Midterm 1 Flashcards
True or false: Human cells outnumber the amount of bacterial cells in the body
False: BACTERIAL cells outnumber human cells
What are bacteriophages?
They are viruses that kill bacteria
- attach to the surface of the cell and inject their DNA
What are some other uses for bacteriophages?
Can be used to treat infections (specific for certain bacteria)
- less threat of antibiotic resistance (but, phage resistance can occur)
- kills infections without killing all of the healthy microbiomes in the body
What are two difference medicinal applications of intact bacteria?
Probiotics and Fecal microbiota transplants
Describe probiotics
- live microbes
- manage inflammation, prevent infections, etc
- not all claims valid…
Describe fecal microbiota transplants (FMTs)
- fecal bacteria from healthy donor used as therapeutic
- helps with gastrointestinal disorders, infections
What is the role of microbes in food production? Provide some examples.
Can ferment carbohydrates, make acids, alcohols
In baking:
- S. cerevisiae (yeast) makes CO2, causes bread to rise
- sourdough: lactobacili make lactic acid
Pickling:
- lactic acid bacteria make lactic acid
- low pH limits microbial growth
Brewing/winemaking:
- yeasts make ethanol from sugars in grape juice (wine), steeped grain (beer)
Discuss how microbes affect dairy products?
Removing microbes:
- raw milk can contain pathogens so it is pasteurized (killed by mild heat)
Inserting microbes:
- to coagulate milk proteins (yoghurt, cheese)
What are the three domains of life?
Bacteria, archaea, and eukarya
What are bacteria and archaea considered and why?
prokaryotes, has to do with the structure of the cell and components of the cytoplasm
Describe the difference between prokaryotes (bacteria and archaea) and eukaryotes (eukarya)
Prokaryotes (are **usually):
- DNA in cytoplasm
- lack membrane-enclosed organelles (like golgi-apparatus or ER)
- single-celled
Eukaryotes:
- DNA surrounded by nuclear membrane
- Membrane-bound organelles
- single celled (e.g. algae) or multicellular (e.g. animals)
What is a key thing about bacteria that have capsules?
They are much more difficult to be controlled by the immune system (which allows it to cause infections easier)
What are major differences between bacteria and archaea?
- Cell wall components (bacteria contains peptidoglycan which is very important for their survival)
- types of lipids in membranes
- transcriptional, translational components
Why are archaea are more similar to eukaryotes than bacteria?
The DNA sequences are much more similar to eukaryotic cells than bacterial cells
How would use taxonomic ranks to name an organism?
in italics we write
genus + species
we capitalize the first letter of the genus
What is a strain?
Descendants of a single pure microbial culture
What is a bacterial species?
Groups of strains with similar properties
True or false: Bacteria replicate through sexual reproduction
FALSE
True or false: Strains have genetic differences
TRUE
How can we identify prokaryotes? (3 ways)
- morphology and composition
- metabolism
- ecology (where were they isolated, what kind of environment?)
What can we visualize through simple staining?
Size, shape, arrangements of cells
What can we visualize through differential staining?
Differentiate between different types of bacteria based on type of cell wall (e.g. Gram staining) or look at cellular components of the bacterial cell (e.g. capsules or flagella)
Describe gram staining and how it shows us cell wall structure
It differentiates between gram-positives and gram-negatives
these diff cell wall structures impact:
- antibiotic susceptibility
- interactions with immune system
Which ones are de-stained by the alcohol, and which ones retain the crystal violet dye?
- Gram negative
- Gram positive
Gram-negative is DESTAINED by the alcohol
Gram-positive retains the crystal violet dye
Rank the following in terms of size (smallest –> largest)
Bacteria and archaea
Eukaryotic Cells
Viruses
viruses < bacteria and archaea < eukaryotic cells
There is _______ predation when the bacterial cell is larger than eukaryotes. Why?
(more or less)
There is less predation when the bacterial cell is larger than eukaryotes because it makes it harder for the eukaryotes to ingest it
What is something that very small bacteria can do when they do not have enough nutrients?
Can act as parasites for other bacteria if they have a small genome through which they can’t make amino acids and vitamins
This means they can take away resources from the cells they are attached to
What are the three major classes of bacterial morphology?
- Cocci (s. coccus) - spherical
e.g. Staphylococcus aureus - Bacilli (s. bacillus) - rods
e.g. Legionella pneumophila - Spirals
e.g. Campylobacter jejuni
Why is the morphology of bacteria crucial, give 3 reasons.
Shape can impact
- motility (capable of moving by themselves, shape can determine how well they move)
- pathogenesis (ability to cause disease)
- ability to evade predators, immune system
Can bacterial morphology change?
Yes. For example uropathogenic E. coli forms long, linear filaments when leaving cells which protects from immune system
What are hyperthermophiles?
- grow at very high temps ( >100 C)
- membranes more viscous (branched, saturated fatty acids. thermostable lipids)
- thermostable proteins (more intramolecular interactions)
Why might thermostable proteins be present for hyperthermophiles?
To counter the denaturing. It acts to keep it folded in the proper shape
What is autoclaving?
Autoclave is a device used to kill bacteria (makes sure things are sterile through high pressurized steam)
What are psychrophiles?
- Grow at low temps
- make cryoprotectants, antifreeze proteins (prevent ice from forming, protect membranes)
- membranes have more UNsaturated fatty acids (to keep them more fluid)
- proteins are more flexible (fewer H-bonds, ionic interactions, etc)
Why do you think psychrophiles need proteins that have fewer hydrogen bonds, ionic interactions, etc?
Because the proteins need to be able to move better
What are acidophiles?
- grow at low pH
- keep cytoplasm near neutrality (exclude/pump out H+)
- surface proteins acid stable
- intracellular proteins work best at neutral pH
Why do you think surface proteins of acidophiles are acid stable?
