Lecture 2: Brief Review of Bacteria Flashcards
What is the role of the cell membrane (plasma membrane)
Is responsible for a broad range of activities including solute transport, electron transport, establishment of electrochemical gradients, ATP synthesis, synthesis of lipids, secretion of proteins, secretion and uptake of intercellular signals
The cell wall of bacteria is made up of
peptidoglycan
The cell wall protects the the cell from bursting due to ___
turgor pressure
What is turgor pressure?
Exists because bacteria live in environments that are more dilute than the cytoplasm. This causes a net influx of water. This results in pressure (turgor) being directed out against the cell wall
Gram ___ has a thicker layer of peptidoglycan
gram positive
Explain the purpose and process of the gram stain.
Is used to differentiate Gram-positive from Gram-negative bacteria by using the physical properties of the cell walls (thickness/ amount of peptidoglycan)
Cells are dyed with crystal violet dye, iodide is added, this binds crystal violet and traps it in the peptidoglycan (called a mordant)
Cells are destained using ethanol or acetone
Gram-positive cells retain the dye and remain violet, gram-negative cells lose their colour
Counterstaining is then preformed with Safranin or Carbol Fushin which stains Gram-Negative cells pink or red, allowing them to show up under light microscopy
Explain the four main surface structures of gram positive bacteria
- Teichoic acids; comprise 30-60% of the dry cell weight, anchored to the peptidoglycan, several capsule functions
- capsule; used in classification of a varit
- fimbrae and pili
- flagella
organelle of locomotion
flagella
fimbrae and pili
proteins on the cell surface found in some gram positive and most gram negative
Explain the four main surface structures of gram negative bacteria
Lipopolysaccharide: consists of lipid A, core and repeating oligosaccharide (O-antigen)
Capsule: used in classification, variety of roles. It is a polysaccharide layer that lies outside of the cell envelope of bacteria.
Fimbrae and pili: proteins on the cell surface found in most gram negative
flagella: organelle of locomotion
what are fimbrae and pili and what is their function?
-They are protein fibrils extending from the cell surface found in most gram negative and few gram positive bacteria. -Functions are not known in all cases, can be short (0.2um), long (20um), skinny (3nm), or fat (14nm)
-Many mediate attachment to other cells, or surfaces
-Adhesive pili have adhesins, which are proteins in the pili that allow the pili to stick to things
-Some pathogens have pili that allow them to stick to human cells
Some mediate genetic exchange
What are adhesins?
They make up a part of adhesive pili which are proteins in the pili that allow pili to stick to things. Some pathogens have pili that allow them to stick to human cells.
-Some mediate genetic exchange.
What is used for bacteria to attach to each other and transmit DNA from a donor cell to a recipient cell?
Sex pili
What is sex pili?
- used for bacteria to attach to each other and transmit DNA from a donor cell to a recipient cell
- These pili are different from other pili
- They are found in enteric bacteria (E. coli and Pseudomonas) but are not universal among bacteria
- In E. coli the sex pili is coded for by a conjugative transmissible plasmid, the F plasmid that resides in donor strains
T or F: sex pili are found in enteric bacteria like E coli and Pseudomonas but are not universal among bacteria
True
What is the role of the F plasmid?
In E. coli the sex pili is coded for by a conjugative transmissible plasmid, the F plasmid that resides in donor strains
What are flagella?
- Swimming bacteria have one or more flagella
- Organelle of locomotion that protrude from the cell surface
- Flagellum is a stiff helical filament that rotates like a propeller
- Unrelated to the eukaryotic flagellum in composition, structure, and mechanism of action (i.e. sperm)
Several bacteria are serotyped based on their cell structures which include?
Capsule (K) Antigen: Capsular Polysaccharide, associated with cell surface non-covalently and protects bacteria from host immune system. The K antigen repeat units form a high molecular weight structure called as ‘capsule’
Lipopolysaccharide (O) Antigen: also known as lipoglycans and endotoxins, are large molecules consisting of a lipid and a polysaccharide composed of O-antigen, outer core and inner core joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, and elicit strong immune responses in animals
Fimbriae (F) antigen: Protein antigen found on the surface of some gram-positive, and some gram-negative bacteria, rarely used in classification
Flagella (H) antigen: Based on reaction with the Flagellin protein, that arranges itself in a hollow cylinder to form the filament in a bacterial flagellum.
microorganisms can exist in a single environment within foods, in a variety of physiological and physical states. what are they?
