Chapter 20-Antimicrobial Agents

_______________:The use of drugs to treat a disease (not necessarily infectious)

Antimicrobial drugs: Interfere with the growth of microbes within a hostAntibiotic: Substance produced by a microbe that, in small amounts,

____________ another microbeSelective toxicity: A drug that kills harmful microbes without

damaging the host

DISCOVERY and PURIFICATION of PENICILLIN

• 1928 – ___________ discovered penicillin, produced by Penicillium.

• 1940 – Howard Florey and Ernst Chain performed first clinical trials of penicillin.

Figure 20.1

Naturally occurring antimicrobialsMetabolic products of bacteria and fungi

_________: Streptomyces sp., Bacillus sp. _________: Penicillium sp., Cephalosporium sp.

THE ACTION OF ANTIMICROBIAL DRUGS• Broad-spectrum

• Affect wide range of G+ and G- bacteria

• Disadvantage is disruption of ___________

• Ex. Tetracycline

• Narrow-spectrum

• Affect small, __________ range of bacteria

• Gram positive only or gram negative only

• Ex. Penicillin G affects G+ but not G- bacteria

TYPES OF ANTIMICROBIAL ACTION

Drugs may kill or inhibit bacterial growth1._________________________ the growth of microorganisms Bacteriostatic drugs rely on host immunity to eliminate pathogen2._________________________ microorganisms

Bacteriocidal drugs are useful in situations when host defenses cannot be relied upon to control pathogen

• ____________ REACTIONS• Allergies to penicillin

• Allergies often life threatening

• TOXIC EFFECTS• Ex.: Aplastic anemia

• Body cannot make RBC or WBC

• SUPPRESSION of _______________• Antibiotic associated colitis

• Toxic organisms given opportunity to establish themselves

• ANTIMICROBIAL ________________• Microorganisms have innate or adaptive resistance to

antibiotics

ADVERSE EFFECTS OF ANTIMICROBIAL DRUGS

MAJOR ACTION MODES OF ANTI_______________ DRUGS

ANTI_____________ ANTIBIOTICS

MODE of ACTION: Interference with essential processes of Mycobacterium tuberculosis

1. _________ (NIH) – inhibits synthesis of _______ acid

2. Ethambutol – inhibits incorporation of mycolic acid into

the cell wall

MODE of ACTION: Blocks _______________

1. Rifampin

AMANTADINE and RIMANTADINE Mode of action: block the ______________ of

influenza virus after it enters cell

Reduces severity and duration of disease

ZIDOVUDINE ____ and _____________ Mode of action: blocks nucleic acid synthesis

ANTI-___________ DRUGS

• Mode of action:• Inhibition of ergosterol synthesis

• Amphotericin B• Produced by Streptomyces species• Treatment of ____________ fungal diseases• Toxic to kidneys

• ___________________• Treatment of athlete’s foot and vaginal yeast

infections• Ketoconazole

• Less toxic than miconazole• Topical application for cutaneous mycoses

ANTI_______________ DRUGS

Figure 20.15

• Chloroquine

• Inhibits DNA synthesis

• Plasmodium species - __________

• Metronidazole

• Damages DNA

• ___________ sp., Trichomonas sp.

ANTI-____________ DRUGS

• Niclosamide

• Prevents ATP generation

• _______________

• Praziquantel

• Alters _________ permeability

• Flatworms

• Mebendazole

• Interferes with ________________________

• Effective against tapeworms and roundworms

• Used in livestock industry

ANTI-________________ DRUGS

KIRBY BAUER ANTIMICROBIAL SUSCEPTIBILITY TESTING:

Figure 20.17

FOUR MAIN MECHANISMS of ANTIBIOTIC __________________________

Resistance genes are often on plasmids or transposons that can be transferred between bacteria.

• Misuse of antibiotics selects for resistance

• Misuse includes:

• Using ___________________ antibiotics

• Using antibiotics for the common cold and other _________________ conditions

• Use of antibiotics in ________________

• Failure to complete the prescribed regimen

• Using someone else's leftover prescription

ANTIBIOTIC ______________

• Staphylococcus aureus• Common cause of __________________ infections

• Becoming increasingly resistant

• In past 50 years most strains acquired resistance to penicillin

• Due to acquisition of ____________ genes

• Until recently most infections could be treated with methicillin (penicillinase resistant penicillin)

• Many strains have become resistant

• MRSA methicillin resistant

Staphylococcus aureus

• MRSA strains are becoming resistant to vancomycin

ANTIMICROBIAL RESISTANCE