So that they are less susceptible to hydrolysis
What are alkaliphiles?
- grow at high pH
- some live in soda lakes (high salt conc. with pH 9-12)
- keeps cytoplasm near neutrality (increase H+ uptake, retention, produce acidic metabolites)
- extracellular enzymes (e.g. proteases) work at high pH
What is commensalism?
Where one benefits and the other is not benefited/harmed
True or false: Most microbial cells in the human adult are commensals
True
How can commensals benefit us?
- Nutrient digestion
- Vitamin production (e.g., B12, K)
- Maintaining immune system (can maintain it in an alert state)
- Blocking disease-causing organisms (“colonization resistance”)
Which property is the most likely to be associated with a hyperthermophile?
a) Enzymes have few hydrogen bonds
b) Pumps protons out of the cytoplasm
c) Membranes contain a lot of saturated fatty acids
d) Grows best in soda likes
c)
needs to be viscous to protect against them falling apart
What are two medias that bacteria can be cultured in?
Liquid media (e.g., broth cultures)
Solid media (e.g., agar plates)
What are pure cultures?
Only one strain
On agar plates, bacteria form colonies. Each colony is usually derived from a single cell, We can use a colony to inoculate a pure culture.
What are the four types of growth media?
Defined media, complex media, differential media and selective media
What is defined media?
Synthetic; known composition
- can use to study nutritional needs (e.g. minimum requirements for growth aka minimal media)
- avoids complication of complex medium components (less batch-to-batch variability)
What is complex media?
Contains more complex ingredients (can contain partially hydrolyzed animal tissues, milk, yeast)
- E.g. peptone, tryptone, yeast extract
- composition not fully defined
- very rich; can support many species
- useful for bacteria with unknown nutritional requirements
What is differential media?
distinguishes between different kinds of bacteria
e.g. blood agar
- used to detect hemolytic bacteria (bacteria that are capable of degrading RBC)
- hemolysis is defining feature of some pathogens (different kinds of hemolysis)
- doesn’t favour or disfavour certain species
What are the three kinds of hemolysis?
alpha-hemolysis
beta-hemolysis
gamma-hemolysis
Describe alpha-hemolysis
Definition: Alpha-hemolysis is a partial or incomplete hemolysis of red blood cells.
Mechanism: In this process, the hemoglobin within the red blood cells is oxidized, leading to a greenish discoloration on blood agar plates.
Appearance on Blood Agar Plates: Alpha-hemolysis is often seen as a narrow zone of greenish discoloration surrounding bacterial colonies grown on blood agar plates.
Example Bacteria: Streptococcus pneumoniae is a common bacterium associated with alpha-hemolysis.
Describe beta-hemolysis
Definition: Beta-hemolysis is complete or full hemolysis of red blood cells.
Mechanism: Bacteria producing beta-hemolysins release substances that completely break down the hemoglobin in red blood cells, resulting in the complete destruction of the cells.
Appearance on Blood Agar Plates: Beta-hemolysis is characterized by a clear zone surrounding bacterial colonies on blood agar plates. The clearing is due to the complete lysis of red blood cells, leaving an empty space around the colonies.
Example Bacteria: Streptococcus pyogenes is an example of a bacterium associated with beta-hemolysis.
Describe gamma-hemolysis
Definition: Gamma-hemolysis is not hemolysis at all; there is no significant interaction between the bacteria and red blood cells.
Mechanism: The term “gamma” here implies no change or activity regarding hemolysis. The bacteria do not cause damage to red blood cells.
Appearance on Blood Agar Plates: There is no observable zone of hemolysis around the bacterial colonies on blood agar plates.
Example Bacteria: Many bacteria fall into this category, as they do not exhibit hemolytic activity. For example, some strains of Enterococcus faecalis may display gamma-hemolysis.
Describe selective media.
Types of culture media designed to either support the growth of specific microorganisms or inhibit the growth of unwanted ones. Used in microbiology for isolating and identifying specific bacterial species from complex samples.
Example - MacConkey Agar:
Selective for: Gram-negative bacteria
Inhibition of: Gram-positive bacteria through bile salts and crystal violet
Differential Properties: Allows differentiation based on lactose fermentation
Lactose Fermentation: lac+ bacteria produce acidic by-products
pH Indicator: Neutral red turns red under acidic conditions
Summary: MacConkey agar is both selective (for Gram-negatives) and differential (based on lactose fermentation), aiding in the isolation and identification of specific bacterial groups.
What is differential medium?
In the context of microbiology and laboratory techniques, “differential” refers to the ability of a medium (such as agar) or a test to distinguish between different microorganisms or groups of microorganisms based on their specific characteristics or behaviors.
For example, in a differential medium, different types of bacteria may produce distinct observable changes in the medium, such as changes in color, precipitation, or the formation of specific growth patterns. These variations help microbiologists identify and differentiate between bacterial species or strains.
In summary, a medium or test is considered differential if it allows for the discrimination between different microorganisms based on certain observable features or reactions.
What is simple medium?
In a non-differential or simple medium, the goal is to support the growth of a wide range of microorganisms without providing specific features for differentiation. These media typically contain basic nutrients required for bacterial growth but lack indicators or components that would reveal differences in the metabolic or biochemical properties of the microorganisms.
In non-differential media, all microorganisms may appear similar, and there is no specific attempt to distinguish between different types based on observable changes in the medium. Non-differential media are often used when the primary goal is to culture and maintain a broad spectrum of microorganisms without the need for detailed differentiation.
Starting with one E. coli cell which can divide every 20 minutes, how long would it take for to produce more E. coli cells than there are people on Earth (~8 billion)?
< 1 day
3 days
1 week
2 weeks
< 1 day
What is the process by which most bacteria grow?
