F5 Sterilization techniques and antibiotics Flashcards
aseptic / antiseptic / sterile
aseptic: prevent contamination with microbes (that may cause disease)
antiseptic: eliminating microbes (that may cause disease)
sterile: eliminate and prevent contamination with all microbes
Sterilization
elimination of all viable cells (different from disinfection and decontamination)
- heat or heat-pressure
- radiation
- filtration
- chemical
Decimal reduction time (D value)
Thermal death time (TDT)
time to achieve a 10-times reduction of cell number at a given teperature
time to achieve full sterilization at a given temperature
- depends on the organism, environmental conditions (medium, pH, nutrients)
- spores are very heat-stable
dry sterilization
autoclave
oven at >170 °C for several hours
heat-pressure at 121 °C, 15-30 psi, 20 min - 2 hours
Freezing
• inhibition of microbial growth
• little effect on cell viability and enzyme activity -> preservation
• some pathogens die but not all, e. g.:
- protists and multicellular parasites often die
- bacteria and fungi most often survive
pasteurization (pastörisering)
complete sterilization is often neither possible nor necessary (research vs medicine vs food products)
pasteurization (pastörisering) can improve shelf life
• short heat treatment of heat-sensitive products, e.g. milk products
• no sterilization but reduction of bacterial count -> extended storage life
filtration is used for … compounds
heat-sensitive
- sterilizing agents: kill …
- disinfectants: kill …
- sanitizers: kill …
- antibiotics: kill …
- sterilizing agents: kill everything incl. spores
- disinfectants: kill most cells
- sanitizers: kill majority of cells
- antibiotics: kill bacteria
- static:
- cidal:
- lytic:
- static: prevents growth
- cidal: kills
- lytic: kills and disintegrates (löser upp)
Measuring antimicrobial activity, två mått:
Minimal inhibitory concentration (MIC)
• minimal concentration that prevents visible growth of a microorganism
• depends on organism, medium, pH, nutrients, temperature, aeration…
Minimal bactericidal concentration (MBC)
• minimal concentration that kills 99.9% of cells
• CFU determination after MIC
Antimicrobial chemicals:
phenolic compounds
heavy metals
halogens
alcohols
surfactants
antibiotics
phenolic compounds
• denature proteins and disrupt membranes
heavy metals
• bind to proteins and inhibit enzymatic activity
halogens
• highly reactive, oxidize cellular components, e.g. sulfur-containing amino acids, nucleotides, fatty acids
alcohols
• denature proteins and disrupt membranes
surfactants
• lower surface tension of water, dissolve membranes (soaps, detergents)
antibiotics
• various structures and mechanisms
Antimicrobial compounds, three types
- synthetic, e.g. sulfonamides
- natural, e.g. penicillin
- semi-synthetic, natural source but chemically modified -> most modern antibiotics
anitmicrobial compounds are classified according to:
- structure
- mechanism of action
- activity spectrum
anitmicrobial compounds are classified according to:
- structure
- mechanism of action
- activity spectrum
antibacterial mechanisms of action, examples
protein synthesis (eg tetracyclines)
cell wall synthesis (eg penicillins)
anti fungal drugs target …
several different cell structures
examples of mechanistic classes
substrate/building block analogues
allosteric inhibitors
intercalating agents
Antibiotic mechanisms of action: Good targets, bad targets?
good: cell wall synthesis
- structural targets
- multiple targets
- encoded by multiple genes
bad: nucleic acid synthesis, protein synthesis
- single protein targets
- derivatives of existing antibiotics
antibiotic resistance mechanisms, examples
efflux pumps
inactivating enzymes
decreased uptake
phenotypic resistance
intrinsic resistor
acquired resistance
phenotypic resistance: in some situations resistance can be achieved without any genetic alteration; this is called phenotypic resistance
- persisters (persisters are not mutants, but rather bacteria that find themselves in a favorable phenotypic niche, where they have abundances of DNA, RNA, proteins, and/or other cellular components that increase their tolerance to specific antibiotics.)
- biofilms
- swarming (Swarming motility is the rapid and coordinated multicellular migration of bacteria across a moist surface. During swarming, bacterial cells exhibit increased resistance to multiple antibiotics,)
intrinsic resistor: Intrinsic resistance is when a bacterial species is naturally resistant to a certain antibiotic or family of antibiotics, without the need for mutation or gain of further genes.
- metabolic genes
- regulators
- antibiotic inactivation
- target modification
- changes in bacterial permeability
acquired resistance
- horizontal gene transfer
- mutation
challenges in fighting antibiotic resistance
- intrinsic antibiotic resistance
- acquired antibiotic resistance
- phenotypic antibiotic resistance
- horizontal gene transfer
- spread of resistant bacteria
- misuse of antibiotics
- discovery void
solutions to breaking intrinsic antibiotic resistance:
- outer membrane permeabilization (combination approach)
- trapping efflux pumps
ex of antibiotic effective against Gram- / Gram+ bacteria
Gram-
Polymyxins
Gram +
Penicillins
ex of antibiotics cell wall synthesis / protein synthesis / nucleic acid synthesis
cell wall synthesis: Penicillins
protein synthesis: Tetracyclins
nucleic acid synthesis: Trimethoprim