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lab exam 4

Manitol salt agar (MSA) is -----for staphylococci

selective and differential. MSA allows any staph to grow on it and the agar around the staph will turn yellow.

Coagulate test is considered definitive for testing---

S. Aureus, this in the only one that is coagulase positive.

The role of coagulase in the pathogenesis S. Aureus

coagulase creates the fivrin clot for a barrier against the immune system.

What does Alpha toxin do in the pathogenesis of S. aureus?

Alpha toxin causes the cell lysis of RBC's.


loosening,destruction, break up

What are nasocomial infections?

hospital infections

Why are the staphylococci among the leading causes of nosocomial infections?

because staph is found on 30% of us at all times.

Why are staph infections becoming increasingly difficult to treat?

They are becoming multi drug resistant

What precautions are taken in nosocomial settings to prevent staphylococcal infections?

Wash hands, antiseptics, sanitization and sterilization of equipment.

Why might hospital staff be tested for nasal carriage of S. arueus?

to let the hospital know which staff members may spread the infections to patients.

When bacteria from a throat swab are streaked on blood agar, why is the agar stabbed several times with the loop?

stabbing the agar makes the hemolysis look better.

Differentiate between alpha and beta hemolysis...

Alpha is partial hemolysis and will look green. Beta is complete memolysis and will create a clear halp around the organism.


Destruction of red blood cells

What was Rebecca Lancefields contribution to the study of streptococci?

Rebecca Lancefield cdivided the strep based on serological groups.


different capsular types can be identified by ________ testing

A throat swab is typically performed on an indivudual suspected to have streptococcal pharyngitis, or strep throat, On a blood agar what type of hemolysis would be expected in an individual with streptococcal pharyngitis?

B hemolysis, a clear halo around the organism.

What species causes streptococcal pharyngitis?

streptococcal pharyngitis is usually caused by streptococcus pyrogenes.

Why is it important to first confirm the presence of this species before administering any therapy?

It may not be caused by a bacteria but by a virus and would not require antibiotics.

Bacteria are isolated from the blood of a patient with septicemia. You would like to determine whether they are Streptococcus pyogenes or Staphylococcus aureus. What characteristics do the two species share?

Both streptococcus pyogenes and staphylococcus aureus are gram positive.

What tests would be useful for the differentiation of the two species, staph and strep?

Staph are catalase positive and Strep are catalase negative.

Name three test that are useful for the differentiation of S. pyogenes and S. agalactiae....

Bacitracin suseptibility: pyrogenes is suseptible and agalactiae is not. Camp reaction: pyrogenes is negative and agalactiae is positive. Lancefield groups: pyrogenes is A and agalactiae is B.

Name two tests that are useful for the differentiation of pneumococci and oral viridans streptococci?

Optochin: pneumococci are susceptible and Viridans are not.
Bile solubility: pneumococci are positive and Viridans are negative.

What test can be performed to differentiate the enterococci from other group D streptococci?

6.5% NaCl broth is used to differentiate enterococci (+) from group D strep (-).

Name three enteric pathogens of primary medical importance.

Salmonella, Shigella and some strains of E. Coli.

What precautions can me taken to prevent infection and illness caused by enteric pathogens?

Wash your hands and proter food handling.

What selective agents are added to media to preferentially grow enterobacteria for study?

Bile salts.

What type of growth is inhibited from bile salts in media?

Gram positive bacteria.

What characteristic separates Salmonella and Shigella from most of the other enterobacteria?

Salmonella and Shigella do not ferment Lactose.

What media can be used for this differentiation between Salmonella and Shigella from most of the other enterobacteria?

Glucose, Lactose and sometimes sucrose.

What two characteristics separate Salmonella from Shigella?

Salmonella are motile and produce hydrogen sulfide and Shigella are negative for both.

What media can be used to differentiate between Salmonella and Shigella?

SIM media for motility and looks black if H2S production.

Which coliform bacteria are the most difficult to distinguish from the SS pathogens?


What is the primary characteristic used to differentiate them?

