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Microbial control methods

1

Definition of Frequently Used
Terms
• Sterilization
– destruction or removal of all viable organisms
• Disinfection

– killing, inhibition, or removal of disease causing
(pathogenic) organisms
– disinfectants
• agents, usually chemical, used for
disinfection

• usually used on inanimate objects
2

More Definitions…
• Sanitization

– reduction of microbial population to levels deemed
safe (based on public health standards)
• Antisepsis

– prevention of infection of living tissue by
microorganisms
– antiseptics
• chemical agents that kill or inhibit growth of
microorganisms when applied to tissue
3

Impact of biocide exposure

4

Antimicrobial Agents
• Chemotherapy

– use of chemicals to kill or inhibit
growth of microorganisms within host
tissue
• Agents that kill microorganisms or
inhibit their growth

– cidal agents kill
– static agents inhibit growth
5

-cidal vs
...
can
profoundly impact effectiveness
– organisms in biofilms are less susceptible to many
antimicrobial agents
8

Phenolics

• Commonly used as laboratory and hospital
disinfectants
• Act by denaturing proteins and disrupting cell
membranes
• Tuberculocidal and remain active on surfaces long
after application

• Disagreeable odor and can cause skin irritation
9

Alcohols

• Among the most widely used disinfectants and
antiseptics
• Two most common are ethanol and isopropanol
• Bactericidal, fungicidal, but not sporicidal

• Inactivate some viruses
• Denature proteins and possibly dissolve
membrane lipids
10

Halogens - Iodine
• Important antimicrobial agent

• Skin antiseptic
• Oxidizes cell constituents and iodinates
proteins

• At high concentrations may kill spores
• Skin damage, staining, and allergies can be a
problem
• Iodophore
– iodine complexed with organic carrier
– released slowly to minimize skin burns
11

Halogens - Chlorine
• Oxidizes cell constituents

• Important in disinfection of water supplies and
swimming pools, used in dairy and food
industries, effective household disinfectant
• Destroys vegetative bacteria and fungi,
• Chlorine gas is sporicidal
• Can react with organic matter to form
carcinogenic compounds

12

Heavy Metals
• e
...
, ions of mercury, silver, arsenic,
zinc, and copper
• (CuSo4) potent against algae in
swimming pools, fish tanks
...
chrysogenum (P
...
Such as
• Bacitracin, gramicidin, tyrocidin
...


0
...
0%
Barium
chloride
(ml)

0
...
1

0
...
3

0
...
0%
Sulfuric
acid (ml)

9
...
9

9
...
7

9
...
5

3
...
0

9
...
0

%
Transmittan 74
...
6

35
...
4

21
...
08 to
e*
0
...
257

0
...
582

0
...

cell
density
(1-2X10^8
CFU/mL)

20

To do
1
...


2
...

3
...

4
...

5
...

6
...


Effect of chemical agents

Water

Iodine
Listerine

Dettol

Label the plate with the chemicals used
and bacteria species
Inoculate the plate with your bacteria
Use sterile forceps to blot the disk into
the inoculated plate

22

The antimicrobial susceptibility
test

23

The antimicrobial susceptibility test
Disc method

A Kirby-Bauer Plate
...
aureus and various antibiotics
...


24

Approved interpretive criteria for
antimicrobials used in food animals…
Zone Diameter
(mm)
Antimicrobial

S

I

Concentrations
(μg/ml)
R

S

I

R

Clindamycin2 (used for lincomycin testing)

≥21

15-20

≤14 ≤0
...
5

1-4

≥8

Gentamicin

≥15

13-14

≤12 ≤4

8

≥16

Oxacillin

≥13

11-12

≤10 ≤2

---

≥4

Oxytetracycline

≥19

15-18

≤14 ≤4

8

≥16

Penicillin4

≥28

20-27

≤19 ≤0
...
25-2

≥4

Sulfathiazole

≥17

13-16

≤12 ≤256

---

≥512

Tetracycline5

≥19

15-18

≤14 ≤4

8

≥16

Trimethoprim/Sulphamethoxazole6

≥16

11-15

≤10 ≤0
...
5

--

≥4/76
25

The antimicrobial susceptibility test
Tube dilution method
32 ug/ml 16 ug/ml 8 ug/ml

Sub-culture to agar medium

4 ug/ml

2 ug/ml

1 ug/ml

MIC = 8 ug/ml
MBC = 16 ug/ml

27



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