Page 113 - Review of Medical Microbiology and Immunology ( PDFDrive )

mebooksfree.com
mebooksfree.com

mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com Iodine mebooksfree.com mebooksfree.com
mebooksfree.com
mebooksfree.com
PART I Basic Bacteriology
102
been classified into one of the three categories, but some of
the chemicals act by more than one mechanism.
Iodine is the most effective skin antiseptic used in medical
practice and should be used prior to obtaining a blood
DISRUPTION OF CELL MEMBRANES
culture and installing intravenous catheters because con-
tamination with skin flora such as Staphylococcus epidermi-
Alcohol
that inactivates sulfhydryl-containing enzymes. It also
Ethanol is widely used to clean the skin before immuniza-
binds specifically to tyrosine residues in proteins.
tion or venipuncture. It acts mainly by disorganizing the dis can be a problem. Iodine, like chlorine, is an oxidant
Iodine is supplied in two forms:
lipid structure in membranes, but it denatures proteins as
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com prior to blood culture. Because tincture of iodine can be mebooksfree.com
mebooksfree.com
well. Ethanol requires the presence of water for maximal
(1) Tincture of iodine (2% solution of iodine and
activity (i.e., it is far more effective at 70% than at 100%).
potassium iodide in ethanol) is used to prepare the skin
Seventy percent ethanol is often used as an antiseptic to
clean the skin prior to venipuncture. However, because it
irritating to the skin, it should be removed with alcohol.
is not as effective as iodine-containing compounds, the
(2) Iodophors are complexes of iodine with detergents that
latter should be used prior to obtaining a blood culture
are frequently used to prepare the skin prior to surgery because
and installing intravenous catheters. Ethanol will not kill
they are less irritating than tincture of iodine. Povidone-
bacterial spores and therefore cannot be used for
iodine is an iodophor commonly used as an antiseptic.
sterilization.
Detergents
Mercury and silver have the greatest antibacterial activity
Detergents are “surface-active” agents composed of a long- Heavy Metals
of the heavy metals and are the most widely used in medi-
mebooksfree.com mebooksfree.com mebooksfree.com merbromin (Mercurochrome), which contain mercury, are mebooksfree.com
mebooksfree.com
chain, lipid-soluble, hydrophobic portion and a polar
mebooksfree.com
cine. They act by binding to sulfhydryl groups, thereby
hydrophilic group, which can be a cation, an anion, or a
blocking enzymatic activity. Thimerosal (Merthiolate) and
nonionic group. These surfactants interact with the lipid in
the cell membrane through their hydrophobic chain and
used as skin antiseptics. Silver nitrate drops are effective in
with the surrounding water through their polar group and
preventing gonococcal neonatal conjunctivitis (ophthalmia
thus disrupt the membrane. Quaternary ammonium com-
neonatorum). Silver sulfadiazine is used to prevent infec-
pounds (e.g., benzalkonium chloride) are cationic deter-
tion of burn wounds.
gents widely used for skin antisepsis. Benzalkonium
chloride is the active ingredient in Lysol, a commonly used
Hydrogen Peroxide
disinfectant for floors and other surfaces.
wounds and to disinfect contact lenses. Its effectiveness is
Phenols
limited by the organism’s ability to produce catalase, an
Phenol was the first disinfectant used in the operating Hydrogen peroxide is used as an antiseptic to clean
enzyme that degrades H O . (The bubbles produced when
2
2
mebooksfree.com mebooksfree.com mebooksfree.com Hydrogen peroxide is an oxidizing agent that attacks sulf- mebooksfree.com
mebooksfree.com
mebooksfree.com
room (by Lister in the 1860s), but it is rarely used as a dis-
peroxide is used on wounds which are formed by oxygen
infectant today because it is too caustic. Chlorhexidine is a
arising from the breakdown of H O by tissue catalase.)
2
2
chlorinated phenol that is widely used as a hand disinfec-
tant prior to surgery (“surgical scrub”) and in the cleansing
hydryl groups, thereby inhibiting enzymatic activity.
of wounds. Hexachlorophene, which is a biphenol with six
chlorine atoms, is used in germicidal soaps, but concern
Formaldehyde & Glutaraldehyde
over possible neurotoxicity has limited its use. Phenols not
Formaldehyde, which is available as a 37% solution in
only damage membranes, but also denature proteins.
water (formalin), denatures proteins and nucleic acids.
2
–OH groups, which are the main sites of alkylation by the
MODIFICATION OF PROTEINS
hydroxymethyl group of formaldehyde. Glutaraldehyde,
Chlorine Both proteins and nucleic acids contain essential –NH and
which has two reactive aldehyde groups, is 10 times more
effective than formaldehyde and is less toxic. In hospitals, it
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com Ethylene Oxide mebooksfree.com mebooksfree.com
Chlorine is used as a disinfectant to purify the water supply
is used to sterilize respiratory therapy equipment, endo-
and to treat swimming pools. It is also the active compo-
scopes, and hemodialysis equipment.
nent of hypochlorite (bleach, Clorox), which is used as a
disinfectant in the home and in hospitals. Chlorine is a
powerful oxidizing agent that kills by cross-linking essen-
Ethylene oxide gas is used extensively in hospitals for the
tial sulfhydryl groups in enzymes to form the inactive
sterilization of heat-sensitive materials such as surgical
disulfide.
mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com