Microbiology and Pathogens Flashcards
What is a pathogen?
A microorganism that causes disease
What is gram positive bacteria?
Thicker layer of peptidoglycan, so they hold the stain better
What does pathogenic mean?
Capable of causing disease in other organisms
-not all bacteria are pathogenic
How do bacteria cause disease?
-Toxin production = bacteria release chemical toxins causing cell damage
-Tissue invasion = growing and dividing in tissues which disrupts the tissues normal functions
What is an endotoxin?
-In the lipid part of the lipopolyssaccharide
-Attach to the bacteria’s cell wall
-Cause cell damage around the site of infection
-Form on gram negative bacteria
What is an exotoxin?
-They are soluble proteins so are free to move around the body
-Produced by gram positive and negative bacteria
-Can act as enzymes, enzyme inhibitors or bind to proteins
Why do we use a bunsen burner?
To create an upward draft keeping aerosols from landing on your work
What does culturing micro organisms mean?
Growing them
-Scientists do this to study micro organisms better and further
What is a growth medium?
Contains the right levels of nutrients and oxygen for the micro organisms to grow
-liquid nutrient broth = used to grow bacteria in a liquid medium
-nutrient agar = used to grow bacteria on a solid medium
Why do we use different agars?
Used to grow different micro organisms
What is an aseptic technique?
Techniques aiming to avoid contamination to and from the bacteria
How to set up an aseptic technique?
- spray and wipe work surfaces with virkon
- collect a laminate which has been soaked in virkon
- set up a bunsen burner on a roaring blue flame
- sterilise equipment before and after work
- make sure the growth medium is autoclaved before use
- be organised (keep equipment close to the bunsen burner to reduce contamination)
- make sure hands are thoroughly washed before beginning to work
Why are aseptic techniques important?
-Microbiologists want to study a pure culture that is not contaminated by any micro organisms from the environment
-Contaminates may be pathogenic
-Harmless micro organisms can mature/mutate to become harmful
How do you inoculate an agar plate?
-Use a marker to draw on the bottom of the agar to split it in half
-Inoculate one half with distilled water
-Inoculate the other with bacterium
What are the steps of inoculation?
-Sterilise the metal inoculating loop by putting it through the hottest part of the flame (it will glow red)
-Unscrew the lid of the bacterium using the pinky-palm method
-Put the neck of the bottle through the flame
-Place inoculating loop into the bacterium then onto the agar plate in a zigzag movement
-Close the plate then reflame the inoculating loop
How to bacteria reproduce?
Binary fission when conditions are favourable
-a method of asexual reproduction
What is generation time?
The time between bacterial divisions
What is a growth constant?
The number of times the population will double in one unit of time
What are the phases of bacteria?
-Lag phase = where bacteria adapt to their new environment and are not yet reproducing to their maximum rate
-Log phase (exponential phase) = rate of reproduction is close to maximum
-Stationary phase = total growth rate is 0, the number of new cells formed is equal to the number dying
-Death phase = reproduction almost stopped and cell death is increasing
Why does exponential growth not continue?
-Reduction of new nutrients
-Build up of waste products, inhibit further growth and begin producing poison cells
e.g carbon dioxide will build up and change the pH of the culture where growth can’t occur
What is a logarithmic scale?
Useful for displaying bacterial growth when large numbers are achieved
What is a haemocytometer?
Used to count individual cells, it is a special microscope slide with two viewing chambers
What do antibiotics do?
Target bacterial cell processes by disrupting the biochemistry of bacterial cells but not host cells
What are bacteriostatic antibiotics?
-Prevent further bacterial cell growth
-Relies on the hosts immune system to destroy remaining cells
-Not suitable for people with suppressed immune systems
What are bactericidal antibiotics?
-Destroys almost all of the pathogens present
-Suitable for those with suppressed immune systems
What are the types of bacteriostatic antibiotics?
-Antimetabolites = prevent nucleic acid formation so the bacteria’s DNA cannot be synthesised and the bacteria cannot divide
-Protein synthesis inhibitors = prevents transcription and translation
What are the types of bactericidal antibiotics?
-Cell wall agents = prevents cell wall linking so the cell wall is weak and lyses
-Cell membrane agents = creates holes in the membrane so too much water enters the cells
-DNA gyrase inhibitors = DNA cannot coil and won’t fit into the cell
What is the purpose of a control disk?
-It is sterile and soaked in distilled water
-Shows the antimicrobial properties are because of the antibiotic not the disk
What is antibiotic resistance?
Bacteria evolve in response to antibiotics so are no longer affected by them
How does antibiotic resistance happen?
-Mutations may occur during respiration which can change the way the antibiotic binds to the bacteria, making the drug less effective
-These mutations will increase due to natural selection
Why does antibiotic resistance happen?
-Incorrect dosage of antibiotic
-Not completing the course
-Not appropriate for certain conditions
-Not many new antibiotics are being developed
