The hydrophobicity of the surface towards bacteria was estimated by BATH and salt aggregation (SA) tests. Both bacterial strains were found to be hydrophobic. The degree of hydrophobicity values (in %) of the bacterial strains are calculated by the BATH test as given in Table . Both PA-ZK (36.6%) and BS-S1X (35.5%) strains presented almost similar degrees of hydrophobicity on the SS304 surface. On the other hand, the SA test results showed aggregation of bacterial cells with all concentrations of (NH4)2 SO4 (from 0.02 M to 4.0 M).