Chapter 13-Control microbial growth Flashcards
Controlling microbial growth (PHYSICAL METHODS)
heat, filtration, irradiation, washing
Controlling microbial growth (CHEMICAL METHODS)
antimicrobials chemicals
Biosafety levels
BSL 4-microbes dangerous and exotic posing high risk (frequently fatal)
BSL 3-microbes are indigenous and exotic and cause serious or potentially lethal diseases
BSL 2-microbes are indigenous and have varying severity (moderate risk)
BSL 1-microbes are not known to cause disease (minimal risk)
What are the factors that influence the level of control needed?
Identify the situation:
daily life, hospitals, microbiology labs, various industrious
Fomite
inanimate object used by humans that can transmit microbes
What are the most difficult microbes to eliminate?
1-Bacterial endospores: resistant to heat, drying, some chemicals (ex. clostridium botulinum)
2-Protozoan cysts and oocytes: survives harsh conditions, excreted in feces (ex. giardia)
What are the most difficult microbes to eliminate? cont.
3-Mycobacterium species: cell wall structure initiates resistance, contains mycolic acid=more resistance, waxy lipid
4-Pseudomonas species: can grow in presence of many chemical disinfectants, has many R plasmids
5-Naked viruses: lack envelope, resistant to chemical killing
Critical items
MUST BE STERILE: used inside body, penetrate tissue (ex. surgical instruments, catheters, IV fluids)
Semi critical items
Contacts mucous me membrane, nonintact skin, doesn’t penetrate body tissues, sterile but not penetrating (ex. GI scopes)
Noncritical items
contacts unbroken skin; must be clean (ex.bed linens, furniture, stethoscope
D value
time required to reduce population of microbes by 90% (larger starting population will take longer to eradicate)
Methods of control (1-4)
1.Sterilization: eliminates all forms of life
2.Disinfection:inactivated most microbes on fomite surface using antimicrobial chemicals or heat
3.Pasteurization: reduces # of spoilage organisms and pathogens
4.Decontamination: rescues pathogens to a level considered “safe”
Methods of control 5-8
5.Sanitation: reduces microbial populations to acceptable levels for public health
6.Degerming: significantly reduce microbial numbers (hand washing)
7.Antiseptic: antimicrobial chemical safe for use on skin (hydrogen peroxide, alcohol)
8.Preservation: slows/inhibits growth of microbes in food
Aseptic technique
Prevents contamination on sterile surfaces
Sterilization
complete removal/ killing of all vegetative cells, endospores, and viruses from target item or environment
-physical (heat) or chemical (chemicals that achieve sterilization) means
-labs, medical, food industry
Autoclave
-Charles Chamberland
-pressurized steam
-effective against endospores
When is sterilization requires?
lab glassware, surgical instruments, canning process
Dry Heat
Inceration-bacterial loops
Dry heat ovens- sterilizing glass ware
Pasteurization
Kills pathogens and reduce number of spoilage causing microbes while maintaining food quality
-HTST: high temperature short time 72°C for 15 seconds
-UHT: ultra high temperature 138°C for 2 sec
Refrigeration/Freezing
-slows metabolism of bacteria
-does not sterilize foods but can decrease- some microbes live in these conditions
Radiation
Causes damage to DNA and potentially plasma membranes-inhibits replication, some endospores can be resistant
Filtration of air
HEPA filter removes nearly all microbes from air (bacteria will get trapped)
Filtration of liquid
Traps microbes on filter for heat sensitive fluids
Germicidal chemicals
Sterilants: treat heat sensitive critical instruments
High level disinfectants: treat semi critical instruments (GI scopes)
Intermediate level disinfectants: disinfect non critical instruments (stethoscopes)
low level disinfectants:general purpose (floors,walls)
Selecting the appropriate germicidal chemical:
Toxic- How toxic is the chemical
Presence of organic matter
Compatibility with material being treated-tile/fabric
Residue
Cost and availability
Ease of use
Storage/stability-shelf stable
Environmental risk-Where to dump
Alcohols
Kill bacteria, fungi- not endospores
-Denature proteins (inhibiting cell metabolism) disrupt membranes leading to cell lysis
(ex. antiseptic for hands, alcohol pads before vaccine)
Aldehydes
Inactivates enzymes and nucleic acids, kills bacteria/fungi, viruses, endospores
(ex. formaldehyde, formalin)
Ethylene oxide
Gaseous sterilizing agent-fabric, pillows, pacemakers
-cold sterilization for heat sensitive items
Bishiguanides
Antiseptics before surgery (surgeon hand scrub)
(ex. chlorhexidine-common ingredient in skin scream, mouthwash, disinfectant)
-not effective against mycobacterium, non enveloped viruses, spores
Halogens
Chlorine, sodium hypochlorite (bleach), iodine, betadine
Heavy metals
Kill microbes by binding to proteins which inhibits enzymatic activity
-non specific way of killing bacteria
ex. silver, copper, zinc
Phenolic
compound in mouthwashes and throat lozenges, disrupt membrane and denature proteins
Why was triclosan banned?
People had same chance of getting sick than with triclosan
What are the targets in bacterial cells that are affected by germicidal chemicals?
-Cytoplasmic membrane
-Proteins
-DNA
**Most chemicals denature/inactivate proteins
Disk diffusion assay
Testing for the effectiveness of germinal chemicals: ZOI indicates how effective antimicrobial is against microbe
