lab 6

Question 1

skin is rather inhospitable for microorganisms to live

Answer 1

bc it is dry and has a low ph between 4 and 6

Question 2

certain microorganisms flourish in the moister regions

Answer 2

armpits , genitals, face and scalp
underarm odour is cause by bacteria living in your armpits, breaking down substances release in your sweat and releasing foul smelling waste products

Question 3

normal biota of your skin is composed of two groups

Answer 3

transient

resident

Question 4

transient microbes

Answer 4

you skin picks up from the environment , they are unable to establish a permanent residence , they may remain on your skin for a few hours , day or months

Question 5

resident microbes

Answer 5

they thrive on your skin and can be considered your normal microbiota
most are gram positive which are better adapted to the dry conditions
these organisms also convert the oils on your skin to low moleculer weight unsaturated fatty acids, which have antimicrobial activity and prevent growth of gram negative bacteria and fungi
when you knock out the pop of gram positive bacteria, such as when you take certain antibiotics , gram negatives and yeasts can flourish

Question 6

yeast infections occur when the

Answer 6

normal microbiota is inhibited raising the pH to nearly neutral and allowing the yeasts to take over

Question 7

staphylococcus is the main genus of gram positive bacteria found on the skin

Answer 7

staphylococcus epidermis and staphylococcus aureus

Question 8

staphylococcus epidermis

Answer 8

non-pigmented,( white colonies), non pathogenic bacterium that accounts for a large proportion of the bacteria on your skin

Question 9

staphylococcus aureus

Answer 9

less common
usually forms yellow colonies and is often found associated with pimples and boils as well as being the cause of ton of the most common types of food poisoning

Question 10

responsible for causing many nosocomial infections

Answer 10

s. au
an infection caused while in the hospital that was not present when the patient was admitted
strains of s. au that are resistant to every known antibiotic are booming more common and are known as superbugs

Question 11

macConkey agar

Answer 11

used to differentiate lactose fermenters which turn bright red to pinkish purple, from those unable to use lactose
strong lactose fermenter is gram negative

Question 12

to support bacterial growth, a medium must contain

Answer 12

-carbon source (unless the bacterium is and autotroph)
-a nitrogen source (unless its a nitrogen-fixer)
-and inorganic salts
medium may or may not require the addition of various growth factors

Question 13

if the medium is to be used for plates then

Answer 13

agar must be added

Question 14

if the medium will be used to select for a particular group of organisms then

Answer 14

a selective agent should be added

Question 15

for differentiating between groups of organisms a

Answer 15

pH indicator is normally used

Question 16

defined or synthetic medium

Answer 16

all of the elements are in a known quantity

Question 17

complex medium

Answer 17

the exact components of the medium are not known
this occurs when te complex nutrient sources is added to the medium
yeast extract, peptone and trypton are all examples of complex nutrient sources ie you dont know the exact proportions of chemical elements in these ingredients

Question 18

enriched medium

Answer 18

these are complex media to which an extra nutrient source such as blood or serum is added to encourage the growth of fastidious heterotrophs

Question 19

selective medium

Answer 19

supports the growth of the wanted organisms and inhibits the growth of all others
a medium can be made selective by adding an inhibitory agent such as crystal violet (which inhibits gram positive organisms) or by removing a component necessary for growth
Nitrogen-free media selects for those bacteria that can fix atmospheric nitrogen. antibiotics are often used to make a medium selective

Question 20

differential medium

Answer 20

allows many organisms to grow, but lets you discriminate between different bacteria base on the appearance of the colony or the presence of a zone around the colony

Question 21

agar

Answer 21

a complex sulphur containing polysaccharide extracted from a marine alga that is commonly used to solidify petri plates. although agar is organic, it is relatively difficult to break down and cannot used as a nutrient sources by most terrestrial bacteria when added to media agar will melt around 95 and solidify at about 43

Question 22

amino acids

Answer 22

growth factors required by all bacteria for synthesis of proteins. if a bacterium cannot synthesize a particular amino acid itself, then it must be provided in the growth medium for that organism to grow

