antimicrobials. = drugs that couteract infection work in 2 ways: –some have the capacity to kill...
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ANTIMICROBIALS
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ANTIMICROBIALS
= DRUGS THAT COUTERACT INFECTION
• Work in 2 ways:– Some have the capacity to kill the organism
by attacking a part of it that the patient doesn’t have.
– Some have the ability to inhibit the growth of the organism by injuring it and relying on the patient’s immune system to kill the organism.
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ANTIMICROBIALSTYPES:
ANTIBIOTICS, ANTIFUNGALS, ANTIVIRALS, ANTIPARASITICS
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ANTIBIOTICS
• Chemicals that work ONLY on BACTERIA
• SPECTRUM OF ACTION:– The range of bacteria on which the agent is
effective.– Based on Gram Stain
• BROAD SPECTRUM:– Act on both gram positive and gram negative bacteria
• NARROW SPECTRUM:– Act on either gram positive or gram negative bacteria
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ANTIBIOTICS
• BACTERICIDAL ANTIBIOTICS – Antibiotics that kill the bacteria that they act against.
– METHODS:• Either damage key bacterial structures of actively
dividing bacteria during development
OR• Disrupt cell membranes or protein synthesis of the
bacteria and cause bacterial death in existing and multiplying bacteria
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ANTIBIOTICS
• BACTERIOSTATIC ANTIBIOTICS – Antibiotics that inhibit the growth or replication of bacteria.
– METHOD:• Prevent the division of bacteria
• GOAL OF BOTH METHODS IS TO ATTACK BACTERIA AND NOT HURT THE ANIMAL THAT IS BEING TREATED
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ANTIBIOTICS
HOW DO DOCTORS KNOW WHICH ANTIBIOTIC TO CHOOSE?
• They start with choosing one that is effective against a particular bacterium, reaches the site of infection, and one that the animal can tolerate.
HOW DO THEY KNOW THIS?
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ANTIOBIOTICS
Specific antibiotics are tested against specific bacteria in a laboratory setting
using two tests: Agar Diffusion Test (aka antibiotic sensitivity test) and the Broth Dilution Method. This is also known as
culture and sensitivity testing.
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AGAR DIFFUSION TEST
• Used to determine if a particular bacterium is susceptible to a particular antibiotic
• Antibiotic-impregnated discs are placed onto agar plated that are streaked with the specific bacteria being tested.
• Culture media, amount of bacteria used, and amount of antibiotics on discs are controlled.
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AGAR DIFFUSION TEST
• Plates are incubated at a controlled temp. for a controlled time period.
• When time is over, any clear zones around the discs are where bacteria failed to grow. These zones are measured in mm and are compared with a standardized chart to determine if the bacteria is resistant, intermediate, or sensitive to the antibiotic
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An example of a plate from a disc diffusion study. Note the varying sizes of the inhibitory zone present around the
different disks. Each disk is impregnated with a different antibiotic agent. Interpretation of the test requires
comparison of the measured zone diameter with the accepted cutoff values for each antibiotic/organism pair.
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Figure F. Antibiotic-sensitivity testing. Petri dishes were spread-inoculated with Staphylococcus albus (white growth) or Micrococcus luteus (yellow growth) before
antibiotic assay "rings" were placed on the agar surface. The coloured disks at the end of each spoke of the rungs are impregnated with different antibiotics. Clockwise from
the top (arrow) these are: Novobiocin, Penicillin G, Streptomycin (white disk), Tetracycline, Chloramphenicol, Erythromycin, Fusidic acid (green disk) and Methicillin. Clear zones of suppression of bacterial growth around the individual antibiotic disks are
evidence of sensitivity to these antibiotics.
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BROTH DILUTION METHOD
• Once an antibiotic is chosen, the dosing of the drug must begin
• The antibiotic is placed in tubes at various concentrations. The bacteria is then placed into the tubes.
• The lowest concentration of antibiotic that has no visible bacterial growth is the MINIMUM INHIBITORY CONCENTRATION (MIC)
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This figure shows a schematic of the broth dilution test. Bacteria are inoculated into tubes containing culture broth and varying
concentrations of the antibiotic to be tested. The tubes are incubated to allow bacterial growth. The MIC is read as the lowest concentration of antibiotic which inhibited bacterial growth. In the above example,
the MIC would be 8 micrograms/ml. The interpretation of this MIC depends on the organism/antibiotic pair being tested, and is made
following standard NCCLS guidelines.
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MIC - Macrodilution. In this case, bacterial growth occurred at a Tetracycline concentration of 0.8 mcg/ml but not at 1.6 mcg/ml. Thus, the
minimum inhibitory concentration is read as 1.6 mcg/ml.
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HOW DO ANTIBIOTICS ACTUALLY WORK?
5 MAIN WAYS:
1. Inhibiting cell wall synthesis (only when bacteria is growing and dividing), therefore allowing the cell to fill with water
2. Damage the cell membrane, altering its permeability. Substances can enter and leave at any time.
3. Inhibition of protein synthesis at ribosomes4. Interference with metabolism by blocking the action of
enzymes or binding to compounds needed by the bacteria.
5. Impairment of the production of nucleic acids making them unable to divide or function properly
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THINGS TO CONSIDER:
ANTIBIOTIC RESISTANCE• Instead of being inhibited or destroyed by a
particular antibiotic, the bacteria survive and continue to multiply.
• Cont’d antibiotic use promotes the development of antibiotic-resistant bacteria
• Resistance occurs when bacteria change in a way that reduces or eliminates the effectiveness of the antibiotic.
