what is meant by being able to ferment
a certain sugar?

​differential growth media:
allow several different types of bacteria to grow and also contain additives that allow different species to be visually identified

growth media

examples:

​​
               Examples of microbial growth media

1. Trypticase soy agar (TSA) = all purpose nutrient-rich medium containing                                                                                    amino acids, vitamins, and other factors for                                                                                      general bacterial growth
2. LB broth/agar = support general bacterial growth
3. Yeast extract = general bacterial or cell culture complex media
                                       (complex media contains nonspecific compounds) 
4. Mannitol salt agar (MSA) = selective growth medium:
                                                                encourages high NaCl accommodating bacteria
                                                                inhibits low NaCl accommodating bacteria
                                                            = differential growth medium:
                                                                ability to ferment mannitol (mannitol is a type of sugar)
                                                                produces acidic waste. a phenol red indicator additive                                                                    turns colonies yellow
                                                                an inability to ferment mannitol colonies are white  

                                                                Staphylococcus aureus, Enterobacter aerogenes,
                                                                Staphylococcus saprophyticus, Staphylococcus
                                                                hemolyticus, Staphylococcus simulans, Staphloccus
                                                                warneri can ferment mannitol  
 

5. Eosin methylene blue agar (EMB) = selective growth medium:
                                                                                      dyes inhibit gram + bacteria
                                                                                   = differential growth medium: 
​                                                                                       ability to ferment lactose/sucrose produce                                                                                          pink/purple colonies 

​                                                                                       Streptococcus thermophilus, E coli,
                                                                                       Zymomonas mobilis can ferment lactose
​                                                                                                 and/or sucrose. 
6. Minimal Glucose Medium (MGM) = contains only essential nutrients : salts & glucose
                                                                        satisfy microbe's basic metabolic needs without
                                                                        added complexities. no animal, plant, or yeast.
                                                                        (also called defined/chemically defined medium) 

Tryptic Soy Agar (TSA)
​ is non-selective, non-differential

                                           Selective media
    selects for the growth of a desired microbes and represses the                                       growth of non-desired microbes
                                       Differential media
     takes advantage of different biochemical properties of certain            microbes. target microbes exhibit a visible change when grown 

MacConkey agar selects for Gram-negative bacteria due to bile salts and crystal violet. It is also differential based on lactose fermentation, with lactose fermenters producing pink colonies and non-fermenters appearing colorless. 

​MSA 

​
growth media = culture media

Broths or agars that contain nutrients
to encourage microbial growth.
 Different types of media are used to grow
​different types of bacteria. 

Bacteria produce all sorts of different products via fermentation including:
lactic acid
acetic acid
propionic acid

today, we're using
​MSA and EMB 

EMB

why?

selective growth media:
selects for the growth of a particular bacteria while inhibiting the growth of others

can growth medium be both selective & differential?

how?