ANTIMICROBIALS

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.

ANTIMICROBIALSTYPES:

ANTIBIOTICS, ANTIFUNGALS, ANTIVIRALS, ANTIPARASITICS

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

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

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

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?

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.

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.

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

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.

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.

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)

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.

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.

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

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.

ANTIBIOTIC RESISTANCE

WAYS THAT BACTERIA CAN CHANGE TO BECOME RESISTANT:

• MUTATION

• ACQUIRING GENES THAT CODE FOR RESISTANCE

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

CLASSES OF ANTIBIOTICS

• CELL WALL AGENTS

• CELL MEMBRANE AGENTS

• PROTEIN SYNTHESIS AGENTS

• ANTIMETABOLITES

• NUCLEIC ACID AGENTS

DISINFECTANTS & ANTISEPTICS

WHAT’S THE DIFFERENCE?

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

• BACTERICIDAL – chemical that kills bacteria

• VIRUCIDAL – chemical that kills viruses

• FUNGICIDAL – chemical that kills fungi

• SPORICIDAL – chemical that kills spores

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

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?

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

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

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

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

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

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

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

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

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