Microbial growth

Question 1

What is microbial growth?

Answer 1

Increase in cell numbers in a population or increase in microbial mass

Question 2

Bacteria and Archaea are

Answer 2

prokaryotes

Question 3

Fungi, Algae, Protozoa are

Answer 3

eukaryotes

Question 4

what is the bacteria cell wall made out from

Answer 4

Peptidoglycan

Question 5

What is the fungi cell wall made out of

Answer 5

Chitin

Question 6

what is the virus cell wall made out of

Answer 6

capsid, glycoproteins

Question 7

Process of binary fission involves formation of septum - what is a septum

Answer 7

a partition that forms between dividing cells

Question 8

E. coli for example has a generation time of

Answer 8

20 minutes

Question 9

explain the process of binary fission

Answer 9

1) cell elongates and DNA replicates
2) cell wall and plasma membrane begin to grow inwards
3) a cross cell wall forms completely around the divided DNA
4) the cells separate

Question 10

Outline the stages in microbial growth and briefly describe them

Answer 10

1) lag phase
2) exponential/logarithmic phase
3) stationary phase
4) decline/death phase

Question 11

what are the 2 options of how microbes metabolise

Answer 11

Respiration and Fermentation

Question 12

Explain respiration

Answer 12

Complete oxidation (from breakdown of co2 and h2o)
Requires a terminal electron acceptor
O2 is the commonest

Question 13

Explain fermentation

Answer 13

Incomplete oxidation results in intermediate compounds formed
Volatile organic acids
Alcohols

Question 14

Fermentation

Answer 14

Metabolic pathway which occurs in the absence of oxygen
Form of continuous culture
Very common and there are:
Obligate
Facultative fermenters
Many fermentation pathways used by microbes

Question 15

Fermentation in the lab

Answer 15

Continuous culture (and a chemostat) is an open system rather than closed
You take a Known volume of sterile media is continually added at a constant rate, equal volume of waste (inc. cells) removed
When in equilibrium = steady state (SIMILAR ALL culture volume, cell number, nutrient availability, waste)

Question 16

Growth is constrained by the conditions

Answer 16

Nutrients
Oxygen levels
Carbon sources
Other minor elements N, P, S etc.

Waste products

Physical constraints
Temperature, pH, Water, Radiation

Quorum sensing – release of chemical signals to talk to other organisms

Question 17

methods of sterilising

Answer 17

Autoclaving, radiation, dry heat, X-rays, UV

Question 18

Obligate aerobe needs

Answer 18

oxygen

Question 19

Faculative anaerobe

Answer 19

prefer oxygen

Question 20

Aerotolerant anaerobe

Answer 20

ignore oxygen

Question 21

Strict anaerobe

Answer 21

oxygen is toxic

Question 22

microaerophile

Answer 22

less than 2-10% of oxygen

Question 23

pH limitations

Answer 23

Few species grow beyond <pH 2 or >pH 10.
Pathogens generally grow around pH 7.0 (where the host environment is)
Most bacteria grow between pH 6.5 & 7.5

Moulds and yeasts grow between pH 5 & 6
pH often used to preserve food
Historical method to extend the useful life of
Milk
Vegetables
Not commonly used for other products

Question 24

how does temperature affect microbial growth

Answer 24

Microbes cannot grow if temperature is too hot or too cold
Minimum and maximum temperatures of growth vary from microbe to microbe
Reflect habitat but as a general rule
Heat kills, cold preserves

Question 25

Temperature Classes of Microbes

Answer 25

1) psychrophiles (spoilage) 2) mesophiles (spoilage and disease) 3) thermophiles and hyperthermophiles (biotechnology)

Question 26

Impacts of Growth can be

Answer 26

positive - food or commercial products or negative Spoilage Food, materials, pharmaceutical Can release Toxins Can lead to Infection

Question 27

how do we control microbial growth?

