Control of Microorganisms Flashcards
Food poisoning and food spoilage
Bacterial contamination with pathogen:
Salmonella, Listeria. E.coli O157, Campylobacter, Clostridium perfringens
Food spoilage due to bacterial and mold overgrowth
E.coli outbreak
2018: contaminated lettuce, 18 people sick in Quebec and Ontario,
2019: contaminated salad kits, 28 people sick across 7 provinces
2022: contaminated kimchi, 14 sick in Alberta and Saskatchewan.
2023: outbreak of E. coli declared on Sept. 4; source likely food source from central kitchen serving daycares; 264 confirmed cases, mostly among children. 25 hospitalized, 6 with kidney
complications requiring dialysis.
Salmonella outbreaks
April 2023: snake and rodents (including pet food) (n=45)
Nov 2023: contaminated Cantaloupe (n=14)
likely caused by raw pet food
- 40 confirmed cases of XDR (extensive drug resistance)
Salmonella in six provinces including Quebec (21) occurring between July 2020 and September 2023.
– 13 teens hospitalized, no deaths. 43% cases <= 5 yrs.
Medicine and antimicrobial therapy
• Need for sterile or disinfected environment for surgery
• Sterile instruments and devices
• Antimicrobial therapy against infections diseases
• Control of airborne biohazards for immuno-compromised hosts (virus, fungi) or nosocomial (hospital-acquired) transmission of infections (bacteria, virus)
Biohazard control and public health
• Biohazard waste from hospitals, labs
• Laboratory and occupational safety
• Biohazard control to prevent transmission: Ebola, tuberculosis, SARS-CoV2
• Blood and other biological products: HIV and other viruses
Biohazard control and public health —outbreaks
• Ebola, Marburg (hemorrhagic fever viruses)
• Dengue
• Norovirus (cause diarrhea)
• Tuberculosis
Biohazard control and public health—epidemics and pandemics
• Influenza (Spanish flu 2018, H1N1)
• bubonic plague
• HIV/AIDS
• SARS-Cov2
• smallpox
Environmental microbial control
• Potable and filtered water
• Waste and water management
Microbial control
Antisepsis: do sth. to prevent skin infection ex.bandy aids
Sanitization: drop to a safe level ex.wash dishes
Disinfection: have bacteria left
Sterilization: kill all the microorganisms (including spores and viruses)
Bactericidal vs. bacteristatic
Bactericidal: Stop growth
Bacteristatic: Kill cells
Antimicrobial potency
Population death: usually logarithmic
D value: decimal reduction time, the time that drop 1 decimal place
Lower D value: more effective killing agent
Microbial control : Influencing Factors
• Microbial population size
• Microbial composition: e.g. cells vs spores, bacteria vs virus
• Concentration/potency of antimicrobial agents
• Contact time
• Temperature
• Local environment: pH, organic matter
Conditions for achieve microbial death using steam autoclave
Bacteria
Cells: 10 min at 60-70
Spores: up to 12 min at 121
Mold
Cells: 30 min at 60
Spores: 30 min at 80
Viruses
Cells: 30min at 60
Spores: N/A
Microbial control methods (3 big categories)
Physical
Chemical
Mechanical
Physical control
Heat
-Dry:
incineration, dry oven
Sterilize
-Moist:
1.steam autoclave
Sterilize
2.boiling, pasteurization
Disinfect
Radiation
-ionizing : X-ray, gamma
Disinfect/sterilize
-non-ionizing: UV
Disinfect/sterilize
Steam Autoclave
• Uses steam (121-133˚C) at high pressure (15 psi)
• Sterilizes liquids and solid materials
• Kills spores when temp is above 121˚C for 12min
• Steam is more effective (potent) at killing microorganism than hot air
• ~15-30 min depending on volume of material/liquid autoclaved (half fill the autoclave)
• Pro: efficient, cheap, simple, no waste
• Con: high pressure and humidity can damage materials
• Quality control: Geobaccilus spore biological indicator test; heat indicator strip;
Pasteurization
• Used for heat-sensitive products: controlled disinfection typically below boiling point
• Sufficient to kill non-spore forming pathogenic bacteria to reduce spoilage and food-borne illnesses, but does NOT Sterilize
• Typically used in dairy products, eggs, wine, beer…
• Standard pasteurization
~60˚C for 30 min.
