54 terms

Microbiology Lab Practicle 2

Selective Media
used to isolate specific groups of bacteria
Phenylethyl alcohol agar, crystal violet agar, 7.5% sodium choloride agar
Selective media agars
Differential/selective media
can distinguish among morphology and biochemically related groups of bacteria. chemically altar bacteria to show a physical change in appearance of bacterial growth or medium surrounding the colonies, sometime differential and selective media characteristics can be combined.
Mannitol Salt agar, MacConkey agar, EMB agar
Differential Media agars
Enriched media
media that have been supplimented with high nutritious materials to cultivate fastidious organisms
Blood agar
Enriched media agar
Phenylethyl alcohol agar (PEA)
tests for gram positive organisms, and inhibitory to gram negative
Crystal violet agar
selective for gram negative, and inhibitory for gram positive
7.5% sodium chloride agar
inhibitory to most organisms, detects for salt loving organisms (halophilic) most useful in detection of staphylococcus
Mannitol salt agar
contains a high salt concentration, PH indicator for detecting acid. detects for staphlycocci-->yellow zone around bacteria if it ferments the mannitol salt
MacConkey agar
allows the isolation of gram negative two groups: coliform bacilli and (dysentery, typhoid and paratyphoid bacilli)
Coliform bacilli
test used for detection of e.coli (gram negative), if lactose positive (red)
Dysentery, typhoid and paratyphoid bacilli
non lactose fermenters, and therefore appear transparent (no lactose, no color)
EMB agar
selects for gram positive, and lactose positive. e.coli will have a blue-black with a metallic green shine
Enterobacter aerogenes
will produce thick pink colonies
Blood agar
gamma hemolysis, alpha hemolysis, beta hemolysis
Gamma hemolysis
no lysis, no change in appearance
Alpha hemolysis
incomplete hemolysis, green halo around the bacterial growth
Beta hemolysis
lysis of red blood cells with complete destruction and use of hemoglobin by the organism results in a clear zone surrounding the colonies (shiny glowing yellow green)
Triple sugar iron (TSI) agar test
designed to differentiate among the different groups of the enterobacteriaceae which are all gram negative bacilli capable of fermenting glucose with the production of acid AND to distingiush between other gram negative intestinal bacilli
Alkaline slant (red) and acid butt (yellow) with or without gas production (breaks in the agar butt)
only glucose
Acid slant (yellow) and acid butt (yellow) with or without gas production
eats sugars (lactose and sucrose)
Alkaline sland (red) and alkaline butt (red) or no change (orange-red) butt
both reactions the same, eat protein-->basic (non acidic)--> so therefore remains red
the acid-base indicator phenol red is also incorporated to detect carbohydrate fermentation which turns the medium to yellow in the presence of acid
short, gram negative, nonspore forming bacilli
Pathogens, occasional pathogens, normal intestinal flora
Types of Enterobacteriaeae `
salmonella and shingella only in humans
Occasional pathogens
proteus and klebsiella
Normal intestinal flora
Escherichia and enterobacter, which are saprophytic members of the intestinal tract
Indole test
tests for e.coli and turns cherry red if indole positive, however the have to be careful or red pigment vs red chunks (24-48 hrs) Kovac's reagent-->produces the cherry red layer
Citrate test
medium becomes alkaline, this medium turns from green to deep prussian blue (if blue it is citrate positive)
Methyl Red Test
separation of e.coli and e. aerogenes. turn yellow if a negative test, and red if a positive test (tests for presence of ACID)
forming a soluble black ferrous sulfide precipitate seen along the line of stab inoculation, H2S is present (positive) if a pipe cleaner thing is present. culture growth not restricted to line of inoculation. SALMONELLA WILL BE BLACK BUTT
Urease test
identifies proteus vulgares, if ammonia present, it causes the phenol red to turn a deep pink (super base)
Catalase test
by adding H2O2 (hydrogen peroxide) if it bubbles it is catalase positive,
Phenylalanine Deaminase Test (PPA agar)
identifies proteus, if color reaction turns green, its positive THEN dissapears. reageant--> 10-12% ferric chloride solution
Chemotherapeutic agents
chemical substances that destroy or inhibit the growth of microorganisms in living tissue (antibiotics/synthetic drugs)
living bacteria, actinomycetes and fungi that destroy the growth of other microorganisms
Synthetic drugs
made in lab to destroy the growth of other microorganisms
higher concentrations: more rapid death, toxicity must also be considered
Length of exposure
sensitive forms destroyed more rapidly than resistant ones (environment and consistency must also be considered)
Types of microbial population to be destroyed
spores--> resistant, acid-fast-->more resistant than non acid-fast, older less active cells more resistant than young cells
Environmental conditions
Temperature, and pH
the increase in temp increases the rate of reaction in which cells are killed by the chemical reaction taking place
pH conditions affect the microorganism AND the compound, extreme pH are harmful to microorganism but also increase the antimicrobial action of a chemical
Types of mediums
the microorganism may not stand a change against the combo of chemical and organic cellular molecules
Phenol Coefficient test
determined by dividing the highest dilution of chemical being tested that destroyed the microorganism in ten minutes but not five minutes
Skin normal flora
Genitourinary tract
protozoa such as Trichomonas
strep and staph, hemolytic microorganisms
The Blood agar plate differentiates between
A chocholate agar plate detects
neisseria (ghonnorea): pink to purple black colonies
A mueller hinton tellurite or tinsdale agar plate detects
cornyebacterium (diptheroids), or colonies with a black appearance
Sabouraud agar plate detects
yeast; mold colonies will appear fuzzy, powdery growths arising from a mycelial mat
MSA plate will detect
staphlyococci causing a yellow concentration around the growth