Question 23

beef extract

Answer 23

an extract of beef concentrated into a paste that contains a large amount of amino acids and peptides
it is also a source of carbohydrates, vitamins and minerals and trace metals

Question 24

bile salts

Answer 24

these are used to simulate gut conditions and are effective fore selection of enteric organisms
gram positive organisms are inhibited by bile salts in macConkey agar, colonies produces by strong lactose fermenting microbes will exhibit dark red ring of precipitated bile salts around the colony

Question 25

blood agar

Answer 25

an agar medium used to determine if an organism produces hemolysis which will break down the red blood cells in the medium. different patterns of hemolysis can be observed. - B-hemolysis is characterized by a clear zone around the colonies and is a characteristic of staphylococcus aureus which causes numerous skin and wound infections and streptococcus pyogenes, which causes strep throat (complete lysis of blood cells-complete zone of clearing on the plate ) - alpha-hemolysis greenish coloured zones from the partial destruction of the red blood cells and are characteristic of streptococcus pneumoniae (incomplete lysis of red blood cells and results in a green zone of clearing) - lots of bacteria are also non-hemolytic and will not produce a zone of clearing on the place .gamma-hemolysis

Question 26

is blood agar selective or differential or both?

Answer 26

not selective - wide variety of bacteria can grow on it blood agar is considered an enriched medium- so packed with nutrients that even bacteria that cant grow on t-soy may be able to grow on it we call these picky eaters fastidious because the require many growth factors blood agar is differential because you can easily see whether or not bacteria are hemolytic by their appearance on the plate

Question 27

why do bacteria produce hemolysins

Answer 27

- bc blood serum supplies nutrients to animal cells, we would expect it to be nutrient rich and an excellent growth medium for bacteria. however there is one essential nutrient that is not biologically available in the liquid fraction of blood: iron. animals use iron binding proteins called transferrins to sequester an iron in the blood thus limiting its availability. the activity of transferrins is considered to be an important component of the immune system and a demesnes against bacteria that would otherwise cause blood borne infections - unfortunately for animals, some enterprising bacteria have discovered that blood has another important pool of iron: the hemoglobin of red blood cells . hemolytic enzymes that destroy red blood cells release the heme, making the iron biologically available

Question 28

bromcresol purple

Answer 28

pH indicator that is yellow below pH 5.2 and purple in the alkaline range

Question 29

crystal violet

Answer 29

a basic stain that can also be used in a medium to inhibit the growth of gram positive organisms

Question 30

glucose

Answer 30

a readily utilized carbon and energy source for heterotrophic bacteria

Question 31

growth factors

Answer 31

small organic compounds that are essential for the growth of all bacteria if a bacterium cannot synthesize a particular growth factor, then is must be provided in the medium -amino acids, purines ,pyrimidines ,and vitamins

Question 32

streptococcus mutans

Answer 32

- responsible for producing the acid that results in the destruction of your tooth enamel - the bacteria produces the acids as an end result of carbohydrate fermentation and also converts sucrose to dextran, a sticky polysaccharide that helps the bacteria adhere to youre teeth

Question 33

hemolysins

Answer 33

these are enzymes used to break down red blood cells. this ability is associated with virulence like the level of pathogenicity of the organism and so pathogenic strains of staphylococcus, streptococcus and clostridium exhibit beta hemolysis complete clearing

Question 34

lactose

Answer 34

a disaccharide that can be used as a carbon and energy source by some bacteria often added to media along with a pH indicator to differentiate between lactose fermenters and lactose non-fermenters

Question 35

macConkey agar

Answer 35

medium usually used to distinguish bw members of the enterobacteriaceae (gram negative enteric bacteria). one of the distinguishing features of an enteric organisms is the ability to ferment lactose to acid end-products. Acid from lactose fermentation will accumulate in the medium and cause the colony growth to turn dark pink. strong lactose fermenters produce so much acids that the bile salts in the medium precipitate around the colonies. weak lactose fermenters will turn a light shade of pink non-lactose fermenters will appear white or colours gram positive does not grow on plate at all

