Microbiology Chapter 13

Compare autoclave sterilization with pasteurization

-Autoclave (steam sterilization): Combines pressure (15 psi) and heat (121 C) for 20 min which will kill all spores. -Pasteurization; heating food (milk) to a moderately high temperature long enough to kill Coxiella burnetii, the causative agent of Q fever and the most heat-resistant, non-spore forming pathogen known. its aim is to kill pathogens without affecting the texture, color, or taste of the product.

Differentiate bacteriostatic agents from bactericidal agents

-Bacteriostatic (algistatic, fungistatic, or virustatic): Antimicrobial chemicals that inhibit or control growth of microbes (Ex: chloramphenicol) -Bactericidal: Antimicrobial chemicals that kill microbes (EX: gentamicin)

Classify antibiotics by the molecular targets

-Cell wall synthesis: Penicillins, cephalosporins, bacitracin vancomycin -Mycolic acid synthesis: Isoniazid -Protein synthesis: Chloramphenicol, tetracyclines, aminoglycosides, macrolides, lincosamides -Cell membrane: polymyxin, amphotericin, imidazoles (antifungals) -Nucleic acid function: Nitroimidazoles, nitrofurans, quinolones, rifampin, some antiviral compounds, especially antimetabolites -Intermediary metabolism: sulfonamides, trimethoprim

Describe the four basic mechanisms of antibiotic resistance

-Modify the target so that it no longer binds the antibiotic -Destroy the antibiotic before it gets into the cell -Add modifying groups that inactivate the antibiotic -Pump the antibiotic out of the cell using specific transport proteins (for example, tetracycline export) or non-specific transport proteins

Explain how disinfectants are compared

-Phenol coefficient test: involves inoculating a fixed number of bacteria into dilutions of the test agent. At times intervals, samples are withdrawn from each dilution and inoculated into fresh broth. The phenol coefficient is based on the highest dilution (lowest concentration) of a disinfectant that will kill all the bacteria in a test after 10 min of exposure, but leaves survivors after only 5 min of exposure. -Use-dilution test: Useful in determining the ability of disinfectants to kill microorganisms dried onto a typical clinical surface. The organism is exposed to different dilutions of a disinfectant for a fixed set of time. The entre surface in then placed in broth containing chemicals that neutralize the disinfectant. Successful disinfection results in no bacterial growth in the broth

Describe the major targets of anti fungal agents

-Polyenes: disrupt membrane integrity -Azoles: interfere with the synthesis of ergosterol, a cholesterol specific to fungi -Allylamines: Inhibit ergosterol synthesis -Echinocandins: block fungal cell wall synthesis -Griseofulvin: Blocks cell division -Flucytosine: inhibits DNA synthesis

Discuss selective toxicity for antiviral drugs

-Prevent virus uncoating or release: Inhibit M2 protein on influenza so it can't bind to the membrane receptors, neuraminidase inhibitors prevent the release of virus particles -Antiviral DNA and RNA synthesis inhibitors: Drugs resemble normal DNA but add a phosphate group that stops DNA synthesis once inserted, -Nucleoside and non nucleoside reverse transcriptase inhibitors: zidovidine is a nucleoside analog recognized by reverse transcriptase that is incorporated into a replicating HIV DNA molecules and prevents further DNA synthesis, delavirdine binds directly to reverse transcriptase and inactivates the enzyme -Protease Inhibitors: Drugs such as nelinavir and lopinavir block HIV protease, which leaves the polyprotein uncleaved and the virus cannot mature to infect other cells -Entry inhibitors: CCR5 inhibitors block virus envelope protein gp120 from binding to the host surface protein CCR5, that is needed together with CD4 for the virus to bind to certain T cells. Fusion inhibitors do not prevent initial binding, but prevent HIV membranes from fusing with T-cell membranes and thereby halt viral entry

Explain the different between refrigeration and lyophilization

-Refrigeration (4-8C or 39-43F): Is used for food preservation because most pathogens are mesophilic (grow best between 20C (68F) and 40C (104F) and grow poorly, if at all, at cold temperatures. Listeria monocytogenes is an exception and grows well in cold. -Lyophilization: Freeze-dries microbial cultures for long-term storage. Cultures are quickly frozen at very low temperatures (limits ice crystal formation) and placed under vacuum, which causes frozen water to transition directly from solid to gas form (sublimation). The process removes all water from the medium and cells, leaving just the cells in the form of powder, viable for years.

