Lecture 1

Question 1

What are the main differences between prokaryotes and eukaryotes?

Answer 1

Prokaryotes are single-celled organisms without a nucleus. Eukaryotes can be unicellular or multicellular organisms.

The main defining difference between the 2 is that eukaryotes have a central nucleus containing the genetic information of the organism while prokaryotes do not.

Question 2

What are the common shapes of bacteria?

Answer 2

Coccus (Cocci): Round
Bacillus (Bacilli): Rod
Vibrio (Vibrios): Curved
Spirillum (Spirilla): Spiral

Question 3

What are some common arrangements of bacteria cells?

Answer 3

Coccus (Cocci): single cell
Diplococcus: pair of cells
Tetrad: 4 cells arranged in a square (2x2)
Streptococcus (Streptococci): cells arranged in a chain
Staphylococcus (Staphylococci): cells arranged in a cluster

Question 4

The shape of a bacteria is defined by the?

Answer 4

Cell wall

Question 5

What is the function of the flagellum

Answer 5

Motility of the bacteria

Question 6

What are some of the components of a bacteria that are non-essential for its survival?

Answer 6

1. Capsule (thick polysaccharide layer)
2. Plasmid (contains non-essential DNA materials, but may confer advantageous properties such as antimicrobial properties)
3. Fimbriae
4. Pilus

Question 7

Most important organelle of a bacteria cell

Answer 7

Nucleoid (contains free DNA material)

Question 8

What are the features of gram positive bacteria?

Answer 8

1. Blue colour after gram staining
2. Consists of a thick layer of peptidoglycan
3. More resistant to microbial deactivation strategies as the thick layer of peptidoglycan confers strong mechanical protection to the bacteria cell.

Question 9

What are the features of gram negative bacteria?

Answer 9

1. Pink/red colour after gram staining
2. Consists of a much thinner layer of peptidoglycan as compared to gram positive bacteria.
3. Hence, they are less resistant to microbial deactivation strategies
4. Presence of a lipopolysaccharide layer
5. More complicated pathogenesis methods due to the presence of various components on the surface of the cell (e.g. lipopolysaccharide, lipids, lipoprotein etc.)

Question 10

Features of the phospholipid bilayer of a bacteria cell

Answer 10

Consists of a hydrophilic polar region (negatively charged phosphate groups) at the outer surface of the cell and a hydrophobic region (non polar fatty acid) on the inner surface of the cell.

Question 11

Features of the cytoplasmic cell membrane

Answer 11

Highly selective in the molecules that can pass through it (restricts the movement of some molecules while facilitating the movement of other molecules).

Question 12

Transport mechanism of molecules across the cell membrane

Answer 12

1. Simple diffusion (for small molecules; does not require the input of energy) - able to penetrate the phospholipid bilayer without any restriction
2. Passive transport - movement through the phospholipid bilayer through carrier or channel proteins without the need for energy input.
3. Active transport - movement through the phospholipid bilayer against a concentration gradient through a carrier protein. Requires energy input to move against the concentration gradient.

Question 13

Bacteria nomenclature

Answer 13

Genus (Capitalized) and species name (Italicized)

Question 14

What are Serotypes/Serovar?

Answer 14

Distinct variations within a species of organisms. Bacteria are classified into the different serotypes based on the shape of the surface antigens as it is unique to every bacteria.

Question 15

What is the process that bacteria undergo to replicate themselves?

Answer 15

Binary Fission - Asexual reproduction process whereby one cell is split equally into 2 without the mixing of genetic material.

Question 16

What are the steps in Binary Fission

Answer 16

Step 1: Chromosomes replication to give 2 identical copies of the genetic information.

Step 2: The replicated DNA will then be separated. Invagination and septum formation of the cell wall occurs.

Step 3: Finally, the bacteria cell separates into 2 identical cell containing identical DNA.

Question 17

Why do bacteria undergo binary fission?

Answer 17

It is to increase the surface area to volume ratio of the bacteria cells to increase the rate of uptake and transport of nutrients from the external environment through the cell membrane into the bacteria cell.

Question 18

What is the generation time of a bacteria cell?

Answer 18

It is the time taken for a bacteria cell to complete the process of binary fission and divide into 2 equal cells.

Question 19

What is a biofilm?

Answer 19

A biofilm is a colony of bacteria cells that are attached to each other and also often to a surface

Question 20

How do bacteria communicate?

Answer 20

Bacteria can communicate via quorum sensing, which involves the secretion of autoinducers to enable autoinducer receptors of other bacteria cells to detect these signals. It enables them to monitor the external environment and to coordinate population wide bacterial behaviour.

Question 21

Examples of microorganisms

Answer 21

Yeast, Mould, Virus

Question 22

Sources of microorganisms infection in food

Answer 22

1. Environment (air, water, soil)
2. Living organisms (animals, humans, plants, pests etc.)
3. Food ingredients (fruits, vegetables, spices, herbs, poultry etc.)
4. Manufacturing process (facility, equipment, storage, transport, retail etc.)