Question 36

macconkey agar is both

Answer 36

selective and differential - useful in identifying potential human pathogens and used to detect fecal contamination - lactose fermenters produce acid s. au gram positive e. co- strong s. flexneri-nonlactose e. aerogens -weak

Question 37

mannitol

Answer 37

a carbohydrate that is a carbon source for some bacteria

Question 38

mannitol salt agar

Answer 38

this medium favours those organisms that can tolerate high salt concentrations like staphylococcus and distinguishes those that can ferment mannitol s. au can - yellow colonies s. ep cannot white colonies selective, differential, and complex white colonies are surrounded by red (original plate colour) whereas yellow colonies are surround by yellow staphylococcus are halotolerant- can grow in high salt concentrations complex- peptone differential bc it van be used to differential bw mannitol fermenters and non fermenters bacteria that can ferment mannitol will produce acid as an end product of fermentation, acid reacts with the phenol red and changes the colour to yellow s. ep can still grow by metabolizing other components of the medium like peptones and beef extract

Question 39

methyl green

Answer 39

a dye that forms a complex with large fragments of DNA. if an organism can produce enzymes to degrade the DNA the dye will become unbound from the DNA and a clear zone will result around the colony

Question 40

molybdenum

Answer 40

a micronutrient that serves as an important co-factor for enzymes involved in N fixation. often added to N free medium for the culture of N2 fixing bacteria

Question 41

neutral red

Answer 41

pH indicator that is red below pH 6.8 and clear in the alkaline range

Question 42

phenol red

Answer 42

a pH indicator that is yellow below pH 6.8 and pink/red in the alkaline range

Question 43

peptone

Answer 43

hydrolyzed proteins that are formed by the enzymatic or acidic digestion of a variety of materials like soybean meal, casein (milk protein) animal tissues, gelatin, provides a source of carbon and energy for heterotrophic bacteria and supplies some growth factors such as amino acids (soytone, tryptone)

Question 44

purines and pyrimidines

Answer 44

growth factors required by all bacteria fro synthesis of nucleotides and nucleic acids. if an organisms cannot synthesize a particular purine or pyrimidine, it must be provided to it in the medium

Question 45

sheep's bloods

Answer 45

added to blood agar to provide essential growth factors and nutrients for many bacteria but is particularly useful for culturing fastidious organisms. fastidious organisms are those microbes that are difficult to culture bc they have a very specific nutritional requirements. also helps to differentiate bacteria base on their patterns of hemolysis

Question 46

sodium chloride

Answer 46

provides a saline environment for osmoregulation at low concentrations (7.5%) of salt that will kill many bacteria

Question 47

soytone

Answer 47

an enzymatic digest of soybean meal that provides a source of amino acids peptides, vitamins and other growth factors

Question 48

sucrose

Answer 48

a disaccharide that serves as a source of carbon for some heterotrophs

Question 49

tomato juice

Answer 49

a source of addition vitamins to support the growth of lactobacillus species and other fastidious lactic acid bacteria. the natural acidity of tomato juice gives the medium a low pH that can encourage the growth of mildly acidophilic bacteria, but may discourage the growth of some neutrophiles

Question 50

t-soy

Answer 50

``` tryptic soy agar used for cultivating a wide range of bacteria including some fastidious organisms 15g/L tryptone 5g/L soytone 5g/L NaCl 15g/L agar ```

Question 51

tryptone

Answer 51

an enzymatic digest of casein (milk protein) that provides a source of amino acids, peptides, vitamins and other growth factors

Question 52

vitamin

Answer 52

a growth factor that serves as a precursor for the synthesis of coenzymes, required by all bacteria. if a bacterium cannot synthesize a particular vitamin then is must be provided in the growth medium

Question 53

yeast extract

Answer 53

an extract of lysed yeast cells which supply a complex mixture of amino acids, vitamins, and other growth factors