The UV radiation and salinity effect on three bacterial strains isolated from seawater and developed under laboratory conditions

BERSANO, M.A.; FOLABELLA, A.M.; ZAMORA, A.S.; ESCALANTE, A.H.

Mar del Plata

Congreso; X Congreso Argentino de Microbiología General SAMIGE; 2014

Sociedad Argentina de Microbiología General

The main purpose of the present study was to determine, under UV radiation and different saline concentrations, the growth and survival of Escherichia coli, Staphylococcus spp. and Enterococcus spp. frequently used as indicators of recreational water quality. E. coli, Staphylococcus spp. and Enterococcus spp. were isolated from seawaters of Mar del Plata beaches. For the assays, suspensions of each strain were done in growth exponential phase, with a concentration determined by Mac Farland N° 3 scale, and by spectrophotometry. UV assay: suspensions were UV irradiated (26 cm distant) at 0, 10, 20, 30, 60, and 120 secondes. A 3 ml aliquot was taken from each irradiated suspension, and from controls (0 secondes), and the optic density was measured. Simultaneously, the bacterial count of these suspensions was carried out by means of pour plate technique. After 20 secondes of UV exposure, a total inhibition of E. coli and Staphylococcus spp. development was registered. Meanwhile, Enterococcus spp. decreased its development slightly and inversely to exposure time, being viable up to 120 secondes. Salinity assay: the three bacterial strains growth in nutritive broth and at 0%, 5% and 10% ClNa concentrations was evaluated. One of the replicates was used as assay control, and the others were inoculated with 5 ml of bacterial suspension. The incubation was carried out at environmental temperature during 144 hours. Aliquots were daily removed, the absorbancy was measured, and bacterial count by pour plate technique was done, employing an appropriate culture medium, and incubating at 37°C during 24 or 48 h, according to the strain under study. At 0% ClNa assay, an increase in the counts of all strains, and then, a slight decrease, more evident in Enterococcus spp., were registered. This decrease could be attributable to the culture medium depletion. At 5% ClNa assay, the growth was similar to that registered at 0% ClNa one, but lower for all bacterial strains. At 10% ClNa assay, Staphylococcus spp. counts increased, while those of the other strains decreased. According to the results obtained from both assays it can be concluded that: a) the UV radiation was the most effective factor inhibiting E. coli and Staphylococcus spp. growth, while Enterococcus spp. instead, decreased its counts but persisted up to the end of the assay; b) the three strains developed at low ClNa concentrations, and c) at 10% ClNa concentration, Staphylococcus was the only genus enable to develop. As Escherichia coli, Staphylococcus spp. and Enterococcus spp. are frequently mentioned as indicators of bacteriological quality for recreational waters, the present study will bring information about the effects of the herein assayed factors upon the development and survival of these microorganisms. This information could be then employed to improve depuration actions in different aquatic systems, and to select the more efficient indicator, according to the local environmental conditions.