Microbiology Lab Exam 2 Flashcards
bacteria
bacteria are prokaryotic, one-celled organisms. Individual bacterial cells are visible only with the aid of a high-powered microscope.
bacteria can be grown in a laboratory setting on sterile petri dishes containing a gelatin-like nutrient called agar.
bacteria reproduce by binary fission. Population of cells grow very rapidly (exponential growth).
colony
when a population of bacteria has multiplied to a million or more cells, a colony can be seen on the surface of the agar plate with the naked eye.
- morphological characteristics of a bacterial colony, such as shape, margin, opacity, and color can be used to identify the species of bacteria in the colony.
chemotherapeutic agents
chemicals used to treat disease
antimicrobial drugs
antimicrobial drugs or disinfectants used to control bacterial growth are all ANTIMICROBIALS
Alexander Fleming
In 1928, Alexander Fleming identified mold Penicillum notatum, excreting compound toxic to Staphylococcus aureus in culture.
different categories of antimicrobial chemicals that are used to control bacterial growth
- antibiotics
- disinfectants
- antiseptics
antibiotics
antimicrobial drugs naturally produced by microorganisms (be able to kill off and prevent infection, but uses a living thing to do it)
disinfectants
any substance or process that is used primarily on non-living objects to kill germs, such as viruses, bacteria, and other microorganisms that can cause infection and disease (ex: alcohols, chlorine)
antiseptics
antimicrobial substances that are non-damaging to living tissue/skin while reducing the possibility of infection, sepsis, or putrefaction (ex: mouthwash, alcohols, ethyl alcohol, rubbing alcohol, hydrogen peroxide)
sterilant
destroy all microorganisms (heat- sensitive critical instruments)
high-level disinfectants
destroy viruses, vegetative cells (do not reliably kill endospores; semi-critical instruments used)
intermediate-level disinfectants
destroy vegetative bacteria, mycobacteria, fungi, and most viruses (disinfect non-critical instruments)
low-level disinfectants
destroy fungi, vegetative bacteria except mycobacteria, and enveloped viruses (do not kill endospores, naked, viruses; disinfects furniture, floors, walls)
bacterial susceptibility
“susceptible” means “weak to”- for example to certain disinfectants, antibiotics
a bacterial species can be susceptible to some specific antibiotic drugs, meaning it can’t grow in the drugs presence. The opposite of susceptible is resistant.
Kirby- Bauer test
the Kirby- Bauer test, also called the disc diffusion test is a standard test to determine a bacterium’s susceptibility to antibiotics, disinfectants, or antiseptics
basics of the test:
1) the bacterium is swabbed on the agar and the antibiotic discs are placed on top
2) the antibiotic diffuses from the disc into the agar in decreasing amounts the further it is away from the disc
3) if the organism is killed or inhibited by the concentration of the antibiotic, there will be NO GROWTH in the immediate area around the disc: this is called the zone of inhibition (ZOI)
size of the disc= 7mm (if there is no zone at all)
selective toxicity
cause greater harm to microbes (interfere with essential structures or properties common in microbes but not human cells: which will kill more effectively and which microbes it will target) **kill off bacteria without killing us
bacteriostatic drugs
drugs that inhibit bacterial growth (patient’s defenses must still eliminate)
bactericidal drugs
drugs that kill bacteria
zone of inhibition (ZOI)
area of media where bacteria are unable to grow, due to prescence of a drug that impedes their growth
antimicrobials
a substance that kills microorganisms such as bacteria or mold, or stops them from growing and causing disease
antimicrobials
a substance that kills microorganisms such as bacteria or mold, or stops them from growing and causing disease
innate or intrinsic resistance
the innate ability of a bacterial species to resist activity of a particular antimicrobial agent through its inherent structural or functional characteristics, which allow tolerance of a particular drug or antimicrobial class (something your born with, for ex: mycoplasma lack a cell wall, so they resist penicilin, or outer membrane of gram-negatives resist many drugs)
acquired resistance
it is said to occur when a particular microorganism obtains the ability to resist the activity of a particular antimicrobial agent to which it was previously susceptible. (spontaneous mutations, horizontal gene transfer, bacteria conjugate)
** something that happens from generation to the next (mutations occurred, change in DNA sequence randomly)
spontaneous mutation
occur during replication. happen at a low rate but can have a significant effect. Just a single-base pair change in gene encoding a ribosomal protein yields resistance to streptomycin.
combination therapy of multiple drugs is often used; unlikely cells will simultaneously develop resistance to all drugs