Binary fission
Briefly describe the process of binary fission
- Chromosome is replicated
- Cell elongates
- Septum forms, chromosomes partitioned
- Daughter cells separate
What is FtsZ, and what role does it play in bacterial cell division?
FtsZ is a tubulin-like protein that forms a Z ring in the middle of the bacterial cell. It accumulates in the center of the cell, forming a ring, and is crucial for initiating the cell division process.
Describe the formation of the division complex at the Z ring.
The division complex forms at the Z ring, and as the Z ring constricts, it invaginates the membrane, pulling the ring towards the center of the cell. This process also pulls the membrane and the cell wall with it.
What happens during the contraction of the Z ring in bacterial cell division?
The contraction of the Z ring leads to the invagination of the membrane, pulling the ring towards the center of the cell. Simultaneously, it pulls the membrane and the cell wall, contributing to the formation of the division septum.
What is the role of the division complex in bacterial cell division?
The division complex, formed at the Z ring, is responsible for constricting the ring, invaginating the membrane, and pulling the membrane and cell wall towards the center of the cell. This process ultimately results in the formation of the division septum, composed of peptidoglycan.
What is budding in bacterial replication, and how does it occur?
Budding is a bacterial replication strategy where a small, new cell, or bud, emerges from the surface of the parent cell. The bud gradually enlarges and eventually separates, forming a new, independent bacterial cell.
Explain the process of spore formation in bacteria.
Spore formation is a bacterial replication strategy where a bacterial cell undergoes sporulation to produce a durable, resistant spore. The spore is a dormant form that can withstand harsh conditions, ensuring the survival of the bacterium in unfavorable environments.
How does budding differ from binary fission in bacterial replication?
Budding involves the emergence of a small bud from the parent cell, gradually growing into a new cell. In contrast, binary fission is the division of a bacterial cell into two identical daughter cells.
What advantage does spore formation provide to bacteria?
Spore formation allows bacteria to withstand adverse environmental conditions. The spore is a highly resistant and durable structure, ensuring the survival of the bacterium in conditions that may be detrimental to the vegetative cell.
Describe the population growth through binary fission
It grows exponentially,
since the population doubles every time it divides
What is the outcome of binary fission in bacterial replication?
Binary fission results in the formation of two identical daughter cells from a single parental bacterial cell.
Define generation time (doubling time) in the context of bacterial replication.
Generation time, also known as doubling time, is the time required for a bacterial population to double in size. It serves as a measure of the growth rate of a bacterial population.
How is the generation time affected by environmental conditions and bacterial species?
The generation time is condition-dependent and varies among bacterial species. For example, E. coli has a generation time of approximately 20 minutes, while M. tuberculosis has a longer generation time of about 12 hours
What is a batch culture in bacterial growth studies?
A batch culture refers to a closed vessel containing a single batch of growth medium. Bacteria are inoculated into this medium to study their growth dynamics over time.
How does the bacterial growth curve in a batch culture typically progress?
The bacterial growth curve in a batch culture consists of four phases: lag phase, exponential (log) phase, stationary phase, and death (decline) phase.
Describe the lag phase in the bacterial growth curve.
The lag phase is the initial phase of the bacterial growth curve, characterized by a period of adaptation and preparation for growth. During this phase, there is little to no increase in the cell count.
Explain the exponential (log) phase in the bacterial growth curve.
The exponential phase is a phase of rapid bacterial growth in the curve. The population increases exponentially, and the graph shows a steep incline in the log of viable cell count.
What happens during the stationary phase in the bacterial growth curve?
The stationary phase is a phase in the bacterial growth curve where the growth rate slows down, and the number of new cells produced is balanced by the number of dying cells. The log of viable cell count remains relatively constant during this phase.
Describe the death (decline) phase in the bacterial growth curve.
The death phase is the final phase in the bacterial growth curve, characterized by a decline in the number of viable cells. This may be due to nutrient depletion or the accumulation of waste products.
What happens during the lag phase of the bacterial growth curve?
During the lag phase, cell numbers stay constant initially.
Metabolic activity increases as cells get ready to divide.
Cells perform tasks like making ATP, ribosomes, and enzyme co-factors.
Cellular components undergo repair.
Adaptation to nutrients present occurs.
Production of transporters and catabolic enzymes takes place.
What characterizes the log (exponential) phase in the bacterial growth curve?
Cell number increases exponentially.
Graph shows a straight line during this phase.
Cells divide as fast as possible, influenced by species/strain, growth medium, and environmental conditions (e.g., temperature, oxygen).
The population is uniform and metabolically active.
What happens during the stationary phase in bacterial growth?
Growth slows due to limited nutrients.
Accumulation of toxic waste products.
High cell density (~10^9 cells/mL).
Viable cell count stabilizes.
Cells remain metabolically active but division slows.
Balance between division and death.
What characterizes the death phase in bacterial growth?
Little nutrients, abundant waste.
Decrease in viable cell numbers.
Cell death occurs.
Some cells become viable but nonculturable due to stress response.
Programmed cell death in some.
Nutrient release through “altruism.”
May last for months to years, contributing to evolutionary processes.
During which growth phase is the generation time of a bacterial cell likely to be the shortest?
Lag phase
Log phase
Stationary phase
Death phase
Log phase
What is the primary purpose of direct counting methods in bacterial enumeration?
A. To estimate viable cell count
B. To differentiate between gram-positive and gram-negative bacteria
C. To assess metabolic activity
D. To identify bacterial species
A) to estimate viable cell count
How are cells counted in direct counting methods using a Petroff-Hausser chamber?
A. Using a spectrophotometer
B. Under a microscope with a counting chamber
C. On a bacterial growth curve
D. Through a PCR reaction
B)
What is a potential limitation of direct counting methods?
