Lab Culture Stuff Flashcards
why is a mannitol salt plate red?
phenol red
what does phenol red indicate for?
pH
< 6.8 (yellow)
6.8 - 8.2 (red)
> 8.2 (pink)
what effect will bacteria that produce alpha hemolysins have on a 5% sheep blood agar plate?
there will be a red to green colour change and a clearing in the location of the colony only, as alpha hemolysins partially break down the haemoglobin of the sheep blood cells.
what effect will bacteria that produce beta hemolysins have on a 5% sheep blood agar plate?
there will be a red to green colour change and a clearing in the colony and surrounding regions, as beta hemolysins completely break down the haemoglobin of the sheep blood cells.
what effect will bacteria that produce gamma hemolysins have on a 5% sheep blood agar plate?
there will be no colour change, as gamma hemolysins do not break down the haemoglobin of the sheep blood cells.
capnophiles
organisms that thrive in the presence of high amounts of carbon dioxide
at what temperature do you incubate strep cultures?
37C (human body temperature)
when would you use a 5% sheep blood agar plate?
to check for the presence of hemolysins
advantages of solid media:
(a) Bacteria may be identified by studying the colony character, (b) Mixed bacteria can be separated. Solid media is used for the isolation of bacteria as pure culture. ‘Agar’ is most commonly used to prepare solid media.
agar
a polysaccharide extract obtained from seaweed, agar is most commonly used to prepare solid media
why is agar an ideal solidifying agent for preparing solid media?
it is : (a) bacteriologically inert (i.e. no influence on bacterial growth), (b) It remains solid at 37°C, and (c) It is transparent.
name the six types of routine laboratory media:
(1) basal media, (2) enriched media, (3) selective media, (4) indicator media, (5) transport media, and (6) storage media.
basal medi
basal media are those that may be used for growth (culture) of bacteria that do not need enrichment of the media. examples: nutrient broth, nutrient agar and peptone water. Staphylococcus and Enterobacteriaceae grow in these media.
enriched media
media that are enriched usually by adding blood, serum or egg. examples: enriched media are blood agar and Lowenstein-Jensen media. Streptococci grow in blood agar media.
selective media
these media favour the growth of a particular bacterium by inhibiting the growth of undesired bacteria and allowing growth of desirable bacteria. examples: MacConkey agar, Lowenstein-Jensen media, tellurite media (tellurite inhibits the growth of most of the throat organisms except diphtheria bacilli). Antibiotic may be added to a medium for inhibition.
indicator (differential) media
an indicator is included in the medium. a particular organism causes change in the indicator, e.g. blood, neutral red, tellurite. examples: blood agar and MacConkey agar are indicator media.
transport media
media are used when specie-men cannot be cultured soon after collection. examples: Cary-Blair medium, Amies medium, Stuart medium.
storage media
media used for storing bacteria for a long period of time. examples: egg saline medium, chalk cooked meat broth.
blood agar
most commonly used medium. 5-10% defibrinated sheep or horse blood is added to melted agar at 45-50°C. blood acts as an enrichment material and also as an indicator. certain bacteria when grown in blood agar produce haemolysis around their colonies. certain bacteria produce no haemolysis. types of changes : (a) beta (p) haemolysis. the colony is surrounded by a clear zone of complete haemolysis, e.g. Streptococcus pyogenes is a beta haemolytic streptococci, (b) Alpha (a) haemolysis. the colony is surrounded by a zone of greenish discolouration due to formation of biliverdin, e.g. Viridans streptococci, (c) gamma (y) haemolysis, or, no haemolysis. there is no change in the medium surrounding the colony,
