micro notes pack 3 Flashcards
what’s the three main purpose of culture media and the five functions of culture media
1) growth and isolation of all bacteria present
2) determination of pathogens vs contaminants or colonizers
3) achieve sufficient growth for testing (identification and susceptibility)
_____________
1) recover small numbers of potential pathogens
2) cover for a wide variety of potential pathogens
3) inhibit normal flora
4) aid in preliminary screening of potential pathogens
5) allow differentiation of organisms in mixed cultures
What are nutrient media? explain what nutrient media is
MH and TSA
supports non-fastidious organisms
non selective and no inhibition
what are enriched media? explain what enriched media is
BAP CNA ^^CHOC BRU ^^BHIB with Fildes ^^Trypic Soy Thioglycollate broth
supports fastidious organisms
no inhibition
what are examples of selective media? explain what selective media means
CNA MAC MAC-SORB **Selenite broth **GN broth
inhibitory agents suppresses some organisms
selects for growth of a particular organism
what are examples of differential media?
BAP
MAC
BRU
MAC-SORB
aid in distinguishing using factors
BAP
blood agar plate
enriched - 5% sheep blood to a base medium
differential - hemolysis pattern
what are the two enrichment broths?
selenite broth
GN broth
enhance a particular pathogen while suppressing others
agent becomes inhibitory to all after time and the broth needs to be subcultured
CNA - what does it stand for?
CNA - colistin Nalidixic Acid blood agar enriched - 5% sheep blood selective - antibiotics inhibit GN selects for GP
CNA promotes growth of positive bacteria
- *not differential -> hemolysis is changed with drugs
- **inhibits swarming GNB proteus
MAC
MacConkey Agar
Selective
Differential
Selective - due to Crystal violets and bile salts
grows - GNB
inhibits - GP bacteria
Differential - GNB and their ability to ferment lactose
neutral red indicator - red when ferment lactose
90% LF - lactose fermenters
pink/magenta - opaque
if they make beta-galactosidase and permease, it can metabolize lactose and make acid products
pH indicator red
10% NLF - non-lactose fermentors
colourless and clear
CHOC
chocolate agar
enriched
supports growth of fastidious organisms
- gently cooked horse blood provides
hemin (X-factor), hemoglobin, NAD (V-factor)
- *sheep blood have NADase, destroys NAD (V-factor)**
- *horse blood provides NAD - V-factor**
in house (has lipids) commercial ( no lipids) - no RBC, cannot support lipophilic organisms
MAC-SORB
Maconkey-Sorbitol Agar
selective - GNB, inhibits GP
differential - NSF vs SF
SF - majority is pink
most strain of E. Coli and Enteric GNB are SF
NSF - clear and colorless
potentially E. Coli O157:H7 - which may cause hemolytic uremic syndrome (possibly fatal)
MH
Mueller Hinton basal media nutrient clear/pale straw colour won't support fastidious organisms used in broth and plates
plates -> AST using Kirby-Bauer disk diffusion method
highly standardized for reproducibility and validity - strictly controlled for various factors
broth -> CAMHB
cation adjusted mueller hinton broth
AST testing/broth dilution
BRU
BRUCELLA for anaerobes (fastidious microorganisms) - peptones/dextrose/yeast
differential - hemolysis
enriched - sheep blood, hemin, Vitamin B, growth factors
sodium bisulphite - added to maintain
aerobic environment
maintain acidity, low pH
TSA
Tryptic soy broth/ tryptic soy agar
nutrient - basal media used as a base (plate/broth)
- soy digests - nutritious
- won’t support fastidious organisms, but will support more than MH
TSB is often used for the suspension of isolates
BHIB
- brain/heart influsion broth with fildes
- supports fastidious organisms
- looking out for CSF H. influenzae - causes meningitis
- has no selective properties
- CSF, amniotic and synovial fluid
- clear, so when it’s turbid it’ll select growth
THIO - thioglycollate broth
enriched media broth - recovers anaerobes - casein, soy, salt, dextrose, vitamin K1, hemin -reducing agents sodium thioglycollate with L-cysteine sodium sulphite
-adding 0.075% agar makes it more viscous and decreases oxygen diffusion
- THIO is used with an Eh indicator - Resazurin
if O2 is high, it turns red due to high Eh
name the three types of obligate anaerobes
aerotolerant anaerobes - can grow in CO2 incubator, but doesn’t use oxygen metabolically, it can withstand 15-19% oxygen
moderate anaerobes - most of the clinically significant anaerobes
-can grow when exposed to less than 3% oxygen, won’t work on routine incubator
strict anaerobes - absolutely no O2 exposure
bacteria are classified by optimal growth temperature
psychrophiles 0-20
mesophiles 25-45
thermophiles 45-70
what is microaerophilic organisms?
grow best in low oxygen tension of 5-10%
and increased CO2 8-10%
they grow in the presence of oxygen but do not use it as a terminal electron acceptor
what is capnophiles
^^^^^^grow best in increased CO2
5-10%
vary in their need for CO2
obligate capnophiles - cannot grow in the absence of CO2
What is Eh and describe Eh indicators
Eh is the tendency of a substance to donate or accept electrons
measured in volts or mV
when reduced Eh indicators = colourless (no oxygen)
when oxidized, methylene blue is blue, resazurin is pink (oxygen present)
aerobic cellular respiration
uses oxygen as terminal electron acceptor
makes CO2, water and ATP
anaerobic cellular respiration
uses inorganic terminal acceptor other than oxygen
makes CO2, reduced species and ATP
fermentation
organic compounds acts as both donor and acceptors of electrons
anaerobic - no oxygen required
products vary and can include ethanol, lactate, propionate, acetate, succinate, formate, butanediol butyrate, butanol, CO2 and H2
