Which of the following statements is true of disinfectants ? On which types of surfaces are they used?
Give an example of a microbial growth control method that is not bacteriostatic?
autoclaving..... it's not bacteriostatic because it sterilizes the equipment ... thereby destroying all microbes on an object.
Seventy percent alcohol is effective against
enveloped viruses. Some viruses have an outer envelope which is needed to invade a host cell. and damage to that envelope interrupts viral replication. Since water is necessary for protein denaturization, 100% alcohol is not as effective as 70%.
The dairy creamer used in restraurants is usually sterilized by
UHT (ultra high temprature) sterilization. UHT uses high heat (140C for 1-3 sec.) to kill all microbes in dairy products.
Which of the following is NOT a feature associated with filtration.
Varying thicknesses of membrane filters used has nothing to do with filtration. Fluid is passed through a sieve which traps particles (cells or viruses) which are larger than the pore size of the filter. Membrane filters are made of nitrocellulose of plastic and have specific pore sizes. Filtration can also be used to estimate the number of bacteria in a fluid.
Which type of radiation is non ionizing and has the shortest wavelength?
Ultraviolet light. UV light does not have enough energy to detach electrons (Ionize) from atoms or molecules. Other examples are radio waves, and micro waves.
What is used for microbial control in fresh fruits and vegetables?
Gamma rays. Penetrate much farther than electron beams but require hours to kill microbes. FDA has approved Gamma for microbial control in meats, spices and fresh fruits and veg. G.I. kills larvae and insect eggs as well as the cells of fruits and veg. which prevents both microbial spoilage and overripening.
explain electron beams
E. beams are produced by cathode ray machines and can kill micorbes in just seconds because they are highly energetic. They cannot sterilize thick objects or objects coated with large amounts of organic matter, so they are mostly used to sterilize spices, meats microbio plasic ware, dental and med. supplies such as gloves, syringes and suturing materials.
Explain x rays
X-rays travel farthest through the matter, but have less energy than gamma and require a prohibitive ammount of time to use for micro. control.
Lysol is an example of which group of chemical antimicrobial agents?
Phenolics: intermediate to low level disenfectant compounds derived from phenol molecules that denature proteins and disrupt cell membranes. They are often modified by the addition of a halogen or an organic functional group. They sometimes have a dissagreeable odor, can irritate skin and even cause brain cancer in infants. Other examples of phenolics include pine and clove oils as well as triclosan.
Which of the following is an appropriate pairing of microbe and biosafety levels ?
methicillin resistant staphylococcus aureus (MSRA) and BSL-2. BSL-2 is for handling moderately hazardous agents like msra, hepatitis and influenza. Access is limited when work is being performed and extreme precautions are taken with contaminated sharp objects. Procedures which might produce aerosols are conducted within safety cabinets.
Intermediate level agents which include betadine, iodine, chlorine, bromine and fluorine. Effective against vegetative bacterial and fungal cells and well as fungal spores, bacterial endospores, protozoal cysts and many viruses.
For handling microbes not known to cause disease in healthy humans such as ecoli. Hand washing and disinfecting surfaces is considered a suitable level of precaution.
All work is done in a biosafety cabinet. Entry is through double doors, all air leaving the lab is hepafiltered. Designed for experimentation on microbes such as TB, anthrax bacteria and viruses of yellow fever and rocky mountain spotted fever.
Most secure lab for highly pathogenic micro which cause severe or fatal disease in humans. (ebola, smallpox, lassa fever). Highly controlled access with electronic airlocks, shower in shower out, space suits.
Common use for bromine (halogen)
used to treat water in pools, hot tubs etc.... similar uses to chlorine.
Which of the following is a sterilizing agent?
peracetic acid: a sporicide used to sterilize surfaces and food processing equipment which leaves no toxic residue.
What heavy metal was once used to prevent the transmission of gonorrhea from an infected mother to her newborn?
List examples of some heavy metal ions used for microbial control
arsenic, zinc, mercury, silver, and copper.
How do heavy metals work in controlling microbial growth?
H.M. are antimicrobial because they combine with sulfur atoms in molecules of cysteine (amino acid)which denature the proteins.
How are H.M. used in a modern setting?
No longer used in vaccines, with the exeption of whole-cell pertussis and some vaccines against tetanus, flu and meningococcal meningitis.
What would be used to sterilize items that should not, or cannot be exposed to heat or water?
ethylene oxide, because it is a microbicidal and sporicidal gaseous agent. It denatures proteins and DNA by cross linking organic functional groups. It's also extremely hazardous and poisonous and usually used in combination with nitrogen gas or carbon dioxide.
Which microbe endospores are used to measure the effectivness of autoclave sterilization?
bacillus stearothemophilus: they are impregnated into a tape and then placed into a sterile growth medium. If the spores don't grow into vegetative cells, the materials that have been autoclaved are considered sterile.
