W19 Microbiology Flashcards
How do prokaryotes divide?
Most bacteria/prokaryotes divides by Binary Fission
Some by budding
What are the 4 sequential phases of Bacterial population growth?
Lag phase
Exponential or Log
Stationary
Death phases
What is a microorganism?
Microorganisms (or microbes) are organisms that are too small to be seen with the unaided eye so require a microscope
What are the Major groups of microbes? (5)
- Bacteria
- Fungi (yeasts and moulds)
- Parasites (protozoa, helminths, ectoparasites)
- Microalgae
- Viruses and prions
Which are the smallest and biggest of the following microorganisms?
Viruses, Bacteria, Yeasts, Protozoa, Prions, Moulds
Moulds > Protozoa > Yeasts > Bacteria > Viruses > Prions
What are the types of microorganism diversity?
Cellular = formed by cell(s)
- A single cell (monocellular) – e.g. bacteria
- More cells (pluricellular) – e.g. moulds
-Consist of Prokaryotic (e.g. bacteria) or
- Eukaryotic cells (protozoa, yeasts, moulds)
Acellular = without a cellular structure (e.g. viruses and prions)
What are the 3 domains?
What are the differences based on?
Bacteria, Archaea, Eukarya
Classification mainly based on differences in the
sequences of nucleotides of ribosomal RNAs (rRNA)
What are the features of Viruses?
- Acellular (do not have a cellular structure)
- Small infectious particles consist of nucleic acids surrounded by a protective coat of protein(s)
- Coat may be enclosed in a lipid envelope
- They do not divide
- They need to infect a cell to replicate their particles
What are prions?
What are they made up of?
Simpler infectious particles made up of only proteins (no nucleic acids)
What are the Impact of Microbes on the Environment and Human Activities? (6)
organic?
produce?
synthesis?
generation?
Fix?
O2?
- Organic waste decomposition (e.g. sewage)
- Production of food (e.g. cheese, bread, beer by fermentation)
- Drugs/enzymes synthesis (e.g. penicillin, insulin,
etc.) - Digestion and molecule generation (e.g. vitamins, etc)
5.Nitrogen fixation (converting atmospheric N2 to ammonia, NH3) - Oxygen generation (photosynthesis)
How can microbiota be helpful? (3)
prevent?
produce?
break down?
- Prevent growth of pathogens
- Produce growth factors (e.g. vitamins B and K)
- Breaking down toxic molecules, boosting the immune system and antimicrobial chemicals
Do microbes cause disease?
Microbes are present in and on the human body
>100 trillions microorganisms harboured per person (≈10X higher human cells)
But Less than 1% of microbes cause diseases (pathogens)
Majority of microbes are helpful and not harmful
What are the different types of bacteria called? (for info)
Coccus
Bacillus
Vibrio
Coccobacillus
Spirillum
Spirochete
What are the different arrangements of bacteria called? (for info)
Pairs
Clusters
Chains
Tetrads
How are bacteria named?
Genus and Species
Name is italicised and genus is capitalised
e.g. Escherichia coli becomes E. coli
Bacteria and Archaea are what type of cell?
What features do they have?
Prokaryotes
- Without a nucleus
- Without membrane-bound organelles
(such as mitochondria, lysosomes, etc)
- Simple organisation
What is the plasma membrane structure of bacteria?
What is the function?
Phospholipid bilayer
Composition:
* 40% lipids (mainly phospholipids), 60% proteins
* Lacking sterols (cholesterol of human cells)
* Contain sterol-like molecules (hopanoids)
* Fluid-mosaic model like eukaryotes
=Serves as a selectively permeable barrier:
Controls movements of molecules across the cells
What are mesosomes?
Functions?
Plasma membrane infoldings
Site for DNA replication and cellular respiration
Bacteria cell wall:
What are the functions?
Why is it important?
What is the composition?
Functions
* Maintain bacterial cell integrity and shape
* Prevents the cell from bursting when water flows into the cell by osmosis
* Can contribute to pathogenicity (ability to cause disease)
Evidence of importance
* Only a few bacteria do not posses cell walls (e.g. mycoplasma)
* Target of many antibiotics (anti-bacterial drugs)
Composition
* Structural difference between these two groups
(Gram+ and Gram-)
What is the composition of peptidoglycan/murein?
