Bacteria As Pathogens Topic 6 Flashcards
Structural differences between gram pos and gram neg bacteria
Gram neg- single thin layer of peptidoglycan with an outer membrane
Gram pos- thick multi layers of peptidoglycan and no outer membrane
How do bacteria cause disease: endotoxins
Normally gram neg
Released when bacteria die and cell wall breaks down
Lipid part of the lipopolysaccharide outer membrane is the toxin
Examples of endotoxin bacteria
Salmonella and E.coli
Endotoxins and anti biotics
Some anti biotic treatments release endotoxins to destroy bacteria by lysis of cell wall
How do bacteria cause disease: exotoxins
Mostly gram pos
Soluble proteins produced inside pathogenic bacteria as they grow and metabolise- released into body following lysis
Where do exotoxins act?
Widespread- can act from a distance of infecting bacteria
Examples of exotoxins bacteria
Staphylococcus
How do bacteria cause disease: host tissue invasion
Pathogen invades tissue and damages cells
Symptoms of disease are caused by response of host to cell damage
Cell damage is often linked to exotoxin production or endotoxin presence in bacterial cell walls
Bacteriostatic anti biotics
Stops growth of bacteria by interfering with their metabolic processes- DNA replication, protein synthesis
Bactericidal anti biotics
Destroys bacteria by preventing formation of the cell wall
What is penicillin?
Bactericidal- cell wall agents
Broad spectrum anti biotic
Affects many different types of bacteria
Narrow spectrum anti biotics
Affects specific bacteria. Better to use because it does not effect helpful bacteria and is likely to work more effectively
What does the effectiveness of anti biotic treatment depend on?
How easily the drug can reach affected area
Local pH
If anti biotic is destroyed by host bacteria
How susceptible the bacteria is to the anti biotic
Why is it difficult to treat gram negative bacteria?
Cell wall increases risk of toxicity
Channels are present in gram negative which prevent entry of anti biotics
Risk of resistance is greater due to outer membrane
Gram neg can have both exotoxins and endotoxins
What is biological conjugation?
Transferral of anti biotic resistant gene among bacteria through pili using plasmid
What are healthcare associated infections and give 2 examples
Infections patients get while receiving treatment for medical conditions
MRSA
Clostridium difficile
Prevention and control of infection
- limit AB use
- finish AB course
- hygiene measures
- isolation of patients
- screening
- monitoring levels of HAI
What is a pour plate culture
Inoculate plate with bacterium dilution
Spread evenly over sterile agar surface
Tape on lid and leave colonies to grow
Streak plate culture
Using an inoculating loop streak bacterium over surface of 1/4
Sterilise look and streak next quarter dragging original bacterium from streak 1
Continue for 4 times
This will dilute bacteria further for every quarter allowing colonies to be seen
What is a selective media?
Growth medium containing a very specific mixture of nutrients so only a particular microorganism will grow
What is a differential media?
Biochemically distinguish between related groups of microorganisms- they will use the nutrients differently creating specific coloured colonies
What does nutrient broth contain?
Protein source from blood, meat or yeast and sugars as respiratory substrate
What is the aim of aseptic technique?
Only inoculate bacterium you desire
Avoid contaminating yourself and environment
Name 3 ways of counting bacteria
- Haemocytometer
- Dilution plating
- Optical method (turbidity)
How do you measure fungus growth?
Measure area pi r 2 at the start of growth then again at end of growth
Calculate percentage change
What are the density dependent limiting factors of bacterial growth?
Nutrients
Oxygen
Assimilation is toxic waste
Space
Name the 4 phases of the growth curve
Lag phase
Log/ exponential growth
Stationary phase
Death phase
Lag phase
Adaption to environment. Slow growth rate as bacteria are producing carrier proteins absorbing nutrients and producing enzymes to digest nutrients
Log/ exponential growth phase
Binary fission begins. exponential growth occurs, unrestricted growth. cell division rate is higher than cell death rate
Stationary phase
Limiting factors begin to impact. Cell division rate equals cell death right. It has reached its carrying capacity.
Death phase
Death rate is greater than division rate so the population declines. Decline maybe slowed by the breakdown of dead cells releasing nutrients.
Generation time
The time it takes for cell count to double each generation
Exponential growth rate constant
The number of times the population will double in one unit of time
When are metabolites produced?
Produced by an organism in its metabolic processes
Primary metabolites
Essential proteins and enzymes for growth. Unhelpful for human use.
Secondary metabolites
Begins to be produced in the log phase. Requires established population. Antibiotic chemicals or substrates can be derived which are helpful for human use
