Culture Question

Does anyone know much about starter cultures?
What is the difference between LHP, F-RM52, M-EK-4, F-LC etc.?
When do you use which culture? Does it matter?
Also, in the Ruhlman book he always use use 20 grams of  a starter culture yet the instructions on the culture packet say "Each 25-gram packet of Bactofermâ„¢ F-LC will do 220 pounds (100 kilo) of meat. You can use the whole packet in 100 pounds of meat or use half of the packet and refreeze remaining culture. Use ¼ of a packet in any production under 50 pounds of meat."  Whats the deal, do you follow the book or what the culture packet says?