ANTIMICROBIALS Chapter 10

Antimicrobials/antibiotics: drugs that kill or inhibit the growth of microorganisms (bacteria, protozoa, viruses, fungi). cidal: drugs that kill microorganisms. A must for people/animals with compromised immune systems. -static: drugs that inhibit replication but do not directly kill the microorganism. Once the drug is removed, the organism can multiply again. Rely on body’s immune system to kill the drug. NOTE:/disinfectants and antiseptics are antimicrobials that are applied to surfaces (of the body or an inanimate object) Terms

Rules of antimicrobial therapy -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

Culture and Sensitivity Obtaining a sample from the infection site Growing the bacteria that were present in the infected area 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! Culture and Sensitivity

MIC- minimum inhibitory concentration Measures the susceptibility of a bacterial strain to the effects of an antimicrobial. The MIC is 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 One antimicrobial is not effective against all strains of bacteria. One strain of bacteria is not effected by all antimicrobials. MIC- minimum inhibitory concentration

-Definition: microorganisms developing the ability to survive in the presence of antimicrobials that should kill them Genetic changes that provide bacteria with a mechanism to defeat the effect of antimicrobials that would normally destroy or inactivate them 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

Drug resistance We can 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. 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 and/or the growth of resistant bacteria. Educate food animal producers and clearly write the withdrawal times on prescribed medication! Residues

How antimicrobials work Antimicrobials usually attack a microorganism at these sites: cell wall, cell membrane, ribosomes, critical enzymes/metabolites, nucleic acids Interfere with the ability to form its cell wall during cellular division. Damage the cell membrane during or after cell division. Interfere with protein synthesis by attacking ribosomes used during translation. Interfere with enzymes needed for metabolism in the bacterium. Attack RNA and DNA which is needed for cellular division and protein synthesis. It is important that the antimicrobial not effect the DNA of the mammal. How antimicrobials work

Gram positive/Gram negative review http://www.buzzle.com/articles/gram-negative-vs-gram-positive.html http://www.uphs.upenn.edu/bugdrug/antibiotic_manual/gram.htm Gram positive/Gram negative review