What are methods used to limit microbial growth?
Refrigerate, freeze, boil, pasteurization, acidification, increase osmotic pressure, oxygen removal, drying, gamma irradiation, hydrostatic pressure, chemical additives
What are some sterilization methods?
Autoclave (moist heat), dry heat, incineration, alcohol flame, gamma irradiation, UV light, membrane filtration, or chemicals
What are drugs that destroy microbes, prevent their multiplication or growth or prevent their pathogenic effect?
Antimicrobials
Who discovered penicillin?
Alexander Fleming
What is an antibiotic?
A low molecular substance produced by a
microorganism that at a low concentration inhibits or kills other microorganisms.
What is an antimicrobial?
Any substance of natural, semisynthetic
or synthetic origin that kills or inhibits the growth of
microorganisms but causes little or no damage to the host.
T/F: All antibiotics are antimicrobials, but not all antimicrobials are antibiotics.
True
What are natural antimicrobials?
Produced by bacteria or fungus- Streptomycin, penicillin, tetracycline
What are semi-synthetic antimicrobials?
Chemically altered natural compounds- ampicillin, amikacin
What are synthetic antimicrobials?
Chemically designed in the lab- sulfonamide, enrofloxacin, marbofloxacin
How are antimicrobial agents classified?
- Chemical structure
- Mode of action
- Type of antimicrobial activity
- Spectrum of antimicrobial activity
What are the different chemical structure families of antimicrobials?
Macrolide, Aminoglycoside, Tetracycline, Beta Lactams, Sulfonamides
Examples of β lactam antibiotics?
Penicillin, ampicillin, cephalosporins
What do β lactam antibiotics do?
Inhibit peptidoglycan (cell wall) synthesis. Also bind and inhibit penicillin binding proteins.
What is an enzyme present in bacteria which
can cleave β lactam ring and inactivate penicillin and
contribute to resistance?
β lactamase
What prevents degradation of penicillin by β lactamase?
Clavulanic acid
What do Aminoglycosides do?
Inhibit protein synthesis (30s subunit of bacterial ribosome)
Give some examples of 30S protein synthesis inhibitors?
Tetracyclines, Streptomycin, Gentamicin, Amikacin
Give some examples of 50S protein synthesis inhibitors.
Erythromycin, Azithromycin, Chloramphenicol, Clindamycin, Lincomycin
Which antibiotic aids in inhibition of DNA synthesis?
Quinolones- Ciprofloxacin, Enroflaxacin, Metronidazole
With respect to DNA synthesis inhibition, what is resistance due to?
Mutations in the gene for DNA gyrase
What does Metronidazole do?
Makes breaks in the DNA
What are 2 RNA Synthesis Inhibitors?
Rifampin and Mupirocin
What antibiotic inhibits tRNA synthetase (Translation)?
Mupirocin
What antibiotic inhibits RNA polymerase (Transcription) and is active against Mycobacterium tuberculosis?
Rifampin
What are Sulfonamides and Trimethoprim responsible for?
Competitive inhibitors of dihydrofolate reductase. –> Folic acid synthesis inhibitors
What are broad spectrum antibiotics? Give 1 example.
Active against gram (+) and (-) bacteria
Tetracycline
What are narrow spectrum antibiotics? Give 1 example.
Limited activity, useful against a particular species of either gram (+) or gram (-) bacteria.
Tobramycin
What is the difference between Bactericidal and Bacteriostatic activity?
Bactericidal- kills bacteria
Bacteriostatic- inhibits bacterial growth
Give some examples of Bactericidal antibiotics.
Aminoglycosides, β lactams, Fluoroquinolones, Metronidazole (narrow spectrum)
Give some examples of Bacteriostatic antibiotics.
Tetracyclines, Clindamycin, Macrolides, Sulfonamides, Trimethoprim (broad spectrum)
Antimicrobial Susceptibility Testing (AST)
A lab test to determine whether a bacteria is
susceptible to a particular antimicrobial agent.
What are two types of AST?
- Disk diffusion test( Kirby Bauer test)
2. Broth/Agar Dilution Test
What is Minimum inhibitory concentration (MIC)?
Minimum amount of drug required to inhibit bacterial
growth
Are higher or lower MIC values better for treatment?
Lower
What is a Susceptibility break point?
A drug concentration above which an organism is
considered resistant and at or below this value organism is susceptible to that drug.
What are the three break point values are set at?
Susceptible, Intermediate, or Resistant
Briefly discuss how the Kirby Bauer test works.
Agar is cultivated with bacteria, small paper disks with antibiotic contained is placed on the agar, incubate, measure zone of inhibition
What is MBC?
The minimal concentration of a drug that kills the bacteria.
What is the Gradient Diffusion Test?
Uses diffusion and dilution
What are the possible results of susceptibility?
Susceptible- High likelihood of therapeutic success
Intermediate- Uncertain therapeutic outcome
Resistant- High likelihood of therapeutic failure
When does Antibiotic Resistance happen?
When bacteria change and become resistant to the antibiotic used to treat the infections they cause
What are 2 types of antimicrobial resistance?
Innate resistance, Acquired resistance
What type of resistance has preexisting genomic properties?
Innate resistance
What type of resistance is acquired by mutation or horizontal gene transfer?
Acquired resistance
How do you prevent infectious diseases?
Vaccines, management, hygiene practices