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MICR 2420 > Physical, chemical and biological control of microbes > Flashcards

Physical, chemical and biological control of microbes Flashcards

1
Q

define: sterilization, disinfection, antisepsis, sanitation

A

sterilization = killing of all living organisms

  • ex pressurized steam (autoclave), chemicals, radiation

disinfection = killing or removal of pathogens from inanimate obejcts

  • chlorine black, phenos (lysol), gluteraldehyde
  • cleaning lab benches

antisepsis = killing or removal of pathogens from the surface of living tissues

  • boric acid, isopropyl alcohol, hydrogen peroxide
  • cleaning skin before surgery

sanitation = reducing the microbial population to safe levels

  • ex: detergents containing phosphates, industrial strength cleaners
  • commerical dishwashing, cleaning public restrooms
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2
Q

what is the D value?

A

decimal reduction time

  • length of time is takes an agent or ocndition to kill 90% of the ppulation
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3
Q

exmaples of physical methods of control

A

Heat

  • boiling, dry heat oven, incineration, autoclave, pasteuization
  • menatures proteins and alters membranes

Cold

  • refrigeration and freezing
  • inhibits or stops metabolism - freezing amy kill microbes

Pressure

  • high pressure processing (denatures proteins and can cause cell lysis) and hyperbaric oxygen therapy (inhibits emtabolism and growth of anaerobes)

Desiccation

  • Simple desciccation, reduce water activity and lyophilization
  • inhibits metabolism

Radiation

  • ioinizaing radiation ( alters molecular structures) and nonionizing radiation (leads to mutations)
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4
Q

describe heat to kill microbes

A
  • moist heat more effective
  • boiling water kills most calls

killing spores and thermophiles may requries combo of high pressure and temp

  • at high pressure the bp of water rises to a temp rarely experienced by microbes - even endospires die under these conditions
    ex: steam atoclave ; 121 C and 15 psi for 20 min
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5
Q

describe pasteuization

A
  • can use diff time and temp combonations
  • LTLT (lot temp long time) 63 C for 30 min

HTST: 72C for 12 seconds

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6
Q

describe filtration

A
  • micropre filters with pore sized of 0.2um can remove microbial cells but not viruses from solutions
  • samples from 1 mL - several litres can be drawn through
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7
Q

describe irradiation

A
  • UV light: poor penetrating power only used for surface sterilization
  • Gamme rays, electron beams and X rays: have high penetrating power and used to irradiate foods and other heat sensitive items
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8
Q

what is deinococcus radiodurans

A
  • highly resistant to physical measures of control
  • able to survive radiation bc has exceptional capabilities for repairing DNA damage by radiation

*was genetically engineered for use in bioremediation (clear nuclear waste contiminated sites)

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9
Q

what factors influence the efficiacy of a chemical agent?

A
  • presence of organic matter
  • type of organism present
  • mode of growth ie biofilms

corrosiveness

-stability, odor and surface tension

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10
Q

how has bacteria developed to be resistant to disinfectants?

A
  • altering fatty acid synthesis proein which is normally targeted by triclosan

*if have big lipid bilayer durrounding microbe - the disinfectant which wants to dehydrate well will have trouble

  • producing membrane spanning multidrug efflux pumps (if can shut off pumps/transporters that are importing the chemical)
  • forming multspecies biofilms which offer collaborative protection
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11
Q

what are antibiotics

A

compounds produced by one microbe that adversely affets other microbes

*term antibiotics also used for chemotherapeutic agetns that are clincally useful but chemically synthesized

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12
Q

describe the antibiotic revolution

A
  • began 1928 by discoery of penecillin by alexander flemming
  • contaminating mold had inhibited growth of Staphlococcus aurenus colonies - mold identified as Penicillium notatum
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13
Q

describe how antibiotics must exhibit selective toxicity

A
  • antibiotic must affect the target organism - but NOT affect huamns
  • may have side effects at high concentrations
    ex: cloramphenicol interferes with ribosomes and at high levels interferes with erythrocyte development
  • also amny cause allergic response

*drug should affect microbe physiology that does not exist or is greatly modified in humans

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14
Q

bactericidal vs bacteriostatic

A

bactericidal antibiotics: kill target organisms

Bacteriostatic antibiotics: prevent growth of organisms - cannot kill, the immune system will remove the intruding microbe

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15
Q

what is the issue with braod spectrum antibacterial agents-

A
  • kill wide array of non resistance cells but the drug resistant pathogens will then proliferate bc less competition for resources and can cause a super infection

*will also infect your gut microbiota

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16
Q

what are typical targets of antibiotics

A
  • cell wall synthesis, cell membrane integrity, DNA synthesis, RNA synthesis, prtoein synthesis and metabolism
17
Q

what antibiotic targets the cell wall? how?

A
  • prevent peptidoglycan synthesis and cell wall formation
  • B lactams: ex penicillin
  • glycopeptides: ex vancomycin (connected to staph)
18
Q

what antibacterial target the plasma membrane?

A

goal is to destroy membrane integrity

  • poymyxins and lipopeptides
19
Q

what antibiotics target the ribosomes?

A
  • different drugs will target teh different subunits, act to inhibit protein synthesis
    ex: chlorampheicol, macrolides and tetracyclines - targets the 50S subunit
    ex: aminoglycosides and tetracyline acts on 30 S subunt
  • Rifampina nd actinomycin D inhibt transcription and RNA synthesis
20
Q

what antibacterial targets DNA synthesis? what tarets RNA synthesis

A

DNA synthesis: fluroquinolones

*drugs all end in floxacin

RNA synthesis: rifamycins

21
Q

what antibiotics target the metabolic pathways?

