MICRO EXAM 2 / CH 8.

Mechanical Barriers Membrane Filters

-Filtration = reduce microbial solutions in heat sensitive material (ampicillin). can sterilize liquids and gases (including air). acts as a barrier to retain contaminating microorganisms rather than destroying them. -Filter pore size of 0.2𝜇M can remove bacteria but not viruses -also used to sterilize pharmaceuticals, antibiotics oils, culture media, ophthalmic solutions. -membrane filters/depth filters. separates large molecules.

Cidal agents

-KILLS -Include bactericides, fungicides, and viricides

Pattern of microbial death

-Microorganisms are not killed instantly when exposed to a lethal agent. -Population death usually occurs exponentially.—population reduced by the same faction at constant intervals -Measure of agent's killing efficiency. -(D value) Decimal reduction time—time to kill 90%. (know how to calculate.) -Z value is change that causes 90% reduction.

Efficiency Evaluation of Chemical Agents

-Phenol coefficient test -potency of a disinfectant is compared to that of phenol -useful for screening but may be misleading -Use dilution test -determines rate at which elected bacteria are destroyed by various chemical agents -Normal in-use testing - testing done using conditions that approximate normal use of disinfectant

Physical Agent: Irradiation

-UV light -poor penetration -effective for only surface sterilization -tanning beds UV irradiate your skin -direct to melanoma -DNA repair systems are overwhelmed -PSA: Don't use tanning beds -the UV light causes thymine dimers to form thus resulting in a kink of the DNA

Mechanical Barriers Air Filtration

-air filtration / HEPA (High-efficiency particle absorption) -0.3uM filter (99.9% captured) -Biological safety cabinet (BSC)

Sterilization

-all living cells, spores, acellular entities (viruses) are either destroyed or removed from their habitat. -a sterile object is completely free of viable microorganisms, spores, and infectious agents. -when sterilization is achieved by a chemical agent this chemical is called a sterilant.

FDA bands 19 Chemicals used in antibacterial soaps

-ban use of antibacterial like TRICLOSAN -targets several cell constituents at high concentration -low concentration only inhibits FA synthesis

Antisepsis

-chemical agents applied to tissue to prevent infection by killing or inhibiting pathogen growth. -rubbing iodine on skin before shot to lower bacteria

Physical Agents: Cold (refrigeration)

-cold -not terribly effective -slows bacteria growth and prevents spoilage -Listeria Monocytogenes -growth at low temperatures -soft serve ice-cream -deli meats -raw milk -can pass through the placenta infect the baby in pregnant women and can cause an abortion

Physical Agent: Gamma Rays

-gamma rays, electron beams, and X-rays -deeper penetration than UV -to kill salmonella enteric-a on chicken -act on DNA covalent bonds

Physical Agents: Pasteurization

-heating to kill microbes -originally used in production of beers and wines -later used for milk -Is pasteurized milk sterile? No just reduced microbial load.

Physical Agents: Autoclave

-high temperature and pressure -one or other is effective, but both is best -autoclave combines both to sterilize -use of steam (eliminates spores) -moist heat better than dry heat -121 degree C at 15 psi -dormant endospores are used to test the autoclave and if they germinate after that means that the sterilization did not work.

Static agents

-inhibit growth -Include bacteriostatic and fungistatic.

D and Z value

-it is possible to determine the temperature change at a given D value that decreases the microbial population by one log cycle (90%). this temperature change refers to as Z value (predicted from semilogarithmic plot of D values vs. temp)

Disinfection

-killing, inhibition, or removal of pathogenic organisms -disinfecting agents are usually chemical, used to carryout disinfection and usually used on inanimate objects -lysol, bleach -disinfection does not necessarily sterilize an object because viable spores and a few microorganisms may remain

Chemical agents TPS how do they work?

-many options -alcohols = interrupt hydrogen bonding (OH) -iodine -chlorine -Phenol ex, non polar molecules interrupt membranes (C and H's)

Biological control of Microorganisms

-natural control mechanisms -predation = bdellrivibrio - bacteria that preys on other bacteria and germinated inside them (specific for bacteria cells) can use this Bactria to kill another bacteria) -viral mediated lysis = bacteriophage - bacteria can get into viruses -toxin mediated killing

Which three of the following infective agents would ionizing radiation be effective against?