What method would be the most effective and safest means of preparing a sterile solution of a protein compound?
filtration, because alcohol or heat can denature a protein. Why not lyphilization? UV?
In practical terms, what statement provides the definition of sterilization?
Sterilization eliminates harmful microorganisms and their spores for endospores.
The preservation of beef jerky from microbial growth relies on which method of microbial control?
A sample of ecoli has been subjected to heat for a specified time and 90% of the cells have been destroyed. Which term best describes this event?>
decimal reduction time
What is the major structural component of a bacterial cell wall?
Its peptidoglycan layer. (Peptidoglycan is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria (but not Archaea), forming the cell wall.
An antimicrobial that inhibits cell wall synthesis will result in what?
Cells become more susceptible to osmotic pressure because the cell walls have become weakened.
What types of drugs will inhibit cell wall synthesis ?
beta lactams, vancomycin, cyloserine, bacitracin,isoniazid (NH1) and ethambutol.
Which type of cells do beta lactams work against?
Beta lactams work against BACTERIAL cells by inhibiting peptidoglycan formation and therefore cell wall synthesis by irreversibly binding to the enzymes that cross link NAM subunits.
Which drug specifically targets cell walls that contain arabinogalactan mycolic acid?
Ethambutol. Leprosy and TB have unique complex cell walls that contain a layer of arabinogalactan mycolic acid in addition to the usual peptidoglycan layer found in prokaryotic cells. ethambutol and isoniazid disrupt formation of this extra layer.
what type of drugs inhibit the synthesis of fungal cell walls?
echinocandins. They inhibit the synthesis of the enzyme glucan, without which fungal cells cannot make cell walls.
Which of the following is not a target of drugs that inhibit protein synthesis?
Interference with alanine-alnine bridges, because these a-a bridges occur in cell walls
list two examples of aminoglycosides and explain how they work.
streptomycin and gentamicin change the shape of the 30S subunit, making it impossible for the ribosome to read the codons of mRNA correctly.
How do tetracyclines work?
by blocking the tRNA docking site, which prevents the incorporation of additional amino acids into a groing polypeptide.
explain antisense nucleic acids
Antimicrobials that block protein synthesis by binding to the mRNA are
Which of the following statements is true of selective toxicity?
Selective toxicity takes advantage of structural and or metabolic differences between host and pathogen.
Which drugs interfere with cell wall synthesis by blocking alanine bridge formation?
Cycloserine and vancomycin
What types of compounds act as antimicrobials by interfering with the function of nucleic acids?
How are nucleotide analogs most often used and why are they used that way?
Nucleotide analogs act as antimicrobials by interfering with the function of nucleic acids.
...Minimum inhibitory concentration is the smallest amount of a drug that will inhibit growth and reproduction of a pathogen.
Explain an MIC test
...There are two types. Broth dilution and diffusion susceptibility. See below....
Explain an MBC test
...An MBC test determines the amount of drug required to kill the microbe, rather than just the amount to inhibit it as the MIC does. Samples are taken from either clear MIC tubes or from zones of inhibition from a series of DS tests, and transfered to plates containing a drug free growth medium. The drug concentrations which show growth after incubation are bacteriostatic, and the concentrations which do not show growth are bacteriocidal.
Explain a broth dilution test
...In broth dilution, bacteria is added to wells containing broth. Turbidity indicates bacterial growth, and lack of turbidity indicates inhibition or microbial death.
Which is a measurement of a broth dilution test?
Lack of Turbidity (cloudiness). Turbidity indicates bacterial growth, but a lack thereof indicates that the bacteria were either inhibited or killed by the antimicrobial agent.
define probiotics and explain their use
...Probiotics are live microorganisms thought to be beneficial to the host organism. Found in yogurt, etc.
what is an alternitive to the use of chemotherapy involving microbial antagonism. Explain.
B-lactamase production is an example of which of the following types of resistance?
Inactivation of the drug
were the first widely used antimetabolic antimicrobial and iderectly inhibit nucleic acid synthesis.
What drugs were the first widely used antimetabolic antimicrobial and inderectly inhibit nucleic acid synthesis
how do sulfonamides work?
They inhibit the conversion of PABA to dihydrofolic acid by competing with PABA molecules for the active site of the enzyme involved in the production of DHF, ergo also RNA and DNA.
Paba is crucial in the synthesis of DNA and RNA because many organisms convert PABA into dihydrofolic acid and then dhf acid into tetrahydrofolic acid, which is a coenzyme in the synthesis of purine and pyrimidine nucleotides.
Did Paul Erlich coin the term antibiotics for the "magic bullet" antimicrobials he pursued?
No, "magic bullet" is the term he coined for chemo therapy
Do beta lactam drugs act by inhibiting formation of the cytoplasmic membrane?
