Public: The microbiota of a few organ systems Flashcards
What does the gastrointestinal tract consist of?
stomach, small intestine, and large intestine
What are the functions of the gastrointestinal tract?
digestion of food, absorption of nutrients, and production of nutrients by the indigenous microbial flora
How many microbial cells are in the GIT?
10^13 to 10^14 microbial cells
Where in the respiratory tract do microbial organisms colonise? Where are they less likely to colonise?
Upper respiratory tract
The lower respiratory tract lacks microflora in healthy individuals
Give examples of some microbiota in the upper respiratory tract
staphylococci, streptococci, diphtheroid bacilli, and gram-negative cocci and others
Name the organs in the upper respiratory tract
sinuses, nasopharynx, pharynx, oral cavity, larynx
Name the organs in the lower respiratory tract
trachea, bronchi, lungs
Altered pH can cause what to happen in the urogenital tract?
can cause potential pathogens in the urethra (such as Escherichia coli and Proteus mirabilis) to multiply and become pathogenic
Which organisms commonly cause urinary tract infections in women?
E. coli and P. mirabilis
What is the pH of the vagina like?
Slightly acidic (maintained by lactic acid), contains significant amounts of glycogen
Name a resident organism of the vagina. What does it do?
Lactobacillus acidophilus
Ferments the glycogen in the vagina, forming lactic acid to maintain the acid environment of the vagina
Define virulence
the relative ability of a pathogen to cause disease
How can virulence by measured?
Virulence can be estimated from experimental studies of the LD50 (lethal dose50)
= The amount of an agent that kills 50% of the animals in a test group
Highly virulent pathogens show little difference in the number of cells required to kill 100% of the population as compared to 50% of the population
Define attenuation
The decrease or loss of virulence
Define invasiveness
Ability of a pathogen to grow in host tissue at densities that inhibit host function
Can cause damage without producing a toxin
What is the causative agent of diphtheria?
Corynebacterium diphtheriae
Describe Corynebacterium diphtheria using the following points:
1) Gram positive/negative
2) Motile/non-motile
3) Morphology
1) Gram positive
2) Motile
3) Clubbed morphology
Clinical presentation of diphtheria
Pseudomembrane formation (in throat)
Difficulty swallowing
Systemic effects – heart complications, coma, death
Describe the pathogenesis of diphtheria
Inhalation of aerosols
Colonisation of throat
Produces single chained A-B toxin (DT)
Pseudomembrane formation in throat
AB toxin inhibits EF2 in eukaryotic cells
Inhibits protein synthesis
Death in 3 to 5% children
What is the causative agent of whooping cough? (pertussis)
Bordetella pertussis
Describe Bordetella pertussis using these points:
1) Gram positive/negative
2) Aerobic/anaerobic
3) humans/animals
4) Shape
1) Gram negative
2) Aerobic
3) Humans only
4) cocco-bacillus
Clinical presentation of whooping cough (pertussis)
Paroxysms of cough (whoop)
CNS effects
Secondary pneumonia
Describe the pathogenesis of whooping cough (pertussis)
Attachment and replication on ciliated URT mucosa
Toxin production
Pertussis (exo)toxin
Tracheal cytotoxin (TCT)
Invasive adenylate cyclase toxin
Loss of mucociliary clearance
Violent coughing fits
Secondary pneumonia
What are the 3 stages of pertussis disease progression?
Stage 1 - Catarrhal stage
Stage 2 - Paroxysmal stage
Stage 3 - Convalescent stage
Describe the catarrhal stage of pertussis
May last 1-2 weeks
Symptoms: runny nose, low-grade fever, mild, occasional cough
Highly contagious
Describe the paroxysmal stage of pertussis
Lasts 1-6 weeks, may last up to 12 weeks
Symptoms: fits of numerous, rapid cough characterised by “whoop” sound, vomiting and exhaustion after coughing fits (called paroxysmals)
Describe the convalescent stage of pertussis
Lasts about 2-3 weeks
Susceptible to other respiratory infections for many
Recovery is gradual. Coughing lessens but fits of coughing may return.
What is the causative agent of Cholera?
Vibrio cholera
Wat is the shape of Vibrio cholera? Is it gram negative or gram positive?
comma shaped
gram negative
Clinical presentation of severe cholera
Severe = rice water stools
Pathogenesis of cholera
An acute infection of the GI tract (small intestine)
Production of cholera toxin
Adenylate cyclase upregulation
Massive fluid loss to GIT
Death through dehydration
Mortality
Up to 60% (untreated)
<1% electrolyte replacement
Short term carriage in up to 20% cases
Traveller vaccination?
Name some non-invasive pathogens
Corynebacterium diphtheriae
Bordetella pertussis
Vibrio cholera
Name some partially invasive pathogens
Shigella sonnei – mild infections
Shigella flexneri – severe infections
Shigella dysenteriae – very severe
Possible causative agents of Shigellosis?
Shigella sonnei – mild infections
Shigella flexneri – severe infections
Shigella dysenteriae – very severe
Describe Shigella organisms using the following questions:
1) Gram positive or negative?
2) Shape?
3) Aerobic/anaerobic
4) Spore forming/non spore forming?
1) Gram-negative
2) Rods
3) Facultative anaerobes
4) non spore forming
Clinical presentation of shigellosis
Blood and puss in diarrhoea
Pathogenesis of shigellosis
Attachment and invasion of distal ileum and colonic epithelia
Shiga toxin (an A-B toxin) Not excreted!!
Partial invasion – no deeper than lamina propria
1.1 million deaths p.a.
Name some primary invasive pathogens/diseses
typhoid (enteric fever)
rubella, chickenpox, measles - URT
polio, hepatitis -GIT
Causative agent of enteric fever (typhoid)
Salmonella enterica serovar Typhi
Primary invasive pathogen
Clinical presentation of typhoid (enteric fever)
Systemic infection
Constipation/diarrhoea
Fever
3 week symptom duration
3% become chronic carriers
Transmission of enteric fever (typhoid)
No animal reservoir
Person to person spread or consumption of contaminated foods
No animal reservoir
Primary infection via jejunum or distal ileum (i.e. small intestine)
pathogenesis of enteric fever (typhoid)
Bacteria induced uptake by M cells of epithelia
exocytosis of macrophage containing viable bacteria
systemic dissemination
Give an example of a disease without bacterial colonisation
food poisoning
true food poisoning (toxinoses) is
Consumption of food containing toxins (chemical or bacterial origin
Causative agent of botulism
Clostridium botulinum
Clostridium botulinum
1) Aerobic/anaerobic
2) spore forming/non spore forming
3) LD50
4) heat stable or not? How to inactivate the toxin?
1) obligately anaerobic
2) spore forming
3) Botulinum toxin (LD50 <0.01ng)
Highly potent neurotoxin
4)Heat stable
15 minutes boiling to inactivate
Toxinoses of Staphylococcus aureus food poisoning
creamy foods, custards etc
Cause of Staphylococcus aureus food poisoning
enterotoxins
Symptoms of Staphylococcus aureus food poisoning
Rapid (1 – 6 h) symptoms- nausea, vomiting, abdominal pain, diarrhoea
Bacillus cereus food poisoning
1) Aerobic/anaerobic?
2) spore forming/non spore forming?
1) obligately aerobic
2) spore forming
What are the two disease forms of Bacillus cereus?
1) emetic toxin
2) enterotoxins Nhe and HBL
Describe the emetic toxin disease form of Bacillus cereus
Heat stable
Short incubation
Describe the enterotoxins (Nhe and HBL) of Bacillus cereus
Heat liable
Diarrhoea form
Longer incubation