Distinguish transcription inhibitors from translation inhibitors

-Rifampin selectively binds to bacterial RNA polymerase and prevents transcription. -50S subunit: oxazolidinones (linezolid) prevent 70S subunit formation, Macrolides (erythromycin, azithromycin) prevent peptidyltransferase activity and translocation -30S subunit: Aminoglycosides (streptomycin, gentamicin) inhibits translocation and causes misreading of mRNA. Tetracyclines (doxycycline, minocycline) prevent aminoacyl-tRNA entry into the A site

Distinguish between sterilization, disinfection, antisepsis, and sanitation

-Sterilization: Is the process by which all living cells, spores, and viruses are destroyed on an object -Disinfection: is the killing, or removal, of disease-producing organisms from inanimate surfaces; it does not necessarily result in sterilization. Pathogens are killed, but other microbes may survive -Antisepsis: is similar to disinfection, but it applies to removing pathogens from the surface of living tissues, such as the skin. Antiseptic chemicals are usually not as toxic as disinfectants, which frequently damage living tissues -Sanitation: closely related to disinfection, consists of reducing the microbial population to safe levels and usually involves cleaning an object as well as disinfection

List factors that can affect the efficacy of a disinfectant

-The presence of organic matter -The kinds of organisms present -Corrosiveness -Stability, odor, and surface tension

Explain how drug resistance develops

Antibiotic resistance can arise spontaneously through mutation or through gene duplication followed by random mutations that "repurpose"the duplicated gene or genes.

Discuss the emergence of microbial resistance to disinfectants

Disinfectants that have multiple targets at high concentrations may have only a single target at lower concentrations, which can develop resistance. Low-level resistance to disinfectants can be achieved through membrane-spanning, multidrug efflux pumps that pump several different biocides, detergents, and organic solvents out of the cell

Outline strategies to counteract drug resistance

Dummy target compounds that inactivate resistance enzymes have been developed. Also limiting infections will limit the use of antibiotics and resistance.

Discuss how the effectiveness of an antibiotic is tested, and differentiate minimal inhibitory concentration (MIC) from minimal bacteriostatic concentration (MBC)

Effectiveness is determined by measuring how little of it is needed to stop growth. This is measured in terms of an antibiotics minimal inhibitory concentration (MIC): the lowest concentration of the drug that will prevent the growth of an organism. Minimum bactericidal concentration (MBC) is determined by a tube dilution test and them the antibiotic is removed. Antibiotic can be removed by pelleting cells in the no growth tubes by centrifugation and replacing the antibiotic-containing medium with fresh medium. If cells grow, they were not killed. The lowest concentration tube that still does not show growth represents the MBC.

list the basic forms of commercial disinfectants

Ethanol, iodine, chlorine, and surfactants

Explain the spectrum of activity for antiviral drugs

Linked to the molecular target: for instance, RNA virus inhibitors, DNA virus inhibitors, or retrovirus inhibitors

Explain what is meant by spectrum of activity, and discuss its clinical importance

Narrow spectrum of activity means it only affects a few species, whereas another antibiotic may inhibit many species.

Describe the process of cell wall synthesis, and indicate the targets for various cell wall antibiotics

Peptidoglycan isn't found in mammalian cells, therefore antibiotics that target peptidoglycan synthesis should selectively kill bacteria.

List the basic targets of antiviral agents

Prevent virus uncoating or release, inhibit DNA and RNA synthesis, inhibit nucleoside and non nucleoside reverse transcriptase, and entry inhibitors

Explain the concept of selective toxicity and its importance for clinically useful antibiotics

Selective toxicity is when antimicrobials selectively kills or inhibits the pathogen but not the host, which is possible because key aspects of a microbe's physiology are different from those of eukaryotes

Describe the uses of filtration and laminar flow biological safety cabinets

Since many drugs are sensitive to heat or chemical sterilization, they use filtration through filters with pore sizes of 0.2 um to remove microbial cells and size 20nm to remove viruses. Laminar flow biological safety cabinets are ventilated workbenches in which air is forced through high-efficiency particulate air (HEPA) filters to remove more than 99.9% of airborne particulate material 0.3um in size or larger.

Discuss decimal reduction time and its use in sterilizing material

The length of time it takes an agent (or condition) to kill 90% of the population, leaving 10% of the original population alive. if 90% of the cells die in 1 min the D-value is 1 min, however in the next minute only 90% of the remaining 10% will die.

Describe the chemotherapeutic index

The ratio of toxic dose to therapeutic dose (higher the chemotherapeutic index the safer the drug). Therapeutic dose: minimum dose per kilogram of body weight that stops pathogen growth. Toxic dose: the maximum dose tolerated by the patient.

List conditions in which irradiation can be used to sterilize

irradiation is when food is bombarded with high-energy electromagnetic radiation. Food consumed b NASA astronauts use irradiation to safeguard against food-borne illness in space