why is controlling microbial growth important
- to prevent the spread of disease in humans, animals, and plants
- to remove contaminants from water
- important in food, to prevent the presence of pathogens
- to prevent/delay food spoilage
- to control microbial growth in drinking water
what is an antimicrobial agent
- a chemical, physical, or biological product that kills or inhibits the growth of microorganisms
what is sterilization
- sporocide, sterilizing agent
- destroys all forms of microbial life including spores
- used on inanimate objects
what is disinfection
- disinfectants
- destruction or removal of most to all organisms but not endospores
- used on inanimate objects
what is antisepsis
- antiseptics, germicide
- kills or inhibits growth of microorganisms
- sufficiently non toxic to be applied to living tissues
what is chemotherapy
- chemicals used internally to kill or inhibit growth of microbes in host tissues
what conditions influence effectiveness of antibacterial agent activity
- population size, more microbes = more treatment
- population composition
-> endospores more resistant compared to vegetative forms
->enveloped vs non enveloped viruses - concentration/intensity of agent = more concentrated or intense, the more rapidly microorganisms are destroyed
- duration of exposure (contact time) = longer exposure time, the more organisms are killed
- temperature = increase in temp, enhances activity
- other environmental factors = can aid in destruction or offer protection
what is decimal reduction time
- population death during treatment is usually exponentials
- calculate treatment time required for a certain reduction in abundance
- calculate D value at different temperatures based on Z value
what does D and Z value mean
D value - decimal reduction time = treatment time required to reduce the number of organisms by one log
Z value - thermal resistance constant = change in T required to change the D value by one log
how are physical methods used to control microbial growth
- filtration = microbes become trapped in the filter membrane
-> used for liquids and gases - heat
-> autoclave = combine heat and pressure
-> pasteurization = used in food industry, raises temp to certain value to kill or remove mirobes
-> boiling - radiation
-> UV disinfection = damages nucleic acids by causing thymine-thymine dimerization, ds breaks in DNA -> drinking water and wastewater
-> ionizing radiation = free radicals oxidize cell components -> some foods (meats)
how are chemical methods used to control microbial growth (non-chemotherapeutic)
phenolics -> joesph lister pioneered the use of phenol in medicine
-> antiseptic and disinfectant
-> lysol
-> denature proteins and disrupt cell membrane
alcohols -> 70% ethanol used widely in research labs for disinfecting countertops and equipment
-> disinfectants, antiseptics, and sanitizers
-> denature proteins and dissolve membrane lipids
halogenated compound -> chlorine in drinking water and pools, bleach disinfecting lab benches, cultures
-> oxidation of cellular materials and destruction of vegetative bacteria and fungi
aldehydes -> glutaraldehyde commonly used in hospitals/surgeries
-> disinfectants
-> formaldehyde
-> inactive nucleic acids and proteins by cross linking and alkylating molecules
quaternary ammonium compounds -> BAC is the active ingredient in purell hand wipes
-> cetylpyridinium and benzalkonium
-> amphipathic
-> denature proteins, disrupt microbial membranes
-> detergents
gases -> ozone used in drinking water production
-> ethylene oxide = kills by reacting with
DNA and proteins to block replication and enzymatic activity (sterilizer)
-> hydrogen peroxide
heavy metals -> AgCl2
-> disinfecting agent
-> inactivate proteins, often via their sulfhydryl groups.
how are biological methods used to control microbial growth
- use of predatory bacteria
- Bdellovibrio bacteriovorus invades and destroys Gram-negative bacteria from the inside.
- used in wastewater treatment or to reduce pathogens without chemicals. - bacteriophage
- viruses that specifically infect and lyse bacterial cells.
- used to target bacterial infections, especially antibiotic-resistant strains. - colicin
- Bacteriocins are antimicrobial peptides produced by bacteria to kill closely related species.
- disrupt bacterial membranes or interfere with cell wall synthesis.