What ate the 2 monosaccharides it consists of?
- A rigid multi-layered network made up of linear chains
- Each chain is a polymer of a repeating identical disaccharide unit
(made up of the following 2 monosaccharides) in long rows: - N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
A tetrapeptide chain of 4/5 amino acids is linked to NAM
* Chains are linked by peptide cross bridges between tetrapeptide side chains of NAMs
* Archea do not posses peptidoglycan
How can you distinguish between gram +/-
What are the results for gram positive ?
What are the results for gram negative ?
Gram staining:
* Gram-positive (cells are stained BLUE/PURPLE due to the crystal violet-iodine complex – the primary stain/mordant)
- Alcohol dehydrates peptidoglycan (thick layer) forming crystals inside and the dye is retained
Principles:
* Gram-negative (cells stain RED/PINK as the counterstain – e.g. safranin)
- Alcohol dissolves the outer membrane and leaves holes in peptidoglycan
- Crystal violet-iodine complex washes out; cells are colourless
- Safranin (pink) added to stain cells
What is the process of gram staining?
What are the steps? (4)
- Distinguishing groups of bacteria
according to their cell wall structure
- Primary staining with Crystal violet
- Mordant application- Iodine Treatment
- Decolorisation
- Counterstaining with Safranin
What are the features of gram+?
Consists of a thick structure (several layers) of peptidoglycan, separated from the plasma membrane by a thin periplasmic space.
* Also contains teichoic acids, made up of an alcohol and a phosphate group (negative charge)
- Bind to and regulate movement of cations into cell
- Regulate cell growth and prevent cell lysis
- Linked also to the cell membrane
What are the features of Gram -ve bacteria?
Composition?
- Cell wall is thinner, more complex and more susceptible to mechanical breakage
Consists of:
- A thin peptidoglycan layer
- Periplasmic space, containing degradative
enzymes and lipoproteins
- Outer membrane (the most external)
What is the outer membrane composition in gram negative bacteria?
- Consists of:
- Phospholipid bilayer
- Lipopolysaccharides (LPS): acting as antigen and endotoxin
- Porins: membrane pores that allow
the passage of molecules - Lipoproteins
Main differences in the cell wall of Gram+ and -bacteria
Gram +ve
- THICK peptidoglycan
- Teichoic acids
Gram -ve
- THIN peptidoglycan
- Outer membrane (containing LPS, lipoproteins, porins)
- Periplasmic space
What are the functions of the Outer membrane in Gram- bacteria?
- Evade phagocytosis and immune system
- Permeability barrier to antibiotics
(penicillin), digestive enzymes, etc
What are the functions of the glycocalyx?
- Confer pathogenicity (only capsule)
- Prevent phagocytosis by host phagocytes
- Avoid desiccation by preventing water loss
- Aid in attachment to solid surfaces
What are.
Nucleoids?
Plasmids?
Ribosomes?
-Nucleoid: central region containing circular DNA (up to 3500 genes).
- Plasmids: small, nonessential, circular DNA (5-100 genes; e.g., antibiotic resistance, production of toxins, digest antibiotics). They replicate independently.
- Ribosomes: bacterial ribosomes are termed 70S ribosomes (50S + 30S), which distinguish them from the 80S of eukaryotic cells. Selective antibiotic target.
What are flagella?
structure?
function?
- Hairlike filamentous appendages external to the cell
- Propel bacteria (process requiring ATP) toward or away from stimuli, detected by chemoreceptors
- May also be a sensory organelle
(detecting chemicals, temperature, etc)
What is the composition of bacterial flagella? (3)
- Three parts, made of protein flagellin:
- Filament: outermost region
- Hook: attaches to the filament
- Basal body: consists of rod and pairs of rings; anchors flagellum to the cell wall and membrane
What are fimbriae?
What are they involved in?
- Thin hairlike appendages that allow for attachment
- Some types are involved in a twitching motility (how bacteria move along surfaces)
What are sex pili?
