L1 Intro to Microbial World Flashcards
Infection
when microorganisms invade host tissue and multiply
Subclinical infections
asymptomatic (no symptoms apparent) but immune response is induced
Localised infections
confined to one area of the body. e.g. ear infection
Systemic infections
infection spreads to other organ systems
Disease
Harmful alteration to the host
Pathogen
A microorganism capable of causing disease
Pathogenesis
a process by which disease arises (not unique to infectious disease)
Pathogenicity
the measure of the ability of a pathogen to cause disease
Pathogenic determinant/virulence factor
a feature of a pathogen that influences how well it can cause disease (pathogenicity/virulence)
Endemic
disease that is always present in a given population. There is a permanent reservoir (human or
other animals)
Epidemic and Pandemic
Epi- a sudden rapid rise in the incidence of a disease in a particular population
Pan- Global epidemic
Outbreak
a relatively high number of infections are observed where no cases or only sporadic cases
occurred in the past
Epidemiology
‘Father’: John Snow
Study of occurrence, spread and control of disease
Koch’s Postulate
4 postulates that must be satisfied to prove a link
between a particular microbe and a disease.
Describe the 4 Koch’s postulates
- assumption: suspected pathogen is present in ALL cases of the disease but is absent from healthy animals (e.g. rat)
- sus. pathogen must be grown in pure culture.
- cells from a pure culture of sus. pathogen must cause disease in a healthy animal.
- sus. pathogen must be reisolated & shown to be the same as original.
Describe/explain the progression of infectious disease
6 steps.
- attachment and/or entry into body
- local or general spread in the body
- multiplication
- evasion of host defences
- shedding
- cause damage in host (can occur at any step)
Infectious disease
- caused by an infectious agent
- infected person can be transmitted to others
Difference between Gram-positive (G+) and Gram-negative (G-) in bacteria
G+ : thick cell walls, can retain purple stain
G- : no cell wall, cannot retain purple stain, is stained red/pink
Why it is important to know about the bacterial characteristics, particular to health care setting?
To accurately ID bacteria and do rapid tests to choose treatment.
Gram status, morphology and functional
characteristics are sufficient information for choosing appropriate
treatment for patient.
Binary Fission in bacterial reproduction
Bacterial cells undergo Binary Fission to reproduce a cell into two parts which involves:
- DNA replication to get two copies
- Moving of the DNA strands to opposite ends of the cell
- Splitting of the cell in the middle into two separate bacteria that has the same genetic material
Generation Time is time taken for one cell to reproduce itself. E.g. every 20 mins, each bacteria multiply into 2.
Name the 4 growth phases in bacterial reproduction.
- Lag Phase: Initial adaptation to conditions
- Logarithmic Phase: Exponential increase in cells
- Stationary Phase (limiting nutrients): Rate of cell division equals cell death
4: Death Phase (nutrients run out): Decrease in cell numbers
Ways to measure bacterial growth.
Turbidity is a direct indication of growth that can be measured using a spectrophotometer (light source): the cloudier the fluid = more bacterial cells.
Optical density (OD): More cells = more scatter = higher OD