Question 23

What are some common foodborne viruses?

Answer 23

Rotavirus, Norovirus, Hepatitis A

Question 24

Characteristics of foodborne viruses

Answer 24

1. Unable to multiply in foods, and hence they do not cause spoilage in foods.
2. However, they are extremely resistant to the environment (e.g. pH, temperature) and is able to survive in our digestive tract.
3. Can remain infectious for several weeks

Question 25

How do viruses multiply?

Answer 25

Viruses are obligatory intracellular parasites and they cannot replicate on their own. Hence, they need to infect a host and make use of the host to replicate its own genetic material.

Step 1: The virus will attach itself to a host
Step 2: The virus will attempt to infiltrate the cell wall/membrane and hijack the cell.
Step 3: It then releases its viral genetic material and use the proteins and nucleic acids available in the cell of the host to make copies of itself using it’s own genetic template.
Step 4: The replicated viruses will then leave to attempt to invade other cells, causing serious health implications to the host.

Question 26

What are endospores?

Answer 26

It is a dormant, tough and non-reproductive structure that is not found in all bacteria (not all bacteria can form spores). These spores are highly resistant to antimicrobial treatment.

The formation of the endospores are triggered by changes in the environment.

Question 27

Antimicrobial strategies targeting endospores

Answer 27

As endospores are highly resistant to antimicrobial treatments, it sis therefore not efficient to attempt to eliminate the bacteria when it has developed an endospore.

As such, understanding the conditions that favour the reversal of the endosperm formation/non-formation of the endosperm will encourage the bacteria to revert back to its vegetative state, which is less resistant to antimicrobial treatments.

Hence, the bacteria will be much easier to eliminate.

Question 28

Bacteria life cycle growth phases

Answer 28

Lag phase: Period of time where the bacteria population is adapting to the environment and conditions of a new environment (e.g. Bacteria contaminating a piece of food)

Exponential phase: Period of time where the bacteria population starts to undergo binary fission perfectly and the number of bacteria increases exponentially.

Stationary phase: Bacteria population starts to stagnant as the bacteria population has to compete with each other for the limited resources (e.g. Nutrients) that are available, and also due to the accumulation of toxic waste materials

Death phase: growth of bacteria slow down

Long-term stationary phase: Bacteria population decreases until and equilibrium where the amount of nutrients available is able to support the maximum number of bacteria in the environment.

Question 29

Stress response of bacteria to changing environmental conditions

Answer 29

Optimum range (unlikely in real life scenarios; mainly in laboratories): bacteria have the perfect conditions for growth (e.g. Optimum temperature, nutrients, pH etc.)

Sub-optimum growth condition: Phase where the growth conditions are suboptimal but the bacteria is still able to adapt to the stress and develop increased resistance to extermination
• Note: When the bacteria are in perfect optimum conditions and are growing very rapidly, it does not necessarily mean that they have high resistance against metabolic treatments.

Sub-lethal phase: The growth conditions continue to deteriorate further, and the bacteria suffers damage but the damage can be easily repaired by providing them with more nutrients.

VBNC (viable but not cultivable): stage where the bacteria is still alive but is unable to be cultivated using conventional methods.

Lethal stage: bacteria is dead

Question 30

What are aseptic techniques and what are some examples?

Answer 30

Procedure used in the prevention of contamination (and infection) during the handling and manipulations of microbial cultures.

This is to ensure that you are detecting what you want to detect to prevent contamination of other bacteria from other sources (e.g. Hands/other microbial samples) that may interfere with the expected experimental results.

Examples include: dry heating, moist heating, pre-sterilized plastic tools using radiation or ethylene oxide gas, UV radiation and filtration techniques for heat sensitive liquids.

Question 31

What is the difference between detection and enumeration?

Answer 31

Investigation for the presence or absence of a target organism in a defined volume/weight of a subsample. It is qualitative in nature in a sense that it only provides information about the presence or absence of the specific organism of interest, but not the amount/concentration that it is present in.

On the other hand, enumeration is a more quantitative analytical method that aims to quantify the number of bacteria present in the sample.

Question 32

Explain resuscitation

Answer 32

Sub lethally injured cells have the capability to repair themselves and return to a normal physiological state with initiation of growth and cells division under favorable conditions.

In general: 2-4 hat a suitable incubation temperature in a nutrition rich non-selective medium.

Question 33

Qualitative and quantitative test in sample preparation

Answer 33

Qualitative test:
Repair stressed or sub lethally injured cells in the food. This is to ensure that the target organism can be accurately identified during the analysis

Quantitative test:
Dilution to make present MO countable, reduce reaction volumes and to remove interaction/inhibition by food components

Question 34

Purpose of the enrichment step?

Answer 34

It is necessary to increase the target-pathogen concentration and to resuscitate physiologically stressed or injured cells. The enrichment phase is mostly an overnight or 24 h process.