LAB - Intro to MLSCI Lab

Question 1

microorganisms that are unable to establish permanent colonization or infection and are considered an insignificant finding when
recovered in clinical specimen

Answer 1

transient colonization

Question 2

microorganisms that are able to establish permanent residency on or in human bodies, generally exist in a symbiotic relationship with
their human host, but may result in disease when there is a disturbance in microbiome or host environment or invasion into normally sterile body sites

Answer 2

persistent colonization

Question 3

microorganisms primarily associated with human host infection, immunological response, and disease

Answer 3

pathogenic infection

Question 4

microbiological procedures can be subdivided into:

Answer 4

microscopy, culture, biochemical tests, immunoassays, and molecular tests

Question 5

presumptive assignment to a genus level is based on these two things

Answer 5

gram stain and colonial morph

Question 6

Lined yellow biohazard buckets

Answer 6

cultures, specimens, tubes

Question 7

unlined crocks

Answer 7

non-fixed biohazard contaminated slides

Question 8

lined crocks

Answer 8

contaminated gauze, disposable pipettes, swabs, spreaders, etc.

Question 9

upright bunsen burner important notes

Answer 9

• stopcock ON (vertical) when wanting to flame
• flame material at httest part of flame, where the inner cone ends and outer cone begins
• adjust air supply by rotating collar until fierce blue flame is achieved for high heat
• do not adjust gas pressure using stopcock; use desk supply tap

Question 10

Principle of gram stain

Answer 10

• differential stain
• crystal violet diffuses into organisms and forms a water-soluble lake with the iodine trapping agent (mordant)
• decolorizing agent acetone alcohol dehydrates the walls of gram pos organisms and a barrier forms through which the dye cannot pass = purple; gram neg organisms have a higher lipid content in their cell wall which is dissolved by acetone alcohol thus allowing the CV to escape - take up safranin = pink
• stain depends on the organism having an intact cell wall to begin with

Question 11

heat fixation of smears

Answer 11

• removes all water and kills and fixes bacteria to the slide so they are not washed off during staining
• direct smears from clinical specimens should be fixed by flooding with methyl alcohol for one minute = better preservation of cells = PMNs, monocytes, epithelial cells

Question 12

Most persistent problem encountered in gram staining

Answer 12

over decolorization

• non-intact cell wall (excess heat fixation, cell wall damage due to host…)
• decolorizing for too long
• low concentration of crystal violet
• excessive washing
• not enough iodine
• excessive counterstaining

Question 13

Streaking/spreading for isolation

Answer 13

• do not streak too close to edge of plate = contaminants!
• toe, heel, toe, heel
• 4 quadrants

Question 14

Brightfield microscopy

Answer 14

• light from an incandescent source is aimed toward a lens beneath the stage called the condenser - through specimen - objective lens - second magnifying lens (oculars) - eye

Question 15

Darkfield microscopy

Answer 15

useful for examining live delicate organisms (ex: spirochetes of syphilis); difficult to stain!

• special condenser that provides oblique light only
• organisms show up as brightly illuminated objects against a black background

Question 16

phase contrast microscopy

Answer 16

examination of transparent biological material without staining
- reveals differences in cells and their structure not discernible by brightfield or darkfield