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Control of Microbial Growth - Coggle Diagram
Control of Microbial Growth
Definitions
Chemotherapy
- the use of chemical substances to treat a disease
Antibiotic
- substance produced by microbes that in small amounts inhibits the growth of other microbes (bacteria)
Disinfectants
- chemical substances that destroy or inactivate microorganisms on non-living surfaces
Sterilization
- destruction/removal of all forms of microbial life, including endospores; performed with an autoclave
Commercial Sterilization
- sufficient heat treatment to kill endospores of
Colostridium botulinum
in canning food
Disinfection
- destruction of vegetative pathogens
Antiseptics
- destruction of vegetative pathogens on living tissue
Degerming
- removal of microbes from limited areas, such as skin around an injection site
Sanitation
- treatment to lower microbial counts on eating/drinking utensils to safe public health levels
Selective Toxicity
- killing microbes without damaging the host; goal of chemotherapy
Microbial Action
Efficacy (death rate)
depends on # of microbes, environment (organic debris, biofilms), time of exposure, & microbial characteristics (acid fast, endospores, Gram +/-)
Bacteriocidal agent
is 99.9% reduction in # of viable bacteria; it directly kills bacteria
Bacteriostatic agent
prevents bacteria from reproducing without necessarily killing them; keeps bacteria in stationary phase
Mode of Action
- how antibiotics act on bacteria cells;
1)
alteration of membrane permeability: Penicillin, Bacitracin, Vancomycin
2)
damage to proteins: Erythromycin, Tetracycline, Streptomycin
3)
damage to nucleic acids: Sulfanilamide, Trimethoprim
Physical Methods of Microbial Control
Autoclave
uses moist heat & pressure; preferred method of sterilization; classified as bacteriocidal; 15psi and 121 degrees C is perfect condition
Dry Heat Methods (
Medical Waste Incinerator
,
Flame
, and
Bactecinerator
) also bacteriocidal
Autoclave temp and pressure is measured with
autoclave tape/indicator strip
Pasteurization
- mild heating to kill spoilage organisms; for milk: heat to 72 degrees C for 15 sec; also bacteriocidal, does not sterilize the milk;
thermoduric
organisms
Streptococcus species
and
Lactococcus species
survive
Filtration
- for clear liquids & gases only using filters w/ holes typically of 0.2 microns; HEPA filters are 0.3 microns
Low temperatures are
bacteriostatic
and should not be used to kill bacteria;
Listeria monocytogenes
grows at refrigerated temperatures; dangerous to pregnant women; spoilage on deli ham is called
Pseudomonas fluorescense
--Gram +, small rods, random arrangement
Osmotic Pressure
- food preservation method using salt or sugar to cure meats & preserve fruits
Ionizing Radiation
(gamma rays & x-rays) (10^-5nm - 10^-3 nm) destroys bacterial DNA
Non-Ionozing Radiation
(UV light) (200nm - 400nm) damages DNA by producing
thymine dimers
but does not penetrate well
History & Safety
1910- Ehrlich coined the term chemotherapy & used Salvarsan (an arsenic cmpnd) against Syphylis
1928- Fleming discovered penicillin, produced by
Penicillium notatum
which inhibits
Staphylococcus aureus
1940- Florey & Chain held first clinical trials with penicillin
Fungi, Protozoans, & Helminths are difficult to treat because they are eukaryotes & resemble human cells
Broad Spectrum Drugs
save time but destroy normal flora; this can result in superinfection where opportunistic pathogens like
Candida albicans
(yeast inf.) or
Clostridium difficile
flourish
Narrow Spectrum Drugs
like Penicillin G most likely affect Gram+ cells
Antimicrobial substances affecting Gram- cells must contend w/ the lipopolysaccharides & porins in the outer membrane: Streptomycin, small hydrophilic drugs
Norovirus
causes gastroenteritis and is transmitted through fecal/oral route
can survive temps as high as 140 degrees F
prevention on surfaces is using solution of 25 Tbsp of bleach per 1 gallon water
Tests
Broth Dilution Test
can estimate
MIC
and
MBC
; growth in wells = resistance to that antibiotic; test includes rows of wells in decreasing conc. of antibiotic for each row of bacteria
Minimal Inhibitory Concentration (MIC)
- the well that has an 80% decrease of the well directly to the R
Minimal Bacteriocidal Concentration (MBC)
- the well that kills all bacteria; shows no growth
Kirby-Bauer Test (Disc Diffusion Method)
is simple & inexpensive; determines effectiveness by measuring
zone of inhibition
(ring around antibiotic)
E-Test
(type of Kirby-Bauer test?) can estimate MIC only & is expensive but accurate
Therapeutic Dose
- amt. of medication needed to have desired effect (want amount to be low)
Toxic Dose
- amt. needed before undesirable side effects & health is impaired (want amount to be high)
Therapeutic Index
- ratio of toxic dose divided by the therapeutic dose; the larger the index, the safer the medication
Resistance
Mechanisms of antibiotic resistance
include enzymatic destruction (ex Beta lactamase), prevention of drug penetration, alteration of drug target site, & rapid ejection via efflux pump
Resistant genes found on plasmids or transposons that can be transferred between bacteria
Streptomyces species
- filamentous soil bacteria that produce 50% of antibiotics: Chloramphenicol, Tetracycline, Erythromycin, Neomycin, Streptomycin
Actinomycetes
: soil microbes
Antifungal drugs
Polyenes
treat systematic fungi but are nephrotoxic: Amphotericin B
Antiretroviral Drugs
Neuraminidase Inhibitors
used to treat influenza include Zanamivir (Relenza; inhaled) and Oseltamivir phosphate (Tamiflu; oral)
Zidovudine (AZT) & Acylclovir are examples of
nucleoside analogs
used to treat HIV & genital herpes, respectively
Tenofovir is
nucleotide analog
Disinfectants
Bisphenol
agents like
Hexachlorophene soaps
were effective against Staph infections in infants but could cause neurological damage
Triclosan
works best against Gram+ bacateria; put in plastic toys
Halogens
- fluorine, chlorine, iodine
Iodine
in an alcohol base is a
tincture
;
Iodophors
like
Betadine
(water base) are used as surgical scrub & classified as disinfectant
Quaternary Compounds like
Zephiran
are used in medications to treat acne;
Cepacol
used in mouthwashes
Resistance of Microbes (most to least)
prions
endospores of bacteria
mycobacteria (contain mycolic acid)
cysts of protozoa
vegetative protozoa
Gram- bacteria
fungi (including fungal spore forms)
viruses without envelopes
Gram+ bacteria
viruses with lipid envelopes