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Flashcards in Chapter 20 & 21 Deck (37):


An exception to the concentration as these are more effective when some water is used (should be diluted to 75%); proteins dissolve in water which allows these to damage proteins:
- Effectiveness: low-intermediate
- Toxicity: varies
- Actions: disrupt cell membranes and denature cellular proteins; evaporates quickly


Types of Alcohols

- Ethyl (ethanol, grain): non-toxic; more expensive than isopropyl
- Isopropyl (rubbing): more effective microbial agent, but more toxic to animals (vapors can damage CNS of humans)
- Neither kills endospores


Hydrogen Peroxide

- Effectiveness: low
- Toxicity to humans: none
- Actions: large amounts quickly overwhelm any catalase and peroxidase found within the cell; acts as a free radical which is highly toxic to living oranisms


Surface-Action Agents

- Effectiveness: Anionic (soaps)- essentially none; used in removing microorganisms but does not kill them; Cationic (quaternary ammonium compounds)- low effectiveness; ineffective against gram- bacteria
- Toxicity to humans: none-low
- Action: no action; disrupts cell membranes


Heavy Metals

- Effectiveness: low
- Toxicity to humans: little on skin, but toxic if placed on wounds; topical only (used on burns)
- Action: denatures proteins
- e.g., mercury containing compounds including metaphen, silver containing compounds including silver nitrate; in the past used to prevent gonorrheal infections in the eyes of newborns, but ineffective and was irritating


Phenol (corbolic acid) and its Derivatives

- Effectiveness: intermediate; often ineffective against non-enveloped viruses
- Toxicity to humans: very toxic to tissues; used as a topical antiseptic only (surgeon hand creams)
- Action: damage cell membranes and denature proteins
- Examples: Lysol (phenol derivative & 79% alcohol)- very effective; Chlorhexidine (hand cleanser)


Ethylene Oxide

- Effectiveness: high
- Toxicity to humans: high; carcinogenic
- Action: denatures proteins and mutates DNA strands
- Usually in vapor form; does not require water to function well; slow acting; explosive; used extensively in hospitals when items may be damaged by heat or water


Chlorine and Iodine

- Effectiveness: intermediate
- Toxicity to humans: slightly toxic; irritating to tissues and a potential carcinogen
- Action: denatures proteins, DNA


Dry Heat

Hot dry ovens or direct exposure to flame are used for this process; quickly incinerates microbes; used to sterilize glassware, powders, oils; flame of a Bunsen burner reaches 1870 degrees C



- Used to completely destroy most hospital items
- Using dry heat ovens, steriliztion of all living cells and endospores would require (at minimum): 150-180 degree C heat; 2-4 hours of contact time
- Disadvantages: time, many items cannot tolerate such heat extremes


Moist Heat

- This process would be considered boiling or steaming items
- Kills most vegetative forms of bacteria in minutes, but will not destroy endospores
- Boiling of water brings the temperature up to 100 degrees C
- Pasteurization: Flash Method- heats the fluid to 72 degrees C for 15 seconds, usually conducted as the fluid flows through pipes (very common); Holding Method- liquid heated in bulk to 63 degrees C for 30 minutes


Disadvantages to Moist Heat

- Some viruses and bacteria can tolerate short boiling times
- Endospores can survive several hours
- Does not usually sterilize the items, but greatly reduces the number of bacteria found on or within a substance


Moist Heat Under Pressure (the autoclave)

- Most medical and laboratory products are sterilized in this manner
- When water is present, all macromolecules are denatured at relatively low temperatures
- Complete sterilization possible (including endospores)
- Typical Criteria: 15psi (no direct role in destruction of bacteria, 121 degrees C, 15 minutes
- Disadvantages: expensive, cannot be used on something that will be ruined when it comes into contact with water at high heat


Harvey Chemiclave

- When an alcohol/formaldehyde vapor is pressurized and heated
- Very quick turnaround time
- Used often with dental instruments
- Disadvantages: expensive, cannot be useed if articles will be damaged by chemicals, heat, or pressure


Non-Ionizing Radiation (UV light)