*Hair-like tubular structure
* Conjugation pili involved in DNA transfer from
one cell to another
How do Flagella and bacteria move?
- Flagella rotate to “run” or “tumble”
- Direction of flagella determines the movements
What occurs in the lag phase of bacterial population growth?
Lag phase
- Little or no cell division occurs
- Intense metabolic activity. Individual cells increase in size
What occurs in the log/ exponential phase of bacterial population growth?
- Rapid and constant population growth (exponential manner)
- Number of cells produced > Number of cells dying
What occurs in the stationary phase of bacterial population growth?
- Population size begins to stabilize
- Number of cells produced = Number of cells dying
What occurs in the death phase of bacterial population growth?
- Population size begins to decrease
- Number of cells produced < Number of cells dying
What is the generation time?
What does t stand for?
Time required for a bacteria to complete the cell cycle
* E. coli divides every 20 minutes.
* Most bacteria divide every 1 to 3 hours.
* Some bacteria (M. tubercolosis) require over 24 hours to divide.
Some bacteria stain gram-positive and others stain gram-negative because of differences in the structure of their;
a) Plasma membrane
b) Cell wall
c) Capsule
d) Flagella
e) Ribosomes
Cell wall
Which ONE of the following molecules is only contained in the cell wall of Gram +?
a) Porins
b) Lipopolysaccharides (LPS)
c) Sterols
d) Teichoic acids
e) Cellulose
Teichoic acids
Which ONE of the following about the bacterial scientific name is correct?
a) It must be written in bold
b) Includes the Domain
c) All bacteria belong to the same Genus
d) It has been introduced to honour the discoverer
e) It is made of Genus and species
It is made of Genus and species
What are inclusion bodies?
Granules as reserve deposits of nutrients in the form of high molecular weight polymers. E.g. glycogen, polymeric phosphates, etc.
What are Biofilms?
Where are they found?
- Microbial communities
- Form slime or hydrogels that adhere to surfaces
- Bacteria communicate cell-to-cell
- Share nutrients
- Shelter bacteria from harmful environmental factors or microbicides
Biofilms are ubiquitous in nature. They are also found in the digestive system, dental plaque and involved in infections. Also found in sewage treatment systems.
What are the physical reqiurements for bacterial growth?
pH
Osmotic pressure
Temperature
What are chemical requirements for bacterial growth?
Oxygen
Organic growth factors
Ions, Trace elements
Carbon source
Nitrogen, Sulphur and Phosphate
Physical Requirements for Growth: Temperature
What is the optimismum growth temp for psychophiles?
Psychotrophs
Psychrophiles - “Cold-loving” (<15°°C)
Psychrotrophs - (20-30°C)
What is the optimum growth temperature for
Mesophiles?
Thermophiles?
Hyperthermophiles?
Mesophiles - “Middle loving” (25-40°C)
Thermophiles - “Heat-loving” (50-60°C)
Hyperthermophiles - (>80°C)
Each bacteria species has its own……temperatures (3)
- Minimum growth temperature
- Optimum growth temperature
- Maximum growth temperature
What is control of temperature important for?
Control of temperature is essential for the storage of pharmaceutical products and food
Physical Requirements for Growth: pH
Optimum pH?
neutrophiles
acidophiles
alkalophiles
What inhibits microbial growth?
grow between pH 6.5 and 7.5
grow in acidic environments (pH 0-5)
prefer the pH range of 8.0 to 11.5
Acidity= used for food preservation (e.g.: pickling)
Alkalinity (pH>8) but not used
Physical Requirements for Growth: Osmotic pressure
What is the osmotic pressure of bacteria?
Similar requirements to human cells (isotonic solutions)
* Hypertonic environments (higher in solutes than inside the cell) cause plasmolysis due to high osmotic pressure (water moves from inside to outside)
Why might primitive civilisations have used salt as a food preservation
technique?
- To increase the osmotic pressure.
- High concentration of salt outside the cell means a hypertonic environment
- Water moves from inside to outside the cell, causing plasmolysis
- Only halophiles tolerate high osmotic pressure
Why is Carbon a chemical requirement for growth?
