Lecture Exam 3 Flashcards
Physical requirements for microbial growth
Temperature, pH
What are psychrophiles?
Cold loving microbes
What are mesophiles?
Moderate-temperature-loving microbes
What are thermophiles?
Heat-loving microbes
What are acidophiles?
Bacteria tolerant of acidity
What is an example of acidophiles?
bacteria genus Clostridium
What do chemical buffers do?
They stabilize the pH of the media, so it is not affected by acid accumulation.
What are the chemical requirements for microbial growth?
Carbon
Nitrogen, Sulfur, and Phosphorus
Trace elements
Oxygen
What are trace elements?
Mineral elements needed for growth
What are some examples of mineral elements?
Iron, copper and zinc
Microorganisms can be classified into obligate aerobes, facultative anaerobes, and obligate anaerobes based on
their requirements for oxygen.
What are obligate aerobes?
Microorganisms that require oxygen to grow.
What is an example of obligate aerobes?
bacteria Pseudomonas aeruginosa
What are facultative anaerobes?
Microbes that can grow with or without oxygen
What are some examples of facultative anaerobes?
E.coli, Staphylococcus, Streptococcus
What are Obligate anaerobes?
Microorganisms that are unable to use oxygen for their growth.
What is an example of an obligate anaerobe?
genus Clostridium
What is binary fission?
When bacteria normally reproduce, divide or multiply.
What is the doubling time aka generation time?
the time it takes for a bacterial cell to double its cell population
We need to use logarithmic scale when plotting a bacterial growth curve because bacterial population doubles its numbers at each generation which leads to a large population of bacterial cells over a short period of time
A typical bacterial growth curve contain how many phases and what are they?
4;
the lag phase, the log phase, the stationary phase, and the death phase
What is happening during the lag phase?
bacterial cells are undergoing metabolic activity involving the synthesis of enzymes and various chemical molecules that are required for their growth later.
What happens during the log phase?
This is the phase where bacterial cells begin to divide or to split. Its population is doubled
Microbiologists like to work with bacterial cells from log phase for experiments because bacterial cells are most active at this phase.
What happens during the stationary phase?
The rate of growth slows down. You first start to see dead cells.
Where is the equilibrium?
where there is a balance between cell deaths and new cells formation.
What happens during the death phase?
The death phase continues until the bacterial entire population dies out
What causes cell death?
What exactly causes bacterial cell to die is not clear, but exhaustion of nutrients, accumulation of waste products, and harmful changes in pH may all play a role.
What is direct measurement of bacterial growth?
To determine the precise bacterial cell numbers present in a bacterial culture obtained at each time point.
Plate counts method
- Start with newly inoculated culture (test tube)
- Inoculate a tsa plate with the culture
- Place newly inoculated culture tube and tsa plate in incubator
- Incubate overnight or for duration of time point
- Repeat for other time points
- Count the number of colonies formed on the agar plate.
What are cfus?
Colony forming unit
1 clump of viable cells = 1 colony
Plate counts method in order to plot a growth curve
1) serial dilution (1st step) of the bacterial culture from each time point;
2) use pour plate method OR spread plate method (2nd step) to inoculate an agar
plate such as Tryptic Soy Agar with the diluted culture from each time point
What are the advantages of using plate counts method?
This method only counts the number of VIABLE cells (no dead cells) present.
What are the disadvantages of using plate counts method?
- Time consuming
- Not reliable because colonies are not individual cells
- Have to do serial dilution
What are the disadvantages of using pour plate method?
- Heat-sensitive bacteria can be killed by warm melted agar
- Bacterial colonies form on the surface and below the surface making it difficult to observe colonies.
What cell count does the coulter counter measure?
The total cell counts. including viable and dead cells
What are the advantages of using coulter counter?
Its quick and precise
What are the disadvantages of using coulter counter?
The machine counts both viable and dead cells
Indirect measurement of microbial growth
To estimate bacterial growth in a liquid bacterial culture obtained from each time point.
Measuring turbidity
to measure the cloudiness to indirectly measure bacterial growth
What is a spectrophotometer?