- vegetative
- injured
- viable, not culturable (VBNC)
- communicating in structured communities (biofilms)
- sporulated
___ can lead to injured cells
sublethal stressor
what are injured cells?
cells that are unable to grow on selective media, but are able to grow on non selective media
why is microbial injury important in food microbiology?
1- If injured cells appear dead due to the use of selective media in thermal (or other) studies, the thermal (or other) resistance will be underestimated and the true “kill” values will be low
2- Injured cells make escape routine detection post-processing leading to faster spoilage or a safety problem
3- The “selective agent” may be a common food ingredient such as salt, organic acid, or suboptimal temperature.
___ the process by which cells recover from injury
repair
Repair of cells requires what 2 factors
de novo RNA and protein synthesis
how may recovery in injured cells manifest itself
extended lag phase
what is restablished during repair
membrane integrity
Adding ____ can help overcome damage caused by oxygen toxicity
peroxide detox agent
_____ is also critical ie L monocytogenes can start repair immediately at 37 degrees celsius but repair is delayed for almost a week at 4 deg C
temperature
What does VBNC stand for
viable but no culturable
what does VBNC mean (explain)
defined as a state in which cells cannot be cultured on any media even though their viability can be demonstrated by non culturable methods.
____ can each exist in VBNC states
Salmonella, Campylobacter, Escherichia, Shigella, Vibrio
T or F: VBNC is a survival strategy for non-sporulating species
True
T or F: The VBNC state is morphologically different from that of a normal vegetative cell
True
Explain the cytological method used to demonstrate viability of cells
- Structural integrity of the bacterial cytoplasmic membrane indicates life, while deterioration of this membrane indicates that the cell is dead
- Fluorescent nucleic acid stains (red) are incubated with cells, if they permeate the cell it indicates the cell is dead
- Counter stain is used to stain the cell wall (green)
- Bacteria with intact cell membranes stain green, whereas bacteria with damaged membranes stain red
VBNC most often is induced by ____
- nutrient limitation, which might appear irrelevant to food
- salt concentration
- exposure to chemicals
- temp shifts
VBNC can be resuscitated by ____ and ____
- temp shifts
2. gradual return of nutrients
Vibrio vulnificus is commonly found in
shellfish such as oysters
as many as ___ of bacteria in the biosphere may be unculturable
99%
cellular communication happens in two different ways. state them.
- signal transduction: two component regulatory systems where one protein spans the membrane, picks up a signal and then reacts based on a response regulator protein.
- quorum sensing: systems are built on autoinducers which diffuse through the cellular membrane to initiate a specific response when a certain population density has been reached.
regulates genes that would be superfluous to isolated cells but are useful to large populations
quorum sensing
what happens to the communication in structured communities when the bacterial population is low vs when it is high
When the bacterial population is low, the extracellular concentration of the signal molecule is low, and the signal molecule diffuses away from the cell
When there is a large population of cells all producing signal molecules its extracellular concentration increases and it diffuses back into the cells.
In gram negative bacteria ____ acts as signaling molecules
N-acyl homoserine lactones (AHLs)
how do probiotic bacteria prevent infections by pathogenic bacteria
that Lactobacillus acidophilus prevents E. coli O157:H7 infection by producing small biologically active molecules that interfere with the quorum sensing systems of E. coli O157:H7, this limits the ability of the pathogen to adhere to tissues and cause lesions
how is signal transduction different from quorum sensing
Unlike quorum sensing the trigger molecule does not diffuse into the cell
Two component signal transduction consist of
a histidine kinase receptor and a response regulator
explain the process of signal transduction
A signal molecule binds the N-terminus on the “out-side” of the membrane spanning kinase.
The protein kinase transduces the signal across the membrane via a conformational change that increases kinetic activity on the cytoplasmic side.
This phosphorylates a response regulator protein that modulates gene expression, enzymatic activity, flagellar rotation or another phenotype.
what organisms use signal transduction?
