Lecture 3- Microbial Growth

Question 1

Microbial growth

Answer 1

-is when there is an increase in cell numbers in a population/microbial mass
-growth is essential for survival
-cell has infinite life span

Question 2

Options for microbial growth

Answer 2

*Respiration;
-complete oxidation, requires a terminal electron acceptor + oxygen is the commonest

*Fermentation;
-incomplete oxidation results in intermediate compounds formed, volatile organic acids + alcohols
-metabolic pathway which occurs in the absence of oxygen
-very common and they are also; obligate and facultative fermenters

Question 3

What conditions is growth constrained by?

Answer 3

-nutrients; oxygen levels, carbon sources
-waste products
-physical constraints; temperature, pH, water and radiation
-quorum sensing

Question 4

pH

Question 5

Temperature

Answer 5

-microbes cannot grow if temp is too hot/cold
-minimum + maximum temps of growth vary from microbe to microbe
-reflect habitat
-heat kills, cold preserves

Question 6

Temperature

Answer 6

-microbes cannot grow if temp is too hot/cold
-minimum + maximum temps of growth vary from microbe to microbe
-reflect habitat
-heat kills, cold preserves

Question 7

Impacts of growth

Answer 7

*positive= food/commercial products
*negative= spoilage; food, materials, pharmaceutical, toxins and infection

Question 8

Sterilisation, heat

Answer 8

Sterilisation;
Aim= to completely remove all contaminants from; liquids, gases, surfaces and equipment

Heat;
-commonly used to reduce the bioburden of food and health care products
-effectiveness depends on the approach and the organisms; boiling and incineration
Moist heat= slide 29

Question 9

Dry heat

Answer 9

-higher temp
-longer exposure times; up to 2 hours
-used for= instruments, powders and glassware

Question 10

Filtration

Answer 10

-physical removal of particles from liquids or gases
-membrane filter methods are used to sterilize heat-sensitive liquids
-HEPA filters sterilize air in clean rooms, biological safety cabinets

Question 11

Radiation damage

Answer 11

-ionizing radiation= x rays + gamma rays, mutations —> death
-ultraviolet radiation= mutations —-> death
-visible light= at high intensities generates singlet oxygen, oxidising agent

-radiation radiolysis & gaseous (alkylation) - slides 36 + 37

Question 12

Preservation

Answer 12

-extend shelf life; canning, bottling etc, follow heat treatment; treat, seal and keep
-chemical approaches; salt, sugar and oils; water activity
-organic acids
-chemicals

Question 13

Solutes and water activity

Answer 13

-reflects the amount of water available to organisms; controlled by= drying and an addition of solute molecules
-reduced by adsorption to surfaces

Question 14

Tolerance to Aw

Answer 14

-gram negative bacteria = less tolerant than gram positive
-fungi can grow at lower Aws than bacteria
-Aw has a big impact on spoilage of pharma products

Question 15

Chemical additives

Answer 15

*nitrates and nitrites; nitrites & botulism
*sorbic acid and sorbate
*benzoic acid; foods
*antioxidants
- often prevent growth rather than kill

Question 16

Biocides/antiseptics/antibiotics

Answer 16

*biocides= toxic compounds used on inanimate objects; skin
*antiseptics= antimicrobial compounds used topically; wounds, skin, surgical sites etc
*antibiotics= antimicrobial medicines

Question 17

Relative susceptibility of microorganisms

Answer 17

-effectiveness classed as high, intermediate or low
*high-level; kill all pathogens including endospores
*intermediate-level; kill fungal spores, protozoan, cysts, viruses and pathogenic bacteria
*low-level; germicides kill vegetative bacteria, fungi, protozoa and some viruses