An instrument used to measure turbidity.
Spectrophotometer:
The poor the reading of the percentage of light been
transmitted, the more the cloudiness/the turbidity appeared in the culture to interfere
with the passage of light, which indirectly indicates the more the growth in the culture
What is measuring metabolic activity?
A method to indirectly estimate bacterial growth.
What is an example of measuring microbial metabolic activity to indirectly estimate the bacterial growth in a culture?
Lactose fermentation performed by lactose fermenting gram negative bacteria.
What is lactose fermentation?
The breakdown of sugar lactose to produce lactic acid in the absence of oxygen. (So, the more the acid production (indicated by the dropping of the pH of the culture)
in a given liquid bacterial culture indirectly indicates the more the bacterial growth
in the culture.)
Bacteria E. coli are
facultative anaerobes.
Microbiologists like to work with bacterial cells from which of the following phases of growth curve for experiments?
log phase
Plate Counts method counts
the number of viable cells ONLY.
Microbiologists prefer to use which of the following plating (aka inoculating) methods for plating a diluted bacterial culture on an agar plate?
the spread plate method
Which of the following gives poor reading of the percentage of light been transmitted when using a spectrophotometer?
a tube of bacterial culture
What is sterilization?
The removal or destruction of all microorganisms
What is disinfection?
A chemical treatment to kill or inhibit the growth of microbes on non living objects.
What is a disinfectant?
Actual chemicals used for disinfection
What is antisepsis?
A chemical treatment to kill of inhibit microbes on living tissues
What is an antiseptic?
the actual chemicals used for antisepsis
What is degerming?
Mechanical removal of germs
What is sanitization?
the removal of microorganisms from eating utensils and food preparation
What is a bactericide (noun) bactericidal (adj)?
A substance or treatment capable of killing bacteria.
What is bacteriostasis (bacteriostatic)?
A substance or treatment that only inhibits the growth of bacteria
Mechanisms of Action of microbial control agents(how does a physical method or chemical agent kill microorganisms or slow down microbial growth):
- By changing the microbial membrane permeability (interfering with regulation)
- By denaturing the 3-D structure of microbial proteins or microbial DNA and RNA
Boiling
Is a moist heat
Kills vegetative cells
only needs 10 min
Does not kill endospores
Not a reliable method because if you don’t boil for the full time it won’t be effective.
What is the mechanism of action for boiling?
Denaturation of protein
Autoclaving
An example of moist heat
Effective and reliable
Is used to sterilize culture media dna equipment that can tolerate high temp and high pressure.
What is the mechanism of action for autoclaving?
The denaturation of microbial proteins
Pasteurization
A heat treatment
A mild heat treatment for milk and other beverages
Achieved at 72*C for 15 sec
What is the mechanism of action for pasteurization?
Microbial protein denaturation
Direct flaming
A dry heat method
Examples: Bunsen burner using gas and Bacti-cinerator using electricity
What is the mechanism of action for direct flaming?
Denaturation of microbial proteins
Hot air Sterilization
A type of dry heat
placed in oven at 170*C for 2 hours
Used to sterilize empty glassware and other instruments
What is the mechanism of action for hot-air sterilization?
Denaturation of microbial proteins
Filtration
The removal of microorganisms by passing the liquid through a filter with pores small enough to retain microbes.
What is filtration used for?
to sterilize heat-sensitive material.
What is the mechanism of action for filtration?
to seperate the microorganisms from the liquid passed through.
Low Temperature
Physical method to control growth of microbes
Refrigerate at 4*C
Has a bacteriostatic effect. Will not kill but will slow down growth
Desiccation
A physical method to control microbial growth
It is where water has been withdrawn from the environment.
It is a condition where microbes cannot grow but can remain viable
Has a bacteriostatic effect.
This is how we preserve bacterial cultures for long term in lab.
Osmotic pressure
A physical method to control microbial growth.
Where water is withdrawn from the cell itself by cultivation in a concentrated salt or sugar environment.
Microbial cells become dehydrated and die.
