2What are antibiotics?Definition: chemicals produced by one microorganism to kill or inhibit the growth of other microorganismsNow included the semi-synthetic antibioticsEffective against bacteriaAntibacterial drugs – largest group of antibioticsGeneral terms used to include other microbes are antimicrobial drugs or antimicrobialsDifference between disinfectants/antiseptics and antimicrobial drugs
3Antibiotic spectrum Broad vs. narrow spectrum antibiotics Benefits and problems with each
11Modes of action of the antibiotics: 2. Inhibition of protein synthesisbinding to 70S ribosomedifferences between 70S and 80S ribosomesex. chloramphenicol, erythromycin, streptomycin, tetracyclineshost mitochondria may also be affected
19Antagonism vs. synergism of 2 or more antibiotics Ex. Tetracycline penicillin (Why?)Synergism:Ex. TMP-SMZ (SMX) trimethoprim and sulfamethoxazole
20Prophylaxis – preventative use of antibiotics Ex. of their use:1. before surgery – i.e. appendix removal2. before dental work in heart patients3. in AIDS patients to prevent many infections
21Factors affecting antimicrobial activity in vivo – In the environmentA. metabolic state of pathogenEx. Mycobacterium tuberculosisB. distribution of drug is different in different tissuesEx. blood/brain barrier and necrotic tissueC. location of pathogenEx. Chlamydia inside host cellsD. interfering substancesEx. low pH in stomach; binding to proteins in body, etc.
22Factors affecting antimicrobial activity in vivo – Concentration of antibiotics in bodyA. absorption, inactivation, excretionB. distribution of the drug – systemic vs. local vs. topicalC. variability – dosing flutuations, how long antibiotic lasts in the body.
23Antiviral drugsNucleotide analogs (look similar to the bases + sugars of DNA) Ex. AZT – looks like thymine; acyclovir – looks like guanineEnzyme inhibitors Ex. reverse transcriptase inhibitor – important in controlling HIV infectionInterferons – naturally produced by our immune systemsEx. alpha, beta, and gamma; prevents further infection
25Antifungal drugs Targets for antifungal drugs??? Possible side effects???Ex. amphotericin B and imidazole affect sterol productionGriseofulvin – binds to keratin in skin cells, treats skin fungal infections
26Antibiotic resistance (also called drug resistance) What is happening?As microbes are exposed to drugs, the ones with defenses against them survive
27Microbial defense mechanisms against antibiotics Change receptor for drugBind to drug and inactivate it, ex. penicillinase (b- lactamase)Change target site, ex. change ribosome structureChange metabolic pathwayMDR pump– multi-drug resistance pump
28How does drug resistance develop in different microbes? Antibiotics overprescribed and not regulatedMany countries do not require a prescriptionImproper dosageAntibacterial soaps/surfaces, etc.Antibiotics in animals (used as our food source)People insisting on receiving antibiotics, even for viral infectionsNosocomial infections and the chronically infected