A. They are highly sensitive.
B. They can only be applied to gram-negative bacteria.
C. Living and dead cells may appear similar.
D. They provide information on bacterial species.
C. Living and dead cells may appear similar.
Why is calculating cells/mL important in direct counting methods?
A. To identify bacterial species
B. To assess metabolic activity
C. To estimate viable cell count
D. To differentiate between gram-positive and gram-negative bacteria
C. to estimate viable cell count
True or False: Direct counting methods are suitable for distinguishing between living and dead cells.
False
What are direct counting methods in bacterial enumeration?
Cells directly counted with a counting chamber (e.g., Petroff-Hausser).
Sample pipetted under coverslip.
Counting done using a microscope.
Cells/mL calculated using grid size and chamber volume.
Living and dead cells may appear similar in this method.
Describe the process of plate counting in bacterial enumeration.
A. Cells are counted using a spectrophotometer.
B. Samples are added to a counting chamber.
C. Cells are added to an agar plate, and the number of colonies is counted.
D. The number of cells is estimated using a PCR reaction.
C. Cells are added to an agar plate, and the number of colonies is counted.
What does “CFUs” stand for in the context of plate counting?
A. Cellular Fusion Units
B. Colony-Forming Units
C. Cell Fragmentation Units
D. Culturable Fungal Units
B. Colony-Forming Units
Why is it said that one colony can come from more than one cell in plate counting?
A. Each cell gives rise to multiple colonies.
B. Colonies often merge during growth.
C. The process involves cell fusion.
D. One cell can divide to form multiple colonies.
A. One colony can come from more than one cell.
What is the “Great plate count anomaly” in plate counting?
A. Plate counts give larger counts than direct counts.
B. Plate counts give smaller counts than direct counts.
C. It refers to an unexpected increase in bacterial growth.
D. It is a phenomenon only observed in gram-negative bacteria.
B. Plate counts give smaller counts than direct counts.
True or False: Plate counting is suitable for distinguishing between living and dead cells.
False
Why do plate counts often yield smaller counts than direct counts?
A. Living cells are excluded in plate counting.
B. Dead cells are included in plate counting.
C. Viable but nonculturable cells are not counted.
D. All of the above.
D
Briefly explain the concept of “Colony-Forming Units (CFUs)” in plate counting.
CFUs represent the number of viable cells that give rise to a single visible colony on an agar plate.
What is the significance of the “Great plate count anomaly” in plate counting, and why do plate counts often yield smaller numbers than direct counts?
The “Great plate count anomaly” refers to the observation that plate counts are usually smaller than direct counts. This discrepancy is due to factors like the exclusion of living cells, inclusion of dead cells, and the inability to count viable but nonculturable cells.
Describe the process of viable counting methods using plate counting.
In viable counting methods, a sample is added to an agar plate, and the number of visible colonies that grow is counted. This method allows the enumeration of only viable cells, providing Colony-Forming Units (CFUs) as an estimate.
What is the limitation of plate counting in distinguishing between living and dead cells?
Plate counting is unable to differentiate between living and dead cells, as both can form visible colonies on agar plates.
A 1 in 10 dilution is prepared of a blood sample, and 0.5 mL of the diluted sample is added to an agar plate. 90 colonies grow. What is the CFU/mL of the original blood sample?
1,800 CFU/mL
900 CFU/mL
180 CFU/mL
90 CFU/mL
1,800 CFU/mL
explanation:
Number of Colonies = 90
Volume of Plated Sample = 0.5 mL
Dilution Factor = 1/10
CFU/mL = 90/(0.5 × 1/10)
= 90/0.05
= 1800
Provide the formula for calculating CFU/mL
CFU/mL= number of colonies/(Volume of Plated Sample×Dilution Factor)
How is the number of cells related to absorbance in spectrophotometry/turbidimetry?
Cells scatter light, and absorbance (optical density; OD) is related to the number of cells.
Dead cells also contribute to light scattering.
In spectrophotometry/turbidimetry, how does absorbance change with cell density?
Low cell density results in low absorbance/OD.
High cell density leads to high absorbance/OD.
How do chemical and physical properties of the environment impact microbial growth?
Factors such as osmolarity, pH, temperature, and oxygen levels influence microbial growth.
Microbes are adapted to specific environments, and their protein activities, membrane composition, and metabolic pathways are shaped accordingly.
Provide examples of environmental factors that can influence microbial growth.
Examples include osmolarity, pH, temperature, and oxygen levels.
What is osmosis, and how does it work in the context of bacterial membranes?
Osmosis is the movement of water through a semi-permeable membrane driven by different solute concentrations.
Bacterial membranes are semi-permeable, allowing water to cross freely through aquaporins and diffusion.
The cytoplasm of bacteria has a high solute concentration.
Define isotonic, hypertonic, and hypotonic solutions in the context of osmosis.
Isotonic solution: Osmolarity is the same as the cell.
Hypertonic solution: Osmolarity is higher than the cell.
Hypotonic solution: Osmolarity is lower than the cell.
Describe the effects of an isotonic solution on bacterial cells.
Isotonic solution: No net movement of water. The osmolarity is the same inside and outside the cell.
What happens to bacterial cells in a hypertonic solution? What is the word for this process?
Water leaves the cell, leading to cytoplasm shrinkage, a process known as plasmolysis.
Explain the impact of a hypotonic solution on bacterial cells.
Water enters the cell, causing cytoplasm to swell. This condition can lead to osmotic lysis.
True or false: The cell wall is not impacted by the osmolarity of the environment
True, it is NOT impacted by the osmolarity of the environment
What is the response of bacterial cells to hypertonic conditions, and what does it cause?
Response to hypertonic conditions: Plasmolysis occurs, causing membrane damage.