No, they work against BACTERIAL cells by inhibiting peptidoglycan formation and therefore cell wall synthesis by irreversibly binding to the enzymes that cross link NAM subunits.
If a subculture of an MIC test grows in an MBC test, does it mean that the concentration of the drug was bacteriacidal?
No. An MBC test determines the amount of drug required to kill the microbe, rather than just the amount to inhibit it as the MIC does. If the concentration were bacteriacidal, the drug would kill the microbes and the subculture would not grow.
Explain broth dilution tests
In broth dilution, bacteria is added to wells containing broth. Turbidity indicates bacterial growth, and lack of turbidity indicates inhibition or microbial death.
Explain diffusion susceptibility testing
Same as the Etest. Plastic strips containing the antimicrobial agent are inoculated with the microbe of interest. Antimicrobial activity is indicated by a zone of inhibition. The M.I.C. can be noted where the zone of inhibition intersects a scale printed on the strip.
Do humans synthesize THF from PABA?
No, instead we convert folic acids into THF. As a result, our metabolism is not affected by sulfonamides.
The enzyme reverse transcriptase converts the information in a(n) __________ molecule into the form of a(n) __________ molecule.
In which of the following types of solutions would a cell be at risk of bursting? Why?
hypotonic. Hypotonic solutions cause cells to absorb extra water; extremely hypotonic solutions could cause cells to burst under the resulting osmotic pressure.
Mycobacteria have unique properties due, in part, to the presence of __________ in their cell walls.
RNA polymerase is most important for the success of what processes?
transcription. RNA polymerase is responsible for the production of mRNA from a DNA template in the process of transcription.
A drug that inhibits the growth of protozoan cells would NOT be expected to affect which of the following cell structures?
The cell wall. Protozoa have a cytoplasmic membrane, ribosomes, and mitochondria, all of which would be viable targets for growth-inhibiting drugs. However, protozoa cells have no cell wall and would therefore be resistant to drugs attacking that structure.
The enzyme reverse transcriptase converts the information in a(n) __________ molecule into the form of a(n) __________ molecule.
RNA, cDNA Reverse transcriptase, produced by viruses such as HIV, converts the information in the RNA genome of the virus into a complementary DNA (cDNA) form.
Which of the following types of RNA molecules contains the information necessary for making a protein?
mRNA. During the process of translation, the ribosome uses the information in mRNA molecules to generate the amino acid sequence of a protein.
Which of the following cellular structures or molecules is the most SIMILAR in both bacteria and humans?
Tetracyclines inhibit which of the following?
Tetracyclines bind to the small subunit of the ribosome, thus interfering with protein synthesis.
Why are some drugs that inhibit protein synthesis in bacteria also harmful to humans?
Eukaryotic mitochondria have 70S ribosomes. The mitochondria of human cells have 70S ribosomes, which can be affected by some drugs that inhibit protein synthesis in bacteria.
What was the first practical antimicrobial agent to be widely used?
sulfanilamide. Sulfanilamide was the first practical antimicrobial agent: it was relatively nontoxic, broad-spectrum, and could be made in large quantities, unlike most other antimicrobials of the time.
Which of the following does NOT block the formation of folic acid in bacteria?
metronidazole. Sulfanilamide, dapsone, and trimethoprim all inhibit formation of folic acid in bacteria, albeit by different mechanisms. Metronidazole is a drug that kills cells by directly damaging their DNA.
Quinolones target which of the following molecules?
DNA gyrase. DNA gyrase is an enzyme essential for the successful replication of DNA in bacterial cells, and is specifically targeted by drugs such as quinolones and fluoroquinolones.
Why are viruses more susceptible to nucleotide analogs than their host cells?
Viruses replicate their nucleic acid more rapidly than host cells do. Nucleotide analogs are useful drugs because they are preferentially incorporated by viral polymerases into viral nucleic acids. Since viruses replicate their nucleic acid more rapidly than cells do, they accumulate analogs more rapidly in their DNA and RNA, eventually causing their genetic processes to stop.
All of the following drugs result in the disruption of fungal cytoplasmic membranes EXCEPT:
polymyxin. Fluconazole and turbinafine inhibit the synthesis of ergosterol in fungal cells, whereas amphotericin B binds to ergosterol, thereby disrupting the cytoplasmic membrane. Polymyxin targets bacterial cytoplasmic membranes, which usually do not contain sterols.
β-lactamases protect which of the following from damage by antimicrobial drugs?
the cell wall. By breaking β-lactam rings, β-lactamases protect the bacterial cell wall from damage by drugs such as penicillin.
Which of the following drugs does NOT inhibit protein synthesis by interacting directly with ribosomal subunits?
fomiversen. Chloramphenicol, erythromycin, and streptomycin all interfere with protein synthesis by interacting with some portion of the bacterial ribosome. Fomiversen blocks protein synthesis by binding to mRNA molecules instead.