[W2] Commensals and Pathogens Flashcards
(31 cards)
What is a commensal?
A microbe that colonizes the host without causing damage.
Commensals are part of the normal flora of the host.
What is an opportunistic pathogen?
A microbe that is normally harmless but can cause disease in immunocompromised individuals or if it gains access to a new niche.
Opportunistic pathogens exploit favorable conditions to cause infections.
What is a carrier?
An infected host not showing symptoms but capable of transmitting pathogens.
Carriers can spread diseases without being aware of their own infection.
What’s the difference between endogenous and exogenous infection?
Endogenous: from the patient’s own flora.
Exogenous: from external sources.
What did the Human Microbiome Project aim to do?
Identify all microbiota in the human body via metagenomic sequencing.
How many bacterial species are associated with humans?
Over 10,000; human microbiome encodes ~8 million unique proteins.
What are common microbial habitats in the body?
Skin, oral cavity, nasopharynx, GI tract, urogenital tract.
What body sites are normally sterile?
Blood, bladder, kidneys, lungs.
What are common gut bacteria?
Bacteroides, Bifidobacterium, Clostridium, E. coli, Enterococcus.
What microbes dominate the skin microbiota?
Staphylococcus, Corynebacterium, Propionibacterium.
What are common vaginal microbes?
Lactobacillus, Candida, anaerobes.
What’s special about the oral microbiome?
Over 700 species across 7 niches; 34% are uncultivated phylotypes.
Name opportunistic pathogens commonly found in microbiota.
Staphylococcus aureus, E. coli, Candida albicans, Pseudomonas aeruginosa, Haemophilus influenzae.
What infections can S. aureus cause?
Skin infections, pneumonia, sepsis, endocarditis, food poisoning.
What infections can E. coli cause?
UTIs, meningitis, sepsis; some strains cause gastroenteritis.
What does Staphylococcus epidermidis often cause?
Biofilm-related infections on catheters and prosthetics.
What diseases are caused by Streptococcus pyogenes?
Pharyngitis, scarlet fever, necrotizing fasciitis, rheumatic fever.
What is Neisseria meningitidis?
A potentially deadly pathogen that colonizes nasopharynx in ~10% of people.
What is Corynebacterium diphtheriae?
Pathogen that causes diphtheria when it produces the diphtheria toxin.
What determines if a commensal becomes pathogenic?
Access to new niche (e.g. catheters), host immunodeficiency, virulence factor expression.
What is a common cause of nosocomial infections?
Biofilm formation on medical devices by commensal-origin bacteria.
List key steps in bacterial pathogenesis.
Reservoir and transmission, entry into host, adhesion, immune evasion, multiplication, dissemination, host damage (toxins, immune response).
What are superantigens?
Toxins that activate many T-cells non-specifically → cytokine storm (e.g. TSST-1 from S. aureus).
What are cytolytic phospholipase toxins?
Enzymes that hydrolyze membrane phospholipids (e.g. α-toxin from C. perfringens).