• This can happen when the drug is not used properly, not given for the proper length of time, or not given at the proper dosage.
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ANTIBIOTIC RESISTANCE
WAYS THAT BACTERIA CAN CHANGE TO BECOME RESISTANT:
• MUTATION
• ACQUIRING GENES THAT CODE FOR RESISTANCE
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ANTIBIOTIC RESIDUES
• = THE PRESENCE OF A CHEMICAL OR ITS METABOLITES IN ANIMAL TISSUES OR FOOD PRODUCTS
• Great concern for people:– They can cause allergic reactions– They can produce resistant bacteria – Cooking or pasteurization does not eliminate
residues
• Withdrawal times are set to help eliminate antibiotic residues in food products
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CLASSES OF ANTIBIOTICS
• CELL WALL AGENTS
• CELL MEMBRANE AGENTS
• PROTEIN SYNTHESIS AGENTS
• ANTIMETABOLITES
• NUCLEIC ACID AGENTS
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DISINFECTANTS & ANTISEPTICS
WHAT’S THE DIFFERENCE?
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DEFINITIONS
• DISINFECTANT – kills or inhibits the growth of microorganisms on inanimate objects
• ANTISEPTICS – kills or inhibits the growth of microorganisms on living tissue
• GERMICIDE – chemical that kills microoorganisms
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• BACTERICIDAL – chemical that kills bacteria
• VIRUCIDAL – chemical that kills viruses
• FUNGICIDAL – chemical that kills fungi
• SPORICIDAL – chemical that kills spores
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IDEALLY, DISINFECTANTS SHOULD BE:
• stable when stored or used
• Easy to apply
• Unlikely to damage the objects they’re applied to
• Nonirritating
• Broad spectrum
• Inexpensive
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THINGS TO REMEMBER WHEN CHOOSING A DISINFECTANT:
1. Be sure that it is appropriate for the surface that you will be applying it to
2. Keep in mind what microorganisms you want to attack
3. The surface may need to be free of debris before the disinfectant is applied
4. When diluting the chemical, start with water and then add the chemical to it to avoid splashing the harsh substance
5. Does the disinfectant have a minimum contact time?
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ALL PRODUCTS MUST HAVE AN MSDS (MATERIAL SAFETY DATA SHEET)
THAT INCLUDES:
• Product name and chemical ID• Name, address, phone # of manufacturer• List of hazardous ingredients• Physical state of product• Fire/explosion info• Potential chemical reactions• Emergency and clean-up procedures• Required protective equipment• Precautions when using
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EXAMPLES OF DISINFECTANTS:
PHENOLS• Use on laundry, floors, walls, equipment• Increase permeability of cell membrane,
cell components leak out• Effective against G +, some G -, fungi, and
some enveloped viruses• NOT effective against spores or
nonenveloped viruses (PARVO)• DON’T use as an antiseptic – irritating and
neurotoxic• EX: Lysol
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EXAMPLES OF DISINFECTANTS
QUATERNARY AMMONIUM COMPOUNDS
• Use on instruments, rubber, inanimate objects• Dissolve lipids in cell walls and membranes• Effective against G + as well as G – organisms
and enveloped viruses• NOT effective against PARVO• Not irritating• Site of application must be clean• EX: Roccal
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EXAMPLES OF DISINFECTANTS
ALDEHYDES
• Use on instruments• Affects nucleic acids and/or protein
structures of microbes• Broad-spectrum, fungicidal, bactericidal,
virucidal• EX: Gluteraldehyde, Formaldehyde
– The latter is also called Formalin, which is used to “fix” biopsy samles
– Formaldehyde is toxic and a carcinogen
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EXAMPLES OF DISINFECTANTS
ETHYLENE OXIDE
• Use on rubber goods, blankets, lensed instruments
• Destroys DNA and proteins• Bactericidal, fungicidal, virucidal• Gas sterilization• Slow to act – may take up to 3 hours to
complete sterilization• Explosive, carcinogen
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EXAMPLES OF DISINFECTANTS
ALCOHOLS
• Used on instruments, thermometers, and skin• Coagulates proteins and dissolves lipids in cell
membranes• Broad-spectrum bactericidal, also works against
enveloped viruses, NOT parvo• Non-irritating, non-toxic, inexpensive• Not recommended as an antiseptic (pain)• Site of application must be clean to be effective
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EXAMPLES OF DISINFECTANTS
HALOGENS
• Use chlorine on floors, cages. Use iodophors on thermometers and as a pre-sx scrub
• Interfere with proteins and enzymes of microbe• Bactericidal, virucidal, fungicidal• Bleach is inexpensive, corrosive, irritating. Used
as a 1:10 solution• Iodine is brown, used as a topical antiseptic as a
scrub, solution, or tincture. Can be corrosive and irritating if contact period is prolonged
• Ex: Chlorines: Chlorox, Iodophor: Betadine
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EXAMPLES OF DISINFECTANTS
BIGUANIDES
• Use on skin wounds, pre-sx scrub, oral cleaning solutions, cages
• Denatures proteins• Bactericidal, virucidal for enveloped (NOT
parvo)• Mild, nontoxic, fast acting• Residual activity of 24 hours• EX: Chlorhexidine
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EXAMPLES OF DISINFECTANTS
HYDROGEN PEROXIDE
• Has been used in wounds• Releases oxygen when it reacts with
cellular products and compromised tissue• Damages proteins, can damage animal
tissue• Only rec. to be used for oral infections and
surface wounds