Structural backbone for all organic compounds
- Obtained from organic molecules (Chemotrophs) or CO2 (Photoautotrophs)
Why are Nitrogen, Sulfur and Phosphorus
chemical requirements for growth?
N= to form amino acids, DNA, and RNA
S= to form proteins and some vitamins (thiamin and biotin)
P= to form DNA, RNA, ATP, and phospholipids
Why are trace elements chemical requirements for growth?
e.g. Fe, Cu, Zn in small amounts
Used as enzyme cofactors
Why are Organic growth factors chemical requirements for growth?
To form vitamins, amino acids, nitrogenous bases
Why are Oxygen chemical requirements for growth?
- Structural backbone of all organic compounds
- Can classify microorganism based on their oxygen requirements:
- Obligate Aerobes - require oxygen to live. E.g. Pseudomonas, causing infections in humans, mostly in hospital patients
- Facultative anaerobes – can grow via fermentation or anaerobic respiration when oxygen is not available. Grow best in aerobic
conditions. E.g. E.coli - Obligate anaerobes – do not tolerate oxygen and are harmed by it. E.g. Clostridium bacteria that cause tetanus and botulism
What is a Culture?
What is a Culture medium?
What is Inoculum?
Culture= Microbes growing in/on culture medium at appropriate conditions (physical requirements
Culture medium= Nutrients prepared for microbial growth in a laboratory (chemical requirements)
- Have to be sterile (not contain living microbes) and contain nutrients and incubate
- Inoculum: introduction of microbes into a medium
What is Agar?
What is it used as?
- Complex polysaccharide
- Used as a solidifying agent for culture media in Petri plates (liquefies at 100°C and Solidifies at ~40°C)
- Generally not metabolized by microbes
Specific culture media:
What is Selective media?
- Suppress unwanted microbes and encourage desired microbes
E.g. Saboraud’s Agar: 5.6pH discourages bacterial growth. Used to isolate fungi.
Specific culture media:
What is Differential media?
- Allow distinguishing of colonies of different microbes on the same plate
- E.g. Blood Agar: to distinguish bacteria that destroy red blood cells (hemolysis).
Specific culture media:
What is Enrichment Culture?
- Encourages the growth of a desired microbe by increasing very small numbers of a desired organisms to detectable levels (without suppressing other microbes).
How do you obtain a pure culture?
Individual organisms must be isolated
Streak-plate method is commonly used
What are Aseptic techniques?
Procedures under suitably controlled conditions to maintain the sterility, free from external sources of contamination
What is a streaking techinque?
In which a sterile loop is inserted into a sample and streaked onto a plate in a pattern (e.g. 3 sectors), to obtain individual colonies.
What is Colony formation?
A population of cells arising from a SINGLE cell (also referred to as CFU, colony forming unit)
Measuring the microbial growth is crucial for a variety of applications:
- Diagnose bacterial infections from patient specimens (blood, urine, etc)
- Food safety and process hygiene assessment against relevant criteria
- Microbiologic sampling of environmental sources
- Assessing microbial contamination of sterile pharmaceutical products - test for
sterility for Quality Assurance (YEAR 3) - Microbiological assessment of non-sterile pharmaceutical products (e.g.
topical use preparation, herbal remedies) comply with the specifications /
acceptance criteria outlined in the British Pharmacopoeia (YEAR 3)
Direct measurements–count microbial cells
- Plate count
- Filtration
- Direct microscopic count
Indirect measurements–count microbial cells
- Turbidity (mass)
- Metabolic activity
- Cell mass - Dry weight
How do you conduct a Plate count?
- Count colonies (CFUs) of bacteria
sample poured or spread on the surface
of an agar plate - To ensure the right number of colonies (countable), the original inoculum must be diluted via serial dilution (sequential dilutions
in a stepwise manner)
What happens during Membrane filtration?
- Solution passed through a cellulose filter (0.45 μM) that collects and retains bacteria
(bacteria size > pore size) - Filter is applied to a Petri dish and bacteria can grow as colonies on the surface
- Used for low counts
What is a Direct microscopic count?
