**5.6 Isolation and purification**

Microorganisms of 3 samples have been isolated and then purified. Specifically:


PCA has been utilized as sterile agar culture medium. Isolation has been accomplished through suspension dilutions (up to 10<sup>9</sup> ) of samples and plating by inclusion of 1 ml for each dilution. After incubation for 24 hours at 27°C, largest colonies have been purified by smear on PCA plating. Purified strains have been stored at


**Table 5.** *PCA agar– liter<sup>1</sup>*

20°C in PCB at 20% glycerol and at 4°C in slant test tubes, to be collected for the subsequent identification tests. On the same dishes, for sludges and wastewater, prior to smear purification, a bacterium count of colonies of dilutions showing the greatest growth has been made and the results have been expressed in CFU/ml.
