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1. Microbial Control
Sterilization & Disinfection
Bactericidal & Bacteriostatic
Physical & Chemical Agents
Filtration

2. Sterilization:
x Process of killing all microorganisms in
a preparation
x A physical or chemical process that
completely destroys or removes all
microbial life – including spores
(remember ??)

3. Terms:
x Bacteriostatic – having the property of
inhibiting bacterial multiplication, once the
agent is removed multiplication resumes.
x Bactericidal – having the property of killing
bacteria
x Sterile – free of any life form.
x Disinfectant – chemicals used to kill
pathogenic microbes by applying to a surface
but too toxic to apply to living tissues

4. x Septic – characterized by the presence
of pathogenic microbes on living tissue
x Septicemia – presence of microbes and are
actively multiplying
x Bacteremia – presence of microbes which
are not actively multiplying
x Aseptic – characterized by absence of
pathogenic microbes
x Antiseptic – a biocide product that
destroys/inhibits growth of microbes
on living tissues.

5. x Biocide – general term describing a
chemical agent, usually broad spectrum
that inactivates microbes
x Preservation – prevention of bacterial
multiplication in formulated products
like food or phamaceutical products
x Antibiotics – naturally or synthetic
organic compounds that inhibit or
destroy selective bacteria at low
concentration.

6. Antimicrobials/ Antibiotics
x Anti-microbial drugs
x antibacterial
x Minimum Inhibitory
x antimycobacterial
Concentration (MIC)
x antifungal
x Minimum
x antihelminthic
Bactericidal
Concentration x Antiviral
( MBC) (refer to
Pharmacology )

7. Antimicrobial susceptibility
Kirby-Bauer Method

8. Modes of Action:
x Damage to DNA
x Protein Denaturation
x Disruption of Cell Membrane
x Removal of free sulfhydryl group
x Chemical Antagonism

9. Damage to DNA:
x Ionizing radiation:
x Produce breaks in single and double strands
x UV light
x Induces cross linking between adjacent pyrimidines
on one or other of the 2 polynucleotide strands
forming pyrimidine dimers
x DNA- reactive chemicals
x Alkylating agent and other compounds that react
covalently with purine ( GA ) & pyrimidine bases
(CUT) to form DNA adducts/interstrand cross links

10. Protein Denaturation:
x The disruption of the tertiary structure
of protein
x Tertiary structure of protein means it
exists in a folded 3 dimensional state
determined by intramolecular covalent
disulfide linkages and some non covalent
linkages ( i.e. ionic, hydrophobic &
hydrogen bonds )

11. Disruption of Cell membrane or
wall
x Lysozyme
x Enzyme that destroys cell wall or prevents
normal synthesis may bring about lysis of
the cell wall.
x Substances that concentrate at the cell
surface may alter the physical and
chemical properties of the membrane,
preventing normal functions thereby
killing or inhibiting cell function.

12. Other modes of action:
x Removal of Free Sulfhydryl groups
x Oxidizing agents and heavy metals do
wide spread damage
x Chemical antagonism
x Isknown as the interference by a chemical
agent with the normal reaction between a
specific enzyme and its substrate

13. Treatment to control microbes
x Physical Methods x Chemicals
x Heat x Phenols
x Cold x Phenolics
x Radiation -UV , x Alcohols
X-ray x Halogens
x Filtration x Surfactants
x Drying x Heavy metals
x Ultrasonic x Alkylating
waves agents

16. Physical methods:
x Heat:kills by denaturation of enzymes
x Moist heat
x Kills
microbe primarily by coagulation of
proteins
x Boiling – 100 degrees – 10-20 minutes
x Free flowing unpressurized steam
x Fractional sterilization, arnolds sterilizer
x 100 degrees, 30 minutes, 3 consecutive
days

17. Cont. moist heat
x Autoclave
x Steam under pressure
x Temperature 121 degrees, 15-20minutes,
15psi
x Most effective spore eliminator
x Kilit ampule – contains the thermophile –
Bacillus stearothermophilus – check
autoclave efficiency

18. Moist heat pa din:
x Inspissation
x Thickening thru evaporation
x Temperature, 75 – 80 degrees, 2hrs for 3
days
x Usually used for high protein medium that
cannot stand high temperature of the
autoclave

19. Last na moist heat:
x Pasteurization –partial sterilization by
heat, used for milk & related products
x Classic, Low temperature holding (LTH)
x Also known as Batch method, 63 C, 30 min
x High temperature short Time (HTST)
x Flash process, temp 72 C, Time 15 sec
x Ultra high Temp ( UHT ) treatment
x Stored with refrigeration
x 140 C, 3-5 sec ( less than 5 sec, from 74–140 -74

