Source Tracking of Fecal Contamination Along San Luis Obispo (SLO) Creek

Abstract

The primary goal of this project was to identify the biological sources of fecal contamination within and around the Mission tunnel of SLO Creek. Fecal coliform bacteria are used as an indication of fecal contamination that may include disease‐causing bacteria and viruses. Using a library‐based approach, we were able to track the possible sources of this contamination by analyzing specific regions of DNA within isolated E. coli samples. Environmental samples were collected from the Mission Tunnel mouth and underneath the Marsh Street Bridge and E. coli was isolated and identified using biochemical tests. Two regions of DNA (16‐23 and 23‐5 ITS) were amplified from each bacterial isolate and analyzed by a novel bacterial strain typing method known as pyroprinting. These pyroprints were matched to the Cal Poly Library of Pyroprints, which contains data for approximately 7000 E. coli isolates from various wildlife, human, domesticated animal, and environmental sources. Out of a total 843 isolates collected from SLO Creek, 25% matched isolates in the database. Approximately 72% of these matches were to unique hosts, with the majority of unique matches being to cow (51%) and pigeon (25%) isolates. Other matches include those to samples from humans (7%), horses (5%), turkeys (4%), and chickens (3%). The bias toward cow isolates (despite the absence of cows in the immediate area) and the low percentage of total matches indicates that more samples from different hosts need to be collected for the pyroprint library in order to gain a better picture of fecal contamination sources.