Lecture 5

Question 1

Binary fission

Answer 1

• This is how bacteria reproduce

- one parent cell divides into progeny cells

Question 2

Generation time or doubling time

Answer 2

-Time required for complete fission replication

Question 3

what is the common setting for bacterial samples

Answer 3

• temperature - 35-37

- Time - 16-48 hours

Question 4

Fastidious bacteria and give an example

Answer 4

This is bacteria that needs special conditions to grow

e.g - M.tuberculosis

Question 5

Rich/complex media

Answer 5

This media is rich on nutrients which can grow a variety of microbes (Media with Soy )

Question 6

Defined media

Answer 6

This media is tailored for specific organisms to grow

Question 7

Selective Media

Answer 7

• select for the growth of specific organisms

- limits the growth of others

Question 8

Differential media

Answer 8

This media helps us differentiate bacteria based on different characteristics

Question 9

How do we use the MacConkey agar

Answer 9

We use this to diffrentiate betwwen E.Coli and Salmonella

Question 10

What happens when lactose is added to E.coli in a macConkey agar and why ?

Answer 10

• You get a pink colony

- E.coli is a lactose fermenter

Question 11

What happens when lactose is added to salmonella in a macConkey agar and why ?

Answer 11

• Clear colony

- it is a non-lactose fermenter

Question 12

Blood agar - Beta Hemolysis

Answer 12

• Complete lysis of red blood

- clear zone around colony

Question 13

Blood agar-Alpha Hemolysis

Answer 13

• Partial lysis of red blood
• green zone around colony
• strep pneumoniae

Question 14

Blood agar - gamma hemolysis

Answer 14

No lysis occurs

Question 15

Lowenstein-Jensen Agar

Answer 15

Used Mycobacterium TB , high in lipids and oxygen

Question 16

Thayer Martin Agar

Answer 16

-Used for Neisseria species

Question 17

How do you calculate colony forming unit from a calibrated loop

Answer 17

Colonies x dilution factor

Question 18

How do you calculate the bacteria that is present in the initial sample of a serial dilution

Answer 18

CFU/ amount plated x dilution factor (put all the values to the power of and then the amount of colonies to the power of is correct )

Question 19

What are the 4 phases of the growth curve

Answer 19

1) Lag phase
2) Exponential (log)-(maximum rate of division )
3) Stationary phase-population reaches max numbers
4) death phase

Question 20

psychrophilic

Answer 20

growth best at cold temperatures ( e.g food borne diseases like listeria )

Question 21

Mesophilic

Answer 21

grow best at human body temp

Question 22

Thermophilic and Hyperthermophiles

Answer 22

grow best at high tempretures (>65)

Question 23

Aw

Answer 23

• amount of water free to react

- most bacteria need an Aw > 0.9 for optimum growth

Question 24

Why do gram positive bacteria last longer than gram negative bacteria

Answer 24

Gram positive bacteria can survive in low moisture environments due to the thick layer of peptidoglycan wall

Question 25

What are toxic products of aerobic respiration

Answer 25

- superoxide radical | - hydrogen peroxide

Question 26

Superoxide Dismutase

Answer 26

Converts the superoxide radical to hydrogen peroxide

Question 27

Catalase

Answer 27

Converts H202 to water and oxygen ( bubbles)

Question 28

True or False : Staph species are catalase -

Answer 28

false

Question 29

True or False : Strep species are catalase -

Answer 29

true

Question 30

Describe obligate aerobes

Answer 30

- They need oxygen to survive , e.g - M. tuberculosis | - Colony forms at the top of the tube

Question 31

Facultative anaerobe

Answer 31

- These can grow with or without oxygen - colonies form at the top and throughout the tube - e.g E.coli

Question 32

Aerotolerant Anaerobes

Answer 32

- They can tolerate oxygen but do not require it - colonies spread evenly throughout the tube - e.g streptococcus pyogenes

Question 33

Obligate Anaerobe

Answer 33

- Do NOT want oxygen - colonies gather at the bottom of the tube - e.g clostridium

Question 34

Microaerophiles

Answer 34

- Need oxygen - but poisoned by high conc of oxygen - colonies in limbo in the tube

Question 35

Hemolysis pattern of strep pyogenes

Answer 35

Beta Hemolysis

Question 36

Hemolysis pattern of strep pneumoniae

Answer 36

Alpha hemolysis

Question 37

Hemolysis pattern of staph aureus

Answer 37

Beta hemolysis

Question 38

What gives transparent colonies in a macConkey plate

Answer 38

- Salmonella | - Shigella