Effects of divalent cations, EDTA and chitosan on the uptake and photoinactivation of Escherichia coli mediated by cationic and anionic porphyrins

Abstract

The effect of divalent cations, EDTA and chitosan (CS) on the uptake and photoinactivation of Escherichia coli produced by 5,10,15,20-tetrakis(4-N,N,N-trimethylammoniumphenyl)porphyrin (TMAP4+), 5,10-di(4-methylphenyl)-15,20-di(4-N,N,N-trimethylammoniumphenyl)porphyrin (MPAP2+) and 5,10,15,20-tetra(4-sulphonatophenyl)porphyrin (TPPS4-) were examined under different conditions. These porphyrins were rapidly bound to E. coli cells (<2.5min) and the uptake of photosensitizers was not dependent on incubation temperature, reaching values of 0.61, 0.18 and 0.08nmol/108 cells for TMAP4+, MPAP2+ and TPPS4-, respectively. The addition of Ca2+ or Mg2+ to the cultures enhanced the uptake of MPAP2+ and TPPS4- by cells. In contrast, the amount of TMAP4+ bound to cells was decreased. The presence of EDTA produced an increase in the uptake of porphyrins by cells, while CS mainly enhanced the amount of TPPS4- bound to E. coli. The photoinactivation of E. coli cells mediated by TMAP4+ was highly effective even at low concentration (1μM) and short irradiation period (5min). However, a reduction in the phototoxicity was found for TMAP4+ in presence of Ca2+ and Mg2+. In contrast, the phototoxic activity mediated by MPAP2+ and TPPS4- was increased. Addition of EDTA did not show effect on the photoinactivation induced by cationic porphyrins, while a small enhance was found for TPPS4-. Moreover, inactivation of E. coli cells was achieved in the presence CS. This cationic polymer was antimicrobial by itself in the dark. Using a slightly toxic CS concentration, the phototoxic activity induced by TMAP4+ was diminished. This effect was mainly observed at lower concentration of TMAP4+ (0.5-1μM). In contrast, an increase in E. coli photoinactivation was obtained for MPAP2+ and TPPS4- in presence of CS. Thus, this natural polymeric destabilizer agent mainly benefited the photoinactivation mediated by TPPS4-.