1. LECTURE: Chemical Methods of Control
MICROBIOLOGY – ALCAMO
LECTURE:
Chemical Methods of Control

2. Health Care Conditions in the1800’s
Hospitals rarely had running water
Garbage and human waste were
dumped in a pit right outside
Surgeons wiped their hands and
instruments on their jackets and pants
Bed sheets were rarely changed and infection was rampant
1/3 of women giving birth died of puerperal fever – blood disease caused by Streptococcus

3. Health Care Conditions in the1800’s
A Hungarian doctor –
Ignaz Semmelweis – noticed:
More puerperal fever in maternity wards tended by doctors fresh from dissecting cadavers
Less puerperal fever in maternity wards tended by midwives
He thought disease was spread by infected hands and made hospital workers wash their hands
This reduced the death rate among maternity patients significantly

4. Health Care Conditions in the1800’s
Other doctors rejected
Semmelweis’s conclusions
because it put the blame on them
After he died, Pasteur came out with the germ theory of disease
Doctors began to finally realize that infectious MO’s could be transmitted by clothing, utensils and instruments
They began using chemical antiseptics and disinfectants and the death toll declined

5. Health Care Conditions in the1800’s
In the 1860’s Joseph Lister established the principles of aseptic surgery
He used carbolic acid to kill MO’s in operating rooms
Reduced the death
rate post-surgery
from 45% to 9%

6. Lister Video

7. Chemical Agents of Control – Terms To Know
Most chemical agents can only reduce the # of MO. Sterility is unusual.
Two Categories:
Antiseptics: Use on living tissues - mild or very diluted chemicals
Disinfectants: Use on objects –
strong or concentrated
chemicals

8. Chemical Agents of Control - Terms To Know
Bactericidal Agent – kills MO’s
Bacteriostatic Agent – temporarily prevents further multiplication of MO’s without killing them
Sepsis (putrid) – contamination of an object by MO’s:
Septicemia – MO infection of the blood
Antiseptic – against infection
Aseptic – free of contaminating MO’s

9. Chemical Agents of Control Terms To Know
Sanitize – to reduce the MO population to a safe level determined by public health standards
Degerm – to remove MO’s from the surface
- cidal agents – kill Mo’s:
Fungicide
Virucide
Sporicide

10. What Makes a Good Disinfectant
It must kill MO’s
Be nontoxic to humans and animals
Be soluble in water
Get its job done in a short time
Should penetrate surfaces well
Should not corrode instruments
Should be inexpensive and easy to obtain

11. Important Chemical Agents - Halogens
Halogens are highly reactive elements whose atom have 7 electrons in their outer shell
Chlorine and Iodine – Very Reactive
Cause Cell Death by Oxidation –
Oxygen is released and then
combines with and inactivates
proteins (enzymes)

12. Important Chemical Agents - Halogens
Chlorine
Disinfectant that can be used
alone as gas or in a solution
with water
Used in municipal water
supplies to keep bacterial populations low
6 – 10 Drops/Gal Clear Water/1 hour = Drink
Available as calcium hypochlorite – used for wounds in WWI and WWII

13. Important Chemical Agents - Halogens
Available as sodium hypochlorite – bleach to disinfect water (swimming pools) and sanitize factory equipment
Laundry bleach most available and excellent means of MO control
Do not combine bleach with
other chemicals - small but
lethal amounts of Cl gas may
be released!!!!

14. Important Chemical Agents - Halogens
Chlorine is effective against
Gram-positive and
Gram-negative bacteria
Many viruses
Fungi
Protozoa
Not effective against
spores

16. Important Chemical Agents - Halogens
Iodine
Usually an antiseptic
2% in water or alcohol (Tincture)
good for wounds
If solvent evaporates tissue damage
For water disinfection use 18 – 20 Drops/Gal Clear Water/1 hour = Drink
Iodifors – iodine mixed with detergent
Betadyne – for local wounds

18. Important Chemical Agents - Phenol
Has been a key disinfectant
since Joseph Lister used it
Remains the standard
against which other disinfectants are evaluated
It acts by coagulating proteins in the cell membranes of MO’s
But, it is expensive, has a strong odor, and is caustic to the skin

19. Important Chemical Agents - Alcohol
Either antiseptic or disinfectant
70% Ethyl alcohol preferred
Causes denaturation and desiccation
But requires long exposure, limited effect

20. Important Chemical Agents - Heavy Metals
Metal elements with a large molecular weight:
Silver, Mercury, Copper, Lead, Zinc
Can be used as either an antiseptic or a medicine
Cause denaturation
of proteins (enzymes)
Can be very toxic to
host

21. Important Chemical Agents - Heavy Metals
Mercury:
Mercuric chloride was used by the Greeks and Romans for treating skin diseases
Mercury is very toxic to the host, so it is now combined with carrier molecules to make it less toxic
Mercurochrome
Merthiolate
Metaphen

22. Important Chemical Agents - Heavy Metals
Copper:
Potent inhibitor of algae
Copper sulfate is an algaecide used in swimming pools and municipal water supplies

23. Important Chemical Agents - Heavy Metals
Silver:
Silver Nitrate – useful antiseptic
and disinfectant
If it is a strong dilution – used for chemical cautery
If it is a weak dilution – used in a newborn’s eyes to prevent bacterial infection by Neisseria gonorrhoeae
Zinc: Calamine Lotion (antiseptic, anti-itch)
Bismuth: Pepto Bismol (anti-diarrheal)

24. Important Chemical Agents Hydrogen Peroxide
Antiseptic and disinfectant – used as a rinse in wounds and scrapes
Area foams as catalase in tissues breaks down H2O2 to oxygen and water
This results in a highly reactive form of oxygen – toxic to MO’s

25. Important Chemical Agents - Soap
Soap is made of fatty acids combined with sodium hydroxide – high pH bad for certain MO’s
Soap is also a wetting agent that solubilizes particles clinging
to a surface
Soap also removes skin oils
and MO’s slide off skin

26. Soaps Video

27. Important Chemical Agents - Ethylene Oxide
A small compound with excellent penetration capacity and sporicidal ability due to oxidation
Very Dangerous – toxic
and explosive
Used in production of
sterile supplies and by
NASA to sterilize space capsules

28. Ethylene Oxide Video