Chapter 6 Microbial Growth

Helpfulness: +1
Set Details Share
created 5 years ago by Shaianne09
502 views
book cover
Microbiology
No Chapter
updated 5 years ago by Shaianne09
Grade levels:
College: Third year
show moreless
Page to share:
Embed this setcancel
COPY
code changes based on your size selection
Size:
X
Show:
1

Physical Requirement

-temperature

-pH

-osmotic pressure

2

Psychrophiles

  • a cold-loving microbe
  • an organism that grows best at about 15oC & does not grow above 20oC
3

Psychrotrophs

an organism that is capable of growth between about 0oC & 30oC

4

Mesophiles

  • a moderate-temperature-loving microbe
  • an organism that grows between about 10oC & 50oC
5

Thermophiles

  • a heat loving microbe
  • an organism whose optimum growth temperature is between 50oC & 60oC
6

Hyperthermophiles

  • an organism whose optimum growth temperature is at least 80oC
  • also called extreme thermophile
7

pH

- minimum, optimum, maximum

* most bacteria: optimum= 6.5-7.5

* molds and yeasts: optimum= 5-6

* human pathogens: optimum= 7.4 (pH of blood)

8

pH

- acidophiles: acid-tolerant microbes

* stomach pH: 1 (Helicobacter pylori)

* vagina pH: 3-5 (Lactobacillus)

- acids from fermentation preserve foods

- microbial wastes are acidic

* use buffers in media

9

Hypotonic (Osmotic Pressure)

  • a solution that has a lower concentration of solutes than an isotonic solution
  • water moves inside the cell & the cell will lyse
  • gram-negative bacteria are more susceptible to this
  • most microbes is in this type of environment
10

Hypertonic (Osmotic Pressure)

  • a solution that has a higher concentration of solutes than an isotonic solution
  • water moves out the cell & the cell shrink
  • extreme & facultative halophiles
11

Chemical Requirements

  • energy
  • carbon
  • hydrogen
  • nitrogen
  • oxygen
  • phosphorus
  • sulfur
  • trace elements
  • organic factors
12

Carbon

  • 50% of dry weight of a typical bacterial cell
  • obtain through energy sources (carbs,lipids,proteins) or CO2
  • autotroph: CO2 is carbon source
  • heterotroph: organics as carbon source
13

Nitrogen

needed for protein, nucleic acid & ATP synthesis

14

Sulfur (S)

needed for protein (in Cys & Met) & vitamin synthesis (Biotin & thiamine)

15

Phosphorous (P)

  • DNA & RNA
  • phosopholipids
  • ATP
16

Cofactors and Trace Elements

  • potassium, magnesium, calcium
  • trace elements: iron, copper, molybdenum, zinc
  • organic molecules obtained from the environment
17

Oxygen

  • molecular oxygen (o2) yields toxic products
  • aerobes require O2 for aerobic respiration
  • anaerobes don't use O2 for energy production
  • anaerobic respiration & fermentation
18

Oxygen Toxicity

- radicals are formed

* when cells grow in O2 environment

* ionizing radiation

- O2 -: superoxide OH-: hydroxyl ion H2O2: hydrogen peroxide O2 2-: peroxide ion

- unstable; disrupt electron arrangements around other molecules > DNA or cell damage

19

Detoxification

- naturally occurring antioxidants

* tocopherol (vitamin E)

* ascorbic acid (vitamin C)

* melatonin

- detoxifying enzymes

* superoxide dismutase

* catalase

* peroxidase

20

Detoxifying Enzymes

- superoxide dismutase (SOD)

O 2 - + O2 - + 2H+ > H2O2 + O2

- catalase

2H2O2 > 2H2O + O2

-Peroxidase

H2O2 + 2H + > 2H2O

21

Thioglycollate

  • reducing medium
  • take the oxygen & reduce it into water O2 > H2O
22

Obligate Aerobes

organisms that require oxygen to live

23

Facultative Anaerobes

an organism that can grow with or without oxygen

24

Obligate Anaerobes

organisms that does not use oxygen to live & is killed in the presence of oxygen

25

Aerotolerant Anaerobes

an organism that does not use oxygen to live but is not affected by its presence

26

Microaerophiles

an organism that grows best in an environment with less oxygen than is normally found in air

27

Biofilms

- bacteria are usually found in communities

* rarely as isolated species

- matrix of polysaccharide, DNA & proteins

- quorum sensing

* communication via chemical cues

28

Biofilms

- benefits

* share nutrients

* shelter

* increase opportunity for genetic exchange

* cooperative activity

29

Biofilms

- impact human health

* 70% of human infections involve biofilms

~ responsible for most nosocomial disease

* form on catheters & medical devices

* more resistant to antimicrobial agents

30

Culture Media & Techniques

- medium: nutrient preparation used to grow microbes

* H2O, carbon, required elements, O2 (if needed)