Answer 27

1) disinfection 2) sterilisation 3) antibiotics 4) antiseptic 5) preservation

Question 28

Sterilization - aim

Answer 28

Aim to completely remove all contaminants (bacteria, viruses, fungi etc) from: Liquids, Gases Surfaces Equipment

Question 29

Heat

Answer 29

Commonly used to reduce the bioburden of food and health care products Effectiveness depends on the approach and the organisms Boiling Incineration

Question 30

Moist heat

Answer 30

<100oC, @ 100oC, >100oC <100oC = Pasteurization 65oC for 30 min Flash method 72oC for 20 sec Preparation of vaccine: tend to be heated for Heating at 56oC for 30-60 min.

Question 31

@ 100oC & >100oC what is the most common way to use moist heat

Answer 31

Boiling most common application of moist heat not capable of killing endospores or all viruses in reasonable timeframes Autoclaving (>100oC) Stream + pressure 121oC 15 psi for 15 - 20 min. Flash autoclaving at 134oC for 4-5min Will kill all organisms

Question 32

Dry Heat- what is it used for

Answer 32

Higher temperature Longer exposure times 160-180oC Up to 2 hrs Used for Instruments Powders Glassware

Question 33

Filtration (another way of getting rid of microorganisms)

Answer 33

Physical removal of particles from liquids or gases Membrane filter method used to sterilize heat-sensitive liquids HEPA filters sterilize air in clean rooms, biological safety cabinets Often built into homes with air con (hepa filters in air con units)

Question 34

Radiation

Answer 34

Cobalt 60 gamma radiation source rack for disposal items Advantage that can be turned off

Question 35

Radiation damage

Answer 35

ionizing radiation caused by x rays and gamma rays mutations  death ultraviolet (UV) radiation mutations  death visible light = good properties at high intensities generates singlet oxygen (1O2) Oxidising agent

Question 36

Radiation (DNA Damage) Radiolysis

Answer 36

Gamma rays (cobalt 60) 25 KGy @ room temp Convey belts Heat sensitive products Negligible heating Special building H&S big consideration Destroy bacterial endotoxins (G –ve) Not bacterial / mould spores & viruses (resistant)

Question 37

Gaseous (Alkylation)

Answer 37

Ethylene oxide (CH2)2O, 800-120mg/L @ 45-63C Exposure time - long Non-uniform kill Permeable packaging Less product degradation Toxic residues (H&S) Reactive gas (flammable, explosive) Low temperature, humidity Toxic, mutagenic & carcinogenic Damage to proteins, nucleic acids

Question 38

Preservation

Answer 38

Extend shelf life Canning, bottling etc Follow heat treatment Treat, seal, keep Chemical approaches Salt, sugar, oils Water activity Organic acids Chemicals

Question 39

Solutes and Water Activity

Answer 39

water activity (aw) reflects the amount of water available to organisms It is Controlled by drying Addition of solute molecules (osmotic effect) higher [solute] —> lower aw reduced by adsorption to surfaces (matric effect)

Question 40

Tolerance to Aw

Answer 40

Gram negative bacteria less tolerant than Gram positive -ve susceptible to rapid re-hydration Fungi can grow at lower Aws than bacteria Aw has a big impact on spoilage of pharma products Creams Aw of 8.0 – 0.98

Question 41

Chemical Additives

Answer 41

Can be things like Nitrates and nitrites Nitrites & Botulism (link) Sorbic acid and sorbate Benzoic Acid Common in Foods Antioxidants Often prevent growth rather than kill

Question 42

Biocides/Antiseptics/Antibiotics

Answer 42

Biocides are toxic compounds used on inanimate objects Also used on Skin Antiseptics Antimicrobial compounds used topically Used in Wounds, skin, surgical sites etc Antibiotics Antimicrobial medicines

Question 43

Relative Susceptibility of Microorganisms

Answer 43

The Effectiveness classified as high, intermediate, or low High-level will kill all pathogens, including endospores Intermediate-level will kill fungal spores, protozoan cysts, viruses and pathogenic bacteria Low-level like germicides will kill vegetative bacteria, fungi, protozoa, and some viruses