Proteus is positive for urea and the other two are negative

Why is it important to complete morphological and cultural characterizations before pursuing physiological testing?

This gets you started in the right direction and which test to use to determine your unknown.

In regards to taxonomic classification of bacteria, what is the relationship between physiological and genetic differentiation of bacteria?

Physiology is a display of what proteins and enzymes they are producing which comes from their genes.

What is the function of bacterial exoenzymes?

Exoenzymes breakdown macromolecules to smaller molecules that they can take into the cell body and use for metabolites.


Anabolism is biosynthesis fo cell constituents. , Process of building up complex materials (proteins) from simple materials, The process that synthesizes a complex molecule from simpler compounds, thus requiring energy.


produce energy, carry out the breakdown of food materials., breakdown of more complex substances into simpler ones with release of energy


the process by which cells break down molecules to release energy without using oxygen, a process in which an agent causes an organic substance to break down into simpler substances

Why is the catalase test useful for the defferentiation of staphylococci from streptococci?

Staph is catalase (+) and strep is catalase (-)

How is acid or alkaline detected in a culture medium as an end product?

a ph indicator such a phenol red in the broth or agar.

Name two test for reactions that produce acid end products...

KIA and fermentation of carbohydrates

name two tests for reactions that produce alkaline end products...

Urea hydolysis and litmus milk.

What types of gases can be produced as a result of sugar fermentation?


How are these gases detected in fermentation reactions?

Can be collected in a Durham tube.

Name a nonfermentative test in which gas production indicates a positive test result...

Nitrate reduction.

A starch test you must add iodine to see if the starch was broken down. You should see......

a halo for a positive result.

A casein test should produce...

a clear halo in the milk for a positive test result.

A test for Triglycerides shoul turn....

dark blue.

Name two test that demonstrate hydrolysis of proteins or proteolytic digestion besides casein hydrolysis test.

The Tryptophan to indole test and the Litmus milk test.

Kligler's iron agar and SIM are multiple test media, What test do these media have in common?

Both test for cystein to hydrogen sulfide.

What components of the media are included for this test?

They both contain cystein and Iron Sulfate.

Both Kligler's iron agar and SIM are stabged but for different reasons, WHY?

For Kligler's it is to test for the fermentation of the sugars. For SIM it is to test for motility.

What difficulties does one encounter when trying to differentiate bacteria on the basis of physiological tests?

Contamination can give a false positive.

In addition to the morphological, cultural, and physiological tests performed on an unknown, what tests can be conducted to further assist in it's identification?

DNA analysis.

Kligler's iron agar test media

carbohydrate fermentation, hydrogen sulfide production

MR-VP test medua

2,3-butanediol fermentation, mixed - acid fermintation

Phenol red lactose test media

carbohydrate fermentation

SIM medium test media

hydrogen sulfide production, tryptophan degradation

Simmon's citrate agar media

citrate utilization

Skim milk agar media

casein hydrolysis

spirit blue agar media

triglyceride hydrolysis

alpha-naphthol reagent

2,3-butanediol fermentation

dimethyl-alpha-naphthylamine reagent

nitrate reduction

ferric chloride reagent

phenylalanine deamination

Gram's iodine reagent

starch hydrolysis

hydrogen peroxide reagent

catalase test

Kovac's reagent

Tryptophan degradation

Methyl red reagent

mixed-acid fermentation

N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride reagent

oxidase test

sulfanilic acid reagent

nitrate reduction

amylase enzyme

starch hydrolysis

cysteine desulurase enzyme

hydrogen sulfide production

lipase enzyme

triglyceride hydrolysis

protease enzyme

casein hydrolysis

tryptophanase enzyme


urease enzyme

urea hydrolysis

2.3-butanediol product

Voges-Proskauer test

ammonia product

phenylalanine deamination, tryptophan degradation, urea hydrolysis

fatty acids product

triglyceride hydrolysis

indole product

tryptophan degradation

molecular oxygen product


phenylpyruvic acid product

phenylalanine deamination

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