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control of microbes

lecture 9-10

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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