Chapter 12 Flashcards
What is the goal of antimicrobial chemotherapy?
Administer a drug to an infected person that destroys the infective agent without harming the host’s cells
What is prophylaxis?
Use of a drug to prevent imminent infection of a person at risk
What is antimicrobial chemotherapy?
The use of drugs to control infection
What are antimicrobials?
Any antimicrobial drug, regardless of what type of microbe it targets
What are antibiotics?
Substances produced naturally or synthetically that can inhibit or destroy microbes, namely bacteria
What are semisynthetic drugs?
Drugs that are chemically modified in the lab after being isolated from natural resources
What are synthetic drugs?
Drugs produced entirely by chemical reactions in a lab setting
What is narrow-spectrum?
Antimicrobials effective against a limited array of microbial types
What is broad-spectrum?
Antimicrobials effective against a wide variety of microbial types
How are antibiotics naturally synthesized?
As common metabolic products of bacteria and fungi
Why do bacteria and fungi produce antibiotics?
To reduce competition for nutrients and space
What three factors must be known before starting antimicrobial therapy?
- Microbe identity
- Degree of microbe’s susceptibility
- Overall medical condition of the patient
What is the Kirby-Bauer technique?
Technique for testing drug susceptibility that involves plating bacterium on a plate of special medium and placing antibiotic discs onto the plate in order to observe zones of inhibition
What is an antibiogram?
A profile of antimicrobial sensitivity
What is the minimum inhibitory concentration (MIC)?
The smallest concentration of drug that visibly inhibits growth
What factors can lead to treatment factor?
- Inability of drug to diffuse into infected body compartment
- Resistant microbes in infection that were not in the tested sample
- A polymicrobial infection in which some pathogens are resistant to the drug
What is the therapeutic index (TI)?
Ratio of toxic drug dose to humans to minimum effective dose
Which TI values indicate greater potential for toxic drug reactions?
Smaller ratios (when the two values are closer together)
What preexisting conditions must be considered when prescribing drugs?
- History of allergy
- Underlying liver or kidney disease
- Patients that are infants, elderly, or pregnant
What is selective toxicity?
Antimicrobial drugs should kill or inhibit microbial cells without damaging host tissues
Why do penicillins have excellent selective toxicity?
They block the synthesis of the cell wall found only in bacteria
Which drugs are most toxic to human cells?
Those that act upon a structure common to both the infective agent and the host cell
What are the metabolic targets of chemotherapeutic agents?
Inhibition of cell wall synthesis, inhibition of nucleic acid structure and function, inhibition of protein synthesis, interference with cell membrane structure or function, inhibition of folic acid synthesis
Which antibacterial drugs target the cell wall?
Penicillins, cephalosporins, carbapenems, bacitracin, isoniazid, vancomycin
What suffix is typical of penicillin drugs?
-cillin
What prefixes are typical of cephalosporin drugs?
cep-, cef-
What suffixes are typical of carbapenem drugs?
-nem, -nam
Which antibacterial drugs target protein synthesis?
Aminoglycosides, tetracyclines, glycylcyclines, macrolides, clindamycin, synercid, linezolid
Which antibacterial drugs target folic acid synthesis?
Sulfanamides
Which antibacterial drugs target DNA and/or RNA?
Fluoroquinolones
What suffix is typical of fluoroquinolone drugs?
-acin
Which antibacterial drugs target cell membranes?
Polymyxins, daptomycin
Why are bacteria in biofilms less sensitive to the same antimicrobials that work against them when they are free living?
Bacteria in biofilms express different phenotypes than the free-living bacteria
Why are anti-fungal drugs more harmful to humans than antibiotics?
Fungal and human cells are both eukaryotes and have more similarities
What are the four main anti-fungals currently in use?
Polyene antibiotics, azoles, echinocandins, allylamines
What drugs were/are used to treat malaria?
Quinine (previously), chloroquine, primaquine
What treatments are available for protozoan infections?
Metronidazole, amoebicide
What drugs are used to treat helminth infections?
Albendazole, pyrantel, praziquantel, invermectin
What are the three major modes of action for antiviral agents?
- Barring penetration of the virus into the host cell
- Blocking the replication, transcription, and translation of viral molecules
- Preventing maturation of viral particles
What is drug resistance?
Adaptive response in which microbes begin to tolerate an amount of drug that would ordinarily be inhibitory
What caused drug resistance?
Genetic versatility and adaptability of microbial populations
What is intrinsic drug resistance?
Bacteria must be resistant to any antibiotic that they themselves produce
What is acquired drug resistance?
Bacterial resistance to a drug to which they were previously sensitive
Through what methods does drug resistance develop?
- Spontaneous mutation
2. Horizontal transfer of R factors or transposons
What are the mechanisms of drug resistance?
- New enzymes are synthesized that inactivate drug
- Permeability/drug uptake is decreased
- Binding sites for drug are decreased/lower affinity
- Affected metabolic pathway is shutdown/alternate pathway is used
- Drug is immediately eliminated
Why does natural selection favor drug resistance?
When a drug is introduced to a population, those microbes that are sensitive will die, leaving only the resistant bacteria to repopulate
What percent of antibiotic prescriptions are prescribed for non-bacterial infections/ailments?
75%
What is the “shotgun” approach to antimicrobial therapy?
Antibiotics are prescribed first, without determining if the infection is indeed bacteria related
What is the hospital factor?
Hospital environment continually exposes pathogens to a variety of drugs, causing pathogens to develop resistance more rapidly than in nature
What percent of all antibiotics are given to livestock in the U.S.?
80%
Why is it an issue to give livestock antibiotics?
Their enteric bacteria become drug resistant and can spread to humans, causing resistant infections
What are probiotics?
Preparations of live microorganisms fed to animals and humans to improve intestinal biota
What are prebiotics?
Nutrients that encourage growth of beneficial microbes in the intestine
What is a fecal transplant?
Involves transfer of feces, containing beneficial normal biota, from healthy to affected patients via colonoscopy
What are the categories of major side effects from drugs?
- Direct damage to tissues through toxicity
- Allergic reactions
- Disruption in balance of normal microbiota
Which organs are most commonly impacted by drugs?
Liver, kidneys, GI tract, cardiovascular system, nervous system, respiratory tract, skin/bones/teeth
What is the most common complaint associated with oral antimicrobial therapy?
Diarrhea
Why do drugs sometimes cause allergy?
Drug acts as an antigen that stimulates allergic response
What is a superinfection?
Infection that occurs when beneficial resident species are destroyed through antibiotic therapy, allowing other microbes to overgrow and cause disease
