  We present a two-species population model in a well-mixed environment where
the dynamics involves, in addition to birth and death, changes due to
environmental factors and inter-species interactions. The novel dynamical
components are motivated by two common mechanisms for developing antibiotic
resistance in bacteria: plasmid {\it transformation}, where external genetic
material in the form of a plasmid is transferred inside a host cell; and {\it
conjugation} by which one cell transfers genetic material to another by direct
cell-to-cell contact. Through analytical and numerical methods, we identify the
effects of transformation and conjugation individually. With transformation
only, the two-species system will evolve towards one species' extinction, or a
stable co-existence in the long-time limit. With conjugation only, we discover
interesting oscillations for the system. Further, we quantify the combined
effects of transformation and conjugation, and chart the regimes of stable
co-existence, a result with ecological implications.
