Geographical stability of enterococcal antibiotic resistance profiles in Europe and its implications for the identification of faecal sources

This manuscript describes the use of a recently developed microbial source tracking (MST) technique to determine sources of fecal bacteria (enterococci) from four separate European countries. The investigation aimed to evaluate whether the origin of bacterial populations from France, Spain, and Sweden (n = 456) could be predicted using a library of antibiotic resistance patterns of enterococci of known origin assembled in the United Kingdom (n = 2739). Bacterial isolates were exposed to a battery of 31 antibiotic tests and classified into source groups using discriminant function analysis (DFA). Results showed that while on average 72% of the U.K. isolates could be correctly classified as originating from either municipal wastewater (MW), livestock, or wild birds, only 43% of non-U.K. isolates could be successfully classified into the same source categories. The results suggested that patterns of resistance amongst isolates contained in the U.K. library were not representative of those found in the other locations and that it may not be possible to share libraries over large distances, such as those in this study. Future MST studies using antibiotic resistance analysis (ARA) in Europe may therefore require the assembly of watershed specific libraries, increasing the cost of such studies.