Lactic acid

Bacteria were grown in an adapted version of the artificial urine medium (AUM) originally described by Brooks and Keevil (1997) (link). Slight adaptations were made to decrease crystal formation in the medium and to allow for planktonic growth of the isolates. The 1× AUM contained bacto peptone L37 1.5 g/L (BD), NaHCO3 3.15 g/L, urea (Roth) 11.25 g/L, Na2SO4.10H2O 4.8 g/L, K2HPO4 1.8 g/L, NH4Cl 1.95 g/L, bacto yeast extract 15 mg/L (BD), lactic acid (Roth) 1.98 mM, citric acid 600 mg/L, uric acid 105 mg/L, creatinine 1.2 g/L, CaCl2.2H2O 4.44 mg/L, Fe(II)SO4.7H2O 1.8 g/L (Riedel), MgSO4.7H2O 368 mg/L, KH2PO4 1.43 g/L. Chemicals were from Sigma, unless stated otherwise.

Chitosan (CH) was obtained from N-deacetylating lobster (P. argus) chitin in accordance with the procedure reported in our previous studies [46 (link),47 ]. The molecular weight and the degree of deacetylation of CH were 309 kg/mol and 83%, respectively. Lactic acid (BDH, London, UK), acetic acid (Merck, Darmstadt, Germany) and all other reagents used were of analytical grade.