Respiratory Pathogens Flashcards
Name 6 pathogens that contribute to lower respiratory tract infections
- haemophilus influenza
- strep. Pneumoniae
- legionella pneumophila
- mycobacterium tuberculosis
- mycoplasma pneumonia
- chlamydia pneumonia
What are the two factors that affect the degree of pathogenicity of a disease causing organism?
- the proteins it expresses
- how effectively it can integrate environmental information
What does bacterial adhesion involve?
Surface interactions between specific receptors on the mammalian cell membrane (usually carbohydrates) and ligands (usually proteins) on the bacterial surface
What is bacterial invasion?
Bacteria invasion refers to the penetration of host cells and tissues, and is mediated by a complex array of molecules called invasins
What molecules mediate bacterial invasion?
Invasins
Mechanisms that result in the evasion of host defences (x5)
- immunity at mucosal surfaces
- destruction of immune cells
- interference with inflammatory response
- evasion of innate immunity
- overcome acquired immune responses
How does the bacteria overcome acquired immune responses?
Phase/Antigen variation - switching between on and off forms of a gene / allowing the bacterium to change the sequence of a gene
What are endotoxins?
Lipopolysaccharides complexed to proteins that occur in the outer membrane of the envelope of gram negative bacteria
Principal antibody type produced at mucosal surfaces? What molecules cleave these immunoglobulin?
IgA
Proteases
Incubation period of Diphtheria
2-6 days
What does corynebacterium diphtheria cause/what is it characterised by?
Infects mucous membranes (tonsils) - toxin produces acute inflammation and formation of pseudomembrane
Early symptoms of corynebacterium diphtheria
Sore throat
Low fever
Swollen neck glands
Late symptoms of corynebacterium diphtheria (x3)
Airway obstruction
Difficulty breathing
Shock -> hypotension, tachycardia, pale, cold skin, sweating, anxious
What are diphtheria outbreaks associated with? (X2)
Unsanitary/crowded conditions
Immunity gaps, vaccination failure
Is corynebacterium diphtheria I) gram positive or gram negative II) cocci or bacilli III) aerobic or anaerobic IV) motile or non-motile V) growth medium
Gram positive Bacilli Aerobic Non-motile Grows in tellurite agar, which is toxic for other throat flora
How is corynebacterium diphtheria transmitted?
Direct contact droplets/skin
Indirect via contaminated object
Treatment of Diphteria (x2)
- immediate inoculation with diphtheria anti-toxin
- administer penicillin or erythromycin to eliminate the bacteria
Prevention of diphtheria
Active immunisation
Diphtheria Formal Toxoid (DFT Vaccine) - part of multiple vaccine - given at 2,3,4 months ; booster jab at 5 years
How does diphtheria enters the cell?
Endocytosis - proteolytic cleavage takes place in the cell, resulting in 2 fragments
Which bacteria causes whooping cough?
Bordetella Pertusis
Describe the appearance of B. Pertussis (x3)
Small,
Gram-negative
Cocci
Transmission of Bordetella Pertussis
Infection by exposure to infected individual
Clinical features of B. Pertussis infection (x4)
- insidious onset
- catarrhal stage with common cold symptoms
- paroxysmal coughing
- residual cough
What may adults suffering from bordetella pertussis experience? (X4)
- shortness of breath during coughing
- nocturnal coughing
- tingling sensation in back of throat
- post-tussive vomitting
Route of infection of B. Pertussis
The organism infects the ciliated epithelial layer of the respiratory tract without invading deeper, resulting in an acute tracheobronchitis
What mediates the action of B. Pertusis? (X2)
- filamentous hemagglutinin (FHA)
- cell bound pertussis toxin (PTx)
What is pertactin (PRN)?
The outer membrane protein that promotes the attachment of B. Pertussis to tracheal epithelial cells
What is the outer membrane protein that promotes the attachment of B. Pertussis to tracheal epithelial cells
Pertactin
Name 4 toxins involved with bordetella pertussis
- Pertussis toxin
- Adenylate cyclase/hemolysin
- Tracheal cytotoxin (TCT)
- Lipopolysaccharide (endotoxin)
Pathogenesis of B. Pertussis
- Growth on ciliate epithelial and toxin production, killing the ciliate epithelial cells and inducing mucous secretions
- Stimulates inflammatory response
- Kills leucocytes
What does the action of Pertussis Toxin result in?
Kills leucocytes, resulting in disruption of cell function, increased mucous secretion, incapacitating phagocytes function
Systemic consequences: increase in insulin and sensitivity to histamine
Diagnosis of Bordetella Pertussis (x2)
Hold BG culture plate in front of mouth when coughing
Perinasal swab of posterior pharyngeal walls
Treatment of B. Pertussis
Erythromycin for 14 days
Skilled nursing, removal of mucous and vomit
Antibiotic therapy for secondary infections
Vaccination
Growth requirements of haemophilus influenza (x4)
- chocolate or cooked blood agar
- aerobic conditions
- nutritional factor X - haematin
- nutritional factor V - nicotinamide adenine dinucleotide (NAD)
Comparison between haemophilus influenza growth in cooked blood agar plates vs normal blood agar plates
Larger colonies are produced in cooked blood agar than in normal blood agar. This is because the V factor, Nicotinamide adenine dinucleotide, is imprisoned in intact RBCs
Appearance of haemophilus influenza
Small
Gram negative
Bacillus - considerable pleomorphism
(Non-motile)
Route of transmission of H. Influenza
Direct contact with patient
Respiratory droplets
Name 3 diseases caused by H. Influenza
- Meningitis
- Bronchitis
- Pneumonia
Mode of action of haemophilus influenza
Bacteria attaches to epithelial cells and penetrates sub mucosa of the nasopharynx, causing local inflammation and swelling. It can then spread from the initial site to infect bones, joints and CNS.