Dehydration in hypertonic conditions slows the growth of bacterial cells.
What is the optimal water content for cell processes in bacterial cells, and how does hypertonicity affect this?
Cell processes are typically optimal in around 70% water.
Hypertonic conditions, leading to dehydration, can adversely affect the efficiency of cell processes.
How do some bacteria cope with hypertonic conditions?
Some bacteria produce compatible solutes.
Compatible solutes are not toxic at high levels (>1 M) and serve to increase the osmolarity of the cytoplasm, helping the cell adapt to hypertonic environments.
How do bacteria prevent plasmolysis (dehydration) under hypertonic conditions?
Bacteria prevent plasmolysis by producing large concentrations of compatible solutes.
Compatible solutes increase the cytoplasm’s osmolarity, counteracting the hypertonic environment and maintaining cellular integrity.
How do bacteria survive hypotonic conditions?
Bacteria can survive hypotonic conditions by exporting solutes.
Mechanosensitive channels, regulated by the stretching of the cytoplasmic membrane, play a key role.
- When the membrane is stretched, these channels open, allowing solutes to leave, which decreases cytoplasmic osmolarity and osmotic pressure.
How do mechanosensitive channels contribute to bacterial survival in hypotonic conditions, and what is their effect on solute concentration and water movement?
Mechanosensitive channels regulate the stretching of the cytoplasmic membrane in hypotonic conditions.
When stretched, these channels open, allowing solutes to leave, decreasing solute concentration in the cytoplasm.
Decreasing solute concentration reduces the osmotic pressure, preventing excessive water influx and minimizing membrane stretching.
Which of the following would help prevent a bacterial cell from undergoing plasmolysis?
a) Transport solutes from the cytoplasm to extracellular environment
b) Increase the number of mechanosensitive channels in the cytoplasmic membrane
c) Produce large amounts of compatible solutes in the cytoplasm
d) Increase the amount of water leaving the cytoplasm
c) Produce large amounts of compatible solutes in the cytoplasm
plasmolysis occurs when water is drawn out of the cytoplasm, so it wants to prevent water leaving. by producing compatible solutes it increases osmolarity therefore increasing the water entering the cytoplasm
What are the optimal pH ranges for bacterial growth, and what are the categories based on pH?
Acidophiles: Optimal pH < 5.5
Neutrophiles: Optimal pH 5.5 – 8.0
Alkaliphiles: Optimal pH > 8.0
How can pH changes impact bacterial cells, and what is the optimal cytoplasmic pH?
pH changes can disrupt the cytoplasmic membrane and impact protein activity.
The optimal cytoplasmic pH is maintained near neutral pH.
Provide an example of how bacteria maintain cytoplasmic pH.
Bacteria can maintain cytoplasmic pH near neutral by importing or exporting protons.
How does temperature impact enzyme activity in bacterial cells?
Temperature influences enzyme activity, with activity increasing as temperature rises.
However, enzymes can denature and lose activity at temperatures beyond a certain point.
How does temperature affect the viscosity of bacterial membranes, and what adjustments do bacteria make?
Temperature impacts membrane viscosity.
In low temperatures, bacteria incorporate more unsaturated fatty acids.
In high temperatures, bacteria need more saturated and branched fatty acids. They may also increase the presence of ether lipids, which are more resistant to hydrolysis.
What role do proteins play in maintaining DNA stability at high temperatures?
Proteins in bacterial cells prevent DNA melting at high temperatures, contributing to the stability of the genetic material.
What are mesophiles, and what is their optimal growth temperature?
Mesophiles are organisms that thrive at moderate temperatures.
The optimal growth temperature for mesophiles is typically around 37 °C, which is close to human body temperature. (they are adapted to grow best in our bodies)
Provide an example of where psychrophiles might be responsible for microbial growth.
Psychrophiles are organisms adapted to cold temperatures.
They are commonly associated with refrigerated environments and can contribute to the spoilage of refrigerated food.
How does oxygen impact bacterial cells, and what cellular components does it damage?
Oxygen is essential for some bacteria but toxic to others.
It damages cellular components by oxidizing sensitive groups, such as cysteines.
What are reactive oxygen species (ROS), and how do they interact with cellular components?
Reactive oxygen species (ROS) are formed by the reaction of oxygen with cellular components.
ROS can react with proteins, lipids, and nucleic acids, causing damage to these biomolecules.
How do bacterial enzymes, such as catalase, help protect against oxygen toxicity?
Bacterial enzymes, like catalase, play a protective role against oxygen toxicity.
Catalase, for example, helps break down hydrogen peroxide, a reactive oxygen species, preventing its harmful effects.
What are some factors on which bacterial growth depends?
Bacterial growth depends on metabolic pathways and the presence of ROS scavenging enzymes.
How do the growth requirements differ for obligate aerobes, anaerobes, and facultative anaerobes?
Obligate aerobes require oxygen for growth.
Anaerobes can grow without oxygen, while oxygen is detrimental to obligate anaerobes.
Facultative anaerobes can grow with or without oxygen, but oxygen is beneficial rather than essential.
How do oxygen levels impact aerotolerant anaerobes and microaerophiles?
Oxygen does not impact aerotolerant anaerobes.
Microaerophiles require low oxygen levels and cannot survive at atmospheric levels.
Describe the setup of a tube of solid growth medium with varying oxygen levels.
The tube has a gradient with the top being oxic (containing oxygen) and the bottom being anoxic (without oxygen).
What can be observed in terms of bacterial growth in a tube with varying oxygen levels?
Different kinds of bacteria exhibit varied growth patterns along the gradient, with preferences for oxic or anoxic conditions.
How can bacterial growth be controlled by physical methods, and what are some examples?
Physical methods, such as changing temperature and osmolarity, can be employed to control bacterial growth.