-not always effective against viruses, thus: Clostridium spores Mycobacterium tuberculosis Vibrio cholerae

Properties of good chemical antiseptic/disinfectant

-storage = needs to be safe, easy storage -toxicity = less toxic to person applying more toxic to a microbe -odor = needs to be pleasant -surface tension = fit into cracks/crevasses

Sanitation

-the microbial population is reduced to levels that are considered safe by public health standards. -the inanimate object is usually cleaned as well as partially disinfected. -sanitizer on cleaning utensils in restaurants -showering, brushing teeth. -also used for control of microorganisms on or in living tissue.

Which three properties are important for a good, general purpose, chemical disinfectant?

Contains viricidal properties Non-toxic to humans or animals Effective against a range of microorganisms

Which three of the following cellular components are most sensitive to moist heat?

DNA Membranes Proteins

When pairing a depth filter and a membrane filter, which order is best?

Depth filter, then membrane filter

Which of the following agencies of the United States Government regulates the guidelines on the effectiveness of antiseptics?

FDA

Filtration is an effective means of sterilization for which two of the following?

Gases Chemical solutions

How is ionizing radiation different from ultraviolet radiation?

Ionizing radiation produces particles with more energy to penetrate objects.

What are two advantages to using dry heat for sterilization over autoclaving?

It does not corrode metal instruments. Powders can be sterilized by dry heat and remain desiccated.

How does pasteurization preserve beverages?

It kills pathogens and reduces the level of non-pathogens.

Which items are best sterilized by exposure to UV radiation?

Laboratory work surfaces

The mechanism of action of chlorine on microbial cells is _______.

Oxidation of cellular compenents

Autoclave ->

Plastic micropipette tips & Flask of bacterial medium

what items would be best sterilized by ionizing radiation?

Syringes for medical use Empty plastic Petri dishes

True or false: Treatment with moist heat affects nucleic acids, proteins, and cell membranes.

TRUE

Which two of the following comprise a membrane filter?

cellulose acetate polycarbonate

The mechanism of action of alcohols on bacterial cells is to

denature proteins dissolve membrane lipids

Biocides

describes all antimicrobials that can be used to control microorganisms

Chemical compounds like cresols, xylenols, and ortho-phenylphenol are collectively referred to as

disinfectants

When were bacteriophage first used to treat humans?

early 1900's

Which of the following agencies of the United States Government regulates the guidelines on the effectiveness of disinfectants?

environmental protection agency

Upon treatment with a biocidal agent, a microbial population decreases by the same fraction at constant intervals. What kind of decrease is this?

exponential

Ionizing radiation contains enough energy to dislodge electrons from matter and produce chemically reactive _____ _____

free radicals

Predatory bacteria like Bdellovibrio species prey on

gram negative

the most frequently employed physical agents are

heat and raidation

A common phenolic antimicrobial for consumer use is _____.

lysol

Dry heat ->

microscope slides wrapped in foil & empty pyrex flask

Upon treatment of a microbial population with a biocidal agent, after some time the rate of killing slows. This effect is due to:

surviving a resistant strain

Color change on autoclave tape indicates that _______.

the tape (and the contents of the autoclave) has been heated

The D value of a biocidal agent is measured in units of _______

time

Which two of the following may be considered types of biological control? virus infection bacterial predation exposure to radiation antiseptic treatment

virus infection bacterial predation

conditions influencing the effectiveness of Antimicrobial Agent Activity

1. Population size -larger populations vs smaller populations 2. Population composition -microorganisms differ markedly in their sensitivity to antimicrobial agents 3. Concentration of Intensity of an antimicrobial agent -usually higher concentrations kill more rapidly 4. Contact time -the longer the exposure, the more organisms killed 5. Temperature -higher temps enhance chemical activity 6. Local environment -pH, viscosity, concentration of organic matter, and so on. can profoundly impact effectiveness -organisms in biofilms are less susceptible to many microbial agents

standard conditions for sterilization in an autoclave

121°C and 15 pounds of pressure for 15 minutes

Standard autoclave conditions (121°C, 15 pounds of pressure, 15 minutes) will sterilize which two of the following?

250 ml empty Pyrex flasks 3 ml bacterial broth culture in a test tube

In what time frame does chlorine treatment result in disinfection?

30 min

How is cell death related to the time of exposure to an antimicrobial agent?

An equal fraction of the population is killed in each time interval.

Which two of the following may be best sterilized by membrane filtration?

Antibiotics Contact lens cleaner

Which two of the following food products are often sterilized by ionizing radiation?

Apples Cinnamon sticks

What wavelengths of light constitute ultraviolet radiation?

Around 260 nm

What information is obtained following a properly performed phenol coefficient test?

The relative potency of a new disinfectant compared to phenol.

chlorine removes...

bacteria and fungi