If you already know that you have bacterial contamination in your sample and you would like to identify bacterial speciess causing it. Theere are a number of simple agar media that you can streak your contaminants on and you would know atleast the genus level. These tests were used prior to the advent of enterotube or API systems.E.g., if you plate the bacterial sample, or "the sample" without isolating the contaminant bacteria on 3 tubes (16X 45 mm), or 3 petri dishes (35 mm) containing EMB agar, incubate the tubes/petri dishes each at 25 °C, 37 °C, and 42 °C separately for 24-48 hrs. Examine the tubes/petri dishes for a green metallic sheen on bacterial growth. If positive for sheen, the organism in all likelihood is Escherichia coli.

Likewise, if you use Mannitol salt agar which contains a dye (Neutral red) and see a yellow halo around the colonies,alllikelihood is that you have Staphylococcus aureus(?). Ofcourse, you ahve to do the gram stain to ensure that your organisms are either Gram negative small rods (E.coli), or Gram positive cocci in groups like a grape bunch (S. aureus, or other staphylococci. If, however, you wnat to work harder, get a copy of "Cowan and Steele's Manual for the identification of bacteria, prepare each fo the diagnostic culture media yourself. streak the organisms and you will get pretty close ident ification of the organisms. Other alternative is that you do DNA, or mRNA sequqnxing of the organisms and then match with known sequences.

I have mentioned each of simplest. to laborious and modern methods for the identification of bacteria for your benefit.All the best. Happy identifyiing.