Chapter 8: Control of Microorganisms in the Environment Flashcards
Microbes are controlled by
targeting their nutrition,
growth, and development
• This can be done by starving,
poisoning, or inhibiting
growth or replication
Biocide
• Term used rather than antimicrobial –can be chemical,
physical, mechanical, or biological
Sterilization
all living cells, spores, and acellular entities
are destroyed or removed
• When something is sterilized it is completely free of all
viable microorganisms, spores, and infectious agents
Disinfection
killing, inhibiting, or removing
microorganisms that might → cause disease
• Reduces the population of microbes and destroys
potential pathogens
Disinfectants
carry out disinfection, used on →
inanimate objects
• Does not remove → endospores
Sanitization
partially disinfect
Antisepsis
destruction or inhibition of microorganisms
in → living tissue
Antiseptics
chemicals applied to tissue to prevent
infection by preventing pathogen growth or killing
the pathogen
• Not as toxic as disinfectants
Types of microbial substances:
• -cide suffix indicates a cidal agent that kills pathogens
(not endospores)
• Bactericide, fungicide, or viricide
• -static suffix indicates agents that do not kill but
prevent or inhibit growth
• Bacteriostatic and fungistatic
Microbes do not instantly die after being exposed to a
lethal agent
Population is reduced exponentially at constant
intervals
Decimal reduction time (D value)
time required to kill 90% of microorganisms
or endospores under certain conditions
• After a population has a major
reduction the killing can slow due to
resistant microorganisms surviving
Lethal agents are determined to be effective
when microbes are dead, but that can be a
challenge to determine why?
• Viable but nonculturable (VBNC) – bacteria
exposed to certain conditions remain alive,
but are unable to reproduce, temporarily
• Bacteria regain the ability to reproduce and
cause infection after a → recovery period
Viable but nonculturable (VBNC)
bacteria exposed to certain conditions remain alive,
but are unable to reproduce, temporarily
Bacteria regain the ability to reproduce and
cause infection after a
recovery period
Filtration can be used to reduce microbial populations in
→
heat-sensitive solutions
• Can be used to sterilize liquids and gases (air) by acting
as a barrier but does not kill microbes
Membrane filters
porous membranes filter microbes (1µm can trap endospores)
• Remove microbes by → screening them out
• Use to sterilize pharmaceuticals,
ophthalmic solutions (eye drops),
culture media, oils, antibiotics, and other
heat-sensitive solutions
Microorganisms can also be filtered from the → air
• N-95 disposable masks used in hospitals
High-efficiency particulate air (HEPA) filters
found in →biosafety cabinets
• Air moves freely but microorganisms are → resisted
Laminar flow safety cabinets or hoods…
force air through HEPA filters and sends out filtered
air across the opening of the cabinet
• The air flow protects workers from the
microorganisms being handled in the
cabinet and prevents the room from being
contaminated
____ heat can destroy cells and
viruses
Moist
Degrades proteins, nucleic acids,
and the plasma membrane of
microbes
• 10 min boiling kills vegetative cells but not endospores (can survive for hours)
Autoclave
device that uses saturated steam pressure,
121°C and 15 psi
• Hot enough to destroy → endospores
Pasteurization
used on → heat-sensitive substances
• Controlled heating, briefly below boiling
• Used for milk, beer, wine, and other beverages
• Does not sterilize but kills present microbes and →
slows spoilage
Dry heat sterilization is performed in
laboratory settings
Incinerate microorganisms on
inoculating loops
Why does dry heat kill microbes?
