Lect 1 : Microorganisms in foods

Question 1

What is a prokaryote?

Answer 1

A microscopic single-celled organism which does not have a distinct MEMBRANE-BOUND nucleus and (other specialised) organelles

Question 2

What is a eukaryote?

Answer 2

An organism consisting of a cell / cells in which genetic material is DNA in the form of chromosomes, contained within a distinct nucleus

Question 3

What are microorganisms?

Answer 3

Microorganisms are small organisms that cannot be seen with the naked eye.

micro : small
organisms : living things

They are also known as microbes

Question 4

List the 5 types of microorganisms (MOs) and state if they are prokaryotes/eukaryotes/NA (if NA, what category do they belong to?)

Answer 4

1. Bacteria - prokaryotes
2. Yeast - eukaryote
3. Mold / mould : eukaryote
4. Protozoa : eukaryotes
5. Virus : non-living things

Question 5

What is protozoa?

Answer 5

Single-celled animals (prokaryotes)

Question 6

Which is the most important class of microbes?

Answer 6

Bacteria

Question 7

Morphology : name the different shapes of bacteria cells (give singular and plural forms)

Answer 7

1. Round : coccus (plural : cocci)
2. Rod : Bacillus (bacilli)
3. Curved rod : Vibrio (vibros)
4. ## Spiral : Spirillum (spirilla)
5. Pleomorphic : bacteria that can have multiple forms or shapes (FST1101B)

Question 8

Name the different arrangements of bacteria cells (e.g. singular / plural / in fours / in chain / in cluster)

Answer 8

1. Single : Coccus / cocci
2. Pair : Diplococcus (diplococci)
3. Four cells in a SQUARE : tetrad (tetrads)
4. in a CHAIN : streptococcus (“strep” –> “strap’”)
5. Cluster : Staphylococcus (staphylococci)

Question 9

What is the function of a flagella in a bacterial cell?

Answer 9

To provide mobility to the bacteria

Question 10

What are the names for the different number of flagella on a bacterial cell?

Answer 10

1. Monotrichous – a single flagellum
2. Amphitrichous – a single flagellum at both ends
3. Lophotrichous – numerous flagella as a tuft at one end of the cell
4. Peritrichous – numerous flagella all over the cell

Question 11

What is the name of the substance found in the cell walls of both gram positive and negative bacteria? What is it made of?

Answer 11

Peptidoglycan

Peptidoglycan is a polymer made of sugars and amino acids that forms a mesh-like layer outside plasma membrane of bacteria.

Question 12

What is the difference between the cell wall of gram positive and gram negative bacteria?

Answer 12

Gram positive bacteria has a thick layer of peptidoglycan on top of the plasma membrane

Gram negative bacteria only has a thin layer of petidoglycan in between the inner and outer membrane of the plasma membrane

Question 13

to identify if a bacterial cell is gram positive or negative, the gram staining test can be used. What colour will the solution be in both gram positive / negative bacteria?

Answer 13

Gram positive bacteria : gram stain turns purple (blue)

Gram negative bacteria : gram stain turns pink (red)

Question 14

Which of the processes require energy?

1. Simple diffision
2. Passive transport
3. Active transport

Answer 14

3. Active transport

Question 15

How is bacteria named?
What are the conventions when naming (italicise, captialisation etc)

Answer 15

Using the bionomial nomenclature :

Genus species
– both are italicised
– capitalise the first letter of genus
– don’t need to capitalise first letter of species

Question 16

What is a serotype/serovar?

Answer 16

seroTYPE, seroVAR(iation)

It is a distinct variation within a species of bacteria

Question 17

How are bacteria classified into their various serovars?

Answer 17

They are classified together based on their cell surface antigens

Question 18

Serovar in the naming convention of bacteria is italicised. True or False?

Answer 18

False, not italicised

Question 19

Note : E coli naming convention

E coli O157 : H7

What do the letters and numbers of the naming suggest?

Answer 19

O157
- O refers to the somatic antigen (antigen on the cell surface)
- 157 refers to the 157th variation (out of the 173 types of somatic antigens)

H7
- H refers to the flagella antigen
- 7 refers to the 7th type (out of 56 ) types of flagella antigen

**There is antigen for capsular antigen, denoted with letter K and there are 103 types of antigens

Question 20

Why can’t bacteria cells grow infinitely and reach a limit?

Answer 20

As the bacterial cell grows, the (surface) area-to-volume ratio decreases, leading to less efficient transport of nutrients

Question 21

Do young cells or old cells have a larger surface area-to-volume ratio?

Answer 21

Young cells

Question 22

When bacteria cells grow too big, what process do they undergo?

Answer 22

Binary fission

• Understand the mechanism behind it

Question 23

What is generation time (G) of a bacteria?

Answer 23

It is the time that a single cell takes to divide into two.

Question 24

write down the equation involving initial number of cells (x), final number of cells (z), generation time (G) and duration of the study (t)

Answer 24

x. 2^(t/g) = z

Question 25

What does the growth curve show?

