Transcript ANTIMICROBIALS

ANTIMICROBIALS
CHAPTER 10
Antimicrobials: drugs that kill or inhibit the growth of microorganisms (bacteria, protozoa, viruses, fungi).
◦ Antibiotic: a substance produced by one microorganism that suppresses the growth of another microorganism.
-cidal: drugs that kill microorganisms (bactericidal, fungicidal, virucidal). A must for people/animals with
compromised immune systems.
-static: drugs that inhibit replication but do not directly kill the microorganism (bacteriostatic, fungistatic,
protozoistatic). Once the drug is removed, the organism can multiply again. Rely on body’s immune system to kill the
drug.
Pathogen: disease-causing organism
NOTE:/disinfectants and antiseptics are antimicrobials that are applied to surfaces (of the body or an inanimate
object)
Terms
-Kill or disable pathogens without killing the host
-The microorganism must be susceptible to the antimicrobial
-The antimicrobial must be able to reach the site of infection in high concentrations to kill or
inhibit the microorganism
-The animal must be able to tolerate high concentrations of the drug
-Convenience and cost also effect drug selection
Rules of antimicrobial therapy
Obtaining a sample from the infection site, growing the bacteria that were present in the
infected area, and determining which antimicrobials the bacteria are affected by.
◦ The antimicrobial must reach the infection site in concentrations high enough to exceed the
MIC for it to be effective against the bacteria
◦ It is always a good idea to swab for culture and sensitivity just in case!
Culture and Sensitivity
oThe measurement of the susceptibility of a bacterial strain to the effects of an antimicrobial
◦ the LOWEST concentration of drug at which the growth of bacteria is inhibited
◦ If a bacterial strain has an MIC for an antimicrobial and it is low enough to not produce
significant side effects in the host animal, the bacteria is SENSITIVE to the drug
◦ If the concentration required to kill or inhibit the pathogen is so high that significant side effects
would occur in the host animal, the bacteria is RESISTANT to the drug
◦ Some antimicrobials are effective against some strains of bacteria but totally ineffective against
other strains.
◦ Also, a particular bacterium may be highly susceptible to one antimicrobial but totally resistant
to another.
MIC- minimum inhibitory concentration
-Microorganisms developing the ability to survive in the presence of
antimicrobials that should kill them
◦ Genetic changes inherited through generations, spontaneous mutations, or acquisition of
plasmids
◦ Provide bacteria with a mechanism to defeat the effect of antimicrobials that would normally destroy or
inactivate them
◦ Examples: bacteria producing enzymes that make antibiotics useless, bacteria preventing a drug from attaching
to a receptor site on its surface, or bacteria altering their metabolic pathways, allowing them to survive the drug
◦ When a resistant bacteria is able to survive after being exposed to a drug and that bacteria is
able to replicate, a problem of a drug-resistant colony arises.
◦ Once resistant, a bacterium will pass on its resistance to its offspring
Drug resistance
Try to avoid resistance by:
◦ Administering the correct dose at correct intervals for
the appropriate amount of time and in the correct way.
◦ Educating clients on the importance of adhering to
instructions for medications. ALWAYS FINISH THE FULL
AMOUNT OF ANTIMICROBIALS PRESCRIBED. EVEN IF
THE CONDITION HAS RESOLVED!
◦ Cross resistance: when a bacterial strain is
resistant to not only one drug, but other drugs
in the same class
Drug resistance
Definition: the presence of a drug, chemical, or its metabolites in
animal tissues or food products. This is a result of either
administration of that drug or chemical to an animal or contamination
of food products.
Remember the importance of withdrawal times!
◦ Use of drugs in animals intended for food must be withdrawn a specific number of
days before the animal is slaughtered or the food products are sold. This ensures
that the drug has been excreted from the animal’s body (no residues)
◦ Most residues are not eliminated by cooking or pasteurization!
◦ Exposure to residues in food can lead to:
◦ An allergic reaction in a person
◦ A person growing resistant bacteria in their GI tract and killing all of the susceptible
bacteria
Educate food animal producers and clearly write the withdrawal times on prescribed
medication!
Residues
Antimicrobials usually attack a microorganism at these sites: cell wall, cell membrane, ribosomes, critical
enzymes/metabolites, nucleic acids
Cell wall attack:
◦ Antimicrobials can interfere with the bacteria’s ability to form its cell wall during division. The cell wall protects
the cell from rupturing when it absorbs water
◦ Antimicrobials can damage the bacteria’s cell membrane during or after cell division. A leaky membrane allows
medications to enter the cell and/or organelles to leave
◦ Antimicrobials can interfere with protein synthesis by attacking ribosomes used during translation. Ribosomes
are a critical part of forming the amino acid chain. Without them, tRNA and mRNA can’t do their job
◦ Antimicrobials can interfere with enzymes needed for metabolism in the bacterium.
◦ Antimicrobials can attack a bacteria’s RNA and DNA. When they are damaged, cell division is affected as well as
protein synthesis. It is important that the antimicrobial not effect the DNA of the mammal.
How antimicrobials work
http://www.buzzle.com/articles/gram-negative-vs-gram-positive.html
http://www.uphs.upenn.edu/bugdrug/antibiotic_manual/gram.htm