For example, heat can denature proteins, degrade DNA, and disrupt membranes.
What is autoclaving, and how does it contribute to sterilization?
Autoclaving is a sterilization method that uses high-pressure steam.
It effectively kills bacteria by subjecting them to high-pressure steam, ensuring thorough sterilization.
Describe the purpose of pasteurization and how it is achieved.
Pasteurization is a method to kill pathogens using moderate heat.
It involves heating a substance, such as liquid or food, to a temperature that is sufficient to kill pathogens but not high enough to compromise the quality of the substance.
How does cold contribute to the control of bacterial growth, and in what contexts is it often employed?
Cold slows down metabolic processes, making it an effective method for controlling bacterial growth.
Refrigeration is a common application of cold to slow down bacterial growth in various contexts.
How do hypertonic conditions contribute to the control of microbial growth, and what are the effects on cells?
Hypertonic conditions slow microbial growth by inducing dehydration and plasmolysis in cells.
High salt concentrations (e.g., in cured meats) and high sugar concentrations (e.g., in honey and jams) are examples of hypertonic conditions used to control bacterial growth.
How do acidic and alkaline conditions affect bacterial growth, and what are some examples in foods?
Acidic and alkaline conditions slow bacterial growth by impacting protein function.
Examples include acidic foods like pickles and jams.
What are the general targets of chemicals used to control bacterial growth?
Many chemicals have general targets in bacteria, such as proteins, DNA, and lipids.
Differentiate between disinfectants and antiseptics, providing examples of each.
Disinfectants are used for inanimate objects (e.g., bleach).
Antiseptics are used on living tissue (e.g., rubbing alcohol).
How do antibiotics differ from other chemicals in terms of specificity and safety?
Antibiotics have very specific targets in bacteria, such as the cell wall or ribosomes.
These bacterial features are absent or different in human cells, making antibiotics often safer compared to chemicals with more general targets.
In what type of environments do bacteria live, characterized by low nutrient levels and intense competition?
Oligotrophic environments
Why are nutrients quickly depleted in oligotrophic environments?
Due to the high level of competition among bacteria
What is a challenge for bacteria in oligotrophic environments in terms of nutrient availability?
Nutrients are in forms that resist breakdown, such as complex organic polymers
How do bacteria in oligotrophic environments compare to those in lab conditions in terms of generation times?
Bacteria in oligotrophic environments have very long generation times (months, years), while lab conditions may allow for rapid growth (e.g., 20 minutes for E. coli)
What is a characteristic of nutrients in oligotrophic environments that makes them challenging for bacteria to utilize?
There are not many nutrients present, and if they become available, there is intense competition for these limited resources.
Many of the nutrients are in forms that resist breakdown, such as complex organic polymers.
What cellular response is activated in bacterial cells during nutrient limitation or starvation?
Stringent response
how does the overall cell metabolism change during the stringent response?
Overall cell metabolism decreases.
What happens to the genes related to growth during the stringent response?
Genes for growth are downregulated.
What occurs to stress response genes during the stringent response, and what proteins do they produce?
Stress response genes are upregulated, producing proteins that protect DNA, cell wall, etc.
Why are stress response proteins important during the stringent response?
They protect cells from damage, toxic chemicals, etc., making the cells more difficult to kill.
What is the term for growth-arrested bacterial cells that are genetically identical to “normal” cells and form a small subset of the population?
Persistor cells
When can persistor cells form, and is it only associated with starvation?
Persistor cells can form during starvation and also under normal conditions, often in response to other stresses.
Why are persistor cells less susceptible to antibiotics compared to actively growing cells?
Antibiotics work best against actively growing cells, and persistor cells are growth-arrested.
What is a potential consequence of persistor cells being less susceptible to antibiotics?
Persistor cells can contribute to recurrent infections.
Why may antibiotics targeting specific cellular processes not effectively eliminate bacterial cells causing infections?
In infections, some bacterial cells, like persistors, may not be affected. For instance, antibiotics targeting the ribosome won’t be very effective against cells that don’t utilize the ribosome.
What can starvation induce bacterial cells to form, and which bacterial groups are known for this response?
Starvation can induce the formation of endospores, primarily observed in Gram-positive bacteria like Bacillus and Clostridium.
How does the structure and composition of endospores differ from “normal” cells?
Endospores have a distinct structure and composition compared to normal cells but contain the same DNA.
What is the metabolic state of endospores, and how does it compare to persisters? (Metabolically active or inactive)
Similar to persisters, endospores are metabolically inactive.
Where does the endospore formation occur, and what is the state of the mother cell during this process?
Endospores form inside the vegetative mother cell, which is in a growing, metabolically active state.
How are endospores released, and what is the condition of the mother cell during this process?
Endospores are released by lysis of the mother cell.
What are some characteristics that make endospores highly resistant?
Endospores are highly resistant to heat, UV light, desiccation, and are protected from chemicals, antibiotics, and phages due to an impermeable surface.
What extreme measures are often necessary to kill endospores?
Extreme measures, such as autoclaving, are needed to effectively eliminate endospores.
How does the ability of endospores to improve survival in poor conditions contribute to their significance?
Endospores enhance survival in challenging environments, allowing bacteria to endure unfavorable conditions.
Under what conditions do endospores re-form into vegetative cells?
Endospores re-form into vegetative cells under specific and favorable conditions.
What components are found in the core of an endospore?
The core of an endospore contains the nucleoid, ribosomes, and other essential components.
How is the DNA in the core of an endospore protected from various types of damage?
Proteins surrounding the core protect the DNA from heat, UV, and chemical damage.
What are the layers that surround the core of an endospore, starting from the inside out?
The core is surrounded by the cortex (peptidoglycan), coat (protein layers), and, although not shown, the exosporium.
