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control of microbes
lecture 9-10
| Question | Answer |
|---|---|
| aims of using antimicrobial agents | reduce microbial numbers to sanitary/acceptable levelsslow down or inhibit microbial growth and replicationkeill/eliminate microorganisms |
| Influencing the choice of an agent and the effectiveness of its use | numbers of organismstype of organismconcentration of the agentspresence of organic materiallocation of microorganism/infectionenvironment: pH, temp, humidity |
| Heat (physical control) | inexpensive, quick, simplewet: heating or steamdry: incineration, hot air |
| disinfection using heat | denatures and coagulates proteins, breaks hydrogen bonds-->enzymes inactivated--> organisms killedBoiling at 100C for 10 minutes kills vegetative bacterial pathogens, fungi, and virusesmakes food and water safe |
| sterilization using heat | steam under pressure in an autoclave2 atm for 15 minwill kill all organisms with endosporesused iin culturemedia, solutions, dressings, and instruments |
| UV radiation | causes covalent linkages between DNA basesused in liquid, air, and surface disinfection |
| Ionizing radiation | causes release of electronsused for disinfection and sterilization of devices, cosmetics, and water |
| ethylene oxide gas | alkylating agentused for heat sensitive materials like plastic, and complex devices and equipment |
| filtration | physical removal of microorganismsused on heat sensitive liquids, gases |
| Freezing | prevention ofgrowth plus ice crystal formation-->lysisused in food preservation, long term culture storage |
| Refrigeration | reduces or prevents growthused in preservation of lab media, foods, etc |
| Reactions that affect proteins (chemical agents) | denaturation=alteration of protein structurehydrogen and disulfide bonds changed--> function destroyedpermanent or temporaryhydrolysis or oxidation or alkylating agents |
| Reactions that affect membranes (chemical agents) | can be effected by all that affect proteinsalso sufactants and alcohols |
| reactions that affect other cell components (chemical control) | alkylation: disrupts NA and systems used for energy production |
| disinfectants | high levels: viruses, fungi, mycobacteria, and bacterial spores inactivated (gluteraldehyde, peracetic acid)intermediate: viruses, fungi, and mycobacteria inactivated (alcohols, iodophores)Low: nonsporulating bacteria and lipid enveloped viruses (QAC) |
| antiseptics | used in solutions, soaps, handscrubs, sprays or gels. Wide range of activity, rapid, low level of damage, some form of persistenceApplication: skin hygiene, reduction of microorganisms before breaching, treatment of skin or wound infections |
| antifungal (therapeutic antimicrobials) | target a structure or a physiological functionmay be difficult to treat infections because fungi are slow growing and fungal and host cells are both eukaryotic |
| Antifungal categories | polyenes, nucleic acid synthesis inhibitors, ergosterol biosynthesis inhibitors, and echinocandins |
| polyenes | (amphotericin B)bind directly to sterols in cytoplasmic membrane and form a channel/pore-->membrane becomes permeable, cytoplasmic contents leak out |
| nucleic acid synthesis inhibitors | flucytosine (5-fluorocytosine): artificial pyrimidineintracellular deamination be fungal cytosine deaminase activated compound by changing it to 5-fluorouracilinhibits synthesis of DNA,RNA, and proteins |
| ergosterol biosynthesis inhibitors | 1. Azoles:imidazoles,triazolesinhibit cytochrome enzyme converting lanosterol to ergosterolbuild up of ergosterol precursors changes structural & functional characteristics of membrane2. allyamines: inhibit enzyme converting squaline to lanosterol |
| echinocandins | (caspofungin)target fungal cell wallblocks (1,3) B-D-glucan synthetase |
| antifungal resistance | due to:mutations in enzymesdecreased rate of transport into fungal cellalteration of target enzymealteration of ergosterol biosynthetic pathwaygrowth as biofilm |
| antibiotics | target a structure or physiological functionnatural or syntheticsources: actinomyces,filamentous fungi, streptomyces |
| reasons for antibiotic combination | minimize emergence of resistant strainsincrease spectrum of bacteria that will be targetedbetter effect (synergy) |
| sulfonamides | inhibit bacterial NA synthesis, antimetabolitesblock folic acid synthesisstructural analogs of PABA |
| Antibiotic target sites/mechanism of action | inhibit protein synthesisinhibit NA synthesisinhibit metabolisminhibit cell membrane functioninhibit cell wall formation |
