycin)
Fluroquinolones (Severe disease IV initially, ORAL after good response)
Tetracyclines
Rifampicin
Beta-lactams and aminoglycosides have activity against Legionella in vitro but are not clinically effective
Duration of therapy:
–2 weeks for patients with mild disease
–at least 3 weeks for severe disease or immunocompromised patients
When to Suspect Legionnaires?
- Gram stain of respiratory samples w/ many polymorphonuclear leukocytes with few or no organisms
- hyponatremia (Low blood sodium)
- pneumonia w/ prominent extrapulmonary manifestations (diarrhoea, confusion)
- failure to respond to administration of beta-lactams or aminoglycosides