Are the core wall and coat of an endospore considered permeable or impermeable?
The core wall and coat of an endospore are impermeable, preventing the passage of substances in and out of the endospore.
Why is sterilization necessary to eliminate endospores, and what are some examples of situations where this is crucial?
Sterilization is required to kill endospores, especially in medical devices.
What is a health concern related to Clostridium botulinum spores, and under what conditions can these spores become hazardous?
Botulism is a health concern related to Clostridium botulinum spores, particularly in improperly home-canned foods where spores can germinate and produce botulinum toxin.
What bacterial spores can cause anthrax, and what are the potential health consequences?
Bacillus anthracis spores cause anthrax, which can manifest as cutaneous anthrax (skin infection, not as harmful when treated) or pulmonary anthrax (spores inhaled, potentially leading to septic shock and death)
How do bacteria typically exist in the lab, and what is the more common lifestyle in the natural environment?
In the lab, bacteria are usually planktonic (free-floating), while in the environment, most bacteria live in biofilms.
What defines biofilms, and what are they composed of?
Biofilms are communities of cells embedded in a slimy matrix known as extracellular polymeric substances (EPS).
On what types of surfaces can biofilms form, and provide examples?
Biofilms can form on various surfaces, including medical devices such as catheters and artificial valves, as well as host tissues like teeth.
What is the collaborative process required for the formation of biofilms, and what mechanism enables this cooperation?
Biofilm formation requires cells to work together, and quorum sensing (QS) is the mechanism that enables this cooperation.
What is quorum sensing (QS), and how does it function in biofilm formation?
Quorum sensing involves cells secreting autoinducer (AI) molecules, and the concentration of AI is related to the number of cells. This concentration controls gene expression, particularly in biofilm formation.
What effects might high concentrations of autoinducer (AI) molecules have on bacteria in biofilms?
At high AI concentrations, bacteria in biofilms might become more adhesive, leading to the production of structures like pili, and produce extracellular polymeric substances (EPS).
What is the initial step in biofilm formation?
In biofilm formation, planktonic bacteria adhere to a surface, transitioning to a sessile state.
How does the biofilm grow after initial adhesion, and what structures do the cells form?
After adhesion, cells divide and form microcolonies, contributing to the growth of the biofilm.
What interactions occur between cells in a biofilm, promoting cohesion?
In a biofilm, cells stick to each other, and they also adhere to the extracellular polymeric substances (EPS).
Can other bacteria join an existing biofilm?
Other bacteria can join a biofilm, and bacterial cells within a biofilm have the ability to disperse.
What does the term “sessile state” refer to in the context of biofilm formation?
The term “sessile state” in biofilm formation refers to the state of bacteria when they have adhered to a surface and become stationary or attached, as opposed to their free-floating, planktonic state.
How can bacteria attach to host cells, and what are some examples of molecules they may interact with?
Bacteria can attach to host cells using adhesins, such as pili, interacting with molecules like sugars and proteins.
What makes bacterial attachment to host cells specific, and what are some examples of specific adhesion?
Bacterial attachment is specific when adhesins, such as pili, have specificity for certain molecules, like sugars and proteins.
How do bacteria attach to abiotic surfaces, and what makes this attachment non-specific?
Bacteria can attach to abiotic surfaces using non-specific mechanisms, involving bacterial components like lipopolysaccharide.
How can surfaces be conditioned to facilitate bacterial attachment, and what is an example of this phenomenon?
Surfaces can be conditioned, for example, when indwelling medical devices get coated by host proteins, aiding bacterial attachment.
What role do early colonizers and extracellular polymeric substances (EPS) play in bacterial attachment?
Bacteria can attach to early colonizers and EPS, contributing to the development and stability of biofilms.
What characterizes the structure of extracellular polymeric substances (EPS) in biofilms?
EPS in biofilms forms a slime-like matrix composed of glycoproteins, polysaccharides, DNA, and other substances.
How are extracellular polymeric substances (EPS) released, and what are some components of EPS?
Some EPS are secreted, while others are released by cell death (e.g., DNA). Components include glycoproteins, polysaccharides, and DNA.
What role does EPS play in bacterial attachment to biofilms, and how does it contribute to nutrient availability?
EPS helps bacteria stick to biofilms, traps nutrients, and forms channels that distribute nutrients within the biofilm.
How does EPS contribute to the retention of secreted digestive enzymes near bacterial cells?
EPS retains secreted digestive enzymes near bacterial cells within the biofilm.
What is a notable characteristic of EPS in terms of hydration?
EPS is highly hydrated, contributing to the overall slimy and hydrated nature of the biofilm matrix.
less likely to undergo dehydration and plasmolysis
How can surfaces be preconditioned, and what does it mean in the context of bacterial attachment?
Surfaces can be preconditioned by molecules present in the environment. This preconditioning allows bacteria to attach to these surfaces more effectively.
Why is the preconditioning of surfaces important, and can you provide an example in a medical context?
Preconditioned surfaces are crucial for bacterial attachment. In medical applications, this is significant, for instance, in the case of catheters.
How do biofilms enhance bacteria’s ability to tolerate challenging environments?
Biofilms allow bacteria to better tolerate rough environments by providing a protective matrix that shields them from external stresses.
In what way do bacteria embedded in the biofilm matrix potentially benefit in terms of nutrient availability?
Bacteria embedded in the biofilm matrix may have improved nutrient availability, as the matrix can trap and distribute nutrients more effectively.
How does the structure of biofilms contribute to nutrient and oxygen gradients?
The structure of biofilms creates nutrient and oxygen gradients, with cells near the surface having better access to nutrients.
How do cells near the surface of biofilms compare to those in the deeper layers in terms of metabolic activity and waste disposal?
