Comparative effect of growth media on the monitoring of E. coli inactivation and regrowth after solar and photo-Fenton treatment

- Selective media noticeably reduced recovery of photo-treated Escherichia coli.
- PCA supported the growth of injured bacteria with possible membrane damage.
- Catalase and sodium pyruvate enhanced the recuperation of photo-treated E. coli.
- Photo-Fenton inflicted multi-level cellular damages more severely than SODIS.

This study intends to assess the cultivability of photo-treated Escherichia coli K-12 on media with different selectivity (PCA, LBA, T-7, T-7 + TTC, VRBA and MAC) and to establish optimal conditions for bacterial recuperation. For these purposes, immediate and long-term bacterial recovery after SODIS and photo-Fenton are evaluated. Moreover, the use of catalase and sodium pyruvate supplements in the medium is studied. The non-selective medium PCA showed the highest counts for the untreated and treated cells due to its content in nutrients (e.g. glucose) and lack of inhibitors. On the contrary, the selective media showed lower recovery, being the culture media effectiveness: PCA > LBA > T-7 > T-7 + TTC > VRBA > MAC. The presence of inhibitors, such as heptadecyl sulfate in T-7 or bile salts in VRBA and MAC, reduced the cultivability of the treated cells. These compounds can probably diffuse into the cells more easily after SODIS and photo-Fenton as a consequence of the loss of the membrane integrity. In addition, the lack of yeast extract in MAC had a detrimental effect on E. coli recovery. Sodium pyruvate was tested as supplement to PCA, leading to slightly enhanced bacterial immediate recovery after SODIS, SODIS + H2O2 and photo-Fenton. The addition of catalase and sodium pyruvate to the bulk was studied as well, considerably increasing bacterial survival in the long-term due to their ability to neutralize residual H2O2.

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