- Direct microscopic count- Rely on light microscopy and a cell counter
- Placing a small amount of samples on a microscope slide with a special grid
- Stain is added to visualize bacteria
- Cells are counted and multiplied by a factor to obtain concentration.
Direct microscopic count
How do you calculate no. of bacteria?
Number of cells counted/ Volume of area counted
What are the limitations of Direct microscopic count?
- Difficult to distinguish live/dead bacteria
- Often laborious
- Only suitable with high counts
What are indirect methods to estimate bacterial numbers? (3)
- Turbidity/Cell mass - measurement of
cloudiness/optical density (linked to the cell
mass) of liquid media by a spectrophotometer - Metabolic activity - amount of metabolic product is proportional to the population size
- Cell mass / Dry Weight - bacteria are filtered, dried, and weighed; used for filamentous organisms
An organism that uses oxygen when present but can grow without oxygen is called?
obligate aerobe
Facultative anaerobe
In which growth phase is there intense activity preparing for population growth but no growth in population?
Lag phase
Which type of medium suppresses the growth of unwanted bacteria and encourages growth of desired microbes?
Selective media
What are Endospores?
What are they resistant to?
-Resting/dormant/inert form of some bacterial cells
-Produced only by two Gram+ Genera: Bacillus and Clostridium
- It is a mechanism of survival to adverse environmental conditions that would be
lethal for the bacteria (vegetative state) - E.g. nutrients depletion,
- Environmental stresses (extreme temperature, pH),
- Chemical stresses (antibiotics, disinfectants)
- Extraordinarily resistant to desiccation, heat, chemicals, and radiation
- Endospores are able to survive for long periods (up to centuries)
What is Sporulation?
What is Germination
Sporulation: endospore formation
Germination: endospore returns to vegetative state
- Endospores are NOT a form of reproduction
- Only one new cell germinates from each endospore
Sporulation (for info)
- Sporulation is a process of differentiation, normally starts when growth ceases due to lack of nutrients or environmental stress (activating a set of genes to induce this differentiation and quenching genes involved in the germinative life of bacteria)
- It is a cycle of 7 sequential steps
- Sporulation involves the production of many new structures, enzymes, and metabolites along with the disappearance of many vegetative cell components.
What is the structure of an Endospore? !
Ovoid shape and a multi-layered structure.
Contains:
* A core (dehydrated and metabolically inactive),
- containing DNA, ribosomes, essential proteins
and large depots of calcium dipicolinate (Ca-DPA)
- Surrounded by 3-4 different coating layers:
- Core walls: innermost layer
- Cortex: made of peptidoglycan
- Spore coat: fairly thick, and impermeable layer. It confers resistance to chemicals/antibiotics
- Exosporium: thin covering, not always present
A special stain can be used to detect endospores
An endospore develops inside some bacterial cells to enable it to stay dormant for long periods.
Describe Germination: !
- Process of an endospore that revert back to a vegetative cell very rapidly (even after decades), through removal of the stress inducer
- It also requires an activation step (usually heating to damage the spore coat), which is reversible
- Divided in 3 sequential steps, activation, initiation and outgrowth
- During germination, the core is hydrated, spore coats are cracked and the cell metabolism is restored
Some spore forming bacteria are capable of causing disease: (for info)
- Clostridium botulinum – botulism
Flaccid paralysis= muscle weakness - Clostridium perfingens – gas gangrene
Spastic paralysis= tonic muscle spasms - Clostridium tetani – tetanus
- Bacillus anthracis – cutaneous or pulmonary anthrax
Endospores as a weapon for bioterrorism
What is Endospore resistance? !
- Extraordinary resistance to desiccation, heat, chemicals, and radiation in comparison to the vegetative bacteria
- Those features make endospores difficult to eliminate
- Highly resistant to the most common disinfection procedures
- Issues a clinical setting or in aseptic situations (e.g. industrial pharmaceutical preparation)
-Used to test the efficacy of sterilisation methods
Define: Sterilisation !
Sterilisation: Destroying ALL microbial life (including endospores)
- A sterile object is totally free of viable microorganisms
Define Disinfection !
