Bacterial Growth

Question 1

what is the generation time?

Answer 1

time required for a bacterial population to double

Question 2

name the major nutrient requirements for bacterial growth (5)

Answer 2

carbon, nitrogen, phosphorus, sulfur, iron

Question 3

what can bacteria use as sources of C, N, S?

Answer 3

amino acids, peptides, proteins

Question 4

can proteins generally be taken up by bacteria?

Answer 4

NO, generally too big. so many bacteria secrete proteases in order to break down extracellular proteins to use them as nutrient sources

Question 5

microbes secrete what to break down extracellular DNA and RNA?

Answer 5

nucleases. Then bacteria can take up the nucleotides as C, N, P sources.

Question 6

discuss the role of iron in the host/bacterium relationship

Answer 6

the host makes iron-binding factors which make iron unavailable to bacterial invaders. also, bacteria make iron chelators (internal granules) that store iron away from host.

Question 7

define growth factors

Answer 7

organic compounds that are not metabolized to supply energy, but are rather used to make metabolites that the bacteria cannot synthesize themselves.

Question 8

name 3 conditions/parameters that affect bacterial growth

Answer 8

1. temp. most grow best at body temp.
2. pH
3. osmotic conditions (does not require tight regulation due to cell wall)

Question 9

why is it impt to be able to determine the number of bacteria in a sample?

Answer 9

because in some fluid, some bacteria will always be present. it is the concentration that is diagnostic for determining an infection.

Question 10

name 4 ways to determine the number of bacteria in a sample

Answer 10

1. optical measurements/turbidity. become faintly turbid at 1 x 10^6/mL.
2. determination of metabolic activity.
3. direct measurement of numbers using a microscope
4. serial dilution and subsequent colony counting on plate.

Question 11

4 phases of bacterial growth curve?

Answer 11

lag phase, log phase, stationary, death

Question 12

describe the Lag phase

Answer 12

metabolic activity, but no increase in numbers. cell mass and size will increase first, along with synthesis of macromolecules needed for growth.

Question 13

describe the log phase

Answer 13

exponential growth phase. binary fission -> generation time (doubling of population). dependent on growth medium, temp, etc

Question 14

describe the stationary phase

Answer 14

the number of viable cells remains constant due to accumulation of waste, exhaustion of nutrients, change in pH. some cells die, others continue to divide -> steady state.

Question 15

describe the death phase

Answer 15

death rate exceeds rate of reproduction. cells may assume unusual shapes making it difficult to identify them.

Question 16

what are some of the favorite foods of bacteria?

Answer 16

major nutrient sources are glucose and other sugars, proteins, peptides and amino acids, lipids, organic acids and alcohols

Question 17

can it be helpful to know what nutrition sources a bacterium is using?

Answer 17

yes, it can be diagnostic. for example, bacteria can use glucose, maltose, sucrose

Question 18

nitrogen sources in addition to amino acids and peptides?

Answer 18

nitrate, ammonia

Question 19

why is it important that bacteria find a source of iron?

Answer 19

The ability to scavenge iron is key to
virulence. Iron is often required for the generation of ATP via the electron
transport chain.

Question 20

how might a bacterium get iron from a host?

Answer 20

Low phosphorus levels can induce phospholipase production. Host cell lysis by phospholipase activity yields iron

Question 21

define siderophores

Answer 21

have extremely high affinity for iron. made by bacteria, iron chelators that can extract iron from host reserves.