* correct pH and temp

* broth vs agar

*steril

- chemically defined vs. complex medium

selective & differential medium

- anaerobic growth

- special culture techniques

* selective & differential medium

31

Selective Media

- supports growth of specific organisms while inhibiting others

- eosin methylene blue (EMB)

* selects for gram-negative

~ enterobacteria- enteric/gut bacteria

~ facultative anaerobes

* dyes inhibit growth for gram-positive

32

Phenylethyl Alcohol (PEA) Agar

  • selects for gram-positive species
  • little/no growth of gram-negative
33

Mannitol Salt Agar

  • selects for facultative halophiles (7.5% salt)
  • staphylococcus
34

Sabouraud's Agar

selects for fungi (pH 5.6)

35

Differential Media

- distinguishes between microbes based on identifiable reactions with the medium

36

Blood Agar

- differential media

- contains 5% sheep's blood

- hemolysins: exotoxins that destroy RBCs

* alpha-hemolysis > partial lysis

* beta-hemolysis > total lysis

* gamma-hemolysis > no lysis

37

Alpha-Hemolysis

  • greenish-brown halo
  • Streptococcus pneumoniae
38

Beta-Hemolysis

  • clear halo around colonies
  • Streptococcus pyogenes
  • Staphylococcus aureus
39

Gamma-Hemolysis

most bacteria

40

Eosin Methylene Blue (EMB) Agar

  • selects for gram-negative species
  • differentiates between lactose/sucrose fermenters and non-fermenters
41

Mannitol Salt Agar

  • selects for Staphylococcus (high salt 7.5%)
  • differentiates between mannitol fermenters and non-fermenters
42

Anaerobic Growth

-reducing media

* contains ingredients that deplete O2

* example: Thioglycollate medium (liquid)

- anaerobic jars

* used for plate cultures

* colony growth

- anaerobic chamber

43

Special Culture Techniques

- animals

* some microbes don't grow on artificial media

* Mycobacterium leprae

~ mouse foot pads and armadillos (low temp)

* Treponema pallidum

~ rabbit testes

44

Special Culture Techniques

- cell culture (intracellular bacteria: example: Chlamydia)

- growth of capnophiles

* require elevated CO2 but are aerobic

~ intestines, respiratory tract, body tissues

* CO2 incubator

* candle jar

45

Bacterial Growth

- most reproduce by binary fission

- budding

* outgrowth of cell that grows and separates from parent

46

Bacterial Growth

- external spores (conidiospores)

* filamentous bacteria

* spores develop into new cells

* more common for fungi

-fragmentation

* new cells grow from fragments

47

Generation Time

- time required for cell number to double

- factors affecting generation time

* species of microbe

* environmental: temp, pH, nutrients, type of media

48

Logarithmic Growth

- exponential growth

- cell # increases by a constant factor for each unit of time

- Log: the power to which a base number is raised to produce a given number (Log101=10 & Log106=1000000)

* bacterial growth is linear on log graph

49

Lag Phase (Phases of Growth)

little or no change in the number of cells, but metabolic activity is high

50

Log Phase or Exponential Growth (Phases of Growth)

bacteria multiply at the fastest rate possible under the condition provided

51

Stationary Phase (Phases of Growth)

there is an equilibrium between cell division & death

52

Death Phase or Logarithmic Decline (Phases of Growth)

the number of deaths exceeds the number of new cells formed

53

Measurement of Growth

  • population numbers (cells/ml or cells/g)
  • direct measurement
  • indirect measurement
54

Direct Measurement

  • technique that involves some counting
  • count small sample & determine total population
55

Indirect Measurement

  • estimation of cell numbers without counting cells
  • turbidity, mass, spectrophotometry
56

Plate Count

- most frequently used

- advantage: measures only living cells

- disadvantage: takes time

- cell vs colony forming unit

* colony can form from 1 cell or a clump of cells

* plate counts are in CFU/mL

- serial dilutions to get good # colonies/plates

* 30-300 CFU/mL

- pour plate

- spread plate

57

Filtration Method

- volume passed through membrane (bacteria trapped)

- transfer to plate & grow

- count colonies & divide by number of mL filtered (CFU/mL)

- good when bacteria # is small

* can't count 1 CFU/mL

*example: water samples (coliform bacteria)

58

Direct Microscopic Count

  • count number of cells spread over grid using a microscope
  • average # microbes in several squares
  • average X conversion factor X dilution factor
  • advantages: quick (no incubation required) & counts all cells (live & dead)
  • disadvantage: difficult to count motile bacteria
59

Turbidity

- indirect

- uses spectrophotometer

* measures amount of light passing through a sample

* % transmittance

* absorbance

- # cells is directly proportional to turbidity of culture

* increase # cells/ml (turbidity), increase absorbance

- advantage: quick & easy

- disadvantages: must be read during log phase & needs to be correlated to direct measurement