- Disinfection: REDUCES the number of pathogenic microorganisms (not endospores) to the point where they no longer cause diseases
(-Disinfectant: agents applied on inanimate objects/surfaces (toxic to human tissue)
-Antiseptic: agents applied on living tissue)
Define Sanitisation:
Reduces the microbes to safe levels by public health standards.
What is Antimicrobial chemotherapy? !
Drug treatment for specific infections used
internally to SELECTIVELY kill or inhibit growth of microorganisms within host tissues, targeting a unique structure of the specific microbe
Why is control of bacterial growth important? !
- Prevent infections, food/environmental/pharmaceutical spoilage
- Different microbes have different resistance to distinct antimicrobial control measures
- The goal of any sterilisation process is the
destruction of bacterial endospores, viruses and cellular organisms - Sterilisation is an essential stage in the processing of any product destined for parenteral administration, or for contact with broken skin, mucosal surfaces, or internal organs
Most resistant- Least resistant bacteria: !
Prions>Endospores> Mycobacteria>Gram-ve>Fungi>Gram+ve>Viruses with lipid envelopes
Rate of microbial death
- Death of the whole population is not instantaneous:
- Death continues in a logarithmic manner as the time or concentration is increased.
Treatments to control the microbial death
Effectiveness of the control agents depends on: (info)
- Time of exposure
- Microbial characteristics
- Number of microbes
- Environment (organic matter, temperature, biofilms)
Treatments to control the microbial death
Effects on the microbes: (info)
- Alternation of membrane permeability
- Protein denaturation
- Damage to nucleic acids
Treatments to control the microbial death:
What are some Physical treatments? (4)!
- Temperature
- Heat (moist and dry)
- Cold temperatures
- Filtration
- Radiations
- Osmotic pressure
Treatments to control the microbial death
What are some Chemical treatments?
(important)
*Alcohols
*Halogens
*Iodine
*Chlorine
*Phenolics
*Aldehydes
*Quaternary ammonium compounds
*Sterilizing gases
*Heavy metals
Temperature: Heat !
- Elevated temperatures (> Max temp.) to kill microbes
- Moist heat: hot water, boiling water, or steam between 60°C and 135°C (autoclave, pasteurisation). Kills microbes by denaturating their proteins
- Dry heat: hot air or an open flame (Bunsen Burner, incineration), which ranges from 160°C to thousands of degrees Celsius. Kills microbes by dehydrating the cell, and oxidation effects
- Moist heat is much more effective than dry heat
*Boiling does not destroy endospores and does not sterilise
Moist heat - Autoclave !
Autoclave: preferred sterilisation method, unless material is damaged by heat, moisture, or high pressure
* Closed chamber with hot saturated
steam under pressure
* 121.5° C for 15 minutes, to sterilise microbes/endospores (prions requires more time)
* Steam must directly contact material
* Strips containing harmless endospores are used as quality control
Moist heat – Pasteurisation !
- Pasteurisation (moist heat disinfection): Developed by Louis Pasteur to prevent the spoilage of beverages. Used to reduce microbes responsible for spoilage of beer, milk, wine, juices, etc.
- Except for UHT, Pasteurisation does not sterilise!
What are the 3 Methods of Pasteurisation? !
- Classic Method of Pasteurisation: 65 o C for 30 minutes
- Flash Pasteurisation (HTST): Used today. 72 o C for 15 seconds
- Ultra High Temperature Pasteurisation (UHT): 140°C for 4 seconds and then cooled quickly in a vacuum chamber. This is a sterilising method
What is the effect of Cold (Low temperatures) on microbial growth?
Does it kill them?
What is refrigeration and freezing temperature used for?
- Low temperatures (< optimal temp.) slow down microbial growth
- Reduces metabolic rate of most microbes to stop their proliferation and toxin production, but often do not kill microbes
- Refrigeration temperatures (4-8°C) are used for food preservation
- Freezing temperature (<0°C) can be used for long-term storage and preservation of some bacterial cultures (useful for analysis)
- Placing solutions in glycerol at -70°C
What is Filtration (of microbes)? !
