Assessing the microbial quality of a tropical watershed
with an urbanization gradient using traditional and
alternate fecal indicators
Tasha M. Santiago-Rodriguez, Gary A. Toranzos and
Javier A. Arce-Nazario
ABSTRACT
Urbanization affects the microbial loading into tropical streams, but its impact on water quality varies
across watersheds. Rainfall in tropical environments also complicates microbial dynamics due to
high seasonal and annual variations. Understanding the dynamics of fecal contamination in tropical
surface waters may be further hindered by limitations from the utilization of traditional microbial
indicators. We measured traditional (Enterococcus spp. and Escherichia coli), as well as alternate
(enterophages and coliphages) indicators of fecal contamination in a tropical watershed in Puerto
Rico during a 1-year period, and examined their relationship with rainfall events across an
urbanization gradient. Enterococcus spp. and E. coli concentrations were 4 to 5 logs higher in
non-urbanized or pristine sites when compared to enterophages and coliphages, suggesting that
traditional fecal indicator bacteria may be natural inhabitants of pristine tropical waters. All of the
tested indicators were positively correlated with rainfall and urbanization, except in the most
urbanized sites, where rainfall may have had a dilution effect. The present study indicates that
utilizing novel indicators of microbial water quality may improve the assessment of fecal
contamination and pathogen risk for tropical watersheds.
Tasha M. Santiago-Rodriguez
Department of Biology,
California Polytechnic State University,
San Luis Obispo, CA, 93407,
USA
and
Center for Applications in Biotechnology,
California Polytechnic State University,
San Luis Obispo, CA 93407,
USA
Gary A. Toranzos
Department of Biology,
University of Puerto Rico,
San Juan PR 00932,
Puerto Rico
Javier A. Arce-Nazario (corresponding author)
Department of Biology,
University of Puerto Rico,
Cayey PR 00736,
Puerto Rico
and
Instituto de Investigaciones Interdisciplinarias,
University of Puerto Rico,
Cayey PR 00736,
Puerto Rico
E-mail: javier.arce@upr.edu
Key words | coliphages, Enterococcus spp., enterophages, Escherichia coli, rainfall, urbanization
INTRODUCTION
The microbial quality of tropical watersheds is traditionally
monitored using Enterococcus spp. and Escherichia coli.
These two indicators have an extensive history of being used
for water quality regulatory purposes under United States
laws, especially the Safe Drinking Water Act (NRC ).
While these bacteria are found in the gut of warm-blooded ani-
mals and may indicate fecal contamination, they are also
natural inhabitants of pristine waters and originate from non-
fecal sources; thus, their detection may not always indicate
fecal contamination (Fujioka et al. , ; Solo-Gabriele
et al. ; Noble et al. ; Byappanahalli et al. ;
Boehm & Sassoubre ). In addition, traditional indicator
bacteria-culturing methods provide results at 18–24 h and
additional confirmation steps are required, preventing immedi-
ate actions to be taken to prevent potential risks to public health
(Wade et al. ; Noble & Weisberg ). For these reasons,
alternate indicators of fecal contamination may exhibit a higher
source-specificity and may be more cost- and time-efficient
(Sinton et al. ; Griffin et al. ; Bonilla et al. ; Purnell
et al. ; Kent et al. ; Rusinol et al. ). For instance,
polymerase chain reaction (PCR)-based methods, such as quan-
titative PCR (qPCR), are increasingly being utilized to
determine the microbial quality of waters. PCR-based methods
have several advantages, including high-specificity and the
reduced time to obtain results (Wade et al. ), but there
are significant drawbacks. These still primarily target
796 © IWA Publishing 2016 Journal of Water and Health | 14.5 | 2016
doi: 10.2166/wh.2016.041
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