Significance of the capsule of haemophilus influenza
Polyribosyl Ribotol Phosphate (PRP) capsule protects the bacteria from phagocytosis, reducing its susceptibility to the antibacterial role of serum
Name 3 factors promoting the adhesion of haemophilus influenza to mucosa
- P2 (+ other outer membrane proteins)
- Fimbriae / Pili
- Non-pilus adhesins
What does P2 target?
Sialic acid oligosaccharides in mouth
What does fimbriae/Pili and non-pilus adhesins target in the adhesion of H. Influenza to mucosa?
Mucosal cells of the nasopharynx
Treatment of H. Influenza (x2)
Antibiotics
Immunisation - Hib (capsule type B) vaccine given at 2,3,4 months
Antibiotics for treating H. Influenza caused meningitis
Cefotaxime
Cephalosporins e.g. Ceftriaxone
Antibiotics for treating H. Influenza caused bronchitis
Amoxicillin/Erythromycin
Antibiotics for treating H. Influenza caused pneumonia
Flucloxacillin / Amoxycillin
What is pneumonia?
An acute inflammation of the lungs, where the alveoli and branchioles of the lungs become plugged with a fibrous exudate
Appearance of Streptococcus Pneumoniae
Encapsulated
Gram positive cocci
Oval/lancet shaped
Arranged in pairs (diplococci)
Haemolytic activity of strep. Pneumoniae
Alpha-hemolytic
Is s. Pneumoniae
- Optochin sensitive/resistant?
- catalase positive/negative?
Optochin sensitive
Catalase negative
Who are more likely to present with pneumococcal pneumonia?
The very young and very old
Mode of action of pneumococcal pneumonia
- invasion of lower respiratory tract by aerosol
- normally bypass ciliated epithelial
- progress to alveolar and cell wall - promotes binding to cells expressing the platelet activating factor receptor
- teichoic acids are exposed on cell surface and present in the cell wall
- overcomes IgA through secretion of proteases
- overcomes mucociliary escalator by the production of cytotoxin that kills ciliated epithelial cells (pneumolysin)
- bacteria multiplies in nutrient-rich oedema fluid
- erythrocytes, neutrophils and macrophages accumulate as the fluid becomes purulent
Name 5 virulence factors involved in phagocytic survival of S. Pneumoniae
- cell wall initiates inflammation - teichoic acid activates C5a and alternative complement pathway
- pneumolysin - pore forming (type II) toxin - disrupts membrane and inhibits oxidative burst
- hydrogen peroxide
- phosphorycholine - present on cell wall; binds to PAF receptor and induces receptor mediated endocytosis
- capsule
Symptoms of pneumonia (x6)
- normally preceded by 1-3 days of viral respiratory infection
- abrupt onset
- severe shaking chill, sustained fever at 39-41deg
- productive cough with blood tinged sputum
- chest pain
- lobar pneumonia - confined to lower alveolar lobes
- 5% mortality rate
- bacteraemia may occur, in 25-30% of patients with pneumonia
Treatment of pneumonia (x3)
- amoxicillin
- erythromycin
- more advanced beta-lactams (eg cephalosporins)
Control of pneumonia
Vaccination
- pneumococcal vaccine at 2, 4, 13 months
- anti-capsular vaccine consisting 23 capsular polysaccharides
What is Legionnaires disease caused by?
Legionella pneumophila
What does legionella pneumophila cause? (X2)
Legionnaire’s disease
Pontiac fever
Where can legionella be found? (X4)
- circulating water droplets
- cooling towers
- warm water baths
- decorative fountains
Route of transmission of legionella
Via inhalation of water droplets
No person-person spread
What is Legionnaire’s disease?
Atypical, acute lobar pneumonia with multi-system symptoms
What is Pontiac fever?
Non-pneumonic legionellosis
Symptoms of Pontiac fever (x5)
Dry cough Malaise Headache Fever GI problems
Describe the appearance of Legionella Pneumophila
Gram negative Facultative intracellular Slender unencalsulated rods Cocco-bacillary appearance Strict aerobes Fastidious
Symptoms of Legionnaire’s disease (x6)
- cough, fever, swears, loss of appetite, headache, general pains
- rapidly degenerates, yellow/green sputum can be stained with blood
- tight chest, breathlessness, sharp pain in the side of chest
- confusion and diarrhoea
- complications: heart, brain, kidneys
Diagnosis of Legionella pneumophila (x3)
- culturing
- direct antibody test
- rRNA identification
Treatment of legionella pneumophila
Erythromycin/Azithromycin
PONTIAC FEVER IS NOT TREATED
Control of legionella
Clean water systems
Monitor hot water systems
Hot water to be above 50 deg as bacteria thrive in 20-45deg
Name 6 upper respiratory tract infection pathogens
- strep. Pyogenes
- corynebacterium diphtheria
- bordetella pertussis
- haemophilus influenza
- oral spirochaetes
- fusobacterium