- In general, will alter the structure of DNA molecules by creating thymine dimers
- Many of these mutations can be repaired by the bacterial cell, but in high doses the DNA molecule is rendered non-functional (unable to repair all damage)
- Used as disinfection tool most often
- Often placed near air ducts in sterile areas like operating rooms
- Very good at reducing the number of living organisms (99%+)
- Very good against actively reproducing cells, but less so against endospores
- Disadvantages: readily passes through air, sightly through liquids, and much less so through solids; damaging to human tissues


Ionizing Radiation (X-rays and Gamma Rays)

- Very high energy wavelengths
- Action: breaks linkages between adjacent nucleic acids and in the process produces free radicals
- Used in food preparation and becoming ever more popular in the hospital community
- Can penetrate fabrics, plastics, liquids, and foods
- Very good potential, just not in wide used as of yet



- Contain pores that range from 0.02 micrometers to 8 micrometers; the larger sized pores will catch the bacteria as it travels through, and smaller will even catch viruses but not very small toxins or viruses
- Effective in removing microorganisms from liquids and gases that are heat sensitive, but does not destroy microbes; used extensively in food processing market to being placed in air handlers in sterile environments (operating rooms)


Modes of Action

- Cell Wall: disrupt synthesis of or digest, causing lysis
- Cell Membrane: cause leakage
- Protein and Nucleic Acid Synthesis: bind to ribosomes preventing protein synthesis; bind to DNA preventing transcription and translation; change base pair pattern of DNA
- Altering Protein Function: alter shape (denature)



The study of the cause, frequency and distribution of disease


Epidemiology Questions

- What pathogen is responsible for the disease?
- What is the source (reservoir) of the disease?
- Who in the population is at risk?
- How is the disease spread?
- How many people have the disease?
- Geographically, where is the disease located?


Communicable Disease

An infectious disease caused by a pathogen that can be transmitted from person to person


Rate of Disease

Describes the proportion (percentage) of a population who have the disease; e.g., if 100 people of 1000 were infected were sick, this population would be 100/1000 or 10%; looks at the entire population, not just those exposed


Attack Rate of Disease

Describes the proportion (percentage) of a population that develop the disease after they have been directly exposed to the pathogen; out of 1000 people, 100 drank contaminated water and 10 developed chronic diarrhea: 10/100 or 10%



Describes the rate of disease along with time of the month or year; describes your chance of developing a disease at a certain time of year or a certain season



The proportion (percentage) of people who have contracted the pathogen and died from the disease



A disease found in unusually high frequencies within a population


Pandemic (Pan = all)

An epidemic spread across the world



Disease is constantly present within a given population; flu, colds never leave our population


Chain of Infection

- Reservoir: pathogen is found in a source in which it is capable of living, growing, and spreading to other hosts (another person, other animals, the environment)
- Portal of Exit: if the pathogen is found in another human, then it must escape their reservoir through some orifice
- Mode of Transmission: a person must come in contact with the exposed material from the portal of exit
- Portal of Entry: how the organism enters the body


Portal of Exit/Entry

- Digestive System: anus or mouth (feces, vomit)
- Urinary System: urethra (urine)
- Respiratory System: mouth, nose (mucus)
- Reproductive System: vagina, urethra (vaginal fluid, semen)
- Breaks in the skin
- Eye


Droplet of Transmission

Inhalation of large vaporized respiratory droplets (sneeze, cough)


Incubation Period

The length of time between exposure to the pathogen and onset of disease symptoms



Hosts that are showing symptoms of a disease; easy to identify and therefore easy to isolate to slow the transmission of the pathogen through a population



Hosts that are not showing symptoms, but can potentially still transmit the pathogen to another host; difficult to identify hosts so easy for disease to spread through the population



The number of pathogens a person (host) is initially exposed to; large are more likely to cause disease and will shorten the incubation time while small are less likely to cause disease and will lengthen the incubation time


Herd Immunity

A disease has a difficult time spreading to susceptible hosts because only a few reservoirs exist


Population Characteristics That Can Increase Susceptibility to a Disease

- Malnutrition
- Crowding
- Fatigue
- Stress
- Age
- Gender
- Genetics: blood types AB, A, B, O (from most to least) resistant to many intestinal bacteria