Ionizing Radiation (X-ray)
Physical method to control microbial growth
Used for the sterilization of dental and medical supplies (gloves and plastic syringes)
More effective because more penetrating
Non-ionizing radiation (UV light)
Physical method to control microbial growth.
Used for the sterilization of hospital rooms, operating rooms and cafeteria.
What is the mechanism of action for radiation?
To damage the structure of microbial DNA or RNA
Phenolics
Organic molecules (contains carbon)
Disinfectants
Stable and persist for long periods of time
Ex: Lysol
What is the mechanism of action for phenolics
Changing the permeability and denaturing microbial proteins
Chlorhexidine
An antiseptic
Used for surgical scrubs
Found in prescribed mouth wash
What is the mechanism of action for chlorhexidine?
By changing the permeability of the plasma membrane
Halogens
A group of chemical elements that are effective antimicrobial agents
Iodine
The oldest and most effective antiseptic
Chlorine
Used as a disinfectant to disinfect water but can also be used in bleach
Fluorine
can be found in toothpaste as an antiseptic
What is the mechanisms of action for iodine?
denatures microbial proteins
What is the mechanisms of action for chlorine?
Alters cellular components in the microbe
Alcohol
Effectively kills bacteria and fungi.
Both a disinfectant and an antiseptic.
The recommended concentration of ethanol is 70%
70% can penetrate better than 100%
What is the mechanisms of action for alcohol?
Denaturation of protein and changing the permeability.
Heavy metels
can be used as antiseptics including silver, mercury, and copper.
What is the mechanisms of action for heavy metals?
denaturation of emzymes and other microbial proteins
What are the 3 types of Surface-Active Agents?
Soaps, Acid-anionic detergents, and Cationic detergents
Soaps
Good degerming agents
Not good antiseptics
Acid-anionic detergents
Chemical molecules carrying negative electric charge.
non-toxic and non-corrosive to humans but fast acting
What is the mechanism of action for acid-anionic detergent?
denaturation of microbial proteins
Cationic detergents
Carries a positive charge
What are Quats?
The most widely used cationic detergents, but cannot destroy endospores, mycobacteria and genus Pseudomonas.
What is the mechanisms of action for cationic detergents
protein denaturation and changing microbial membrane permeability.
Bacterial species belong to both genus Pseudomonas and genus Mycobacterium are major causes of nosocomial infections (hospital-acquired infectious disease)
Peroxygens
Hydrogen peroxide is an example. Hydrogen peroxide is a good disinfectant but not a good antiseptic.
Why is hydrogen peroxide not a good antiseptic?
It breaks down too quickly when exposed to an open wound.
The breakdown of hydrogen peroxide to water and oxygen is a chemical reaction catalyzed (aka accelerated) by an enzyme called CATALASE. This enzyme called catalase is actually produced by bacteria Staphylococcus aureus. Staphylococcus aureus, if you still remember, is a member of our skin resident microbiota.
Which physical method is used to sterilize heat-sensitive culture media, antibiotic solution, or enzyme solution?
filtration
Is hydrogen peroxide a good antiseptic?
No
Among the physical methods of controlling microbes, low temperature is
bacteriostatic
What is the mechanism of action behinds any type of heat treatment?
denaturation of microbial protein
Which of the following is NOT considered as a moist heat sterilization?
pasteurization
What is the definition for antibiotics?
antimicrobial drugs ONLY used to treat bacterial infectious disease
Antibiotics can be produced …
NATURALLY by bacteria themselves like genus Streptomyces
or fungi themselves like genus Penicillium
or
SYNTHETIC by chemist in the lab
What is selective toxicity?
when the chosen antimicrobial drug should ONLY kill or inhibit the harmful microbe
What is the first Mechanism of antimicrobial drugs?
The inhibition of cell wall synthesis
How does selective toxicity apply to the inhibition of cell wall synthesis in the microbial cells?
Because the cell wall of bacteria contains peptidoglycan and that is what the drug targets. Us as humans do not have the peptidoglycan layer.
What is the second Mechanism of antimicrobial drugs?
The inhibition of protein synthesis
How does selective toxicity apply to the inhibition of protein synthesis in the microbial cells?
