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BIO 205L MIDTERM 2025/2026 LAB QUESTIONS
AND ANSWERS/MICROBIOLOGY GRADED A+
Why do transient microbiota (flora) not become entrenched?
Come into contact with skin constantly, but most are unable to multiply there and will die. pH of skin is usually acidic (ranging from 4-6). The epidermis (outer layer of skin) has a low water content and is frequently dry, so normal skin flora is associated with the apocrine and sebaceous glands in the skin which provide not only moisture, but also other nutrients for microbial growth. Washing skin with soap and water sloughs off dead outermost layers of skin and may expose normal flora.
Person safety
Ø Lab coat or apron
Ø Gloves
Ø Safety glasses
Ø Closed toe and covered heel shoes
Ø Hair should be tied up
disposal - Microscope slides
white paper biohazard discard pouches or the red plastic biohazard boxes
disposal - broken glass
white paper biohazard discard pouches or the red plastic biohazard boxes
disposal - petri dishes
orange/red biohazard trash bags in the white metal cans with foot pedal to open
disposal - plastic tubes
orange/red biohazard trash bags in the white metal cans with foot pedal to open
disposal - paper trash contaminated with microbial culture
orange/red biohazard trash bags in the white metal cans with foot pedal to open
disposal - tube and flask media
plastic discard tubs on the bottom of the cart, use racks for tubes, remove all labels
disease-causing for humans
pathogenic
diphtheroid Corynebacterium and Propionibacterium, species of Staphylococcus such as Staphylococcus aureus and Staphylococcus epidermis, and Malassezia yeast
Common resident microbes of the skin include...
may be present on the body temporarily but do not become firmly entrenched
Transient microbiota (flora)
the top 2 reasons for nosocomial infections in the US
Staphylococcus aureus and Pseudomonas aeruginosa
disposal - micropipette tips
plastic discard beakers on the bench tops or in the orange/red biohazard trash bags in the white metal cans with foot pedal to open
disposal - swabs
plastic discard beakers on the bench tops or in the orange/red biohazard trash bags in the white metal cans with foot pedal to open
disposal - tongue depressors
plastic discard beakers on the bench tops or in the orange/red biohazard trash bags in the white metal cans with foot pedal to open
disposal - glass serological pipettes
long plastic discard tubs on the bench tops provided only when needed
disposal - gloves
tall boxes labeled for glove discard only
disposal - non-contaminated paper trash
regular trash cans
disposal - unused media
do not discard; return to top of cart
Rhodophyta (red algae)
solid media in Petri dishes; the surface is used for isolation and growth of microorganisms
Plates
test tubes containing solid medium, which has been allowed to solidify in an upright position, and are usually used for anaerobic growth
Deeps
test tubes containing solid medium that has been allowed to solidify at an angle and the surface of the agar is used for the maintenance of stock cultures of microorganisms
Slants
nutrient medium designed to favor the growth of certain microbes and to inhibit undesirable competitors
Selective medium
selective only; it selects for Gram-positive organisms but tells nothing of the physiology of the organism growing on it
Phenyl ethyl alcohol agar (PEA)
medium which provides a visible indication of a physiological characteristic of a microorganism
Differential medium
both selective and differential; selects for growth of salt-tolerant organisms and differentiates mannitol fermenters (change agar from red to yellow) from non- mannitol fermenters (don't change color of agar)
Mannitol salt agar (MSA)
both selective and differential; selects for Gram-negative bacteria and differentiates lactose fermenters from non-lactose fermenters
Eosin methylene blue agar (EMB)
used when using a sample of a population to estimate or generalize to a population
Sample standard deviation
dry heat sterilization method; inoculating loops/needles are held in the flame of a Bunsen burner until flowing red hot. It is important to flame the entire wire loop/needle to minimize contamination.
Flaming
dry heat sterilization method; items to be sterilized like glassware are placed in an oven and heated to 170*C for 2 hours.
Hot-air sterilization
how heat sensitive liquids or gasses are sterilized; the surface of the filter traps particles while allowed the liquid to pass through, this is a physical removal of bacteria or other contaminants.
