MICROBIOLOGY – ALCAMO LECTURE: Chemical Methods of Control
Jan 14, 2016
MICROBIOLOGY – ALCAMO
LECTURE:
Chemical Methods of Control
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
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
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
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%
Lister Video
• http://www.mefeedia.com/news/29703360
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
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
Chemical Agents of ControlTerms 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
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
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 inactivatesproteins (enzymes)
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
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!!!!
Important Chemical Agents - Halogens
• Chlorine is effective against– Gram-positive and
Gram-negative bacteria–Many viruses– Fungi– Protozoa
• Not effective against
spores
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
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
Important Chemical Agents - Alcohol
• Either antiseptic or disinfectant
• 70% Ethyl alcohol preferred
• Causes denaturation and desiccation
• But requires long exposure, limited effect
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
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
Important Chemical Agents - Heavy Metals
• Copper:– Potent inhibitor of algae– Copper sulfate is an algaecide used in
swimming pools and municipal water supplies
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)
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
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
Soaps Video
• http://www.google.com/url?sa=t&source=video&cd=9&sqi=2&ved=0CH8QtwIwCA&url=http%3A%2F%2Fvideo.google.com%2Fvideoplay%3Fdocid%3D-3210455528645505714&rct=j&q=chemical%20disinfection&ei=gXSjTc-QPMi-0QGAlaDQBA&usg=AFQjCNH14lMibDqfMas5Nz5ZNV34-Y9njg&cad=rja
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
Ethylene Oxide Video
• http://www.youtube.com/watch?v=-ICBQg9tcT8