Download control of bacterial growth

CONTROL OF BACTERIAL GROWTH
1. Physical method
2. Chemical method
3. Antimicrobial therapy
Physical method
1. Heat in controlling microorganism
based on:
thermal death point
temperature, under given conditions, will
certainly destroy all the cells
thermal death time
shortest time kills all bacteria except
spore form within certain temp.&
defined condition
1.1 Dry heat
material of nature that heat can penetrate
readily to all part
all bacteria will be destroy hot air oven
cannot be used with liquid or organic material
temp of 170-180 0C, one hour, glassware
1.2 Moist heat
kill all vegetative bacteria, except spore forms
temp.
90-100 0C, 10-30 min (boil)
70 0C
10 min (steam)
surgery instruments, dairy equipments
1.3 Steam under pressure
complete and rapid destruction of bacterial
spores and all microbes
temperature is higher than boiling point
autoclave : consists of a chamber into which
steam may be introduced and maintain
under pressure
when required temperature is reached, the
steam pressure is adjusted to maintain
the temperature for require length of
time
15 lb/ in, at 121 0C, 15 min
2. Freezing (cold):
delay metabolic activity of microbes
freezing and thawing decrease bacterial
population
bacteria kept frozen in ice, remain alive
for a period of time (-400c, -700c)
3. Desiccation (drying) :
controlling the growth of all bacterial life by
removing of water
various species of microbes differ in their
ability to survive drying
* organism produces endospore
more resistant
* young actively growing culture
of an organism is more readily
killed by drying than one which
passed through different
growth phases
vaccine, bacterins, sera
4. Radiation :
causes genetic damage
ultraviolet light (wave length 240-280 nm)
breaks in single and double strands
interfering DNA replication
* irradiation of air in the hospital
* aid in decontamination of lab facilities
* can cause skin & eye damage
Ionizing radiation
•greater energy than UV light
* causes direct damage
* produce toxic free radicals and H2O2
from water within the microbial cells
X- ray, beta, alpha & gamma ray (Cobalt-60)
* industrial processes, food preserve, medical
* sterilize surgical supplies, gloves etc
* carry dead but stainable bacteria may
produce false-positive Gram stain
smear
5. Filtration (live & dead)
microbes removed from a liquid by passing the
liquid through a filter with pore size that
organism cannot enter
nature purifies water though the ground
used in sterilization of media which may be
altered by heat sterilization
pore size
0.45 um for common bacteria
0.22 um for virus etc.
0.3 um for HEPA filter
Chemical method
* cause death of pathogenic vegetative bacterial
* protoplasmic poisons
1.Protein denature
1. Alcohol
toxic to cell at high concentration
ethyl alc. (70-90%) isopropyl (90-95%) are
commonly used
acts as protein denaturants
treatment of infection at superficial lesions
2. Phenol (antiseptic&disinfectant)
denature protein
lysol, hexachlorophene
strong antibacterial agent
usually high concentration (1-2% aqueous soln )
treating contaminated material
3. Heavy metal ions
Mercury, Copper and Silver salt
used at very low concentration
Mercury combining with protein & may precipitate cell
protein
eg. Mercurochrome, Merthiolate,1%silver nitrate
4. Oxidizing agent
Halogens (fluorine, chlorine, bromine,
iodine, astatine Oxidizing agent
inactivating cell by oxidizing essential
components of microbial cell
iodine
- 2% iodine in 50% alc
(tincture) skin disinfectant
iodophor
- used in preparation of
skin before surgery
chlorine
< 1 ppm
- highly oxidizing agent
- kill most vegetative bacteria
- inactivate most virus
- for drinking water
- activity loss quickly in
presence of organic matter
5% Sodium hypochlorite
- decontaminating of glassware
H2O2
5. Alkylating agent
highly lethal to essential all microbes react
with protein in the cell and inactivate them
sporicidal
formaldehyde (37% aqueous soln formalin)
Glutaraldehyde 2% buffer soln
apparatus that cannot be heat treated
6. ethylene oxide gas
-replacing labile H atom on hydroxyl
carboxyl or sulfhydryl grs
esp. guanine and adenine in DNA
- sterilizers resemble autoclave
Microbicidal, sporicidal (autoclave)
10% ethylene oxide in CO2 at 50-60 0C 4-6 hrs.
Penetrate packing material, plastic bag
2. Injury of cell membrane
Detergents (surface-active compound)
compound with hydrophobic and hydrophilic
groups attach to solubilize compound
or alter their properties
(wetting & emulsifier agent)
Anionic detergent :
soap
- highly effective cleanser little
antibacterial effect
- their charge similar to that of
most microbes
Cationic detergents :
quaternary ammonium compound :
benzalkonium chloride 0.1%
- highly bactericidal in the absence
of contaminating organic matter
- react with lipid of cell membrane
of bacteria
- alter membrane surface properties
and its permeability led to
loss of essential cell component
and death
Antimicrobials therapy
Bacteriostatic
having the property of inhibiting bacterial
multiplication : multiplication resumes
upon removal of the agent
Sulfonamide, Tetracycline
Bactericidal
* having the property of killing bacteria
* action differs from bacteriostatic only in
being irreversible
* organism can no longer reproduce
Penicillin, Streptomycin
Mode of Action
1. Inhibition of cell wall synthesis
Prevent cross-linking of peptidoglycan in the
cell wall
inhibiting cell wall synthesis , creating weak
point
penicillin , cephalosporins
Gram positive bacteria are more sensitive
2. Damage to cell membrane function
cell membrane enclosing the cyloplasm
control passage of materials in or out of
the cells
if its function is damaged :
cellular contents (proteins, nucleotide, ions) can
leak from cell cell
damage
death
polymyxin, amphotericin B (topical tr.)
3. Inhibition of nucleic acid function
act by binding to DNA inhibit its replication or
transcription
sulfonamide, nalidixic acid, fluoroquinolone
4. Inhibition of protein synthesis
affecting on ribosome
antibiotics bind to receptors of subunits of
bacterial ribosome and affected a number
of different steps in protein synthesis
tetracycline aminoglycosides
(gentamicin etc.)