Answer 25

It shows the evolution of viable bacteria as a function of time Viable : bacteria that are metabolically or physiologically active -- meaning can reproduce / grow

Question 26

There are different ways of measuring the amount of bacteria cells which results in different growth curves. Two of them are : 1. Optical Density (OD) 2. Colony forming units (CFU) What does OD / CFU mean?

Answer 26

1. OD -- Optical density measures the degree of light scattering caused by the bacteria within a culture. It counts both live and dead cells in a bacterial population 2. CFU -- colony-forming unit is a unit which estimates the number of microbial cells in a sample that are viable, able to multiply via binary fission under the controlled conditions

Question 27

What are the 3 unique features of bacteria?

Answer 27

1. Ability to produce endospores 2. Biofilm formation 3. Quorum sensing

Question 28

What are the 2 of the few main kinds of bacteria GENERA which can produce endospores?

Answer 28

1. Gram positive bacillus 2. Clostridium

Question 29

What are endospores?

Answer 29

Endospores are dormant (inactive) alternate life forms (produced by the genus Bacillus, the genus Clostridium, and a number other genera of bacteria, including Desulfotomaculum, Sporosarcina, Sporolactobacillus, Oscillospira, and Thermoactinomyces.)

Question 30

Where are endospores located in a bacteria cell?

Answer 30

Located in the center/off-center/terminal of the cell --> causes buldging of the cell

Question 31

Endospores are more resistant to physical and chemical antimicrobial treatments. True or false?

Answer 31

True

Question 32

What are the 2 metabolic forms of endospores (in terms of how active they are)? Are they capable of transforming into other forms?

Answer 32

metabolically... 1. inactive 2. dormant (having normal physical functions suspended or slowed down for a period of time; in or as if in a deep sleep.) but are capable of emerging as vegetative cells (normal cells which are actively growing, excluding the cells involved in production of gametes)

Question 33

What is a biofilm made up of?

Answer 33

A biofilm is made up of any group of microorganisms in which cells stick to each other and often to a surface.

Question 34

How do biofilms form? (FST1101B)

Answer 34

Free-floating microorganisms attach to moist surface using pili –> bacteria secrete various biomolecules –> a layer of slime forms around exposed surfaces of microorganisms

Question 35

In a biofilm, MO cells become embedded within a slimy extracellular polymeric substances (EPS). What biomolecules is EPS a conglomeration (assortment) of ?

Answer 35

1. Polysaccharides (long chain sugars) 2. Proteins 3. DNA

Question 36

What is quorum sensing?

Answer 36

It is a way in which bacteria communicate with each other using chemical signal molecules

Question 37

How do bacteria communicate with each other through chemical means?

Answer 37

Bacteria cells ... 1. produce 2, release 3. detect and 4. respond to small hormone-like molecules known as autoinducers (AIs)

Question 38

What does quorum sensing allow bacteria to do? [2]

Answer 38

It allows bacteria to ... 1. monitor the environment for OTHER bacteria 2. alter behaviour on a population wide scale in response to changes in the number and/or species present in a community

Question 39

YEASTS Are they unicellular or multicellular? What is their relevance with foods?

Answer 39

- Unicellular - Yeasts are involved in food fermentation / spoilage

Question 40

YEASTS How do yeasts reproduce?

Answer 40

- Mostly reproduce asexually through budding, or sexually, depending on species

Question 41

Yeasts are capable of forming _____ on _____ culture media.

Answer 41

Colonies, solid

Question 42

MO(U)LDS Are they unicellular or multicellular? What is their relevance with foods?

Answer 42

- Multicellular - They are involved in food fermentation / spoilage / safety

Question 43

MOULDS Under what kinds of conditions do moulds grow in?

Answer 43

Harsh conditions, best in warm and humid envrionments - low pH - with oxygen (strict aerobes)

Question 44

MOULDS How can moulds be an issue to food safety?

Answer 44

Moulds can produce mycotoxins (such as secondary metabolites, Aflatoxin, Patulin, Orchratoxin etc). Mycotoxins are poisonous substances which can cause food poisoning and make people physically sick

Question 45

MOULDS How do moulds reproduce?

Answer 45

They form spore, which are produced asexually (most commonly) and sexually, depending on the species

Question 46

Viruses are non-living things because they cannot reproduce by themselves. True or False?

Answer 46

True, viruses need a host cell for multiplication

Question 47

What is the genetic material held inside the virus?

Answer 47

A single type of nucleic acid, DNA/RNA - which may be single stranded (ss) or double stranded (ds) [number of strands] - linear or circular [shape]

Question 48

Viruses do not have cell walls, but a _____ _____. The _____ _____ is made of ?

Answer 48

virus capsid - made of repeating protein subunits

Question 49

What is the name of the structure that some viruses possess, and some don't?

Answer 49

Lipid envelope

Question 50

What is the difference between viruses that have a lipid envelope and viruses that don't? (in terms of resistance)

Answer 50

Viruses with a lipid envelope are less resistant, as the lipid envelope is much more senstive and fragile compared to the virus capsid

Question 51

Food borne viruses usually (possess/ dont possess) a lipid envelope

Answer 51

Dont possess

Question 52

What are the 3 general properties of viruses?

Answer 52

1. they infect all known organisms 2. Cause a range of diseases 3. Display diversity of morphology (shapes) and genetic makeup