Summary:
Variations in water quality at recreational bathing beaches can have
significant impacts with respect to compliance with related water quality
standards. The beach of Varkiza (22 km south of Athens) was selected for this
study due to the large number of bathers it gathers, its proximity to Athens
and its ‘Blue Flag’ award. The microbial water quality of beaches drastically
changes after rainstorms and this may have potential risks for public health.
Research suggests that sand may act as a bacterial reservoir, providing a
source of faecal indicators to adjacent waters; therefore, there is growing
concern that public exposure to human pathogens may be underestimated.
This study is an initial evaluation of the presence of indicator microbes and
pathogens at the recreational marine beach of Varkiza and the effects of
rainfall in microbial community.
Samples were collected in July 2010, February 2011 and July 2011 from knee-deep
water both in dry weather and 24 h after the rainfall. Sand was collected above
the high water mark. Concentrations of bacteria were calculated in terms of
colonyforming units (CFU) per 100 ml of water or CFU per gram of dry sand. The
specific PCR primers used for 16S rDNA were F984GC and R1378 and the PCR
products were separated by denaturing gradient gel electrophoresis (DGGE). The
separated DNA fragments were sequenced to identify the corresponding microbial
species.
Although the abundance of total bacteria seems not affected by precipitation,
faecal coliform and indicator bacteria concentration was significantly higher
after the rainfall (Staphylococcus spp. 168 %, enterococci 71 %, E. coli 70 %
increase) in summertime. Similar results occurred in the winter samplings
(Staphylococcus spp. 116 %, Enterococcus sp.208 %, E. coli 14.6 %
increase)although their population size was much lower. The detection of
Salmonella was positive in all of the 6 samplings. The sand samples showed a
strong presence of Enterococcus sp. and Candida spp. in dry conditions only in
summer. Finally, 16S rDNA DGGE sequence analysis revealed species affiliated
with: Glaciecolapallidula, Glaciecolanitratireducens,
Pseudoalteromonasatlantica, Alteromonasgenovensis, Novosphingobiumcapsulatum,
Nereidaignava, Ralstoniasolanecearum, Oceanicolapacificus,
Pseudoalteromonasespejiana, Alteromonasmacreodii, Αestuariibacterhalophilus.
Keywords:
Bacteria, Rainfall, Beach, Water, Sand
