Microbio Final Lab Practical (copy)

What is the difference between a substance that is bacteriostatic and one that is bacteriocidal?

What is the difference between a substance that is bacteriostatic and one that is bacteriocidal?

• Bacteriostatic: capable of inhibiting the growth or reproduction of bacteria

• Bactericidal: capable of killing bacteria outright

What is a zone of inhibition? How is it interpreted?

• Zone of inhibition is: the places on the agar where the bacteria was unable to grow (bacteria was introduced in these areas, it was just unable to grow)

• Zone of inhibition is interpreted if there is a clearing around an antimicrobial disks or not.

• Halo around the disk: sensitive to the antimicrobial agent

• No halo around the disk: resistant to the antimicrobial agent

What is the difference between broad-spectrum and narrow-spectrum antibiotics?

• Broad-spectrum: antibiotics act against a wide range of bacteria, both gram negative AND gram positive

• Narrow-spectrum: antibiotics target specific groups of bacteria, either gram negative OR gram positive

Why is Mueller-Hinton agar used to test antibiotic susceptibility?

It is a nonselective, non-differential medium that contains starch, which absorbs toxins produced by bacteria (prevents bacterial toxins from confounding results= unusable results)

What is the difference between an antiseptic and a disinfectant?

Antiseptic: chemical germicides to be used on living tissues Disinfectants: chemical germicides to be used on surfaces

How does antibacterial resistance arise in bacterial populations?

The presence of antibiotics and antifungals pressure bacteria and fungi to adapt Misuse and overuse of antimicrobials

What are some consequences of antibacterial resistance?

-Could make treatable illnesses become incurable -Higher medical costs -Prolonged hospital stays -Increased mortality

MSA

mannitol salt sugar

How is MSA selective? What does it select for?

-Selective because it has a high concentration of salt that makes it an exclusive environment for bacteria.

• MSA is selective for Staphylococcus (other genera can grow, but they may grow weakly)

What is the indicator used in MSA?

pH indicator (phenol red)

What result indicates a positive? What does a negative result mean?

Yellow: positive for mannitol fermentation Red/growth: negative for mannitol fermentation but is likely Staphylococcus Red/no growth: likely not Staphylococcus

EMB

Eosin Methylene Blue Agar

How is EMB selective? What does it select for?

EMB is used to isolate coliforms (G-bacilli who ferment lactose) Selective because methylene blue inhibits growth of gram positive organisms

What is the indicator used in EMB?

Eosin Y and methylene blue are pH indicators

What result indicates a negative? What does a positive result mean? d. What is a fecal coliform?

--Green iridescence : positive for lactose fermentation (strong fermenter) --Pink: negative for lactose fermentation (weak fermenter) --fecal coliform: type of total coliform that mostly exist in feces

Phenol Red (PR) Fermentation Broth a. What is the indicator used in PR broth?

pH indicator phenol red

Between which types or species of bacteria does PR broth differentiate?

Gram negative bacteria

What result indicates a negative? What does a positive result mean?

Yellow: positive for glucose fermentation Pink: negative for glucose fermentation,it is peptone utilization

Catalase Test a. What enzyme does this test for?

Production of the enzyme catalase

What function does this enzyme perform?

Catalase allows for the neutralization of toxic oxygen species such as hydrogen peroxide

Between which types or species of bacteria does the catalase test differentiate? d. What result indicates a negative? What does a positive result mean?

Differentiate staphylococci from streptococci Positive: bubbling aka effervescence, Negative: no effervescence

Citrate Utilisation Test a. What is the indicator used in Simmons’ citrate agar?

pH indicator bromothymol blue

What enzyme does this test for?

Tests for citrate

What function does this enzyme perform?

Citrate is a sole carbon source

Between which types or species of bacteria does the citrate utilization test differentiate?

Used to differentiate fecal coliforms from non-fecal coliforms

What result indicates a negative? What does a positive result mean?

Green: Negative for citrate/ammonium salts usage Blue: Positive for citrate/ammonium salts usage

What causes the color change in bile esculin agar?

Esculin, which when hydrolyzed reacts with ferric citrate and turns black

What enzyme is tested for in bile esculin agar?

Esculin, which when hydrolyzed reacts with ferric citrate turns black

What enzyme does bile esculin agar test for?

Tests for esculinase

What function does this enzyme perform in bile esculin agar?

Hydrolysis of esculin in the presence of bile salts

Between which types or species of bacteria does the bile esculin test differentiate?

Streptococci + Enterococci

What results indicate a negative in a BEA test?

Less than half black: negative for esculin

What does a positive result mean in a BEA test?

More than half black: positive for esculin

What enzyme does SIM test for?

Tryptophanase

What function does the enzyme in the SIM test perform?

Degrades tryptophan to indole which is a byproduct of the hydrolysis of tryptophan

Between which types or species of bacteria does the SIM test differentiate?

The types of bacteria the SIM test differentiate Enterobacteriaceae

What result indicates positive in a SIM test?

A positive result is indicated by a red color change upon adding the Kovac’s reagent for indole production

What result indicates negative in a SIM test?

H2S production is indicated by color change from tan to black.

What is the difference between alpha, beta, and gamma haemolysis?

Alpha haemolysis is incomplete lysis of red blood cells, greenish color around the colony. Beta haemolysis is complete lysis of red blood cells, clearing around the colony. Gamma haemolysis is no hemolysis, looks like a normal colony.

Between which types or species of bacteria does blood agar differentiate?

Blood agar differentiates Enterococcus, Streptococcus, and Staphylococcus.

Why does hemolysis indicate that a species is likely to be pathogenic?

They produce hemolysins that destroy red blood cells and hemoglobin.

What enzyme does the gelatine liquefication test for?

Gelitanase

What function does the enzyme perform in a gelatine liquefaction test ?

gelitanase breaks down gelatin

What does the methyl red test detect?

Fermentation of sugars via the mixed acid pathway

What pH indicator is used in the methyl red test?

Methyl red indicator

How does the methyl red test differ from other fermentation tests?

Other fermentation tests use phenol red whereas this test uses methyl red.

What is haemagglutination?

Agglutination or clumping of red blood cells.

What antigens are present on the surfaces of the erythrocytes in the following blood types?

a. A+: A b. AB-: A and B c. O-: none d. O+: none e. B-: B

What do the following agglutination results signify?

a. Anti-A: agg+, Anti-B: agg+, Anti-Rh: agg-: AB- b. Anti-A: agg-, Anti-B: agg+, Anti-Rh: agg-: B- c. Anti-A: agg+, Anti-B: agg-, Anti-Rh: agg-: A-

What are the consequences of giving a patient the wrong blood type in a transfusion?

In the best case, flu-like symptoms occur ranging from fever to burning at the injection site. In the worst case, the immune system overcompensates and causes mass haemolysis of rbcs. An uncontrollable clotting can be triggered resulting in clots in the veins which kills the patient.

What is the universal donor blood type? The universal recipient type? Why?

Universal donor blood type is O- and the universal recipient is AB+. O- has no antigens on the surface of rbcs to trigger an immune response. AB+ contains none of the relevant antibodies in the antigen, so no antigens can be attacked.

What does ELISA stand for?

Enzyme-Linked ImmunoSorbent Assay

What are the differences between a direct and an indirect ELISA?

Direct ELISA uses one antibody and an indirect ELISA uses two antibodies, primary and secondary.

What are three settings in which one might use an ELISA?

Allergy testing, pregnancy test, and measuring antibodies

What are some drawbacks to ELISA testing?

--Weak or low signal intensity --Narrow dynamic range --Long resulting time --Complex workflow