It will ONLY target bacterial ribosomes but not human ribosomes.
What is the third Mechanism of antimicrobial drugs?
Disruption of the plasma membrane (changing permeability)
Does selective toxicity apply to the disruption of the plasma membrane (changing permeability) in the microbial cells?
No because both human host and fungus contains sterols (a specific group of lipids) and that is what the drug attacks so most antifungal can be toxic to the host cell as well.
What is the fourth Mechanism of antimicrobial drugs?
To inhibit the nucleic acid (DNA/RNA) synthesis
Does selective toxicity apply to the inhibition the nucleic acid synthesis in the microbial cells?
No because drugs that target bacterial nucleic acid synthesis also targets humans nucleic acid synthesis
What is the fifth Mechanism of antimicrobial drugs?
Inhibiting the synthesis of essential metabolites in the microbial cells .
Does selective toxicity apply to the inhibition of the synthesis of essential metabolites in the microbial cells?
No, because the metabolic pathways for synthesizing the essential metabolites are similar in both bacteria and host.
What is a beta-lactam ring?
The common nucleus
What is penicillinase?
Enzymes produced by bacteria that can destroy antibiotics.
Penicillin G
Natural penicillin
Group 1 inhibitor
The prototype (THE OG)
Narrow spectrum
Used against Gram-Positive
Taken by injection
Susceptible to penicillinase
Penicillin V
Natural penicillin
Group 1 inhibitor
Narrow spectrum
Taken orally, Stable in stomach acid
Susceptible to penicillinase
Oxacillin
Semisynthetic penicillin
Resistant to penicillinase
Ampicillin and Amoxicillian
Semisynthetic penicillin
Broader spectrum
Used against Gram Positive and Gram Negative
Susceptible to penicillinase
Carboxypenicillin
Semisynthetic penicillin
Strongest against Gram-Negative especially Pseudomonas aeruginosa
Cephalosporin
Group 1 inhibitor
Resistant to penicillinase
Broader spectrum,
Effective against more Gram-Negative bacteria
Bacitracin
A polypeptide antibiotic
Group 1 inhibitor
Used against Gram Positive
Topical application for superficial infections
Vancomysin
A polypeptide antibiotic
Group 1 inhibitor
Last line of antibiotics for treatment of Staphylococcus aureus
Isoniazid
An antimycobacterial antibiotic
Group 1 inhibitor
Very effective against Mycobacterium tuberculosis
Usually administered with Ethambutol
Ethambutol
An antimycobacterial antibiotic
Group 1 inhibitor
Very effective against mycobacteria, which is acid fast bacteria
Usually used as a secondary drug to Isoniazid when treating tuberculosis
Chloramphenicol
Group 2 inhibitor
Broad spectrum
Simple chemical structure, can diffuse to hard places easily
Serious toxicity (serious side effects)
eg: the suppression of bone marrow activity to form blood cells
Aminoglycosides
Group 2 inhibitor
Significant activity against Gram-negative bacteria
Can affect hearing and damage kidneys
Streptomycin
An aminoglycoside
Group 2 inhibitor
Discovered in 1944 as an alt treatment for TB
Neomycin
An aminoglycoside
Group 2 inhibitor
found in otc topical ointments
Gentamicin
An aminoglycoside
Group 2 inhibitor
Used against bacteria Pseudomonas
Tetracyclines
Group 2 inhibitor
Broad spectrum
Produced by genus Streptomyces
Erythromycin
A macrolide
Group 2 inhibitor
Spectrum is very similar to Penicillin G
Often used as an alt to penicillin
Administered orally in orange flavor
Used against Streptococcal and Staphylococcal infections in children
Polymyxin B
Group 3 disruptor
Very effective against Gram-Negative bacteria
Used for topical treatment of superficial infections
What are the 3 antibiotics in Neosporin?
Bacitracin, Neomycin and Polymyxin B
Cipro
A fluroquinolone
Group 4 inhibitor
Used to treat anthrax
Sulfa drugs
Group 5 inhibitor
Bacteriostatic
