Lecture 1 Flashcards
Oppurtunistic pathogen
Cause disease in compromised hosts
- immunocompromised
- break in physical innate barrier
- break in normal flora
- candida albicans, pneumocysits jirovec
What are the points of entry of a microbe into the host
Skin
Mucous membranes
Opportunistic pathogenic bacteria
Can cause disease in people with immunosuppression
Pseudomonas aerugonisa
Challenges for eradication of disease
- Intracellular infections
- Multiple host organisms
- Genetic plasticity e.g. Influenza A; antigenic shift and drift
Old friends hypothesis- Rook
An alternative to the hygiene hypothesis
It is believed that the immune system depends on certain microbes that evolved with humans
Their absence can cause abnormal function of the immune system
Incidence
The number of new cases of a disease in a given area
The enterotypes that make up the gut microflora
prevotella
bacteroides
ruminococcus
Pathogen
An organism that causes disease
Virulence
The degree of severity of disease
Continuos variable
How is virulence determined
By adherence, invasiveness, toxicity and persistence
How is virulence measured
LD50
the number of microbes required to kill 50% of infected hosts
the fewer the number of microbes required to cause disease, the more virulent
What are virulence factors
Virulence genes
Pathogenicity islands
Hygiene hypothesis outlined by Dr David Strachan
a lower incidence of infection in early childhood could be an explanation for the 20th century rise in atopic diseases by suppressing the natural development of the immune system
Health care associated infection HCAI
MRSA Clostridium difficile Norovirus Seasonal influenza (flu) Escherichia coli
Yersinia pestis
Causes the bubonic plague
morbidity rate
The incidence of a disease across a population and/or geographic location during a single year
Obesity
Reduction in bacteriodetes and an increase in firmicutes
Increase in firmicutes = an increase in the breakdown of polysaccharides
4 bacterial phyla in gut
actinobacteria
firmicutes
bacteroidetes
proteobacteria
Bacterial genus in the gut
Bacterioides, clostridium, faecalibacterium, eubacterium, ruminococcus, peptococcus and bifidobacterium
Probiotics
lactobacillus
bifidobacterium
Primary pathogen
Causes disease when it enters the body
ID50
The number of microbes required to infect 50% of the population
What could influence ID50 and LD50 values of a pathogen
The host
Immunological status
Physiological status
Route of infection
Virulence genes
encode factors allowing pathogen to cause disease (adherence, invasion, nutrient acquisition, modulation of immune system)
- toxins
- attachment proteins
- capsules
Pathogenicity islands
Section of genome, may contain multiple virulence genes, often encode related functions (protein secretion system, toxin production)
Pathogenic bacteria
The bacteria that can cause infection Myobacterium tuberculosis Streptococcus Shigella Campylobacter Tetanus
Koch’s postualtes
Establish a causative relationship between microbe and disease
Endogenous infection
An infection caused by an infectious agent that is already present in the body
Intracellular parasite, bacteria
They have the ability to grow and replicate inside other cells
Intracellular pathogenic bacteria: salmonella, neisseria, myobacterium,
Bacterial pathogen examples
Bacterial vaginosis- the bacteria that change vaginal microbiota caused by overgrowth of bacteria that crowd out the Lactobacilli species
Bacterial meningitis- bacterial inflammation of the meninges
UTI- Escherichia coli
Bacterial gastroenteritis- caused by enteric pathogenic bacteria
Gram negative bacterial pathogens
E.coli
Pseudonomas aerugionas
Neisseria goorrhoeae
Neisseria meningitis
Beta proteobacteria
There are 12 serogroups of N. meningitis
Gram positive bacterial pathogens
Colstridium
Streptococcus pneumoniae
Corynebacterium diptheriae
Requirements for a disease
- Portals of entry
- Establishment
- Avoid host defences
- Damaging the host
Portals of entry
How do pathogens gain access to host tissues
Adherence Adherence factors that help the attachment of microbial pathogens to host tissues Capsules Adherence proteins Lipoteichoic acid Fimbrae
Mucous membranes
Antimicrobial secretions protect against infection
- Fe not available (is needed for microbial growth)
- Long chains of fatty acids in acidic secretion of the skin (lethal to bacteria)
- Lactenin, proteins present in breast milk that are selectively bacteriocidal for Streptococcus pyogenes
