Chapter 4 Microbiology Flashcards
How do bacteria reproduce asexually?
Process called binary fission in which Plasmid DNA replicates and attaches to the mesosome. A Septum (cross wall) develops and two daughter cells are formed.
What are the 3 types of bacteria and there shapes?
Coccus - spherical
Bacillus - rod shaped
Spirillum - spiral/corkscrew shaped
What are some examples of useful bacteria?
Lactobacillus balgaricus - used to make yoghurt (Bacilli)
Streptococcus lactus - used to make cheese (cocci)
E. Coli - used to make insulin (bacilli)
What are some examples of harmful bacteria?
Treponema pallidum - causes Syphilis (spirillum)
Streptococcus - causes strep throat (cocci)
Salmonella typhi - causes typhoid fever (bacilli)
What is a gram stain?
A method of staining the cell walls of bacteria as an aid to their identification.
Outline the process of gram staining?
Heat fix bacteria to a microscope slide and flood with crystal violet. Wash with iodine to fix the stain. Decolourise with alcohol and counterstain with safranin.
What are the characteristics of gram positive bacteria?
After staining, appear violet/purple.
Thick walls of peptidoglycan
No outer layer of lipopolysachharide
What are the characteristics of gram negative bacteria?
After counterstaining appears red
Thin walls of peptidoglycan
Outer layer of lipopolysachharide
What are the conditions necessary for culturing bacteria?
Nutrients (carbon and nitrogen sources) Growth factors (vitamins) Suitable temperature Suitable pH Oxygen Water
What is a defined medium?
Contains only known ingredients
What is an undefined medium?
Contains components that are not all known.
What is a selective medium?
Medium that only allows certain bacteria to grow
What are antiseptics, antibiotics and disinfectants?
Antiseptics inhibits growth of bacteria on the skin
Antibiotics inhibits growth of bacteria within the body
Disinfectants inhibits growth of bacteria on surfaces
Define aseptic techniques
Laboratory practice that maintains sterility in apparatus and prevents contamination of the equipment, personnel and the environment.
What are the 2 types of antibiotics? What do they do?
Bacteriostatic antibiotics inhibit the reproduction and growth of bacteria
bactericidal antibiotics kill bacteria
How do you prevent the contamination of pure cultures and apparatus by bacteria?
Sterilising all apparatus and media before
Flaming the necks of culture vessels before opening and closing
How do you prevent contamination to the environment by bacteria being used in the lab?
Sterilise work surfaces before and after experiments (using disinfectant)
Use correct handling technique (flaming mouth/neck of culture vessels, flaming inoculating loops, lifting petri dish to a 45 degree angle
Define pathogen
An organism that causes disease in its host
How do you discourage the growth of pathogenic microorganisms in the lab?
Only partially seal two sides of a Petri dish, otherwise sealing all the way creates anaerobic conditions and potentially encourages growth of pathogens.
Incubate at 25 degrees Celsius, if higher at around 37 degrees Celsius it is the ideal temperature for pathogens.
What are the different ways of sterilising equipment?
Autoclave
Gamma radiation
Flaming
What is a viable cell count?
The number of living bacteria cells
What is a total cell count?
The number of living and dead cells
What are the two ways of measuring bacteria in a liquid culture?
Directly by counting cells or indirectly by measuring turbidity (cloudiness)
Define colony
A cluster of cells which arises from a single bacteria or fungal spore by asexual reproduction
Outline the process of serial dilutions
The sample is diluted. 1cm3 suspension is added to 9cm3 medium, it has been diluted 10 times (10^-1). This process is repeated to make as many dilutions as needed. Each dilution is spread over a sterile agar plate and incubated at 25 degrees celsius. A dish containing 20-100 colonies is chosen and the colonies counted. The total cell count is found by multiplying the number of colonies by the dilution factor.
What is are the problems of using serial dilutions to measure bacteria growth?
The separate colonies of bacteria counted ASSUMING that each has arisen from a single cell from the original culture which has divided asexually.
Colonies may merge or ‘clump’ and counting may be inaccurate resulting in an underestimate of numbers.
How is a haemocytometer used to measure bacterial growth?
It uses a specialised microscope slide. However, it is not possible to distinguish between living and dead cells so the result is only a total cell count
How is growth measured by turbidity?
A colorimeter can be used to measure the cloudiness of the culture as cell numbers increase. Measurements of the bacterial population are found by the light absorbance of the suspension against the number of bacterial cells. The result is a total cell count as the colorimeter cannot distinguish living and dead cells
