5. Control of Microbial Growth Flashcards
disinfection
destruction or removal of vegetative pathogens but NOT bacterial endospores. usually used only on inanimate objects
sterilization
complete removal or destruction of all viable microorganisms. used on inanimate objects
antisepsis
chemicals applied to body surface to destroy or inhibit vegetative pathogens
chemotherapy
chemicals used internally to kill or inhibit growth of microorganisms within host tissues
-antibacterials
-antibiotics
-antivirals
-antifungals
impact of biocide exposure
most to least:
antisepsis
sanitization
disinfection
sterilization (moist heat, best/quickest way)
“cidal” agents
kill
static agents
inhibit growth
pattern of microbial death
microorganisms are not killed instantly
population death usually occurs exponentially
measure of agent’s killing efficiency
-decimal reduction time: time to kill 90%
must be sure viable but nonculturable cells are dead
-once they recover, they may regain the ability to reproduce and cause infection
D and Z values
D values are the time or dose required for a 90% reduction in microbial concentration via a sterilization process.
Z values measure the resistance of the microorganism to death by the sterilization source.
Filtration
reduces microbial population or sterilizes solution of heat-sensitive materials by removing microorganisms
-also used to reduce microbial populations in air
ex: sterile glucose or sterile penicillin
membrane filters, filtering air
moist heat
destroys viruses, fungi, and bacteria
boiling will not destroy endospores and does not sterilize
degrades nucleic acids, denatures proteins, and disrupts membranes
dry heat is
less effective than moist heat sterilization, requiring higher temperatures and longer exposure times
pasteurization
controlled heating at temperatures well below boiling
used for milk, beer, and other beverages
process does not sterilize but does kill pathogens present and slow spoilage by reducing the total load of organisms present
*increase shelf life
ultraviolet radiation
wavelength of 260 is most bactericidal (DNA absorbs)
-causes thymine dimers preventing replication and transcription
UV limited to surface sterilization because it does not penetrate glass, dirt films, water, and other substances
-has been used for water treatment
ionizing radiation
gamma radiation penetrates deep into objects (sterilizing foods)
destroys bacterial endospores; not always effective against viruses
used for sterilization and pasteurization of antibiotics, hormones, sutures, plastic disposable supplies, and food
chemotherapeutic agents
chemical agents used to treat disease
destroy pathogenic microbes or inhibit their growth within host
penicillin
gram positive activity; beta lactamase and acid sensitive
inhibits cell wall synthesis (“beta-lactam” antibiotics)
penicillin is a beta lactam
beta lactamase breaks down ring and stops action of beta lactam
protein synthesis as a drug target
most of the antibiotics targeting protein synthesis will target translation by binding to the bacterial ribosome
-aminoglycosides
-tetracyclines
-marcolide antibiotics
nucleic acid synthesis as a drug target
quinolones are antibacterial compounds that interfere with DNA gyrase
e.g. cirpofloxacin
growth factor analogs
other antibacterial drug targets
structurally similar to growth factors but do not function in the cell
-analogs similar to vitamins, amino acids, and other compounds
isoniazid
a growth analog effective only against mycobacterium
-interferes with synthesis of mycolic acid (only found in mycobacteria- acid fast)
platensimycin
new structural class of antibiotic
broad-spectrum; effective against MRSA and vancomycin-resistant enterococci
antibiotic targets that target the cell membrane and wall
polymyxins disrupt the membrane and cause leakage and death
antibiotic targets that target peptidoglycan synthesis
beta-lactams
vancomycin
bacitracin
b-lactams
penicillin, cephalosporin, derivatives
interfere with transpeptidation
(formation of cross-links)
vancomycin
binds to pentapeptide precursor and prevents interbridge formation
bacitracin
binds to bactoprenol and prevents new peptidoglycan precursors from reaching site of synthesis
types of drug resistance
intrinsic
acquired
Persisters
intrinsic
born with it in them
mycoplasma resistance to beta-lactam antibiotics and other cell wall inhibitors simply because these bacteria lack a cell wall
(no cell wall- walking pneumonia- should never be prescribed penicillin- useless since no cell wall)
acquired
occurs when there is a change in the genome of a bacterium that converts it from one that is sensitive to an antibiotic to one that is resistance
Persisters
drug-tolerant bacteria lack the mechanisms for antibiotic resistance and “ignore” the presence of antibiotics, usually because they are embedded in biofilms that antibiotics cannot effectively penetrate or are growing too slowly to be inhibited
mechanisms of drug resistance
-modify the target of the antibiotic
-drug inactivation
-minimize the concentration of antibiotic in the cell
-bypass the biochemical reaction inhibited by the agent or increase the production of the target metabolite
antiviral drugs
-drug development has been slow because it is difficult to specifically target viral replication
-antiviral drugs have had mixed success and the vast majority of viral infections cannot be cured
-some antiviral drugs simply limit the duration of the illness or its severity (flu and HIV)
-drugs currently used inhibit virus-specific enzymes and life cycle processes
antiviral drugs for influenza
tamiful
-anti-influenza agent
-a neuraminidase inhibitor
-though not a cure for influenza, has been shown to shorten course of illness
antifungal drugs
fewer effective agents because of similarity of eukaryotic fungal cells and human cells
-superficial and more common
-many have low therapeutic index and are toxic
easier to treat superficial mycoses than systemic infections
-combinations of drugs may be used
