**2.2.2 Test microorganisms**

Antimicrobial activity of twenty-one palladium(II) and platinum(IV) complexes and their ligands was tested against 9 species of bacteria: 6 strains of pathogenic bacteria (including 4 standard strains: *Pseudomonas aeruginosa* ATCC 27853, *Enterococcus faecalis* ATCC 29212, *Staphylococcus aureus* ATCC 25923; *Sarcina lutea* ATCC 9341 and 2 clinical isolates: *Escherichia coli* and *Salmonella enterica*) and 3 species of probiotic bacteria (*Bacillus subtilis* IP 5832 PMFKG-P32, *Bifidobacterium animalis subsp. lactis* PMFKG-P33 and *Lactobacillus rhamnosus* PMFKG-P35 ). All clinical isolates were a generous gift from the Institute of Public Health, Kragujevac. The other microorganisms were provided from a collection held by the Microbiology Laboratory Faculty of Science, University of Kragujevac.

### **2.2.3 Suspension preparation**

Bacterial suspensions were prepared by the direct colony method. The colonies were taken directly from the plate and were suspended in 5 mL of sterile 0.85% saline. The turbidity of initial suspension was adjusted by comparing with 0.5 McFarland's standard (0.5 ml 1.17% w/v BaCl2×2H2O + 99.5 ml 1% w/v H2SO4) (Andrews, 2005). When adjusted to the turbidity of the 0.5 McFarland's standard, bacteria suspension contains about 108 colony forming unites (CFU)/mL. Ten-hold dilutions of initial suspension were additionally prepared into sterile 0.85% saline.
