Endospores and Control of microbial growth Flashcards
What are Endospores?
Resting/dormant/inert form of some bacterial cells
Produced only by two Gram+ Genera: Bacillus and Clostridium
What are the environmental conditions that would be lethal for the bacteria? (mechanism of survival)
e.g. nutrients depletion,
environmental stresses (extreme temperature, pH),
chemical stresses (antibiotics, disinfectants), etc
Resistance of endospores and period of survival?
Extraordinarily resistant to desiccation, heat, chemicals, and radiation
survive for long periods (up to centuries)
Sporulation:
endospore formation
production of many new structures, enzymes, and metabolites along with the disappearance of many vegetative cell components
Germination:
endospore returns to vegetative state
Ensospores are NOT a form of _______
reproduction
only 1 new cell germinates from each endospore
Sporulation is a process of differentiation; when does it start?
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
Describe the endospore structure?
can you draw it ? (slide 7 lec 3 microbiology)
ovoid shape and multi-layered cthat contians;
A CORE= dehydrated and metabolically inactive)
containing DNA, ribosomes, essential proteins and large depots of calcium dipicolinate (Ca-DPA)
What are the layers surrounding the core?
3-4 coating layers
- core walls (innermost)
-cortex (made of peptidoglycan)
- spore coat (fairly thick, impermeable - resistance to chemicals and antibiotics)
- exosporium (thin covering - not always present)
Germination - full detailed definition
Process of an endospore that revert back to a vegetative cell very rapidly (even after decades), through removal of the stress inducer
requires = activation step (heating to damage spore coat; reversible)
core in hydrated = spore coats are cracked and cell metabolism is restored
What are the 3 steps of germination?
1) activation
2) initation
3) outgrowth
What diseases can form from spore forming bacteria?
Clostridium botulinum – botulism [ Flaccid paralysis - muscle weakness]
Clostridium perfingens – gas gangrene
Clostridium tetani – tetanus [Spastic paralysis - two muscle spasms]
Bacillus anthracis – cutaneous or pulmonary anthrax
Why is endospores resistance to heat, chemical and radiation (compared to vegetative bacteria) an advantage?
make endospores difficult to eliminate - resistant to most common disinfection procedures
issues a clinical setting or in aseptic situations - used to TEST efficacy of sterilisation methods
What are the 4 points of control bacteria growth?
1) sterilisation
2) disinfection
3) sanitisation
4) antimicrobial chemotherapy
1) sterilisation
Destroying all microbial life (including endospores)
A sterile object is totally free of viable microorganisms
2) 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
3) sanitisation
reduces the microbes to safe levels by public health standards
4) 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
Different microbes have ________ resistance to distinct antimicrobial control measure
different
What is the main goal of sterilisation?
destruction of bacterial endospores, viruses and cellular organisms
processing of any product destined for parenteral administration, or for contact with broken skin, mucosal surfaces, or internal organs
important - Most resistant to least resistant
Prions
Endospores of bacteria
Mycobacteria
Cysts of bacteria
Vegetative bacteria
Gram - bacteria
Fungi, most fungal spores
Viruses w/o envelopes
Gram + bacteria
Viruses w lipid envelopes
What is the rate of microbial death?
Death of the whole population is not instantaneous:
logarithmic manner as the time or concentration is ^^^
Treatments to control the microbial death = what does effectiveness of control agents depend on?
- Time of exposure
- Microbial characteristics
- Number of microbes
- Environment (organic matter, temperature, biofilms)
Treatments to control the microbial death =
Effects on the microbes
- Alternation of membrane permeability
- Protein denaturation
- Damage to nucleic acids
Treatments to control the microbial death
= TWO types
1) Physical
2) Chemical
Physical treatments to control microbial death
Temperature
Heat (moist and dry)
Cold temperatures
Filtration
Radiations
Osmotic pressure
Chemical treatments to control microbial death
Alcohols
Halogens
Iodine
Chlorine
Phenolics
Aldehydes
Quaternary ammonium compounds
Sterilizing gases
Heavy metals
Chemical treatments to control microbial death
Alcohols
Halogens
Iodine
Chlorine
Phenolics
Aldehydes
Quaternary ammonium compounds
Sterilizing gases
Heavy metals
How does heat affect microbes
Elevated temperatures (> Max temp.) = kill microbes
Moist heat = hot/boiling/steam [60C = 135C] autoclave, pasteurisation). Kills microbes by denaturating their proteins
Dry heat = hot air/ oen flame [bunsen burner] 160C to thousandsC, Kills microbes by dehydrating the cell, and oxidation effects
Is Moist or dry heat most effective?
Moist heat
Boiling does not destroy endospores and not _______
sterilise
Moist heat = Autoclave
121C fro 15 mins to sterilise microbes/endospores
preferred sterilisation method, unless material is damaged by heat, moisture, or high pressure
Closed chamber with hot saturated steam under pressure
Steam must directly contact material
Strips containing harmless endospores are used as quality control
Moist heat = Pasteurisation
disinfection
reduce microbes responsible for spoilage of beer, milk, wine, juices etc.
Except for ____, Pasteurisation does not sterilise!
UHT (ultra high temperature processing)***
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 o C for 4 seconds and then cooled quickly in a vacuum chamber. This is a sterilising method
Cold – Low temperatures
4-8C - used for food preservation
slow down microbial growth
Reduces metabolic rate of most microbes to stop their proliferation and toxin production, but often do not kill microbes
Freezing temperature (<0o C)
what temp is solutions in glycerol?
70C
used for long-term storage and preservation of some bacterial cultures (useful for analysis)
What is filtration? How does it work?
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
What is filtration used in?
sizes of bacteria?
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)
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.
Plasmolysis
As water leaves the cell, plasma membrane shrinks away from cell wall. Cell may not die, but usually stops growing.