Cells near the surface of biofilms are more metabolically active, similar to planktonic cells, and can dispose of waste more easily.
What challenges do cells in the middle of biofilms face in terms of nutrients and oxygen?
Cells in the middle of biofilms experience limited nutrients and oxygen, leading to a dormant state, which is favorable for anaerobes.
How does the structure of biofilms influence the metabolic activity of cells near the surface compared to those in the middle?
The structure creates nutrient and oxygen gradients, allowing cells near the surface to access nutrients, making them more metabolically active and similar to planktonic cells.
What is the consequence of limited nutrients and oxygen for cells in the middle of biofilms, and what type of cells might thrive in this environment?
Cells in the middle of biofilms can become dormant, and this environment favors the growth of anaerobes.
How does the structure of biofilms contribute to waste accumulation, and how does this impact cells near the surface compared to those in the middle?
The structure creates gradients leading to waste accumulation, but cells near the surface can dispose of waste more easily compared to cells in the middle.
How do biofilms support bacterial nutrition in challenging environments?
Biofilms can thrive in nutrient-poor environments by trapping nutrients, digestive enzymes, and utilizing waste and lysed cells, creating a conducive nutritional environment.
What role does genetic diversity play in biofilms?
Biofilms promote genetic diversity by facilitating the acquisition of new DNA, leading to the evolution of novel properties within bacterial communities.
How do biofilms provide protection to bacteria?
Extracellular polymeric substances (EPS) in biofilms act as a protective barrier, shielding bacteria from predators, UV light, desiccation, and other environmental challenges.
How does living in a biofilm contribute to bacterial evolution and antibacterial resistance?
Bacteria in biofilms can assimilate new DNA, fostering genetic diversity. This process may lead to the acquisition of properties, including antibacterial resistance, through the uptake of relevant genes.
Describe how bacteria can form ecosystems within a biofilm.
Bacteria release products within a biofilm, creating interconnected ecosystems where each organism benefits others, contributing to the overall functionality of the microbial community.
How do biofilms protect bacteria against predators?
Biofilms make it challenging for predators to surround and kill bacteria due to the complex structure. Additionally, the biofilm shields bacteria from UV light, and the moisture within reduces the risk of dehydration.
In which medical condition are biofilms commonly associated, particularly on heart valves?
Biofilms play a significant role in endocarditis, where they can form on heart valves, contributing to the severity of the infection.
In the context of medical devices, which type of infection involving biofilms is common, especially with catheters?
Biofilm-related urinary tract infections are prevalent, often associated with the use of catheters.
What ocular infections, linked to biofilms, can occur in individuals using contact lenses?
Biofilms are known to contribute to corneal infections, especially in individuals using contact lenses.
What common oral health issue involves the formation of biofilms?
Dental plaque is a biofilm that forms on teeth surfaces, contributing to oral health issues such as cavities and gum disease.
How do biofilms enhance the colonization of the host, and what additional role do they play in recurrent infections?
Biofilms enhance host colonization by providing a protected environment for bacteria. They also serve as reservoirs of cells, contributing to recurrent infections.
How do biofilms protect bacteria from antimicrobials?
Biofilms can protect bacteria by some cells getting stuck to the extracellular polymeric substances (EPS), creating a physical barrier that limits the effectiveness of antimicrobial agents.
Why are persister cells within biofilms less susceptible to antimicrobials?
Persister cells within biofilms exhibit reduced susceptibility to antimicrobials, making them more resistant to treatment and contributing to the persistence of biofilm-related infections.
How do biofilms protect bacteria from the immune system?
Biofilms limit immune clearance by making bacteria less accessible to immune cells and antibodies. The complex biofilm structure hinders the immune system’s ability to effectively target and eliminate the bacterial population.
What is the major role of pili during the formation of biofilms in the human body?
a) Produce and secrete EPS
b) Detect autoinducer molecules, causing changes in gene expression
c) Bind to molecules on the surfaces of host cells
d) Precondition surfaces in the body, giving bacteria something to attach to
c)
What term is used to collectively refer to all microbes, including bacteria, in the human body?
The microbiome or microbiota encompasses all microbes, including bacteria, living in and on the human body.
Where do bacteria primarily reside in the human body, and how do they adapt to their specific niches?
Bacteria occupy various niches in and on the body, adapting to specific conditions such as nutrient availability, oxygen levels, pH, and other environmental factors unique to each niche.
What is the primary function of the immune system concerning microbes?
The immune system recognizes and destroys microbes, playing a vital role in maintaining the body’s health.
Describe the characteristics of the innate immune response.
The innate immune response is nonspecific and serves as the first line of defense against pathogens, providing immediate protection upon encountering a threat.
What distinguishes the adaptive immune response from the innate response?
The adaptive immune response is specific and slower to respond to unfamiliar pathogens, providing targeted and precise defense mechanisms against specific threats.
What are the primary physical barriers of the innate immune system?
The physical barriers of innate immunity include the skin and mucous membranes, acting as the first line of defense against pathogens.
How do phagocytes contribute to innate immunity?
Phagocytes engulf and destroy bacterial cells, recognizing common features and playing a crucial role in eliminating pathogens from the body.
What are the chemical mediators involved in innate immunity?
Chemical mediators such as antimicrobial peptides and complement (>30 serum proteins) are part of innate immunity. They promote inflammation, form holes in cell walls, and assist phagocytes in recognizing bacteria through opsonization.
How does the complement system contribute to innate immunity?
The complement system, with over 30 serum proteins, forms holes in bacterial cell walls, promotes inflammation, and aids phagocytes in recognizing bacteria through opsonization.
What is the initial step of opsonization in the context of the complement system?
In opsonization, the complement protein C3b binds to the surface of the bacterium, marking it for recognition and destruction.
