| Congresso Brasileiro de Microbiologia 2023 | Resumo: 553-2 | ||||
Resumo:In the Brazilian semi-arid region, cisterns are used for rainwater storage. Microbiological safety is an essential factor for drinking water. In literature, studies have discussed the microbiological quality of stored water. However, many bacterial species have been found to exist in a viable non-culturable (VBNC) state in response to adverse environmental conditions. This state is a condition in which bacterial cells are resistant to cultivation on routine growth media although viable and metabolically active. That can result in false negative results from culture-dependent methods. The present study aimed to understand if occurs bacterial cells resuscitation from the VBNC state in rainwater stored in cisterns after being subject to a water recirculation system. Samples were obtained from three cisterns in the semi-arid region in the state of Ceará. 10L aliquots inserted in kegs were subjected to a recirculation system using a 150L.h-1 submersible pump under 25 +- 1 ºC. Water samples were taken 6, 12, and 24 hours after the start of the system operation. Serial dilutions were performed to proceed with pour-plate cultivation in R2A medium at 30 ºC for 24h. In addition, samples were also filtered on 0.22 µm membrane filters and stained using DAPI to proceed with prokaryotic cells direct counting on an epifluorescence microscope. Statistical analyses were performed for all the data using the Holm-Sidak test at 5% probability using SigmaPlot software v. 12.0. Results indicate that for all cisterns the culturable bacterial density increases after 24h at the start of the system operation compared to the control. For 6h and 12h, there is no difference for control. The average value ranged from 5.6 x 104 +- 1.5 x 103 for control to 1.2 x 106 +- 2.5 x 105 cells.mL-1 for 24h treatment an average variation of 205 times. There was no significant variation between the evaluated times on direct counting using DAPI for one of the cisterns. For a second cistern, all treatments significantly differed from the control. For the third cistern, just 12h treatment differs from the control. Considering the average value for direct counting to all cisterns there is no difference between treatments and control, although the average value of prokaryotic density fluctuated positively between 2.9 x 106 +- 1.8 x 106 in control and 5.6 x 106 +- 0.5 x 106 cells.mL-1 in 24h treatment, that is, an average variation of 1.9 times. The variation between the culturable bacterial density and density of prokaryotic cells by direct counting indicates that after 24h in the recirculation system, resuscitation of a high number of VBNC cells state occurs. In literature, the low oxygen availability is a factor that implicates the bacterial cell entering into the VBNC stage. Water recirculation favors the increase in dissolved oxygen concentration and causes the resuscitation from the VBNC state. In conclusion, this work suggests that cisterns rainwater recirculation favors the resuscitation of bacterial VBNC state and this information can be useful to researchers with culture-dependent methods. Palavras-chave: bacterial metabolism, environmental microbiology, bacterial density Agência de fomento:FUNCAP; FAPEMIG; IFCE; CAPES; CNPq. | |||||