Some bacteria are only transient inhabitants of the intestine and are resistant to colonization, such as many that originate from ingested foods. However, they can still play a key role in the introduction of resistance determinants that have the potential to be transferred to the commensal microbiota in the intestineduring passage (Andremont, 2003; Salyers et al., 2004). Another factor that might be contributing to the emerging resistance problem is the use of antibiotics or analogous compounds in agriculture. The use of these compounds in agricultural settings may lead to a more constant selective pressure for resistance to develop and could potentially contribute to a larger global resistance reservoir with potential introduction, for example via opportunistic pathogens, into the clinical environment (Aubry-Damon et al., 2004; Heuer & Smalla, 2007).