Ex. 13 Streak and Spread Plates

Question 1

streak plating

Answer 1

established [gradient] of bacteria across surface of medium in Petri dish

Question 2

why does streak plating work. the theory

Answer 2

streaking loop repeatedly over surface causes bacteria to fall off one by one. ultimately until cells are sufficiently apart in order to develop into a single isolated colony

Question 3

assumption of streak plating

Answer 3

colony arises from a single cell and therefore a pure culture

Question 4

subculturing

Answer 4

taking material from isolated colony and streaking it again on new plate increases probability of obtaining pure culture

Question 5

T streak method

Answer 5

loop of inoculum spread over primary area. loop is flamed and plate turns 90 degrees. secondary and tertiary quadrants

Question 6

why must loops be flamed

Answer 6

to ensure each section is diluting out only bacteria picked up from loop dragging through previous section

Question 7

failure to sterilized loop results in

Answer 7

overgrowth of entire plate

Question 8

confluent growth

Answer 8

colonies flowing together

Question 9

spread plate

Answer 9

plate where bacterial growth completely covers the surface of agar medium, called bacterial lawn

Question 10

purpose of spread plate

Answer 10

useful when testing susceptibility of bacteria to antiseptics or sensitivity to antibiotics, to grow bacteriophages

Question 11

bateriophages

Answer 11

viruses that infect specific strains of bacteria

Question 12

can spread plates isolate single colonies

Answer 12

yes provided you are plating a very dilute suspension