Microbiology Flashcards
Investigation into numbers of bacteria in milk:
What bacteria are present in milk?
Lactobacillus and Bifido species
What can give milk a sour taste?
Milk Sugar can be fermented into lactic acid
What can fermented milk restore?
a healthy gut flora, it may be consumed by people who are otherwise intolerant to milk
Aseptic Technique Step 1 + 2: what should be done before and after test?
wash hands
clean the work surface
Aseptic technique Step 3: what type of dish and substance is used?
petri dish with sterile agar gel
Aseptic technique step 4: what should be done to petri dish and why?
It is inoculated close to Bunsen Burner: updraughts move airborne microbes away from the plate
Aseptic technique step 5: how should universal jars be used treated?
keep lid in crook of little finger, flame mouth of jars before and after use
Aseptic technique step 6: what is used for transfer of substances?
sterile syringes used and kept on sterile area
Aseptic technique step 7,8,9 : how should sample be added to petri dish
only lift petri dish high enough to add sample
return petri dish lid and secure with adhesive tape strips
ensure initials date and practical time are written around edge of plate
How do you complete serial dilutions?
insert 9.9 cm^3 sterile water into each universal jar before adding milk product, progressively dilute by adding 0.1 cm^3 of each solution.
What is a haemocytometer?
an glass slide with 3x3 grid, has a specific depth, for visual counting of the number of cells in a blood sample or other fluid under a microscope.
What are the shapes of bacteria? (classification)
Cocci (spheres), Bacilli (rods), Spirillum (waved), Vibrio (comma like), Coccobacillus, Spirochete (spiral)
What are some examples of cocci bacteria?
Staphylococci, Streptococci
What are some examples of Bacilli bacteria?
Bacillus anthracis, Salmonella typhi
What is an example of Spirillum bacteria?
Helicobacter pylori
What are protoctists + key characteristics?
Eukaryotes
Have a nucleus
DNA in non circular chromosomes
What is an example of vibrio bacteria?
Vibrio cholerae
What is an example of Spirochete bacteria?
leptospira
What is an example of coccobacillus bacteria?
haemophilus influenzae
What is a colony?
a cluster of cells, or clone, which arises from a single bacterium or fungal spore by asexual reproduction
How do you find the total viable cell count?
the number of colonies is multiplied by the appropriate dilution factor
What is turbidity?
the cloudiness of the culture
What is the function of fimbria? (bacteria)
Fimbria have the adhesive properties which attach the organism to the natural substrate or to the other organism
What is the function of the DNA chromosome? (bacteria)
contains genetic material of the bacterium
What is the function of flagellum? (bacteria)
aid organism movement
used as sensory organs to detect changes in temp and ph
What is the function of the plasmid? (bacteria)
Some have important genes of DNA (some can fix nitrogen)
What is the function of the sex pilus? (bacteria)
conjugation apparatus that pulls two cells together prior to DNA transfer. It help in binding two conjugants
What are the properties of Gram Negative bacteria?
thin walls with large molecules of lipopolysaccharide embedded in the outer membrane (don’t retain crystal violet stain)
thin murein cell wall is sandwiched between 2 membranes
Not affected by antibacterial enzyme, lysozyme, which occurs in human tears and they are resistant to penicillin
What are the properties of Gram Positive bacteria?
lack lipopolysaccharide in the membrane (do retain crystal violet stain)
thick outer wall lined with 1 inner membrane
more susceptible to antibiotics and enzyme, lysozyme
Penicillin kills bacteria by interfering with their ability to synthesise the murein cell wall
What is an example of a gram negative bacteria?
Salmonella
What is an example of a gram positive bacteria?
staphylococcus and streptococcus species
Describe the process of Gram staining
- Apply crystal violet stain
- Apply Iodine. Crytsal violet iodine complex. Fixes colour
- Alcohol/Acetone
- Rinse with water (this destroys and removes outer cell membrane for Gram negative)
- Counterstain with safarin
What is a Gram positive result in gram staining?
retains the crystal violet stain, due to thick outer cell wall, with 1 inner membrane
What is Gram negative result in gram staining?
does not retain crystal violet stain
thin murein cell wall is between 2 cell membranes
when stain is applied outer cell membrane breaks apart and dissolves away under water
What are the conditions required for culturing bacteria?
nutrient broth/ solid nutrient agar
water and specific nutrients may be required
glucose (carbon source)
Optimum temperature of microbe (between range of 25-45 deg. C
Optimum pH value
Why should when culturing bacteria you avoid 37 deg. C
becuase it is human body temperature so to avoid risk of infection don’t culture bacteria at human body temp.
What pH do most bacteria favour?
slightly alkaline (pH 7.4)
What are some examples of selective mediums?
MacConkey Agar (only Gram negative bacteria can grow)
media containing tetracycline (only tetracycline resistant bacteria can grow
What is an obligate aerobe?
oxygen is essential for growth
What is an obligate anaerobe?
oxygen is poisonous, must be without oxygen (Clostridium bacteria - grow in unclean wounds = gangrene)
What is a facultative anaerobe?
grow better with oxygen but can survive without it
What is the lag phase?
little growth bacteria are acclimatising, (taking up water, finding carbon source, switching on genes and synthesising enzymes
What is the exponential/log phase?
where bacterial numbers double per unit time (often every 20 mins)
What is the stationary phase?
bacterial cells are dying at the same rate as being produced
What is the death phase?
more bacterial cells are dying than are being produced
How do bacteria divide?
binary fission
What does binary fission involve?
increase in size, extend cell wall material down the centre and divide in two
What are some of the speeds of reproduction in bacteria?
In 24 hours some species of bacteria can go from 1 cell to 16,777,216 cells
Many bacteria double there numbers every 20 minutes
What does penicillin do?
interferes with bacteria’s ability to synthesise the cell wall
bacteria are unable to divide and weakened cell wall ruptures
What is penicillin called, where is it produced?
a secondary metabolite
produced by the filamentous fungus Penicillium notatum