L monocytogenes, S aureus and Lactic acid bacteria
what organism using quorum sensing?
s enterica serovar typhimurium, enteropathogenic E coli and V cholerae
what is a biofilm?
an aggregation of cells, often of multiple species into heterogeneous complex structures that are attached to a solid surface. They are composed of microcolonies that have defined boundaries that allow fluid channels to run through the biomatrix.
what prevents undifferentiated cells to fill the fluid channels that form the biofilms?
cell to cell communication
why are the channels critical in biofilms?
they bring in nutrients and carry away waste.
why are biofilms important in the food industry?
they are more resistant to heat, chemicals and sanitizers than planktonic cells
what are endospores?
they are differentiated cells that are very resistant to heat and cannot easily be destroyed by chemicals.
what is the difference between prokayrotes and eukaryotes with respect to chromosomes?
pro = have single choromosome that contain most of the genes of that cells while eukaryotes have multiple chromosomes. prokaryotes also have circular chromosomes whereas eukaryotes have linear chromosomes.
what is the core genome?
genes that are shared by all members of a certain group
what is a pangenome?
genes that are present in any member of a certain group
what is accessory genome?
genes that are present in a subset of members of a certain group
what mobile genetic elements contribute to genetic diversity in bacteria?
- bacteriophage
- plasmids
- pathogenicity islands (genomic islands)
- transposons
explain the lytic vs lysogenic bacteriophage pathway
- both start with a vrius particle containing dna attaching itself to the host cell.
- the virus particle injects dna into the host cell which may then undergo the lytic or lysogenic pathway.
the lytic pathway then involves the replication of viral Dna, coat proteins are then synthesized and virus dna particles assembled . The bacterial cell lyses, this releases new infectious virus particles. lysogenic pathway, viral dna is integrates into host dna and then cell division takes place resulting in normal cell growth
plasmids are passed from ____ to ___ cells as well as ____
mother to daughter cells as well as between different unrelated species of bacteria.
what do plasmids carry
they dont carry essential genes, they carry genes which encode for products which can benefit the bacteria under certain circumstances (ie AMR genes)
what are prophages
a bacteriophage genome inserted and integrated into the circular bacterial DNA chromosome or existing as an extrachromosomal plasmid. Prophages can carry genes for virulence factors or toxins required for pathogenesis by pathogens they lysogenize.
the process by which a prophage converts a non pathogenic bacteria to a pathogen
lysogenic conversion
bacteria often carries many defective prophages. what are defective prophages
a bacterioprophage that can no longer form infective phage due the loss of essential genes
explain the concept of pathogenicity islands
Several bacteria have large DNA elements integrated in their chromosome which contain genes that confer special properties on the bacteria that carry them
They allow the bacteria carrying them to occupy special ecological niches (i.e. AMR genes)
They are not carried by all strains of a particular species
They are neither integrated plasmids nor prophages
They are able to move from one bacteria to another, the evidence is that they are found in unrelated strains
They carry an integrase gene that allows them to integrate into a region of the host DNA
They also carry a repeated sequence at the ends of their sequences, which are involved in integration
what are transposons
they are dna elements that can hop from one place in chromosomal dna to another. The transposon dna usually encodes its own transposases so that it carries with it the ability to hop each time it moves.
what are the two types of bacterial transposons?
- insertion sequence elements
2. composite transposons: when two is elements bracket other genes and carry those genes with them when they move
explain the difference between vertical and horizontal gene transmissing?
vertical gene transmission of dna from mother to daughter cells (mother cell divided to daughter cell). Horizontal gene transfer is the movement of DNA from one bacteria organism to another than via vertical transmission.
foodborne diseases can be divided up into three categories
- intoxication
- infection
- toxicoinfection
what is a food intoxication?
- this occurs after the ingestion of a bacterial or mould toxin due to the growth of the bacteria or mould in the food.
- the toxin must be present in its active form
- once the toxin has been produced viability of the microorganism is no relevant
- toxins are often better able to withstand processing better than the organism
what is a toxin (name characteristics etc)
1- The toxin is produced by a pathogen while growing in the food
2- A toxin can be heat stable or heat liable
3- Ingestion of a food containing the toxin is important not the viable microbial cells
4- Symptoms generally occur quickly since no time for growth is required (sometimes in 30 minutes)
5- Symptoms differ with type of toxins
6- Febrile symptom is not present, since your immune system does not gear up to fight the pathogen
what is a food infection?
- Illness occurs after the consumption of viable bacterial cells or viruses
- The viable cells (even in very low numbers) are able to multiply in the digestive tract and cause illness (with bottom or top end symptoms)
- In systemic infections after the gastrointestinal tract is infected the bacterial cells spread to the rest of the body and other organs causing a much more serious illness!
what are toxicoinfections?
Illness occurs from the ingestion of a large number of viable cells of some pathogenic bacteria through the consumption of contaminated food or water
The bacterial cells either sporulate, colonize, or die, and release the toxins
