Physical, chemical and biological control of microbes Flashcards
define: sterilization, disinfection, antisepsis, sanitation
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
what is the D value?
decimal reduction time
- length of time is takes an agent or ocndition to kill 90% of the ppulation
exmaples of physical methods of control
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)
describe heat to kill microbes
- 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
describe pasteuization
- can use diff time and temp combonations
- LTLT (lot temp long time) 63 C for 30 min
HTST: 72C for 12 seconds
describe filtration
- 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
describe irradiation
- 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
what is deinococcus radiodurans
- 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)
what factors influence the efficiacy of a chemical agent?
- presence of organic matter
- type of organism present
- mode of growth ie biofilms
corrosiveness
-stability, odor and surface tension
how has bacteria developed to be resistant to disinfectants?
- 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
what are antibiotics
compounds produced by one microbe that adversely affets other microbes
*term antibiotics also used for chemotherapeutic agetns that are clincally useful but chemically synthesized
describe the antibiotic revolution
- began 1928 by discoery of penecillin by alexander flemming
- contaminating mold had inhibited growth of Staphlococcus aurenus colonies - mold identified as Penicillium notatum
describe how antibiotics must exhibit selective toxicity
- 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
bactericidal vs bacteriostatic
bactericidal antibiotics: kill target organisms
Bacteriostatic antibiotics: prevent growth of organisms - cannot kill, the immune system will remove the intruding microbe
what is the issue with braod spectrum antibacterial agents-
- 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
what are typical targets of antibiotics
- cell wall synthesis, cell membrane integrity, DNA synthesis, RNA synthesis, prtoein synthesis and metabolism
what antibiotic targets the cell wall? how?
- prevent peptidoglycan synthesis and cell wall formation
- B lactams: ex penicillin
- glycopeptides: ex vancomycin (connected to staph)
what antibacterial target the plasma membrane?
goal is to destroy membrane integrity
- poymyxins and lipopeptides
what antibiotics target the ribosomes?
- 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
what antibacterial targets DNA synthesis? what tarets RNA synthesis
DNA synthesis: fluroquinolones
*drugs all end in floxacin
RNA synthesis: rifamycins
what antibiotics target the metabolic pathways?
- 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
describe protein synthesis inhibitor antibiotics
- 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
why are antibiotics considered secondary metabolites
- 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
why is there a rise in atnibiotic resistance?
- 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
examples of microbes resistance to may dff drugs
streptococcus pneumoniae, acinetobacter baumanii
what are the 5 basic forms of antibiotic resistance?
- prevent access and accumulation: block entry, efflux
- Destroy the antibiotic: use B-lactimases
- Modify the target so ti no longer bidns tot he drug: strategic mutations in ribosomes
- overproduce cellular target- ‘mop up’ the drug
- 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)
describe effluc pumps
- 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
How does drug resistance develop?
- De novo antibiotic resistance develops through gene duplocation and/or mutations
- can be acquired primarily via horizontal gene transfer via conjugation, transduction or transformation
what is klebsiella pneumoniae
- carries NDN-1 plasmid (new delhi metallobeta lectamase -1) and numerous other drug resistant genes
how are soem strategies to fight drug resistance?
- 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
biofilms and antibiotic ressitance
- 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
how is drug susceptibilty measured?
- must consider :
the relative effectiveness of different antibiotics on the organism causing the ifnection
average atteinable tissue levels of the drug
What is MIC and MLC?
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
what sit he kirby bauer disk diffusion susceptibilty test
- 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
outline of how drugs are discovered
- identify new targets using genomics
- dsign compounds to inhibit targets
- alter compound strucutre to optimize MIC
- determine spectrum of compound - narrow or broad
- determine pharmaceutical properties (not toxic, persistence in body)
idea for future drug discovery
- 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
describe antiviral agents
- 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
describe antifungal agents
- 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)