A
  • act by inhibiting metabolic pathways

Sulfur drugs/sulfonamides block synthesis of folic acid which si required for synthesis of nucleotides

  • diarylquinolone blocks bycobacterial ATP synthase
  • isoniazid inhibits myoclic acid synthesis
22
Q

describe protein synthesis inhibitor antibiotics

A
  • diff between prok and eukaryotic ribosomes accounts for the selective toxiicty of anibacterial antibiotics

*note also ribosomes of cancer cells are diff

  • protein synthesis inhibitors can be classified into several groups based on struuctre and function - inhibition of ribosome function, translocation of tRNA, mRNA synthesis etc
  • most of these antibiotics work by binding and interfering with function of bacterial rRNA in 30S and 50S subunits

*generally protein synthesis inhibitors are bacteriostatic not bactericidal

23
Q

why are antibiotics considered secondary metabolites

A
  • often have no apparent primary use in producing organism - not essential for survival but enhance ability to survive competition, some ahve quorum senseing like activites
  • microbes prevent self destruction by antibiotic resistance mechanisms
24
Q

why is there a rise in atnibiotic resistance?

A
  • antibiotics are overused and overprescribed
  • used in farm animal feed, run off can end up in our food chain so we are exposed to low levels of antibiotics
25
Q

examples of microbes resistance to may dff drugs

A

streptococcus pneumoniae, acinetobacter baumanii

26
Q

what are the 5 basic forms of antibiotic resistance?

A
  1. prevent access and accumulation: block entry, efflux
  2. Destroy the antibiotic: use B-lactimases
  3. Modify the target so ti no longer bidns tot he drug: strategic mutations in ribosomes
  4. overproduce cellular target- ‘mop up’ the drug
  5. target mimicry: production of a decoy protein that has same drug-binding site are the target (protects a target where modification by mutation not an option)
27
Q

describe effluc pumps

A
  • pump the antibiotic out of the cell preventing accumulation
  • uses specific transporters and transport complexes
  • similar strategy is used in cancer cells

*of particular concern are multidrug efflux pumps - one pump can efflux 2 or several diff classes/types of drugs

28
Q

How does drug resistance develop?

A
  • De novo antibiotic resistance develops through gene duplocation and/or mutations
  • can be acquired primarily via horizontal gene transfer via conjugation, transduction or transformation
29
Q

what is klebsiella pneumoniae

A
  • carries NDN-1 plasmid (new delhi metallobeta lectamase -1) and numerous other drug resistant genes
30
Q

how are soem strategies to fight drug resistance?

A
  • use a dummy target: compounds that inactivate resistant enzymes
  • alter antibiotics structure sot ht it sterically hinders access of modifying enzymes
  • linking antibiotics is antoher strategy currently used to limit resistance (quinolone-oxazolindinone hybrid antibiotic has dual modes of action so can limit development of drug resistance)
  • antivirulence strategies disarm pathogens but do not kill
31
Q

biofilms and antibiotic ressitance

A
  • evena fter bactericidal antiboitic treatment some infections can return
  • subpopulation of dormant organisms called pester cells arise within a population of antibiotic susceptible bacteria
  • the stalled metbaolism of persisters renders them tolerant to bactericial antibiotics during treatment

*found in any biofilm or population of late-exponential phase cells

  • tolerance provides antibiotic resistance at price of not growing
32
Q

how is drug susceptibilty measured?

A
  • must consider :

the relative effectiveness of different antibiotics on the organism causing the ifnection

average atteinable tissue levels of the drug

33
Q

What is MIC and MLC?

A

MIC = loest concentration that prevents visible growth

*varies for different bacterial species and even strains within a species

MLC = minimal/lowest concentration that is lethal

*at MLS may still ahve living (but non growing, dormant, persister organisms) - palte on media without antibiotic and see if colonies form

*if no colonies form then the minimal lethal concentration was achieved

34
Q

what sit he kirby bauer disk diffusion susceptibilty test

A
  • test strain sensitivity to mutliple antibioics
  • use series of round filter paper disks impregnated with diff antibiotics, deliver the 12 disks simultaniously to surface of an agar plate overed with bacterial lawn
  • during incoluation the drugs diffuse from the disks into agar and inhibit growth of the lawn

*size of clear zone relfects sensitivity

35
Q

outline of how drugs are discovered

A
  1. identify new targets using genomics
  2. dsign compounds to inhibit targets
  3. alter compound strucutre to optimize MIC
  4. determine spectrum of compound - narrow or broad
  5. determine pharmaceutical properties (not toxic, persistence in body)
36
Q

idea for future drug discovery

A
  • nanotubes to form hold in bacterial memrbanes
  • molecules that “cork” the efflux systems or type III secretion apparatus/injectisome (innjects virulence factors directly into host cells)
  • use monoclonal antibodies as pathogen specific antimicrobials
  • interfere with quorum sensing
  • antibirulence drugs to target specific virulence factors and block mechansisms

NOTE: potential targets are discovered by rational drug design and combintory chem is used to make ranodm combinatons of compounds that can be tested for enyme inhibitory activity

37
Q

describe antiviral agents

A
  • common cold is a rhino virus and no antibiotic designed for abcteria can touch it
  • here are very few antivirals bc selective toxicity is much harder for viruses: small genome so less targets and overtake hsot machinery so hard to target the virus without harming the host
38
Q

describe antifungal agents

A
  • fungal infections are much more difficult to treat than bacterial infection bc fungi are eukaryotes - selective toxicity issues
  • fungi have efficient drug detoxification systems that modify and inactivate many drugs
  • fungal infections can be divided into 2 main grousp: superficial mycoses (treated topically) and deep mycoses (hyphae penetrate and spread into tissues, treated systemically)

MICR 2420 (29 decks)

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