| inhibitors of protein synthesis | aminoglycosides: target 30S, induce codon misreadingStreptogramins: target 50S, inhibit peptide bond formationTetracycline: target 30S, block binding of aminoacylated tRNA to A sitemacrolides: target 50S, inhibit transpeptidation, translocation |
| cell wall inhibiting antibiotics | glycopeptides, beta lactams, bacitracin, ethambutol, isoniazid |
| Beta lactam anitbiotics | cell wall inhibitors (penicillin, cephalosporin, monobactam, and carbapenem)active only on growing cells (interfere with cross linking)have b-lactam ring as part of structureinhibit transpeptidation (involved in cross linking) |
| mechanism of beta lactam | enters cell-->binds to PBP-->blocks transpeptidation-->cell wall not properly cross linked-->cytoplasmic contents continue to be produced-->bacterial cell eventually bursts (CIDAL effect) |
| limitations on antibiotics | 1.aminoglycosides:not on anaerobes(need oxidative phosphorylation for uptake)2.glycopeptides:not on gram-(large size)3.Nitroimidazoles:not on aerobes(need flavodoxin)4.Penicillin:not on mycoplasma(no cell wall)5.Cephalosporin:not on mycobacterium |
| mechanism of resistance | decreased permeabilityalteration of targetenzymatic inactivation |
| location of resistance genes | chromosomaltransmissible plasmidstransposable elements |
| specific resistance examples | Tetracycline: active drug efflux pump (prevents sufficient accumulation)Chloramphenicol: acetyltransferases (modifying enzymes)Rifamycins: single chromosomal mutation--> altered RNA polymerase |
| beta lactams (resistance) | production of beta lactamases (inactivating enzymes: penicillinases, etc)hydrolytic enzymes cleave ring, inactivate antibioticTEM 1&2 beta lactamases most common |
| beta lactamase inhibitors | (clavulanic acid, sulbactam)inactivate beta lactamases---> can no longer degrade antibiotic--> antibiotic will work again act synergenistically |
| how to prevent antibiotic resistance | wash hands between patientsdo not give into demands for unneeded antibioticsprescribe antibiotics that target a narrow range of bacterisisolate hospital patients with mutli drug resistant infectionsfamiliarize yourself with local data |
| Kirky-Bauerdisk diffusion method | as the distance from the disk increases, the concentration of antibiotic in agar decreasesa large zone of inhibition means a low concentration of antibiotic is able to prevent growth---> microorganism susceptible |
| breakpoint testing | enables mutliple sample testingdefined concentration of agar added directly into agarclinical isolate inoculated on surface of plateincubation....can tell if isolate it sensitive (no growth) or resistant (growth) |
| broth dilution method | dilutions of anitbioticmade in liquid growth mediumMIC: lowest antibiotic concentration at which there is no visible growthMBC: antibiotic concentration at which no growth occurs on agar plate (use samples from MIC) |
| E test strips | polymer strip with gradient of antibiotic concentrationsplace onto place inoculated with clinical isolateMIC=where zone of inhibition meets the strip |
| factors influencing outcome following antibiotic treatment | type and site of infectioncondition of patientpharmacological properties of drug |
| recombination | breaking and rejoining DNA in new combinationsNewly incorporated DNA must be stablehomologous and non-homologous |
| Conjugation | transfer via plasmidsin gram- bacteriarequires production of a pilus (encoded for by F factor...encodes for transfer genes and genes for pilus production) |
| outcomes from conjugation | complete transfer (recipient becomes F+ cell)incomplete transfer (recipient remains F-)complete transfer and integration into chromosome (recipient is Hfr cell)integrated F plasmid initiates transfer from Hfr to new F- cell |
| transformation | aquisition of exogenous DNA from broken/dead bacterial cellsUptake of DNA by DNA binding proteins on cell wall |
| transduction | bacteriophage mediated transferPhage types:1. virulent: after phage replication death of infected bacterium (lysis=phage released)2. temperate: switch between virulent phase and state where phage DNA is stable integrated (prophage) |
| generalized transduction | phage attaches to bacteriainjects DNAbacterial chrom breaks up&phage DNA producedproduction of phage heads and tailscell lyses&new phage releaseddefective phage:bacterial DNA instead of phagephage attaches and injects DNADNA incorporated |
| specialized transduction | phage attaches to bacteriainjects DNAphage integrates into chrom.switch to lytic modedefective phage hybrid (part bacterial, part phage DNA)phage attached and injects DNADNA incorporated |
| transposition | transposons=jumping genesnon-homologous recombinationcan then be transferred to other bacteria |
Created by:
kamarsh
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