Sedimentation-Resuspension of Enterococcus attached to particles in recreational waters using membrane filter technique and qPCR

DOLORES GUTIÉRREZ CACCIABUE; EUGENIA ACEVEDO; GAMBONI, OSCAR; VERÓNICA RAJAL

Florianópolis

Simposio; 17th International Symposium on Health related Water-Watermicro 2013; 2013

IWA

Water pollution is a major problem due to the large number of waterborne diseases that can be transmitted when people come in contact with it. Microorganisms like bacteria, viruses and protozoa can be present and if they are pathogens, the problem becomes worrisome due to the various diseases that they can cause. Despite the improvement on methodologies for microbial detection and on water treatment, microorganisms still survive in water. One of the variables related to this persistence is the presence of solid particles. Microorganisms can be attached mainly to small particles, and thus resist the effect of different factors. Some of these particles could sediment, enhancing microorganisms persistence in water. A sediment resuspension can occur; bringing microorganisms back to the surface and becoming a health risk. Countries have established by legislation the use of bacterial indicators to evaluate microbiological quality of recreational waters and these indicators are usually detected through culture-based methods. However, these techniques allow detecting only culturable cells but can miss starved and damaged cells or cells that are active but non-culturable. Therefore, these methods underestimate the number of microorganisms and the real risk. To address these problems, molecular methods that are culture-independent have been proposed. They can detect a genetic marker using qPCR. Since nucleic acids can remain in the environment longer periods and could be detected after organisms are no longer alive, is important to know how long these genetic markers can persist in water as separate entities of intact cells. Thus, the aims of this work were to assess Enterococcus persistence in water in the presence of particles and to compare the persistence of viable bacteria and DNA using traditional microbiological methods and molecular techniques. With this information, an experiment was carried out in order to see how microorganisms behave in presence of sediments.In order to achieve that, sedimentation-resuspension experiments were carried out in 2 L beakers, seeded with Enterococcus to study their behavior in presence and absence of different sizes of solid particles in two concentrations. These sediments were collected from aquatic environments of the Province of Salta. Detection was performed by traditional microbiological methods and molecular techniques. Results showed that culturable Enterococcus were adsorbed preferably to smaller particles than to larger ones. In the first case, sedimentation was slower, giving microorganisms more protection and allowing them to persist in water for longer periods, enhancing the health risk. On the other side, Enterococcus sediment quickly with large particles or simply die. DNA is more persistent in water than viable cells, and does not sediment with particles, keeping in suspension and suffering a faster transport to other sectors of the aquatic environment.