Lect 1 : Microorganisms in foods Flashcards
- Recognise bacteria, yeast, mold and virus as sources of MO in foods. Know how they reproduce, morphology etc - Recognise the sources of MOs in foods
What is a prokaryote?
A microscopic single-celled organism which does not have a distinct MEMBRANE-BOUND nucleus and (other specialised) organelles
What is a eukaryote?
An organism consisting of a cell / cells in which genetic material is DNA in the form of chromosomes, contained within a distinct nucleus
What are microorganisms?
Microorganisms are small organisms that cannot be seen with the naked eye.
micro : small
organisms : living things
They are also known as microbes
List the 5 types of microorganisms (MOs) and state if they are prokaryotes/eukaryotes/NA (if NA, what category do they belong to?)
- Bacteria - prokaryotes
- Yeast - eukaryote
- Mold / mould : eukaryote
- Protozoa : eukaryotes
- Virus : non-living things
What is protozoa?
Single-celled animals (prokaryotes)
Which is the most important class of microbes?
Bacteria
Morphology : name the different shapes of bacteria cells (give singular and plural forms)
- Round : coccus (plural : cocci)
- Rod : Bacillus (bacilli)
- Curved rod : Vibrio (vibros)
- ## Spiral : Spirillum (spirilla)
- Pleomorphic : bacteria that can have multiple forms or shapes (FST1101B)
Name the different arrangements of bacteria cells (e.g. singular / plural / in fours / in chain / in cluster)
- Single : Coccus / cocci
- Pair : Diplococcus (diplococci)
- Four cells in a SQUARE : tetrad (tetrads)
- in a CHAIN : streptococcus (“strep” –> “strap’”)
- Cluster : Staphylococcus (staphylococci)
What is the function of a flagella in a bacterial cell?
To provide mobility to the bacteria
What are the names for the different number of flagella on a bacterial cell?
- Monotrichous – a single flagellum
- Amphitrichous – a single flagellum at both ends
- Lophotrichous – numerous flagella as a tuft at one end of the cell
- Peritrichous – numerous flagella all over the cell
What is the name of the substance found in the cell walls of both gram positive and negative bacteria? What is it made of?
Peptidoglycan
Peptidoglycan is a polymer made of sugars and amino acids that forms a mesh-like layer outside plasma membrane of bacteria.
What is the difference between the cell wall of gram positive and gram negative bacteria?
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
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?
Gram positive bacteria : gram stain turns purple (blue)
Gram negative bacteria : gram stain turns pink (red)
Which of the processes require energy?
- Simple diffision
- Passive transport
- Active transport
- Active transport
How is bacteria named?
What are the conventions when naming (italicise, captialisation etc)
Using the bionomial nomenclature :
Genus species
– both are italicised
– capitalise the first letter of genus
– don’t need to capitalise first letter of species
What is a serotype/serovar?
seroTYPE, seroVAR(iation)
It is a distinct variation within a species of bacteria
How are bacteria classified into their various serovars?
They are classified together based on their cell surface antigens
Serovar in the naming convention of bacteria is italicised. True or False?
False, not italicised
Note : E coli naming convention
E coli O157 : H7
What do the letters and numbers of the naming suggest?
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
Why can’t bacteria cells grow infinitely and reach a limit?
As the bacterial cell grows, the (surface) area-to-volume ratio decreases, leading to less efficient transport of nutrients
Do young cells or old cells have a larger surface area-to-volume ratio?
Young cells
When bacteria cells grow too big, what process do they undergo?
Binary fission
- Understand the mechanism behind it
What is generation time (G) of a bacteria?
It is the time that a single cell takes to divide into two.
write down the equation involving initial number of cells (x), final number of cells (z), generation time (G) and duration of the study (t)
x. 2^(t/g) = z
What does the growth curve show?
It shows the evolution of viable bacteria as a function of time
Viable : bacteria that are metabolically or physiologically active – meaning can reproduce / grow
There are different ways of measuring the amount of bacteria cells which results in different growth curves. Two of them are :
- Optical Density (OD)
- Colony forming units (CFU)
What does OD / CFU mean?
- 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 - 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
What are the 3 unique features of bacteria?
- Ability to produce endospores
- Biofilm formation
- Quorum sensing
What are the 2 of the few main kinds of bacteria GENERA which can produce endospores?
- Gram positive bacillus
- Clostridium
What are endospores?
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.)
Where are endospores located in a bacteria cell?
Located in the center/off-center/terminal of the cell –> causes buldging of the cell
Endospores are more resistant to physical and chemical antimicrobial treatments. True or false?
True
What are the 2 metabolic forms of endospores (in terms of how active they are)?
Are they capable of transforming into other forms?
metabolically…
- inactive
- 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)
What is a biofilm made up of?
A biofilm is made up of any group of microorganisms in which cells stick to each other and often to a surface.
How do biofilms form? (FST1101B)
Free-floating microorganisms attach to moist surface using pili –> bacteria secrete various biomolecules –> a layer of slime forms around exposed surfaces of microorganisms
In a biofilm, MO cells become embedded within a slimy extracellular polymeric substances (EPS). What biomolecules is EPS a conglomeration (assortment) of ?
- Polysaccharides (long chain sugars)
- Proteins
- DNA
What is quorum sensing?
It is a way in which bacteria communicate with each other using chemical signal molecules
How do bacteria communicate with each other through chemical means?
Bacteria cells …
- produce
2, release - detect and
- respond
to small hormone-like molecules known as autoinducers (AIs)
What does quorum sensing allow bacteria to do? [2]
It allows bacteria to …
- monitor the environment for OTHER bacteria
- alter behaviour on a population wide scale in response to changes in the number and/or species present in a community
YEASTS
Are they unicellular or multicellular?
What is their relevance with foods?
- Unicellular
- Yeasts are involved in food fermentation / spoilage
YEASTS
How do yeasts reproduce?
- Mostly reproduce asexually through budding, or sexually, depending on species
Yeasts are capable of forming _____ on _____ culture media.
Colonies, solid
MO(U)LDS
Are they unicellular or multicellular?
What is their relevance with foods?
- Multicellular
- They are involved in food fermentation / spoilage / safety
MOULDS
Under what kinds of conditions do moulds grow in?
Harsh conditions, best in warm and humid envrionments
- low pH
- with oxygen (strict aerobes)
MOULDS
How can moulds be an issue to food safety?
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
MOULDS
How do moulds reproduce?
They form spore, which are produced asexually (most commonly) and sexually, depending on the species
Viruses are non-living things because they cannot reproduce by themselves. True or False?
True, viruses need a host cell for multiplication
What is the genetic material held inside the virus?
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]
Viruses do not have cell walls, but a _____ _____.
The _____ _____ is made of ?
virus capsid
- made of repeating protein subunits
What is the name of the structure that some viruses possess, and some don’t?
Lipid envelope
What is the difference between viruses that have a lipid envelope and viruses that don’t? (in terms of resistance)
Viruses with a lipid envelope are less resistant, as the lipid envelope is much more senstive and fragile compared to the virus capsid
Food borne viruses usually (possess/ dont possess) a lipid envelope
Dont possess
What are the 3 general properties of viruses?
- they infect all known organisms
- Cause a range of diseases
- Display diversity of morphology (shapes) and genetic makeup