Ultra-high temp (UHT) 135-140˚C for 2-5 seconds
Food industry: food spoilage
• Visible growth of mould
• Gas/odour production by overgrowth of microorganisms
• Softening and rotting due to enzyme production (e.g. proteases) and pigments
• Growth of pathogenic bacteria: Salmonella, E. coli, Listeria, Clostridium, etc…
• But many microorganisms still survive after pasteurization
UV radiation
• short range ~ 260nm UV-C
• Kills microorganisms but at short distance; does not penetrate glass, plastic or water well
• Mainly used on surface
• Disinfects or sterilizes depending on dose, intensity and distance from UV source
• no heat, physical or chemical damage to products used
• Used for water, blood products, air, food and beverages (饮料)
• Toxic to humans: need eye and skin protection
Gamma radiation
• Photons at extremely high frequency and high energy
• Ionizing radiation is biologically hazardous because it can damage DNA and cell structures, but does not make things radioactive.
• Highly penetrating (e.g. glass, plastic); Very fast acting;
• Used for sterilization of medical supplies, pharmaceuticals, biologicals (e.g. tissues) and food products
• Method used in highly specialized sterlization facilities
Chemical control methods
Gases
-steriliaze
-disinfectant
Liquid
-antiseptics (animate)
-chemotherapy (animate)
-disinfectant (inanimate)
Antiseptics
• Kills or inhibits growth of microorganisms but does not sterilize
• Chemicals used to prevent infection or contamination
• Applied to skin/tissue surfaces (e.g. skin) thus less toxic
• Many examples: alcohols, iodine (halogens), triclosan (phenolics), chlorhexidine, boric acid, low % hydrogen peroxide
Problems of use biocides
-Tripartite pump
-Antibiotic resistance mechanism found in both grams negative and positive bacteria
-Need energy
Multi-drug resistance pump (MDR): eject all sorts of compounds that chemically distinct
Induced and unregulated by antibiotics and biocides
Disinfectant
• Kills or inhibits growth of microorganisms, more potent than antiseptics but does not sterilize
• Chemicals used to remove potential pathogenic microorganism
• Applied on inanimate surfaces (e.g bathroom, hospital equipment) thus often toxic
• Examples: bleach, chlorine, high % hydrogen peroxide, ethanol, detergents (quaternary ammonium compounds)
• Choice of compound based on many properties, such as solubility, toxicity, fumes, stability, etc…
Mechanism of action: Antiseptics and Disinfectants
Overview
Antimicrobial effect is not specific to microbial cells (e.g. protein denaturation, membrane disruption, reactive oxidants) = toxicity
Alcohols mechanisms
• ethanol, isoproponol
• denature proteins
• dissolve lipids in membrane
• Practical use 60-70% EtOH for 10-15 min
Phenolics and phenol derivatives mechanisms
Ex. triclosan, Lysol
disrupts cell membrane and denatures proteins
Aldehydes mechanisms
gluteraldehyde, formaldehyde
Highly reactive molecule that crosslink with nucleic acid and proteins to inactivate them
Very toxic
Halogens mechanisms
Ex. chlorine (e.g. bleach = Na hypochlorite), iodine (e.g. Betadine), fluorine, bromine, astatine
• Forms hypochlorous acid (HOCl) which is a highly reactive oxidant; reacts with molecules by oxidation
• can sterilize (kill spores) at high concentrations in some situations; typically used as disinfectants;
• Used as skin disinfectant, in pools
• Cheap, easy to use but toxic
• Practical use: 10% bleach for 10 min
Gas disinfectants and sterilizer
• Useful for heat sensitive items (ex. Plastic), most are very toxic
• Ethylene oxide
• Vaporized hydrogen peroxide
Ethylene oxide
-highly reactive ring structure
-strong alkylating agent that reacts with nucleic acid and protein
-potent sterilizer that can penetrate plastic wraps.