What heat sensitive materials is it used for?
Filtration= Removal of microbes by passage of a liquid or gases through membrane material with defined small pores (<microbe size)
-Solution with microbes is sucked through the layer under vacuum and microbes are retained
- Used for heat-sensitive materials (vaccines, enzymes, antibiotics)
-Pore size for most bacteria: 0.2-0.45 μm
-Pore size for viruses: 0.01 μm - Air filtration using high efficiency particulate air (HEPA) filters in laminar flow biological safety cabinets (0.3 μm)
What is Osmotic pressure?
The use of high concentrations of salts and sugars in foods is used to increase the osmotic pressure and create a hypertonic environment.
What is Plasmolysis?
As water leaves the cell, plasma membrane shrinks away from cell wall. Cell may not die, but usually stops growing.
Different types of radiations kill microbes: !
What is the effect/penetrating power of UV light?
What is the effect/penetrating power of Ionising radiations?
Ultraviolet light: Damages microbial DNA (breaks or mutations)
- Has poor penetrating power
- Used only for surface sterilisation
Ionising radiations (Gamma rays, electron beams and X-rays): to produce reactive free radicals that lead to microbial cell death.
-Have high penetrating power into objects
-Used to irradiate pharmaceuticals and disposable medical supplies, foods and other heat-sensitive items
Chemical agents !
-More often employed in disinfection (inanimate objects/surfaces) and antisepsis (human tissues).
Only a FEW chemical agents achieve sterility.
A number of factors influence the efficacy of a given chemical agent including..? (5)
(How well drug will be able to bind to receptor and cause it to activate)
- The kinds of organisms present
- Degree of contamination
- Time of exposure
- Nature of the material being treated
- Concentration of disinfectant
Commercial Disinfectants and Antiseptics include:
Alcohols: Ethanol and isopropyl alcohol (60 – 80% in water, required) .
Used as an antiseptic to wipe microbes off skin before injections (evaporate, leaving
no residue), in hand sanitisers and cosmetics. Not good for open wounds
o No effect on nonenveloped viruses
Iodine: (tincture= dissolved in alcohol) wound aseptic
Chlorine: Used to disinfect drinking water, pools, and sewage
All of the above damage plasma membranes, proteins, lipids, or DNA
Are used to reduce microbial content from objects
Commercial Disinfectants and Antiseptics include:
Alcohols: Ethanol and isopropyl alcohol (60 – 80% in water, required) .
Used as an antiseptic to wipe microbes off skin before injections (evaporate, leaving
no residue), in hand sanitisers and cosmetics. Not good for open wounds
o No effect on nonenveloped viruses
Iodine: (tincture= dissolved in alcohol) wound aseptic
Chlorine: Used to disinfect drinking water, pools, and sewage
All of the above damage plasma membranes, proteins, lipids, or DNA
Are used to reduce microbial content from objects
Sterilising power: !
Glutaraldehyde
Betapropiolactone
=Used to sterilise medical equipment
=Chemicals that sterilise heat-sensitive
material in a chamber similar to an autoclave
What is Antimicrobial chemotherapy? !
Administration of specific drugs to treat
infectious disease, having selective toxicity against pathogens involved in infections, not host cells.
- Antibiotics- bacterial infections
- Antiviral drugs-virus infections
- Antifungal drugs -fungal infections
- Anthelminthic drugs- worm infections (parasites)
- Antiprotozoal drugs-protozoan infections (parasites)
- Each group has a different class of drugs, possessing different mechanisms of actions and targeting different specific microbial targets
Targets of different classes of antibiotics
(for info)
Selectivity- Take advantage of the difference between the structure of the bacterial cell and the host’s cell
Considering differences in Gram+ and Gram– bacteria
* Antibiotics have a different
spectrum of activity
all bacteria or broad
Gram + or Gram –
few specific species
e.g. Penicillins target the Cell Wall
e.g. Chloramphenicol targets Ribosomes
What is the name of the process that converts an endospore to a germinative bacterial cell?
Germination
The removal or destruction of ALL forms of microbial life is called?
Sterilisation
