CULTURES
How do you establish a pure culture?
By thinning the sample to the point that one cell will form a pure colony forming unit.
This can be done by using a sample from a mixed culture to perform a streak isolation.
Where should you place your hands when lifting and moving a microscope?
By the arm and the base
True/False: Bacterial shapes that are not specifically defined are known as "irregular."
True! It's basic but correct. This is also known as pleomorphism.
What is the difference between incidence and prevalence?
Incidence refers to new cases and prevalence refers to both new and confirmed cases of a particular infectious disease.
*Remember the bathtub analogy
What is the most vitally important aspect of aseptic technique in any lab scenario?
Hand hygiene - Wash 15/20 seconds, scrub back of hand, palms and wrists before checking under fingernails. Rinse thoroughly and dry.
Please... just... wash... your... hands.
Ignaz Semmelweis will thank you from the grave.
False. Defined media include an elaborate list of specific ingredients in the medium.
Undefined media may have complex ingredients in unspecified amounts or with multiple species such as "yeast extract."
True/False: Electron microscopy produces incredibly detailed high resolution images with magnification up to 2 million times.
TRUE
Name 3 aspects of describing colony morphology.
Correct answers include 3 of the following: Pigment, Shape, Margin, Elevation, Size, Texture, Appearance, and Optical Property.
Identify 2 common reasons microbes are useful and 2 common reasons microbes are harmful.
Good:They produce vitamins and hormones that we need. They compete for resources with potential pathogens.
They decompose and work as nature's recycling system.
Bad: They can be parasitic and cause infectious disease
They are opportunistic in causing infections when they are out of their normal environment
Only 1% can be grown in vitro, so the majority of them are unknown to us.
False. We only work with BSL 1 and 2.
BSL 3 requires sustained directional airflow that will not be recirculated.
What is the difference between a colony and a colony forming unit (CFU)?
A colony is just a general term for one distinct cluster of one organism on a plate.
A colony forming unit is more nuanced and addresses the fact that some organisms do not form colonies, some cannot grow on media, and some colonies contain more than one originating cell.
CFUs are used to determine quantifiable measurements.
The cornerstone of Microbiology is the use of microscopy to study microorganisms. Why are some macroscopic organisms included in this Microbiology course?
The helminths and arthropods featured in this unit are often parasitic and therefore included when studying microbes and infectious diseases.
True/False: In many bacterial species, color defines age as this quality may change depending on the growth time and environment of the colony.
True. Some bacterial colonies will remain unpigmented until they begin to age or encounter various environmental conditions such as temperature or low nutrition availability.
Describe the major differences between the Gram positive and Gram negative cell wall.
Gram positive has a much thicker layer of peptidoglycan which floats on a thin, empty periplasm suspended above the plasma membrane. The outer portion contains teichoic acids for structure and signaling.
Gram negative cells have a much thinner peptidoglycan layer that floats within the periplasm sandwiched between the inner plasma membrane and outer membrane. The outer membrane includes a layer of lipopolysaccharide which contains lipid A, a known virulence factor.
The scientific method is employed to ensure certain parameters are met when setting up an experiment. Why is it important to use a control and how does that apply to aseptic technique?
Controls establish a means for comparison in the event that the sample is contaminated or spoiled. The method of adding controls highlight defective aseptic technique this way as well.
What is the purpose of subculturing?
Transfer of cells from an existing pure culture to a fresh growth medium ensures longevity of the colony for continued use in practical lab applications.
Name a unique characteristic of bacterial cells that would help you identify them under a microscope.
Gram Positive cocci arranged in chains are known as?
Streptococci... so are Gram Negative cocci when arranged in chains.
BTW... you will not see Gram Negative cocci used in this course. They are often more virulent than other BSL 2 species.
True/False: Both Eukaryotes and Prokaryotes have a unique genome: linear and circular respectively.
False. The chromosomes are different, but the genome is universal.
Name 3 types of PPE (Personal Protective Equipment).
3 Gs - Gloves, Goggles and Gowns (aprons).
Agar, derived from red algae, is common for use in the Microbiology lab as a solidifying agent for various media at room and other temperatures. Why is it important for the medium to be solid?
It is easier to study the organisms as defined colonies.
Also, life requires cardinal temperatures for growth and balance. Agar is solid at 25 and 37 degrees Celsius. Bacteria are ubiquitous at these temps (both room temp and human body temp.)
True/False: Immersion oil reduces refraction of light lending to impeccable image clarity and resolution. Using immersion oil should only be practiced when the 1000x objective lens is in place on your compound microscope.
False... it's the 100x objective lens. The magnification of the 100x lens + the ocular lens is 1000x.
Pink bacterial rods with a more oval shape are known as... ?
Gram Negative coccobacilli
What is the difference between selective and differential media used in the lab?
Selective media determine whether the organism thrives or fails dependent on the nutrition within the medium.
Differential medium do this as well, but also provide nuance. For example, MSA (Mannitol Salt Agar) is selective for halotolerant species, but differential depending on whether or not the organism ferments sugar.
When performing a streak isolation, the petri plate lid is carefully lifted slightly just enough to allow movement of the loop to brush the agar surface. What is the name of this technique and why is it necessary?
Clamshell technique. It is necessary to prevent contamination by free living microbes that might drop into the plate.