Lab Quiz 4 Flashcards
What is staining used for?
enhance contrast between the sample and its surroundings
Direct stain
stains/colors the organism
Indirect stain
stains the background (everything but the sample)
Simple stain
Uses only one stain
What can a simple stain determine?
cell morphology
size
arrangement
Differential staining used in this lab
Gram stain
spore stain
Gram Staining
stains cell envelope or peripheral structure
spore staining
stains endospores
Gram positive bacterial cells
retains crystal violet- purple
thick peptidoglycan layer
Gram negative bacterial cells
crystal violet washes out
retains safranin counterstain-pink
outer membrane and a thin layer of peptidoglycan
Gram stain procedure
C- crystal violet
R- rinse
I- iodine
E- ethanol
S- safranin
When do somme bacteria sporulate
under environmental stress
EX limited carbon source
How do we create environmental stress to form endospores in lab?
nutrient agar places without glucose
this limits carbon source
Spore positive bacteria
retain malachite green
Spore negative bacteria
safranin stains membrane of vegatative cells
pink
vegatative cells
cells that do not take part in production of gametes
Spore stain formation
weeklong starvation from growing on NA-agar plate without carbon source
Spore stain procedure
M- apply malachite green
M- mordant (heat)
W- application of water (decolorized)
S- Safranin (counter stain)
Total magnification
Lens times ocular
How many on/off switches on microscope?
three
- microscope
- camera
- display
What are the causative agents of bacillary dysentery and typhoid fever?
Shigella
Salmonella
Do not screen for pathogens, WHY and WHAT DO YOU SCREEN
when pathogens are detected its too late to prevent spread of disease
Instead screen for indicator organisms that are highly abundant in feces
What is the most frequently used indicator organism
coliforms
Coliforms
facultative anaerobes
gram negative
rod shaped
lactose fermenters
Where are coliforms found?
colon and feces of healthy individuals
the gastrointestinal tract of other animals
What are coliforms used as an index for
contamination of Shigella and Salmonella
safety of marine and estuary waters used for shell fishing
safety of freshwater and marine swimming areas
Heterotrophic Plate Count
quantitative
determines overall quality of water and effectiveness of disinfectants used
HPC coliforms are detected in two stages
Presumptive test
confirmed test
Presumptive test
uses selective/differential Lauryl-tryptose (LT) broth
LT broth
contains lauryl-sulfate- detergent
contains lactose- supports coliform growth by fermentation
T/F most bacteria can pass through detergents
FALSE
only bacteria in stomach and intestinal tract can withstand detergent
Confirmed test
streaked on Eosin-methylene blue (EMB) agar to verify presence of coliforms
EMB agar
selective- contains dyes that inhibit gram-positive organisms
differential- lactose fermenters form dark colored colonies
Most probable number (MPN)
statistical estimate used to calculate number of coliforms based off LT tube test
How many dilutions per sample for MPN
two
Membrane filtration technique
known volume of water is filtered through thin membrane grid (0.45 um)
Membrane filtration process
all bacteria are retained on filter’s surface
this is immediately transferred to a plate
plate is incubated 32 C
dissecting microscope characteristic coliform colonies are counted
the number of colonies per ml is calculated
Indigenous/normal flora
microorganisms found in many regions of the body
Folmites
inanimate/inert objects that are likely to carry infection
EX. doorknob
Why is skin hospitable?
Skin is very dry
salts create hypertonic environment
sebaceous glands secrete oil/acids that inhibit bacterial growth
Most skin bacteria are…
Gram positive
salt tolerant cocci
catalase positive
EX staphylococcus and micrococcus
What is causative agent of staph infections?
staphylococcus aereus
S. aereus will ferment….
mannitol
What agar is used to differentiate and select S. aureus
mannitol salt agar
Pathogenic strains of S. aureus typically produce…
coagulase
causes fibrin in blood to clot
Common genre that can grow in throat
Streptococcus and staphylococcus
Causitive agent of strep throat
Streptococcus pyogenes
Pathogenic streptococcal species typically produce what?
enzyme called streptolysins
causes cell lysis
hemolysis
When blood cells are being attack by lysis
How is hemolysis determined
streaking bacteria on plates of blood agar
Three patterns of hemolytic activity
alpha
beta
gamma
alpha hemolysis
partial hemolysis
characterized by green cloudy zone around bacterial growth
beta hemolysis
complete lysis
characterized by clear zone around growth
gamma hemolysis
no hemolysis
characterized by no change on blood agar
T/F streptococci can grow in presence of respiratory poisons
TRUE
because they lack a respiratory chain
What out of the three types of hemolysis are pathogenic
Beta hemolytic streptococci
What out of the three types of hemolysis are part of normal flora
alpha and gamma hemolytic streptococci
What are ways streptococcus aureus can be spread?
direct and indirect contact
