Microbiology

Question 1

Investigation into numbers of bacteria in milk:
What bacteria are present in milk?

Answer 1

Lactobacillus and Bifido species

Question 2

What can give milk a sour taste?

Answer 2

Milk Sugar can be fermented into lactic acid

Question 3

What can fermented milk restore?

Answer 3

a healthy gut flora, it may be consumed by people who are otherwise intolerant to milk

Question 4

Aseptic Technique Step 1 + 2: what should be done before and after test?

Answer 4

wash hands
clean the work surface

Question 5

Aseptic technique Step 3: what type of dish and substance is used?

Answer 5

petri dish with sterile agar gel

Question 6

Aseptic technique step 4: what should be done to petri dish and why?

Answer 6

It is inoculated close to Bunsen Burner: updraughts move airborne microbes away from the plate

Question 7

Aseptic technique step 5: how should universal jars be used treated?

Answer 7

keep lid in crook of little finger, flame mouth of jars before and after use

Question 8

Aseptic technique step 6: what is used for transfer of substances?

Answer 8

sterile syringes used and kept on sterile area

Question 9

Aseptic technique step 7,8,9 : how should sample be added to petri dish

Answer 9

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

Question 10

How do you complete serial dilutions?

Answer 10

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.

Question 11

What is a haemocytometer?

Answer 11

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.

Question 12

What are the shapes of bacteria? (classification)

Answer 12

Cocci (spheres), Bacilli (rods), Spirillum (waved), Vibrio (comma like), Coccobacillus, Spirochete (spiral)

Question 13

What are some examples of cocci bacteria?

Answer 13

Staphylococci, Streptococci

Question 14

What are some examples of Bacilli bacteria?

Answer 14

Bacillus anthracis, Salmonella typhi

Question 15

What is an example of Spirillum bacteria?

Answer 15

Helicobacter pylori

Question 16

What are protoctists + key characteristics?

Answer 16

Eukaryotes
Have a nucleus
DNA in non circular chromosomes

Question 17

What is an example of vibrio bacteria?

Answer 17

Vibrio cholerae

Question 18

What is an example of Spirochete bacteria?

Answer 18

leptospira

Question 19

What is an example of coccobacillus bacteria?

Answer 19

haemophilus influenzae

Question 20

What is a colony?

Answer 20

a cluster of cells, or clone, which arises from a single bacterium or fungal spore by asexual reproduction

Question 21

How do you find the total viable cell count?

Answer 21

the number of colonies is multiplied by the appropriate dilution factor

Question 22

What is turbidity?

Answer 22

the cloudiness of the culture

Question 23

What is the function of fimbria? (bacteria)

Answer 23

Fimbria have the adhesive properties which attach the organism to the natural substrate or to the other organism

Question 24

What is the function of the DNA chromosome? (bacteria)

Answer 24

contains genetic material of the bacterium

Question 25

What is the function of flagellum? (bacteria)

Answer 25

aid organism movement
used as sensory organs to detect changes in temp and ph

Question 26

What is the function of the plasmid? (bacteria)

Answer 26

Some have important genes of DNA (some can fix nitrogen)

Question 27

What is the function of the sex pilus? (bacteria)

Answer 27

conjugation apparatus that pulls two cells together prior to DNA transfer. It help in binding two conjugants

Question 28

What are the properties of Gram Negative bacteria?

Answer 28

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

Question 29

What are the properties of Gram Positive bacteria?

Answer 29

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

Question 30

What is an example of a gram negative bacteria?

Answer 30

Salmonella

Question 31

What is an example of a gram positive bacteria?

Answer 31

staphylococcus and streptococcus species

Question 32

Describe the process of Gram staining

Answer 32

1. Apply crystal violet stain
2. Apply Iodine. Crytsal violet iodine complex. Fixes colour
3. Alcohol/Acetone
4. Rinse with water (this destroys and removes outer cell membrane for Gram negative)
5. Counterstain with safarin

Question 33

What is a Gram positive result in gram staining?

Answer 33

retains the crystal violet stain, due to thick outer cell wall, with 1 inner membrane

Question 34

What is Gram negative result in gram staining?

Answer 34

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

Question 35

What are the conditions required for culturing bacteria?

Answer 35

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

Question 36

Why should when culturing bacteria you avoid 37 deg. C

Answer 36

becuase it is human body temperature so to avoid risk of infection don’t culture bacteria at human body temp.

Question 37

What pH do most bacteria favour?

Answer 37

slightly alkaline (pH 7.4)

Question 38

What are some examples of selective mediums?

Answer 38

MacConkey Agar (only Gram negative bacteria can grow)
media containing tetracycline (only tetracycline resistant bacteria can grow

Question 39

What is an obligate aerobe?

Answer 39

oxygen is essential for growth

Question 40

What is an obligate anaerobe?

Answer 40

oxygen is poisonous, must be without oxygen (Clostridium bacteria - grow in unclean wounds = gangrene)

Question 41

What is a facultative anaerobe?

Answer 41

grow better with oxygen but can survive without it

Question 42

What is the lag phase?

Answer 42

little growth bacteria are acclimatising, (taking up water, finding carbon source, switching on genes and synthesising enzymes

Question 43

What is the exponential/log phase?

Answer 43

where bacterial numbers double per unit time (often every 20 mins)

Question 44

What is the stationary phase?

Answer 44

bacterial cells are dying at the same rate as being produced

Question 45

What is the death phase?

Answer 45

more bacterial cells are dying than are being produced

Question 46

How do bacteria divide?

Answer 46

binary fission

Question 47

What does binary fission involve?

Answer 47

increase in size, extend cell wall material down the centre and divide in two

Question 48

What are some of the speeds of reproduction in bacteria?

Answer 48

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

Question 49

What does penicillin do?

Answer 49

interferes with bacteria’s ability to synthesise the cell wall
bacteria are unable to divide and weakened cell wall ruptures

Question 50

What is penicillin called, where is it produced?

Answer 50

a secondary metabolite
produced by the filamentous fungus Penicillium notatum