Surveying BES stream sites for the presence of enteric pathogens.
James A. Higgins, Daniel R. Shelton, Jonathan Russell-Anelli, Jeffrey S. Karns, and Kenneth T. Belt
A team comprised of personnel from the USDA-ARS, the US Forest Service, and CUERE, has been surveying BES streams and those from other locales in the metro Baltimore and Washington, DC areas for the presence of bacterial ( pathogenic E. coli) and protozoal (Cryptosporidium parvum and Giardia intestinalis) pathogens. The polymerase chain reaction (PCR) and gene sequencing are used to detect enteropathogenic E. coli (EPEC) among overall coliforms cultured from water samples. A combination of filtration, immunomagnetic separation (IMS) , and immunofluorescence microscopy are used to detect protozoa.
Beginning in late April 2002, and continuing through the Fall of 2003, over 750 samples have been assayed for the presence of EPEC, with > 50% testing positive by PCR for the tir gene (a gene important in E. coli pathogenesis in the mammalian intestinal tract). BES sites associated with urban runoff (e.g., GFGR and GFCP) have a higher percentage of positive samples than those associated with forested or agricultural watersheds (e.g., POBR, BARN, and MCDN). Beginning in late March 2003 and continuing through Fall 2003, surveys for oocysts of Cryptosporidium parvum and cysts of Giardia intestinalis have been positive for 6 of 23 samples taken from Gwynns Falls Gwynns Run, the collection site with the highest coliform counts. Genotyping of protozoal isolates was accomplished using the hsp70 (C. parvum) and TPI (G. intestinalis) genes, and indicates that the protozoa originate from livestock / human sources. Our data indicate that pathogenic E. coli are surprisingly widespread in a variety of stream ecosystems.
pathogenic bacteria, protozoal pathogens, water quality, urban watersheds