Lab Final Review - Week #7 Flashcards
What are chemotherapeutic agents?
Chemical substances used in the treatment of infectious diseases
What is the mode of action of chemotherapeutic agents?
They interfere with microbial metabolism without producing damage to host cells
What are the two broad categories into which chemotherapeutic agents can be divided?
- antibiotics
2. synthetic drugs
What are antibiotics?
They are substances produced by living organisms which are capable of destroying or inhibiting other cells
What are synthetic drugs?
They are drugs made in a laboratory
What is the mode of action of Penicillin?
Inhibits cell-wall synthesis
What are some possible side effects of taking Penicillin?
Penicillin resistance or sensitivity (allergic reaction)
What is the mode of action of Streptomycin?
In inhibits protein synthesis
What are some possible side effects of taking Streptomycin?
May damage auditory nerve that can result in deafness
What is the mode of action of chloramphenicol?
It inhibits protein synthesis
What are some possible side effects of taking Chloramphenicol?
It may cause aplastic anemia
What is the mode of action of Tetracycline?
It inhibits protein synthesis
What are some possible side effects of taking Tetracycline?
Permanent discoloration of teeth in young children
What is the mode of action of Bacitracin?
Inhibits cell-wall synthesis
What are some possible side effects of taking Bacitracin?
It is only for topical use, it is nephrotoxic if ingested
What is the mode of action of Polymyxin?
destruction of cell membrane
What are some possible side effects of taking Polymyxin?
It is for topical use only, it is toxic if ingested
What is the mode of action of Rifampin?
It inhibits RNA synthesis
What are some possible side effects of taking Rifampin?
appearance of orange-red urine, feces, saliva, swear, and tears
What is the mode of action of Quinolone?
It inhibits DNA synthesis
What are some possible side effects of taking Quinolone?
It affects the development of cartilage
What is sulfadiazine?
A synthetic agent, a sulfonamide
What is the mode of action of Sulfadiazine?
It produces a static effect on microorganisms via competitive inhibition. It competes with an essential metabolite during folic acid synthesis
Why do microorganisms need folic acid?
It is a coenzyme that it essential in the synthesis of amino acids and purines
Why do drugs that inhibit the production of folic acid not have a competitive effect on human cells?
Because human cells lack the enzymes needed for folic acid synthesis and actually acquire their folic acid in a preformed state
What is the Kirby-Bauer method used for?
It is used to determine the drug susceptibility of microorganisms isolated from infectious processes
What is the Kirby-Bauer method?
antibiotic disks are placed on the surface of an inoculated agar and after incubation, the susceptibility of the microorganism is measured based on the zone of inhibition created by the diffusion of the drug
What three outside variables (other than the drug itself) effect the zone of inhibition surrounding an organisms post incubation?
- the ability of the antibiotic to diffuse into the medium
- the number of organisms inoculated
- the growth rate of the organism
What measurement is considered the zone of inhibition?
The diameter with no growth that is displayed in mm
What is the clinical application of the Kirby-Bauer method?
It allows for the determination of with agent would be best to treat patients based on their bacterial infection
What are the 3 reasons behind the use of combination chemotherapy?
- lower bacterial resistance
- reduce host toxicity
- enhance agents bactericidal activity
What is synergism? How is it determined?
Synergism is enhanced bactericidal activity, a result is synergistic when the sum of the effects of the agents being combined is significantly greater than the sum of their individual effects
What is an additive effect?
It is when the interaction of the two drugs combined is no greater than the sum of their separate individual effects
What is the disc - agar diffusion technique?
Two drug infused discs are placed on each half of an inoculated Mueller - Hinton agar plate and following incubation the zones of inhibition are observed to determine either a synergistic or an additive effect.
What are the three distinct tests that can be used to determine the drug susceptibility of an organism?
- Kirby-Bauer method
- Disc-agar diffusion technique
- broth tube dilution method
What is Minimal Inhibitory Concentration (MIC)?
It is the lowest concentration of an antimiwcrobial agent that inhibits the growth of the test organism.
What is the origin of the antibiotic Penicillin?
It is produced my the mold Penicillium Chrysogenum (discovered by Alexander Fleming in 1928
What part of the Penicillin molecule is linked to its activity?
The B-lactam ring in its molecular structure
What type of Pathogen was found to be resistant to Penicillin?
Staphyloccocus aureus (because it produces B-lactamase
What is B-lactamase?
It is an enzyme that breaks a bond in the B-lactam ring portion of Penicillin, thereby compromising its inhibitory activity
What is the broth tube dilution method?
It involves a series of serial dilutions of a drug into an enriched broth medium. Following incubation, the susceptibility of the drug is determined via spectrophotometric absorbance readings
What are the three major species of Staphylococcus?
S. aureus, S. epidermidis, S. saprophyticus
Which Staph species are virulent and which are avirulent?
Generally only S. aureus is virulent, and S. epidermidis and S. saprophyticus are avirulent
How do the different species of staph respond to Mannitol salt agar?
S. aureus -> frementer (yellow halo)
S. epidermidis and S. saprophyticus -> nonfementors
How do the different species of staph respond to a coagulase test?
S. aureus -> produces coagulase (forms network of fibrin)
Others do nothing
How do the different species of staph respond to a Deoxyribonuclease Test?
S. aureus is the only one that produces DNase this can be seen by a pink halo that forms around the growth
How do the different species of staph respond to Novobiocin?
S. epidermidis -> sensitive
S. saprophyticus -> resistant
What is staphylxanthin?
a yellow pigment produces by staph with virulence factors that evades the immune system
What is urease?
a hydrolytic enzyme that breaks down amide compound such as urea
What organism is the urease test specifically useful in identifying?
Proteus vulgaris
Explain the urease test
An organism is inoculated into and grown in a urea broth medium (yellow) which contains a pH indicator called phenol red. If urea is broken down by the presence of urease the broth will turn red.
What are the products of urea being acted upon by urease?
ammonia, carbon dioxide, and water.
What are the primary species of bacteria determined to be normal flora of the skin?
Staphyloccoci, Streptococci, and Micrococci
What is the catalase test?
Hydrogen peroxide is added to a bacterial colony in order to determine the prescence of catalase, which degrades hydrogen peroxide (because it is toxic to the cells) and forms free oxygen gas as a byproduct which can be observed as bubbling.
What is the catalase test used to identify?
It is used to differentiate between staph and strep bacteria. Staphylococci are catalase positive and Streptococci are catalase negative
Why does the presence of organic matter reduce the effectiveness of disinfectants and antiseptics?
Because they could react with the organic matter reducing the amount of disinfectant or antiseptic left to react with the microorganism being targeted