Microbes die as a result of oxidation
and denaturation of cell components
and proteins
• Less effective than moist heat but
does not corrode glassware or
metal instruments
• Can destroy plastics and rubber
Ultraviolet (UV) radiation
260nm is lethal to microorganisms
• Forms Thymine-thymine dimers in DNA
• UV lamps are placed on lab ceilings
or biological safety cabinets to
sterilize the air and → exposed
surfaces
Ionizing radiation
sterilizes by penetrating → deep into objects
• Forms free radicals that destroy or weaken nearby
matter
• Destroys all microbial cells and endospores, but not →
viruses
Cobalt 60 gamma radiation with high-voltage electricity is used for cold sterilization of?
antibiotics, hormones, sutures, and plastic supplies like syringes
Currently being used to sterilize→ meat
and other foods
• Approved by the FDA (Food and Drug
Administration) and WHO (World
Health Organization)
Chemical disinfectants
Chemical disinfectants need to be effective against
many infectious agents at low concentrations and when
exposed to → organic matter
• It must be toxic to infectious agents and nontoxic to
people or corrosive
• Low effectiveness
Chemical antiseptics
Chemical antiseptics are less toxic than disinfectants and
are less effective at killing microbes
• Reduce the number of pathogens to → prevent
infection
• Ex. Hand sanitizers and dilute iodine
Overuse of chemical disinfectant and antiseptic can be hazardous
• There has been antimicrobial resistance seen in →
triclosan
• Found in mouthwash, deodorant, soaps, cutting
boards, and baby toys
Phenolics
were the first widely used antiseptic and
disinfectants
• Used by Joseph Lister (1867) to reduce infection risks →
during surgery
• Used today as disinfectants in laboratories and hospitals
• Lysol
Phenols act by denaturing proteins and disrupting cell
membranes of microbes
Alcohols
are the most widely used disinfectants,
antiseptics, and sanitizers
• Can kill bacteria, fungi, and some enveloped viruses but
→ not endospores
• Ethanol and isopropanol are most commonly used at →
60-80%
• They dissolve membrane lipids
Iodine
is used as skin antiseptic and oxidizes cell
components and iodinates cell proteins to kill
• Can kill → some endospores
• Drawbacks: Damages skin, leaves a stain, and causes →
allergies
Betadine used for _____
wound care
Chlorine
used to disinfect water supplies and → swimming
pools
• Chlorine, sodium hypochlorite (bleach)
• Oxidizes materials in the cell and destroys vegetative
bacterial and fungi
• Almost all microorganisms will be dead 30 minutes
after exposures
what heavy metals have been used as germicides?
Mercury, silver, arsenic, zinc and copper
• Less toxic germicides are used today
Some hospitals use 1% silver nitrate on → newborn’s eyes
Quaternary ammonium compounds
are detergents that
are used for decontamination and have broad spectrum
antimicrobial activity
Detergents
– organic cleaning agents that are →
amphipathic
• Cationic detergents disrupt microbial membranes
and denature proteins
EPA (Environmental Protection Agency) regulates →
disinfectants
FDA (Food and Drug Administration) regulates agents
used on →
humans and animals
• Both have established guidelines for agent → use and
effectiveness
• Six factors
Population size
larger populations of microbes require
longer time to die than smaller ones
Population composition
the nature of the organism
impacts the effectiveness of the agent
• Ex. Endospores more resistant than vegetative cells
• Younger cells are easier to destroy than mature ones
Concentration or intensity of an antimicrobial agent
higher concentrations can sometimes destroy the
organisms → quicker
Contact time
the longer the exposure the more
microorganisms will be killed
Temperature
higher temperatures enhance chemical
activity
Local environment
can offer protection or aid in
destruction
• Heat kills better and faster with an → acidic pH
• Organism matter like biofilms can → protect
Emerging science involving the exploitation of natural
control processes
Predation of microorganisms, viral-mediated lysis, and
toxin-mediated killing
Bdellovibrio is a Gram-negative → predator
• Can destroy human
intestinal pathogens like
Salmonella, Shingella, and
E. coli
• Spraying poultry farms
may reduce potential
contamination
In the early 1900s is was discovered that isolating
bacteriophages from patients with dysentery could be
used to help → fight the disease
• FDA recently approved the use of bacteriophage spray
to eradicate Listeria, Salmonella, and E. coli in food