20. Dry Heat:
x Kills by oxidation effects
x Direct flaming – aseptic technique
x Flaming of mouth of tubes, wires, needles, forceps,
petridishes
x Oven – hot air sterilization
x Temp 160-180 C, 90-120 minutes
x Incineration – burning materials to ashes
x Temp 300-400 C
x Cremation – prevent communicable diseases
x Temp 300-400 C

21. Cold temperature
x Has bacteriostatic effect
x Metabolic rate of microbe is so reduced that
they cannot reproduce or synthesize toxins
x Slow freezing is most harmful to bacteria
x Ice crystals that form and grow disrupt the
cellular and molecular structure of the
bacteria
x i.e.Treponema pallidum in blood bags can be
killed by 3 day refrigeration , 2-8 C

22. Filtration:
x Passage of liquid or gas thru a screenlike material
with pores small enough to retain microbes
x High efficiency particular air (HEPA) filters
x Remove almost all microbes larger that 3 um in
diameter
x Membrane filters – composed of substances like
cellulose esters or plastic polymers
x Used in laboratoy and industry
x 0.1 mm thick
x Pores of membrane filters include 0.22 to 0.45 um
x i.e. Seitz filter, Sintered glass filter, Berkefield,
Chamberland, Colloidon filter

23. Other methods:
x Lyophilization – water is removed by high
vacuum at low temperature
x Most effective method for long term
preservation of microbial culture
x Freeze drying – in which cultures are quick
frozen between -50 to -95 degrees C
x Ultracentrifugation
x Mechanical Shaking – agitation
x Grincing – Trituration

24. Other methods:
x Dessication: microbes cannot grow or
reproduce with moisture, but can remain
viable for years. To grow and multiply
microbes need water
x Osmotic pressure – the use of high conc.
Of salts & sugars to preserve food is based
on the effect of osmotic pressure
x Radiation – UV light or Xrays
x Ionizing– gamma, xrays, high energy e- beans
x Non-ionizing – UV light – damage DNA

26. Chemical Methods
x Non-selective methods
x Disinfectants – inanimate
x Antiseptics – animate
x E.g. alcohols, acids, alkali, halogens, salts of
heavy metal, cresols, lysol, phenols & oxidizing
agents
x Selective chemical agents
x Antibiotics
x Penicillin notatum – penicillin, Bacillus subtilis
= bacitracin, Streptomyces venerulae =
Chloramphenicol

27. Uses of common Germicides
x Sterilization - x Disinfection -
x Ethylene oxide,
x Chlorine compound,
Gluteraldehyde, Alcohols, Phenolic
Hydrogen peroxide compound, Iodophor
Formaldehyde, compound,
Chlorine dioxide, Quaternary
Peracetic Acid Ammonium compd.
x Antisepsis -
x alcohol, Iodophors

28. Modes of Transmission
x Respiratory droplets x Vectors
x Fomites:
x Mechanical
x facial tissue
x Biological
x household surfaces
x Airborne
x eating utensils
x Parenteral
x contaminated
x injections
needles
x Direct contact
x Fecal-oral

30. Portals of Entry
x Skin: x Conjunctiva
x abscess - blood x Mouth
x tetanus - wound x primarily GIT
x plague - insect bite pathogens
x AIDS - injections x Urethra
x Nose: x Vagina
x primarily respiratory x Placenta
Pertussis, colds,
measles , small pox

32. Biological vectors of infection
x Flea - Plague x Mosquitoes
x Anopholes x viral encephalitis
mosquito - Malaria x Filariasis
x Tick : x Body louse
x Lyme disease x endemic typhus
x Rocky Mountain x Tsetse fly
spotted fever x African sleeping dis.
x Aedes mosquito: x Reduviid bug
x Yellow fever x Chaga’s disease

39. Exotoxins:
x Proteins are main x variable effect on
composition host
x produced by some x no fever
Gram (-) & (+) x active immune
x excreted into response
extracellular space x toxoid used as
x heat labile vaccine
(sensitive) x many diseases
x high toxicity

41. Endotoxins:
x Lipid portion main x similar effect for
component all endotoxins
x produced by Gram x fever producing
(-) only x poor immune
x released only upon response
death of bacterium
x toxoid cannot be
x relatively heat
produced
stable
x variety of diseases
x low toxicity