Commensals of the respiritory Tract Flashcards
What are commensals?
Microbiota: the combined microorganisms in a particular environment
Mammals are host to a vast number of microorganisms, number of bacteria ~ number of host cells
Vast majority of resident bacteria are not harmful to the host.
Describe the location of the commensal bacteria of the respiratory tract.
- Skin
- Epithelium
- Upper respiritory tract
- Intestines
How does the body ensure the distal airways remain sterile from upper respiritory tract commensals?
Physical barriers which reduce the particles that get to the lower respiratory tract.
Hairs and structure of nasal turbinates. Movement of cilia and mucus in the trachea (Mucociliary clearance).
Immune cells.
Macrophages.
Non-specific soluble factors.
Defensins.
Lysozyme.
Lactoferrin.
Complement.
Surfactants.
Explain how some respiratory organisms act as commensals and others are pathogenic.
- Location on host
Example: Bite wound Bacteria that colonize the oral cavity as commensals turn
opportunistic pathogens when they are in the blood stream if that epithelial barrier
breaks - Acquisition of virulence genes [bacterial- host interaction lecture]
May change from commensal to pathogen - Change in gene expression
Example: Changes in surface capsule changes ability of macrophages to phagocyte
bacteria and control bacterial growth. - Host specific
Example: Haemorrhagic E. coli are commensals in cattle but cause sever disease in
humans and pigs
Depending on which host determines commensal or pathogenic status - Host controls impaired
All allowing an opportunity for infection through reduce immunity or other controls.
Changes within the host, e.g. pregnancy, stress, reduced maternal antibodies in
neonates (lack of colostrum).
How might host cells controls become impaired?
Environment related
Example: Dehydration or cold can increase mucus viscosity. This will slow the
escalator and reduce function in clearing commensals that make it that far.
Co-infection with other pathogen (Intercurrent disease)
Example: Infection with a virus can damage the mucosal function allowing
overgrowth of commensal bacteria.
What arethe risk factors that predispose calves and other animals to pneumonia?
Close confinement. (only see this in the UK during transportation)
Transportation and other stress.
Poorly ventilated or overcrowded housing
Decline in maternal antibody
Lack / reduced intake of colostrum
Intercurrent infections
List examples of microorganisms found in the normal respiratory tract of veterinary species.
- Streptococcus species.
- Actinobacillus
- Pasteurella multocida
- Bordetella bronchiseptica
- Escherichia coli
Streptococcus Spp
List the: Morphology & gram type, Media type, Respiration, Key tests
Morphology & gram type: Gram positive cocci in chains
Media type: Fastidious require enriched media blood aga
Respiration: Facultative Anaerobes
Key tests: Catalase neg / Usually haemolytic
Actinobacillus species
List the: Morphology & gram type, Media type, Respiration, Key tests
Morphology & gram type: Gram negative rods
Media type: Non enriched media / Most grow on MacConkey
Respiration: Facultative Anaerobes
Key tests: Non-motile / Urease positive / Oxidase-positive / Agglutination of red blood cells
Pasteurella multocida
List the: Morphology & gram type, Media type, Respiration, Key tests
Morphology & gram type: Small Gram negative rods
Media type: enriched media
Respiration: Facultative Anaerobes
Key tests: Non-motile / Oxidase-positive
Bordetalla bronchiseptica
List the: Morphology & gram type, Media type, Respiration, Key tests
Morphology & gram type: Small Gram negative rods
Media type: Non enriched media
Respiration: Obligate aerobes
Key tests: motile / Catalase-positive / Oxidase-positive / Agglutination of red blood cells
Escherichia coli
List the: Morphology & gram type, Media type, Respiration, Key tests
Morphology & gram type: Gram negative rods
Media type: Non enriched media / [ferment lactose – McConkey]
Respiration: Facultative Anaerobes
Key tests: motile / Catalase-positive / Oxidase-negative/ Agglutination of red blood cells
Explain the clinical significance of commensal organisms in the diagnosis of respiratory disease.
Start point:
History
Clinical signs (discharges, coughing etc.)
Clinical exam
Upper or lower respiritory tract?
Visual/imaging:
Endoscopy/Rhinoscopy
Radiography Ultrasonography?
Sampling:
Haematology
Bronchoalveolar lavage lower respiritory tract Tracheal aspiration. upper respiritory tract Swabs upper respiritory tract
Cytology & Microbiology on samples:
-Demonstration of immune cells – look out for intracellular bacteria!
-Culture or visual - bacterial / fungal.
-Demonstration of viral antigens (needs detection method).
How are swabs used in diagnosis?
Tip of double guarded swab showing telescoping protective plastic sleeves that prevent contamination of the swab before site of interest
Type
Length
Transport medium
All need to considered when choosing an appropriate swab for test
Some circumstances you want a double protective swab
How is the bronchoalveolar lavage (BAL) performed?
Collection of a BAL sample. Adequate restraint of animal is essential for this procedure
Look at in in microscope directly with staining/ culture