Filtration
widely used gas for gas chemo-sterilization; toxic and explosive and is released into a chamber where it circulates for up to 4 hours with the items to be sterilized; type of cold-sterilization
Ethylene oxide
no heat is used
Cold-sterilization
includes microwaves, ultraviolet radiation, X-rays, gamma rays, and electrons
Electromagnetic radiation
causes damage to the DNA leading to the death of exposed organisms; cannot penetrate solid, opaque, light-absorbing surfaces and is useful only to sterilize exposed surfaces
Ultraviolet (UV) radiation
causes ions and other reactive molecules to be produced and these reactive molecules can degrade or alter biopolymers such as DNA and proteins
Ionizing radiation
minute living cells that are too small to be seen with the naked eye; they are widespread in our environment and can be found on almost any surface; growing on a solid culture medium (i.e. agar plate) will form colonies if the cells used to inoculate the plate are separated from each other on the surface of the medium
Microorganisms
the nutrients on which microorganisms are grown
Medium
Whole colony shape:
round; irregular; rhizoid
Margin shape:
Smooth, entire; lobate; filamentous
Elevation:
Convex; umbonate (button-like); flat
Optical properties:
Opaque (can NOT see through it); semi-translucent (can see through edges of the colony but not the center); translucent (can see through it)
Surface characteristics:
Dull; shiny; wrinkled; concentric; pigmentation (color)
How to handle media aseptically
- Upon entering the lab, lab bench must be wiped with disinfectant and a clean paper towel to eliminate any contaminates on the surface. Wash hands. Wear gloves. Tie back long hair.
Gently shake culture tube to suspend microorganisms.
Heat loop and wire to red-hot.
Remove cap and flame neck of tube. Do not put down cap.
After allowing loop to cool for at least 5 seconds, remove a loopful of microorganisms. Avoid touching the sides of the tube.
Flame the mouth of the culture tube again.
Replace cap. Place tube in test-tube rack.
Flame mouth of the tube of broth or agar in which the sample will be placed. Place the loopful of microorganism on a slide for a smear or onto an agar plate, or into a tube of broth/slant/deep.
Flame loop again before removing another loopful from culture or setting the inoculating loop aside.
refers to a procedure performed under sterile conditions
Aseptic technique
dry heat sterilization
one containing a single kind of organism; rarely exist in the natural world, but are useful in the lab to study cellular processes without influence from other
Pure culture
pure cultures of this were used to determine the roles of DNA polymerases involved in replication and DNA repair
Escherichia coli
a population of cells which arise from a single cell growing on a solid medium; all of the cells should be genetically identical but for a few (if any) that may have mutated
Colony
an example of a pure culture
Isolated colony
Another way of determining the purity of a broth culture is by ______ the sample. A ______ stain can reveal the different cellular morphologies (shape and/or
arrangement) of the microorganisms present, while a ______ stain like a ______ stain can reveal structural differences.
staining; simple; differential; Gram
transferring the colony to a new plate; commonly used to maintain cultures; this second plating will also allow any hidden cells of a different species to be diluted with streaking the plate for isolation
Subculturing
Adequate magnification must be used when viewing prokaryotic cells because of their small size; most are ____ μm to ____ μm. In general, the oil-immersion objective must be used to observe microorganisms and the total magnification achieved is _____.
0.2; 10; 1000X
Because cells consist mostly of ______ , even under adequate magnification unstained cells may be difficult to see because of lack of ______.
water; contrast
makes cells more visible by providing contrast
Staining
- Coccus, rod/bacillus, and spiral
- Diplo (pairs), strepto (chains), staphylo (clusters), or randomly
round
Cocci
Types of cocci
- Diplococci - cocci that remain in paids
- Streptococci - cocci that remain in chains
- Tetrads - groups of four cocci
- Staphylococci - grapelike clusters
rod-shaped cells that divide only across the short axis
Bacilli
Types of bacilli
§ Diplobacilli - pairs
§ Streptobacilli - chains
short oval cells that resemble cocci; can be induced by less than ideal environmental growth conditions, or simply by the genetic makeup of the cell
Coccobacilli
have one or more twists
Spiral
Types of spiral
§ Vibrios - curved rods
§ Spirilla - helical shape that is rigid
§ Spirochetes - helical, flexible, and resemble a corkscrew (could put a rod through the center)
irregular or variable shape
Pleomorphic
some actinomycete bacteria, e.g., Streptomyces coelicolor, produce filaments of hyphae that form a mycelium (network of hyphae)
Filamentous growth