-Very toxic and flammable
Vaporized hydrogen peroxide
-no damage to non living materials
-no toxic by-product since it is degraded to water and oxygen
Modern approaches
Self sterilizing surfaces
Copper
Nanopillar (NanoSi/NanoZnO)
Can’t replace cleaning, but can supplement cleaning, can decrease the frequency of cleaning
Mechanical control methods
Air filtration: sterilize
Liquid filtration: sterilize
Liquid filtration systems
• Porous membranes
• pore size <~0.45-0.2 micron removes bacteria, fungi and spores; Viral particles require smaller pore size < 50nm (need other methods for virus)
• Used to sterilize heat-sensitive liquids
• Liquid is pushed through
Air filtration systems
• HEPA: High-efficiency particulate air filter
• pore size: 0.1- 0.3 micron
• filters airborne fungi, and bacteria, absorbs viruses
• Used in biosafety cabinets, ventilation systems, portable residential air filtration units.
Clears 99.97% microorganisms
Corrugated（波纹结构） structure
Why does antimicrobial control “fail”?
Food contamination
Blood product contamination
Prosthetic joint infection
• Suboptimal method of microbial control
• High bacterial load
• Highly virulent pathogen
• Resistant micro-organisms:
-Resistance to antiseptics
-Biofilm formation
Biofilms definition
Multicellular bacterial communities with cells aggregated within an extracellular matrix and adherent to a surface
Where are biofilms
Natural environments
Biofouling, waste water treatment, bioremediation
Medical devices
Biofilms cells are highly resistant to biocides and antibiotics
- Poor penetration
- Trapping or inactivation of toxic molecules in the biofilm matrix
-cannot contact the inner cells - Physiological state (slow growth) which makes bacterial become tolerant
-most antimicrobials and disinfection at work better on actively replicating cells
What method use depends on
• Disinfection vs sterilization
• Material: liquid, solid, gas
• Duration (how quickly?)
• Sensitivity to temperature, chemicals, etc
• Toxicity
• “Format” eg packaging, shape, size
• Availability
Grocery store antimicrobial control
Air filtration
Liquid filtration
Pasteurization
Gamma
Disinfectant
Microbiology lab antimicrobial control
Air filtration
Liquid filtration
Steam autoclave
UV (in BSC)
Gas sterilants (plastic)
Chemotherapy (antibiotic)
Disinfectant
Hospital antimicrobial control
Air filtration
Liquid filtration
Incineration, dry oven (medical wast)
Steam autoclave
Gamma
UV
Gas sterilants
Antiseptics
Chemotherapy
Disinfectant
Biohazard control and laboratory safety
BSL1-4
BSL-1
Non-pathogens: e.coli
Microbiology lab
Decontamination of all biological materials
BSL-2
Opportunistic pathogens: S. aureus, P. aeruginosa not infectious through aerosol
Restricted access, use of biological safety cabinets, extreme care with sharps
BSL-3
Pathogens: M. tuberculosis infectious through aerosol
All air in lab is controlled and filtered, and everything is decontaminated
BSL-4
deadly pathogens: Ebola transferred through aerosol
Entrance and exit to lab involves, showers, vacuum room, UV. HAZMAT suit
Biohazard control: limiting transmission of infectious microorganism
• Mode of transmission: contact, airborne, droplets
• Infectious dose: low vs high
• Mortality / morbidity, treatment available or not
• Vector or non-human reservoir: insects, animals, water, etc
• Pathogen to “normal” hosts or only susceptible hosts
Personal protective equipment (PPE)
Protective gloves
Vented goggles
Ear-loop masks
N-95 masks
Gowns
Biohazard control and Ebola virus
• Transmission through blood, urine, semen, saliva +/- droplets
• Likely limited viral survival on inanimate surfaces: possible but low risk of indirect transmission
• Transmission occurs when contact protection is absent or inadequate, and infection status is unknown
Contact, low infectious dose, not motile, animals vector(bats), pathogen to normal host
Antisepsis
Antisepsis: do sth. to prevent skin infection ex.bandy aids
